Tracheal intubation can be accomplished using several techniques, including direct visual (rigid) laryngoscopy, video laryngoscopy, indirect visual laryngoscopy, and guided blind (retrograde) and complete blind (eg, intubation through supraglottic airway [SGA] or blind nasal) intubation. Each technique has its preferred indications, risks, and benefits.
Soft tissue upper airway obstruction is common after induction of anesthesia. Insertion of an oropharyngeal airway or an SGA or application of a jaw thrust often is successful for overcoming soft tissue airway obstruction.
General anesthesia and muscle relaxants facilitate tracheal intubation. A rapid-acting muscle relaxant is used during rapid-sequence induction and intubation.
During general anesthesia, airway management without tracheal intubation has become a well-accepted common practice since the introduction of SGA devices. As with any technique, it is incumbent on the physician to determine which technique is most appropriate given the clinical scenario.
Securing the airway under topical anesthesia with or without sedation (an “awake intubation”) provides the optimal approach for a patient with a severely compromised or difficult airway.
Awake intubation should be encouraged, taught, and practiced regularly to help maintain comfort and skill with the technique.
The availability of a difficult airway cart should be ensured for every anesthetizing location.
Many major anesthetic complications are frequently associated with airway mismanagement, including inadequate ventilation or oxygenation and unrecognized esophageal intubation.
Laryngospasm is common with airway stimulation during light anesthesia. Stridor indicates partial blockade of the airway. Lack of stridor may indicate complete closure of the larynx with no air exchange.
For patients in whom the upper airway is obstructed, establishing emergency ventilation with a supraglottic device (eg, laryngeal mask airway), esophageal device (eg, laryngeal tube), cricothyrotomy, or transtracheal jet ventilation is a must and should be applied as soon as possible to prevent brain injury and death.
Trauma to laryngeal structures can leave patients with vocal cord paralysis and serious voice dysfunction.
Many airway disasters have been reported after patient extubation. A well-planned and prepared extubation is necessary for high-risk patients to minimize airway-related complications.
In the anesthetic environment, an artificial airway conducts gases between the anesthesia machine’s breathing system and the alveoli. Effective management requires keeping the airway free of secretions, contamination, and obstruction while minimizing complications. Critical illness often causes weakness and obtundation sufficient to impair gas exchange. The sedative, narcotic, anesthetic, and relaxant drugs that facilitate surgery predictably compromise airway patency and protection. The Closed Claims Study of the American Society of Anesthesiologists (ASA) Committee on Professional Liability has shown that tragic and costly complications of anesthesia frequently have resulted from problematic airway management.1 Some of the obligations of the anesthesiologist include ensuring that the patient is adequately oxygenated, the lungs are ventilated, and airway patency is maintained. Essential attributes of the expert airway manager include knowledge, sound judgment, skills for a range of techniques, and a plan for all conceivable contingencies.2,3
APPLIED ANATOMY OF THE AIRWAY
Mastery of the airway demands familiarity with normal and variant anatomy and the alterations caused by sedation, anesthesia, and abnormal states.
The pharynx, extending from the sphenoid bone to the sixth cervical vertebrae (C6), parallels the vertebrae. The retropharyngeal space lies between the more superficial buccopharyngeal fascia and the prevertebral fascia. Abscesses may form in this space and infiltrate the superior mediastinum.
The anterior communications of the pharynx take place in the nasopharynx, oropharynx, and laryngopharynx (Figure 32-1). The nasopharynx extends from the skull base to the soft palate at the level of the first cervical vertebrae (C1). From there to the bottom of C3 lies the oropharynx. The laryngopharynx extends from C3 to C6, where it merges with the esophagus (Figure 32-2). There, the cricopharyngeus muscle, originating on the cricoid cartilage, encircles the esophagus to form the upper esophageal sphincter. In anesthetized patients, pressing the cricoid ring against C6 (Sellick maneuver) mimics esophageal sphincter constriction and reduces the risk of passive regurgitation of gastric contents.4
Diagram of a sagittal section of the pharynx illustrating the three subdivisions of the pharynx.
Posterior view of the pharynx showing subdivisions of the pharynx.
The pharyngobasilar fascia anchors the pharynx superiorly to the occipital and the sphenoid bones. In the presence of basilar skull fractures, attempted passage of nasotracheal and nasogastric tubes has resulted in their entry into the cranium. Superficial to the bones that roof the pharynx and C1 lies the pharyngeal tonsil (called adenoids when hypertrophied), a site of potential obstruction or hemorrhage during nasal intubation. In patients whose tongue is large enough to fill the oral cavity, gas enters through the nasopharynx into the lungs with face mask ventilation, but the soft palate, posterior pharyngeal wall, and tongue often form a unidirectional valve that blocks exhalation. Gas trapping is prevented by periodic release of the mandible or by insertion of an artificial airway.
Anteriorly, the nasopharynx opens through the choanae, nasal passages, and nostrils. The filtration and humidification functions of the nose are well served by the convoluted surfaces of the three turbinates on each lateral wall (Figure 32-3). Their fragility can lead to epistaxis after nasal intubation attempts unless the tube is guided parallel and adjacent to the hard palate and perpendicular to the face through the channel beneath the inferior turbinate.
Lateral wall of the nasal cavity demonstrating the superior, middle, and inferior conchae (turbinate bones). [Reproduced with permission from Finucane BT, Tsui BCH, Santora AH. Principles of Airway Management, 4th ed. New York: Springer; 2010.]
The oropharynx opens to the oral cavity at the palatoglossal folds, marking the division between the anterior two-thirds and posterior one-third of the tongue. The posterior third of the tongue forms the anterior wall of the oropharynx. In a sleeping or anesthetized patient in the supine position, muscle relaxation combined with gravity approximates the base of the tongue to the posterior oropharyngeal wall, causing varying degrees of airway obstruction. Partial airway obstruction is aggravated by negative inspiratory pressure collapsing the loose pharyngeal walls inward.
In the absence of an artificial airway, airway patency may be improved by extending the neck or subluxing the mandible anteriorly. This anterior displacement, through stretching of the mylohyoid, geniohyoid, and genioglossus muscles, indirectly relieves oropharyngeal obstructions (Figure 32-4). Mandibular mobility depends in turn on the hinging and gliding motions of the temporomandibular joint (TMJ). For successful rigid laryngoscopy, the tongue is displaced anteriorly for visualization of the larynx.
Sagittal section of the mouth to illustrate the tongue and its innervation.
LARYNGOPHARYNX AND LARYNX
The epiglottis, thyroid, and cricoid cartilages and six smaller, paired cartilages (arytenoid, corniculate, cuneiform) shape the larynx (Figure 32-5). To each side of the larynx and inferior to the aryepiglottic folds are the piriform recesses, which are separated by a prominence in the anterior laryngopharyngeal wall created by the lamina of the cricoid cartilage (Figure 32-6).3 A properly positioned supraglottic airway (SGA), such as a laryngeal mask airway (LMA), seals against the cricoid cartilage and cricopharyngeus muscle inferiorly, the base of the tongue superiorly, and the piriform recesses laterally.5 The superior laryngeal nerves, submucosal in these recesses, can be blocked with local anesthetic-soaked pledgets applied to the piriform sinuses.
Diagrammatic illustration of sagittal section of the larynx. The epiglottis, thyroid, cricoid, and arytenoid cartilages and the position of the vocal cord ligaments are demonstrated.
Diagrammatic illustration of the superior view of the larynx simulating the structures seen during direct laryngoscopy.
The hyoid (Greek: “U-shaped”) bone at C4 suspends the thyroid cartilage by the thyrohyoid membrane, which is penetrated when performing superior laryngeal nerve blocks (Figure 32-7). At C5, atop the 3-cm long thyroid cartilage, is the thyroid notch and laryngeal prominence (Adam’s apple), an important landmark that may be subtle in women. The thyroid (Greek: “shield”) cartilage sends superior cornua cephalad toward the hyoid bone and its inferior cornua to articulate with the cricoid (Greek: “ring”) cartilage. In the midline at C6, the cricothyroid membrane is an easily palpated and avascular site for emergency cricothyrotomy or cannulation for instillation of local anesthetics, jet ventilation, or retrograde wire-guided intubation.
Diagrammatic illustration of the anterior view of the larynx. The larynx is suspended from the hyoid bone by the thyrohyoid ligament. The cricothyroid ligament provides easy and fast access to the larynx. Translaryngeal injection of local anesthetics and transtracheal jet ventilation are performed through this ligament.
The upper edge of the epiglottis blends with the aryepiglottic folds. The tip of a curved (Macintosh) laryngoscope blade fits into the glossoepiglottic reflection. Two lateral valleculae in this reflection are created by the hyoepiglottic ligament, which keeps the resting epiglottis out of the laryngeal vestibule.
Atop the posterior cricoid lamina sit the paired arytenoid (Greek: “ladle”) cartilages with superior, anterior, and lateral projections. The superior projections support the corniculate (Latin: “little-horn”) cartilages, and the anterior and lateral projections attach, respectively, to the vocal cords and various intrinsic laryngeal muscles (Figure 32-5). Corniculate and cuneiform cartilages embedded in the aryepiglottic fold form two prominences, commonly referred to as “the arytenoids,” which serve as important landmarks for intubation during suboptimal laryngoscopy.
NORMAL VOCAL CORD MOVEMENTS AND LARYNGEAL NERVE PALSIES
Normal vocal cord movements include abduction during inspiration, partial adduction during exhalation, and full adduction during phonation. All intrinsic muscles of the larynx are adductors or tensors, with the exception of the posterior cricoarytenoid muscles, which are the sole abductors. All intrinsic muscles of the larynx are innervated by the recurrent laryngeal nerve, with the exception of the cricothyroid, a tensor innervated by the external branch of the superior laryngeal nerve. Laryngeal nerve palsies are classified as central or peripheral and unilateral or bilateral.6-9 Simultaneous malfunction of the superior and recurrent laryngeal branches implies a central lesion or a high interruption of the vagus nerve. Brain infarction or a complete vagus nerve interruption causes the cord to assume a flaccid, wavy, partially abducted, or “cadaveric” position more commonly seen as a result of administering muscle relaxants. Central causes include posterior fossa surgery or brainstem infarctions. Peripheral lesions are more commonly caused by neck or cardiothoracic surgery than by endotracheal tube (ETT) cuff pressure on the larynx. Damage to the superior laryngeal nerve or its external branch results in an inability to sound a high-pitched “C” note, which improves over time as the contralateral muscle compensates. With unilateral nerve injury, the aryepiglottic folds and glottis are asymmetric during phonation. A complete unilateral recurrent laryngeal nerve injury causes hoarseness and a motionless cord that is joined during phonation by the contralateral cord crossing the midline.
Incomplete bilateral recurrent laryngeal nerve palsies result in a glottic opening so small that an emergency surgical airway may be needed. Bilateral complete recurrent laryngeal nerve palsies result in severe hoarseness, but, because the cords neither adduct nor abduct, a safe glottic opening may remain. However, the patient should be carefully evaluated to ensure adequate oxygenation and ventilation. Some patients will require tracheal intubation or tracheostomy.
GLOTTIC AND LARYNGEAL CLOSURE
Three forms of laryngeal airway closure can be distinguished. First, during light anesthesia or phonation, the intrinsic laryngeal muscles approximate the vocal cords during exhalation, causing expiratory stridor or moaning. Second, if the vocal cords are edematous or are resting close together, the Bernoulli effect draws the cords together during rapid inhalation, resulting in inspiratory stridor.10 The third kind of closure involves the entire larynx instead of simply the glottis; the thyrohyoid and other strap muscles contract in a forceful, longitudinal compression of the larynx.11 During deglutition, the Valsalva maneuver, or laryngeal spasm, the thyroid cartilage and hyoid bone approximate, bulging the epiglottis down into the vestibule against the false cords in a ball-valve fashion. Muscle relaxants and maneuvers to elongate the larynx (application of the sniff position, neck extension, and jaw thrust) tend to counteract such closure. Face mask positive pressure is often applied in the setting of laryngeal spasm; however, it may expand the piriform recesses and compress the aryepiglottic folds, compounding laryngeal closure, so it should be intermittently released if the spasm does not resolve.
The lower airway includes the subglottic larynx, trachea, and bronchi. The subglottic larynx is 2 cm in length and extends from the true vocal folds to the lower border of the cricoid ring. The trachea extends from the lower border of the cricoid ring at the level of C6 to the carina at the level of the fifth thoracic vertebrae (T5) posterior to the angle of Louis (manubriosternal junction).12 Neck flexion can advance an ETT in a caudad direction; the Trendelenburg position or laparoscopic pneumoperitoneum can move the carina in a cephalad direction. These maneuvers can move a properly placed ETT into a bronchus.13,14 False reassurance that a tube tip is not in a bronchus often is given by a radiograph taken with the head transiently thrown into extension by removing the pillow while supporting the chest with a film cassette.
During fiber-optic examination, the trachea is distinguished from bronchi by its flat, muscular posterior wall, creating a D-shaped cross section. The right mainstem bronchus is roughly half as long as the 5-cm left mainstem bronchus. Being wider and almost parallel to the trachea, the right mainstem bronchus is more likely than the left bronchus to be accidentally intubated. Also, foreign bodies, aspirated material, and suction catheters preferentially end up in the right bronchus. Tracheobronchial anatomy and other features of the airway differ between infants and adults (Table 32-1).12,14
Table 32-1Comparison of Infant and Adult Airways ||Download (.pdf) Table 32-1 Comparison of Infant and Adult Airways
|Feature ||Infant (Birth to 1 Year Old) ||Adult (Older Than 8 Years) |
|Cricoid-carina distance (cm) ||5-6 ||10-20 |
|Angle: trachea–right bronchus (degrees) ||30 ||20 |
|Angle: trachea–left bronchus (degrees) ||45 ||45 |
|Narrowest portion of airway ||Cricoid cartilage ||Glottis |
|Level of glottis ||C3-C4 interspace ||C5 |
|Inclination of vocal cords ||Anteroinferior ||Horizontal |
|Protrusion of corniculate and cuneiform tubercles into laryngeal aditus ||Prominent ||Minimal |
|Epiglottic cross section ||Omega shaped ||Crescent shaped or flat |
|Glottic-epiglottic angle ||Small ||Large |
|Ease of mobilizing epiglottis to expose cords ||Generally awkward, especially with curved blade ||Usually easy with curved or straight blade |
|Height of thyrohyoid and cricothyroid ligaments ||Almost nonexistent ||Several millimeters |
|Preferred breathing route ||Nasal ||Nasal or oral |
|Prominence of occiput ||Large (no headrest needed to attain the “sniff” position) ||Small (headrest needed) |
Although many anatomic similarities exist between adults and children, several differences deserve consideration. For a more in-depth discussion of the pediatric airway, the reader is directed to Chapters 7, 58, and 59. Infants are obligate nasal breathers with a large head relative to the rest of the body. As a result, any process that obstructs the nares or flexes the head significantly may result in airway obstruction. Laryngoscopy in infants reveals a long and floppy epiglottis relative to that of a typical adult. In addition, the infant larynx may appear more anterior on direct laryngoscopy because of a more cephalad location at the level of the C3 vertebral body, in contrast to the C6 vertebra in an adult. The lower airway in children is anatomically more “funnel shaped” than the adult airway. Although somewhat controversial, the cricoid cartilage is considered the narrowest portion of the airway in children under 8 years of age.15 By the age of 10-12 years, airway anatomy closely resembles adult characteristics.
A difficult airway can present as difficult face mask ventilation, difficult tracheal intubation, inability to ventilate or oxygenate with an SGA, or all three. The major task during preoperative airway evaluation is to identify patients at risk for a “cannot intubate, cannot ventilate” (CICV) situation, which is caused by congenital or acquired anatomic variations or by abnormal afflictions of the upper and lower airway (Box 32-1).16-18 The variations or abnormalities are found by reviewing the patient’s medical record, taking an anesthetic and airway-focused history, examining the patient with reference to the normal and desired mobility of airway structures, and reviewing relevant laboratory and radiologic studies.
BOX 32-1 Some Causes of Difficult Airway Management
Short, muscular neck
Limited neck mobility
Prominent maxillary incisors
Awkwardly placed, incomplete dentition
Long, highly arched palate with narrow mouth
Small mouth opening
Anaphylactic airway edema
Arthritis and ankylosis
Klippel-Feil (short, fused neck)
Pierre Robin (micrognathia, cleft palate, glossoptosis)
Treacher Collins (mandibulofacial dysostosis)
Ludwig angina (floor of the mouth abscess)
Myopathies demonstrating myotonia or trismus
Scarring from burns or radiation
Trauma and hematomas
Tumors and cysts
Technical and mechanical factors
Halo fixation or cervical collar
Airway foreign bodies
Leaks around a face mask
Flat bridge of nose
Large face and head
Poor technique, inexperience, or haste
The Fourth National Audit Project of the United Kingdom (NAP4) prospectively collected data on nearly 3 million anesthetics, recording data on serious adverse outcomes related to airway management.19 One of the key findings of the project is that poor airway assessment contributes to many of the adverse outcomes. Airway assessment is supported by the ASA Guidelines for Difficult Airway Management and all major international organizations with a statement on airway management.20-22
The inability to ventilate presents a more urgent problem than inability to intubate with adequate mask ventilation. Independent risk factors for difficult mask ventilation include age older than 55 years, body mass index greater than 30 kg/m2, facial hair, missing teeth, limited mandibular protrusion, neck radiation changes, Mallampati-Samsoon class III or IV, abnormal neck anatomy, sleep apnea, and a history of snoring.23,24 Special attention should be paid to syndromes associated with a problematic airway.
A suggested approach for airway assessment involves performing an airway-focused history and physical examination. The patients should be asked whether they were ever told they had a difficult-to-manage airway associated with an anesthetic or if they had a postoperative sore throat that was excessively severe or prolonged. The character of the patient’s voice should be noted, and any abnormality such as hoarseness or weakness of the voice should be documented in the medical record. Obstructive sleep apnea (OSA) is an important risk factor for difficult mask ventilation and may modify the plan for postoperative care. The STOPBang screening tool can be used to assess the risk of OSA with high sensitivity and specificity.25 The elements of the STOPBang questionnaire are listed in Box 32-2.26 The patient should also be asked about loose teeth and the presence of dental work, such as caps or crowns and dental appliances like partial or full dentures.
BOX 32-2 STOPBang Questionnaire
Snoring: Do you snore loudly enough to be heard through closed doors? Y N
Tired: Do you often feel tired, fatigued, or sleepy during the daytime? Y N
Observed: Has anyone observed you stop breathing during your sleep? Y N
Blood Pressure: Do you have or are you being treated for high blood pressure? Y N
Body Mass Index (BMI): BMI more than 35 kg/m2? Y N
Age: Age over 50 years? Y N
Neck Circumference: Greater than 40 cm (15.75 in)? Y N
Gender: Male? Y N
The airway examination includes an overall inspection of the neck and facial morphology, looking for factors listed in Box 32-1. The teeth are then examined, noting any teeth that are loose, chipped, or cracked. With the patient sitting straight up, the patient is asked to fully open his or her mouth and protrude the tongue as far as possible. The Mallampati-Samsoon class is assessed27 (Figure 32-8). The patient is then asked to extend his or her neck and tilt the head back as far as possible to assess both atlanto-occipital and cervical spine extension. After returning the head to the neutral position, the patient is asked to protrude the mandible as far anteriorly as possible to assess anterior translation of the mandible in the TMJ. Some patients find this difficult to do, so demonstrating the “upper lip bite test” is often helpful. The submental space and laryngeal cartilages are palpated to check for mobility and signs of changes from radiation or infection. Finally, the location of the cricothyroid membrane is palpated as identification of this landmark is essential for emergency surgical or percutaneous airway rescue maneuvers.
Mallampati-Samsoon classification of airway structures. Note: In class III the soft palate is visible; in class IV only the hard palate is visible. [Modified with permission from Manabea Y, Iwamotob S, Miyawakib H, et al: Mallampati classification without tongue protrusion can predict difficult tracheal intubation more accurately than the traditional Mallampati classification. Oral Science Int. 2014;May11(2):52-55.]
If prior anesthetic records are available, they should be consulted. If the patient gives an unclear history regarding difficult airway management, the medical records should be reviewed to confirm that it was possible to ventilate the patient with a face mask; if the records are unavailable, then serious consideration should be given to securing the patient’s airway prior to induction of general anesthesia. If the patient has had recent imaging of the neck or chest, it should be reviewed if there is any concern about airway obstruction or abnormal anatomy.
PEDIATRIC AIRWAY ASSESSMENT
Adults more often permit a full and comprehensive airway evaluation prior to a procedure, in contrast to children. Nonetheless, it is important to evaluate a child’s airway before an anesthetic or airway intervention. Attention to the child’s appearance, with a focus on any anatomical abnormalities that might complicate mask ventilation or direct laryngoscopy is warranted. A multitude of syndromes may result in a difficult airway (see Chapter 59), but difficult airways may not always be obvious from a distance. Children may have enlarged tonsils and adenoids and severe OSA, a cleft palate, or subglottic stenosis that would not be obvious from a cursory inspection. A comprehensive history, including any prolonged intubation in the neonatal period (subglottic stenosis), snoring at home (obesity or adenotonsillar hypertrophy), or difficulty with breathing or speech, might indicate circumstances that may complicate airway management. A physical examination may uncover anatomic predictors of difficult airway management or loose teeth but should also focus on the child’s respiration. Labored breathing with accessory muscle use, drooling or oral swelling, or noisy breathing indicates pathology that may complicate airway management. An active respiratory infection or airway surgery makes the likelihood of perioperative laryngospasm high.
Part of developing an airway management strategy is to determine whether the patient is best served by an SGA or an ETT. It should also be decided whether to instrument the airway while the patient is awake or after induction of the anesthetic. Despite our best efforts, the majority of difficult tracheal intubations and mask ventilation encounters are not predicted by routine clinical bedside assessment. The cause may be inadequate assessment, overconfidence, the poor sensitivity of clinical tools, or anatomic variants such as supraepiglottic cysts or lingual tonsillar hypertrophy,28,29 which can lead to unexpected difficult ventilation or intubation. The ever-present possibility of instrument failure requires backup plans and familiarity with algorithms for handling unanticipated challenges.
VENTILATION DURING ANESTHESIA
Alveolar ventilation delivers the oxygen (O2) consumed by tissues and removes metabolic carbon dioxide (CO2). An average anesthetized adult consumes about 250 mL/min of O2 and produces 200 mL/min of CO2. Because the normal alveolar effluent contains 5% (1/20) CO2, removing 200 mL CO2 each minute requires 4 L/min (20 × 200 mL/min = 4000 mL/min) of alveolar ventilation. Because one-third of minute ventilation is dead space (ie, does not participate in gas exchange), the required total minute ventilation to maintain normocapnia is 6000 mL/min, or roughly 90 mL/kg/min. Unless the metabolic rate is reduced, alveolar hypoventilation results in hypercapnia. Arterial oxygenation can be sustained during hypoventilation by increasing the fraction of inspired oxygen (Fio2).
In the presence of narcotics, sedatives, and inhaled anesthetics, the brain’s normal compensatory responses to hypercapnia and hypoxemia are blunted. Thus, the spontaneously breathing patient during general anesthesia will become hypercapnic, although surgical stimuli offset ventilatory depression and tend to return Paco2 toward normal. Spontaneous ventilation is acceptable during general anesthesia when muscle relaxants are not administered and airway patency is properly maintained.
The anesthesiologist may assist ventilation by timing the compression of the reservoir bag to the patient’s spontaneously initiated breaths, a task requiring considerable practice.30 Many modern anesthesia machines offer a pressure support ventilation mode that senses when the patient initiates a breath and then provides positive pressure support throughout inspiration. Assisted ventilation can test the quality of a face mask or laryngeal mask seal, minimize atelectasis, and offset the increased work of breathing caused by partial airway obstruction. In an anesthetized patient, apnea may result either from hyperventilation that pushes the Paco2 below the apneic threshold or from a series of breaths large enough to elicit the Hering-Breuer inspiratory reflex. Assisting breathing enough to lower the Paco2 by 5 mm Hg reduces it below the apneic threshold. For this reason, assisted ventilation cannot generally reverse hypercapnia to a meaningful extent without becoming controlled ventilation. In the presence of muscle relaxants, an unfavorable patient position, critical illness, or a requirement for hyperventilation, the anesthesiologist may choose to initiate controlled ventilation (mechanical ventilation if the work is performed by a machine).
An inhalation induction is performed by letting a patient breathe a volatile anesthetic, starting with a concentration low enough to avoid airway irritation and gradually increasing as the central effects of the vapors begin to depress the cough reflex. As alveolar ventilation decreases, breaths are assisted with increasing intensity until ventilation is manually controlled. Pediatric anesthesia practice commonly includes inhalational induction, often with high initial concentrations of sevoflurane (less pungent than either desflurane or isoflurane) for the most uncooperative patients. In addition to pediatric indications, inhalation induction may prove advantageous for adult patients when the ability to ventilate the patient’s lungs after induction of anesthesia is uncertain.30 If worsening of airway obstruction is encountered during inhalation induction, the anesthetic can be turned off with the expectation that the inhaled anesthetics will redistribute within the body, causing the partial pressure of agent in the brain to decrease and the patient to awaken.
Hypoventilation, consequent to depressed ventilatory drive, laryngeal spasm, or most commonly supraglottic soft tissue airway obstruction, results in hypercapnia and hypoxemia. Normally, although room air is 21% O2, alveolar gas has an O2 concentration of 16% because of the presence of water vapor and CO2. Arterial O2 desaturation in hypoventilating patients breathing room air results in part because increasing alveolar CO2 displaces alveolar O2. Small increases in Fio2 elevate alveolar O2 enough to maintain an acceptable arterial O2 saturation during hypoventilation; large increases in Fio2 can maintain close to normal arterial O2 saturation despite profound hypoventilation (Figure 32-9).
Dependency of alveolar oxygenation on alveolar ventilation at low fraction of inspired oxygen (Fio2) values. Supplemental O2 largely frees the Pao2 of its dependency on alveolar ventilation. For example, the broken vertical line shows that a patient breathing room air with an alveolar ventilation of 3.2 L/min has a Pao2 of 100 mm Hg, which would decrease to 50 mm Hg if the alveolar ventilation decreases by 50%. Yet, even at the lower alveolar ventilation, increasing the Fio2 to 0.4 elevates the Pao2 to 200 mm Hg. BTPS, body temperature, standard pressure, saturated (with water vapor). [Modified with permission from Lumb AB. Nunn’s Applied Respiratory Physiology, 6th ed. New York: Elsevier; 2005.]
During apnea, arterial oxygenation can be sustained by apneic oxygenation.31 In this technique, the patient breathes pure O2 long enough to wash nitrogen from the alveoli, leaving only O2, CO2, and 6% water vapor (47 mm Hg vapor pressure at 37°C). If 100% O2 continues to be available to a patent airway, it will be drawn into the alveoli during apnea. Without exhalation, the alveolar CO2 concentration increases 5 or 6 mm Hg the first minute (equilibration between venous and alveolar Pco2) and 3 to 6 mm Hg/min thereafter (metabolic production). Ten minutes into apneic oxygenation that begins with normocapnia, the alveolar composition of gases is 47 mm Hg of water vapor, 72 mm Hg of CO2, and 641 mm Hg of O2. In the absence of metabolic acidosis, the pH is approximately 7.24.
In general, it is the risk of hypoxia that threatens to permanently harm the hypoventilating patient. This realization justifies the popularity of supplemental O2 to lessen the likelihood of hypoxemia during hypoventilation. Except under certain conditions, the consequences of hypercapnia are well tolerated or reversible (Box 32-3).
BOX 32-3 Conditions Aggravated by Hypercapnia
Preexisting metabolic acidosis (eg, lactic acidosis, uremia)
Elevated intracranial pressure
Right-to-left cardiac shunts
Poor myocardial contractility
Proper preanesthetic denitrogenation is recommended by the ASA and other organizations to increase the margin of safety in the case of unanticipated difficult patient ventilation20 (Box 32-4). Eighty percent of the average 2.5-L adult functional residual capacity (FRC) that starts out as N2 is replaced with O2.32 If ventilation becomes impossible, the extra 2 L of O2 may sustain vital organs for up to 8 minutes, enough time to establish other means of oxygenation.33
BOX 32-4 Proper Denitrogenation Technique
High flow of oxygen
Fully open pop-off (APL adjustable pressure limiting); valve
Leak-free mask fit to prevent entraining room air
Tidal breathing for 2 or 3 minutes or a series of four vital capacity breaths
Reservoir bag empties and refills
End-tidal CO2 approaches 40 mm Hg
End-tidal O2 approaches 85%
MONITORING THE ADEQUACY OF VENTILATION AND OXYGENATION
The gold standard for assessing the adequacy of ventilation and oxygenation is the measurement of the partial pressures of CO2 and O2 in sampled blood (ie, arterial blood gas measurement). Because of cost and delay, a number of alternative technologies have become popular since 1980. Clinical observations remain invaluable to anesthesiologists, who should constantly evaluate the validity of pulse oximetric and capnographic data.
Airway management demands constant awareness of the patient’s physiologic status, obtained through observations of skin color, vital signs, chest and abdominal movements, and use of accessory muscles. Even before arterial blood gases deteriorate, anesthesiologists usually are able to detect problems and make adjustments to maintain airway patency and gas exchange (Table 32-2).12,30
Table 32-2Reassuring and Worrisome Signs and Their Implications During Airway Management ||Download (.pdf) Table 32-2 Reassuring and Worrisome Signs and Their Implications During Airway Management
|Reassuring ||Worrisome ||Implication of Worrisome Sign |
|Concurrent pectoral and subcostal rising alternating with concurrent falling ||Stepwise expansion of subcostal region ||Stomach filling with gas or unidirectional expiratory obstruction |
|No retractions ||Subcostal expansion with concurrent pectoral collapse ||Partial upper airway obstruction or intercostal weakness |
|No tug ||Subcostal rocking with no chest expansion ||Complete airway obstruction |
|Breathing without accessory muscles ||Submandibular, intercostal, or supraclavicular retractions ||Partial or complete upper airway obstruction |
|Sequential fogging and clearing of plastic mask ||Inspiratory tracheal tug ||Intercostal weakness with preserved diaphragmatic strength |
|Normal vital signs ||Use of sternocleidomastoid and trapezius muscles ||Respiratory muscle fatigue or weakness |
|Rebreathing bag quickly refills during exhalation ||Stertor (snoring) ||Soft tissue obstruction |
|Volumeter indicates appropriate tidal volumes ||Stridor (harsh, high pitched) ||Laryngeal obstruction |
|Normal breath sounds heard with pretracheal auscultation ||Audible phonation or palpable purring ||Light anesthesia or partial airway obstruction |
In the majority of patients, pulse oximetry affords reliable but noninvasive measurement of the arterial O2 saturation. Provided that hemoglobin concentration and organ perfusion are acceptable, satisfactory arterial O2 saturation makes organ hypoxia unlikely. The reassurance offered by pulse oximetry lets the anesthesiologist proceed carefully during intubation.34 Pulse oximetry is not sensitive to hypoventilation if Fio2 is high, and it gives late notification of esophageal intubation after denitrogenation.35
Most failures of pulse oximetry (eg, movement artifact, vasoconstriction) are obvious. The anesthesiologist may incorrectly assume adequate oxygenation during carbon monoxide poisoning or illumination of the pulse oximeter’s probe by lights of unusual wavelength.
Capnometry, using one of several detection methods, continuously displays the waveform of partial pressure of CO2 sampled at the patient end of the breathing circuit. Assuming a sufficiently large tidal volume free of contamination by ambient gases, alveolar gas reaches the CO2 sampling site, and the displayed partial pressure of end-tidal CO2 (PETco2) closely approximates the alveolar CO2, affording a noninvasive, breath-by-breath method to judge the adequacy of ventilation. In patients with normal cardiopulmonary physiology, expiratory gas has a Pco2 that is 2 to 5 mm Hg less than the arterial Pco2.
Significant and common clinical events create Pco2 gradients (arterial to alveolar to sampled to measured) so that the Paco2 is normally higher than that displayed on the capnometer (Box 32-5). In most patients, the ETCO2 suggests better alveolar ventilation than actually exists because significant amounts of CO2-free inspired gas dilute the sample. For example, during spontaneous face mask ventilation of a patient with elevated intracranial pressure, the peak measured Pco2 displayed by the capnometer may be only 18 mm Hg, but the first few breaths after tracheal intubation may show a Pco2 of 30 mm Hg. The rapid, shallow ventilatory pattern before intubation prevents transport of undiluted alveolar gas to the capnometer.
BOX 32-5 Increased Gradient Between Paco2 and PETco2 Arterial-to-alveolar gradients
Paco2 increases and PETco2 decreases (decreased perfusion relative to ventilation)
CO2 embolism (laparoscopic insufflation)
Right-to-left intracardiac shunting
Sudden increase in ventilation-to-perfusion ratio
Bronchial intubation Alveolar-to-sampled gradient
Anatomic or apparatus dead space
Rapid, shallow breaths
Apparatus dead space (face mask)
Dilution at the sampling site of exhaled gas by fresh gas (eg, loose connection, cracked sampling line)
Low velocity in sampling tubing, causing laminar rather than preferred turbulent flow Sampled-to-measured gradients
Slow capnometer response time with rapid breaths
An important application of capnometry is confirmation of the intratracheal position of an ETT by the appearance of stable CO2 concentrations in sequential breaths immediately after intubation. This application is mandated by the ASA Standards for Basic Anesthetic Monitoring.36 In addition, as of 2010, the American Heart Association guidelines for cardiorespiratory resuscitation added the presence of a “continuous quantitative capnographic waveform” as a recommendation for confirmation of intratracheal tube placement postintubation.37 Despite tracheal intubation, the expected levels of CO2 may fail to appear if the delivery of CO2 to the lungs is limited by low cardiac output, hypovolemia, gas or thrombotic embolization, or cardiac arrest.
AIRWAY MANAGEMENT WITHOUT TRACHEAL INTUBATION
The majority of airway-related deaths and severe neurologic morbidity result not from a failure to intubate the trachea but rather from a failure to ventilate and oxygenate.1 Resourceful anesthesiologists command an array of techniques for ventilation without tracheal intubation when the latter is not indicated or has failed. These ventilation techniques may use a face mask with or without an oral or nasal airway or supraglottic devices such as LMAs or esophageal devices.12,30,38
Positioning to Facilitate Face Mask Ventilation
In the supine position, gravity draws the relaxed tongue and epiglottis into configurations that can obstruct the airway. Patients recovering from anesthesia or obtunded, intoxicated emergency room patients may be safest in a semilateral position with the dependent leg straight and the other one bent, the dependent arm flexed, and the dependent cheek on the bed (the tonsillar position). Gravity will draw the tongue away from the posterior pharyngeal wall, and blood or vomitus can drain out the mouth more easily. If the anesthesiologist suspects that gastric contents have entered the pharynx, the patient’s head is turned to the side, and the table is quickly positioned head down to maximize drainage while the pharynx is cleared with a Yankauer suction catheter.
Students of basic life support are taught to overcome upper airway obstruction by extending the head and neck and by displacing the mandible anteriorly with jaw thrust. Although these maneuvers move the hyoid and attached structures anteriorly, their effectiveness can be limited by two factors. Some vertebral columns can bow anteriorly and impinge on pharyngeal patency. More commonly, the forceful cervico-occipital extension tightens the strap muscles sufficiently to limit the anterior mobility of the larynx and the mandible. For these reasons, anesthesiologists often favor the sniffing position, in which the occiput rests on a firm pad about 10 cm anterior to the scapula. Atlanto-occipital extension and jaw thrust maneuvers then are superimposed. The anterior displacement of the head shrinks the sternomental distance, so the hyoid and its attached structures can be pulled out of the pharynx without tightening the strap muscles. Greater comfort for the awake patient and preparedness for laryngoscopy are additional advantages of the sniffing position. The position is natural in infants and small children because of a large occiput, although padding under the shoulders may be required in smaller children to prevent excessive flexion of the neck with a large occiput.
In some patients, best airway patency is achieved by rotating the head to either side. Airway visualization and manipulation are easier when the operating room table is elevated so the patient’s forehead is brought to the level of the anesthesiologist’s xiphoid.
The skill of sealing a mask to the face develops only after months of hands-on training. Although masks are of a few basic designs (Figure 32-10), facial contours assume an endless variety. Clear plastic masks with large-volume, low-pressure cushions seal easily to most faces (including the faces of patients with a flat nasal bridge) while affording a view of ventilatory condensation and evaporation cycles and early detection of regurgitated gastric contents.
Face masks. Three universal masks are on the left. The Rendell-Baker pediatric mask is shown on the far right.
Most practitioners employ the “EC-clamp” (EC) mask grip when attempting to obtain a good face mask seal. The EC technique derives its name from the resemblance of the operator’s thumb and index finger to the letter C, with the remaining three fingers across the edge of the mandible similar to the letter E (Figure 32-11A). The EC grip allows one person to ventilate a patient with a bag mask, assuming an adequate seal is obtained. Difficulty with EC grip mask ventilation requires an alternative technique. The use of a two-handed mask grip can often improve mask ventilation. There are several recommended two-hand mask grips. One such technique is the mirror image application of both hands in the EC grip (Figure 32-11B). Alternatively, a “thenar eminence” (TE) two-hand grip may be utilized (Figure 32-11C). The TE mask grip is applied by resting the TE of each hand on the ipsilateral border of the mask with thumbs pointing toward the chest. The remaining fingers wrap around the inferior edge of the mandible. It has been suggested that the TE mask grip may be superior to the two-handed EC grip in novice operators.39
A, B, C. Face mask grips. A. One-handed “EC” grip. B. Two-handed EC grip. C. Thenar eminence grip.
Any two-handed mask grip precludes the operator from simultaneous mask application and manual compression of the reservoir bag. A second operator can compress the reservoir bag. In the absence of a qualified assistant, a mechanical ventilator can allow the operator to apply a two-hand mask grip while the machine provides positive pressure to the airway. Pressure control ventilation mode with the peak pressure set at or below 15 cm H2O usually provides good-to-excellent tidal volume with minimal risk of insufflation of the stomach. With volume control mechanical ventilation, excessive positive pressure must be prevented because of the potential for gastric insufflation.40
A mask strap can be used to affix hooks around connectors where the mask attaches to the circuit. When used with the mask, the strap may improve the seal and minimize hand fatigue for the anesthesia provider during long cases (Box 32-6). An undersized mask will not fully seal around the patient’s mouth and nose. An oversized mask often does not provide a good seal because of leakage of gas periorbitally above the nose. Undue submandibular pressure by the anesthesiologist’s fingers may worsen airway obstruction, especially in children. When using mask ventilation for children, the anesthesiologist’s third through fifth fingers must engage only the mandible and not compress the soft tissues overlying the tongue.
BOX 32-6 Achieving a Seal With a Face Mask
Place the mask strap beneath the occiput.
Apply the mask’s nasal groove to the low point of the nasal bridge to avoid pressure on the eyes.
Grip the left mandible with third, fourth, and fifth fingers of the left hand.
Lower the mask so its inferior rim contacts the face between the lower lip and the mental prominence.
If there is a leak between the mask and the cheeks, consolidate the seal by dragging mobile tissue of the left cheek toward and under the mask cushion, stabilizing the tissue with the ulnar margin of the left hand.
Bracing the mentum against the mask, pull the mandible up and forward with the third through fifth fingers while the thumb and index finger grip the mask above and below the connector.
Maintaining the left-sided seal, tilt the mask toward the right cheek, consolidating the seal by dragging the mobile tissue forward to the cushion and by keeping it there with one limb of the mask strap.
The other limbs of the mask strap may improve the seal, especially for anesthesiologists with small hands. Crossing the lower limbs of the mask strap prevents the mask from riding up the face.
A beard or broad mustache may hinder a good mask seal to make controlled ventilation difficult or impossible. For edentulous patients who are too alert to tolerate an oral airway, the lower margin of the mask can be placed against the mucosal reflection in the vestibule of the mouth while the lower lip is drawn over the mask. By inserting an oropharyngeal airway, an anesthesiologist can minimize the furrows in the cheeks of edentulous patients. Inserting an oral airway lengthens the distance between the supramental depression and the nasal bridge, occasionally necessitating substitution for the next larger mask size. For this reason, it is essential to have small, medium, and large masks available.12,30
APPLYING POSITIVE PRESSURE
Essential for applying positive airway pressure are a functioning breathing system (a backup self-inflating resuscitation bag is needed at all anesthetizing locations) and a leak-free mask seal. The anesthesiologist learns to adjust the pop-off valve and speed of reservoir bag compression to keep airway pressures below the 20 cm H2O associated with gastric inflation. Most patients can be ventilated well with peak airway pressures of 15 cm H2O or lower, providing a margin of safety against gastric insufflation.
Fit patients can tolerate generous doses of intravenous (IV) induction drugs without hypotension. A combination of an opioid, a benzodiazepine, and a hypnotic agent acts synergistically and generally renders the airway nonreactive for several minutes, during which inhaled anesthetics may be introduced. Large vigorous breaths and rapid escalations in inspired anesthetic concentrations may precipitate hiccups, coughing, breath holding, and laryngospasm, thereby delaying induction. Increasing sevoflurane or desflurane vaporizer settings by 0.5% increments every 5 breaths depresses airway reflexes before irritating inspired concentrations are reached. Intubating doses of neuromuscular blockers eliminate coughing or hiccups in minutes.
Positive pressure not only ventilates the patient’s lungs but also may overcome minor degrees of soft tissue obstruction of the airway. In a spontaneously breathing patient who is too lightly anesthetized to accept insertion of an oral airway, 5 to 15 cm H2O of continuous positive airway pressure achieved by partially closing the pop-off valve may relieve airway obstruction and increase the minute ventilation. Well-synchronized intermittent positive pressure breaths can achieve the same end. Inflation of the stomach with respiratory gases should be avoided because it decreases thoracic compliance and increases the risk of regurgitation.
An inability to ventilate with a face mask despite proper positioning, jaw thrusts, and a good mask seal may be caused by laryngeal spasm in response to light anesthesia or by soft tissue upper airway obstruction resulting from deepening anesthesia and the onset of muscle relaxation (Box 32-7).2,3 If a careful assessment suggests simple supraglottic obstruction, insertion of a pharyngeal airway to separate soft tissues from the posterior pharyngeal wall is a logical next step (Figure 32-12). Success confirms that the soft tissue had been obstructing the airway, but persisting or worsening obstruction often indicates active closure of the larynx. Active closure may be relieved by administering muscle relaxants or deepening anesthesia with intravenous agents. The anesthesiologist should sidestep the trap created by the pathologic causes of catastrophic obstruction that may be worsened by the loss of muscle tone.
BOX 32-7 Causes of an Inability to Ventilate
Laryngeal spasm or vocal cord adduction
Supraglottic soft tissue relaxation (obstruction)
Soft palate and pharyngeal walls
Chest wall rigidity
Pathologic, glottic, and subglottic
Enlarged lingual tonsil
Tumor or hematoma
Superior vena caval syndrome
Bilateral vocal cord palsy
Tracheal or bronchial compression
Great vessel anomalies
Selector valve accidentally in the “ventilator” position
CO2 absorbent canister preventing gas flow (eg, plastic overwrap not removed)
Artificial oropharyngeal and nasopharyngeal airways.
Until the arrival of the LMA and esophageal devices, oropharyngeal or nasopharyngeal airways were the best devices to relieve simple supraglottic obstructions. They remain inexpensive, safe, and generally effective.30,38 Trial and error often are necessary for even the experienced anesthesiologist to select an oropharyngeal airway long enough to anteriorly displace the base of the tongue without pushing the epiglottis into the laryngeal inlet. The forward portion of the oropharyngeal airway separates the teeth or gums; its flange keeps the device from dropping into the hypopharynx. To prevent displacing the tongue into the hypopharynx, the tongue is drawn anteriorly with a tongue blade held in the left hand while the right hand opens the mouth and inserts the oropharyngeal airway. An alternative method to prevent tongue malposition involves initially inserting the device with the concave side facing the hard palate and then rotating the device 180° as the tip enters the hypopharynx.
The onset of soft tissue relaxation and airway obstruction usually heralds depression of cough and gag reflexes sufficient to tolerate pharyngeal stimulation. If swallowing or gagging is triggered by a tongue blade or airway touching the base of the tongue, waiting until the patient is more deeply anesthetized is suggested; the stimulus itself often restores airway patency. Coughing and breath holding after uneventful placement of an oropharyngeal airway reflects airway irritation by anesthetic vapors. Coughing and breath holding are addressed by turning down the vaporizer and temporarily abandoning attempts at positive pressure ventilation or deepening the depth of anesthesia with intravenous agents.
A nasopharyngeal airway can be inserted before extubation in a patient with a clenched jaw who has an obstructed airway. Unfortunately, unless precautions are taken (Box 32-8), epistaxis may complicate the hasty introduction of an airway through the nasal passages. Because of alignment with the glottic opening, blind tracheal suctioning may be possible by passing a catheter through a nasopharyngeal airway. The need for and tolerance of repeated tracheal suctioning usually are indications for intubation.
BOX 32-8 Precautions for Introducing Nasopharyngeal Airways
Prepare the larger nasal passage with a vasoconstrictor.
Choose a soft, blunt-tipped nasopharyngeal airway.
Soften the nasopharyngeal airway by warming (not applicable for some materials).
Lubricate the airway.
To protect the turbinates, point the bevel medially.
Direct the device directly posteriorly parallel to the hard palate and beneath the inferior turbinate.
If resistance is encountered, withdraw, rotate 90° degrees medially, and readvance with gentle, steady pressure.
Ease a difficult passage using a soft suction catheter as an introducer.
The first modern SGA device was the LMA developed in the early 1980s by Dr Archie Brain.5 The LMA Corporation manufactures several varieties based on the original LMA Classic™ (cLMA) (Figure 32-13). These and other supraglottic devices have achieved great popularity for addressing simple SGA obstruction in a variety of contexts.41,42 Their unique capabilities (Boxes 32-9 and 32-10), relative ease of use, and low incidence of serious complications ensure SGAs have a place in the anesthesiologist’s armamentarium.43-50 Several studies have indicated that trained but inexperienced resuscitators are more likely to be successful ventilating a patient’s lungs with an SGA than intubating the trachea with direct laryngoscopy.51
Various laryngeal mask airways (LMAs) and endoscopic views of them. A. Shown from left to right are the LMA Unique, Classic, ProSeal, and Fastrach. B. The two epiglottic bars of the LMA Unique and Classic prevent entry of epiglottis inside the lumen of the LMA. C. Endoscopic macro view of the larynx when LMA is properly positioned. D. The LMA ProSeal does not have epiglottic bars, but the drain tube supports the epiglottis and prevents it from impacting inside the LMA tube. E. With the LMA Fastrach, the epiglottic elevator bar lifts the epiglottis as the endotracheal tube passes into the trachea.
BOX 32-9 Clinical Use of a Supraglottic Airway Indications
Surgical anesthesia without intubation
Airway management without neuromuscular blocking agent
Emergency ventilation when intubation has failed
Improving airway seal without tracheal intubation
Patient with facial hair
Assisting tracheal intubation
Providing a patent airway with minimal changes in blood pressure, heart rate, intraocular or intracranial pressure, or bronchial tone Contraindications
High risk of aspiration (relative contraindication)
Glottic or subglottic obstruction
Supraglottic pathology interfering with placement
Extremely limited mouth opening or neck extension
Prone position (relative contraindication)
Need for high airway pressure ventilation
BOX 32-10 Benefits and Limitations of a Supraglottic Airway Benefits
Permits ventilation when face mask and intubation have failed
Permits lighter anesthesia and faster emergence
Facilitates blind or fiber-optic tracheal intubation
Provides a good airway for fiber-optic bronchoscopy
Easier to learn than tracheal intubation Limitations
Proper position of the SGA may be difficult to achieve
Probable gas leak with a first-generation SGA when airway pressure is greater than 20 cm H2O
Limited protection against aspiration
No protection against laryngospasm
Becoming adept at proper SGA insertion requires consideration of a patient’s anatomy, patience, and practice.52 Even with suboptimal insertion techniques, success rates with SGAs are high, leading some practitioners to adopt unconventional techniques. Adherence to proper technique maximizes success and reduces complications. An SGA should be deflated with finger pressure on the dorsal aspect of the cuff so that the totally flattened cuff curves away from the aperture (Figure 32-14). A water-soluble lubricant should be applied to the dorsal surface of the cuff and kept from drying. The recommended technique for SGA placement is summarized in Figure 32-15.53 The presence of aperture bars within the mask bowl of an SGA prevents potential epiglottic obstruction of the ventilating lumen (Figure 32-13).
A deflated laryngeal mask airway. The cuff of the laryngeal mask airway is deflated before its insertion. The rim of the cuff should evenly face away from the mask aperture with no folds near the tip.
Technique for placing a laryngeal mask airway (LMA). A. The LMA is held by the index finger and the thumb facing the bowl of the LMA caudally toward the larynx. The index finger is positioned between the shaft of the LMA and the deflated cuff. The occiput is stabilized with the left hand. B. The deflated and lubricated LMA is placed into the open mouth pressed against the hard palate. C. The LMA is advanced behind the tongue and into the oropharynx using the index finger. D. The LMA is pushed farther, deep into the hypopharynx, using the tip of the index finger. E. The index finger is removed. The LMA is pushed farther down to its final position by holding the tube of the LMA with the left hand. Without holding the tube of the LMA, the cuff is inflated with the recommended volume of air. The LMA may protrude slightly on inflation of the cuff. [Modified with permission from LMA Airway Instruction Manual. San Diego, CA: LMA North America, San Diego, 2005.]
During insertion, the SGA must navigate past the soft palate, uvula, tonsillar fauces, oral-pharyngeal angle, tongue, and epiglottis. Placing the patient in the sniffing position with marked cervico-occipital extension aligns laryngeal structures to help accommodate the mask. A gloved hand flattens the tip of the mask against the hard palate to start it on a path that will not engage the epiglottis. The patient must be at a sufficiently deep plane of general anesthesia if an SGA is to be inserted easily and function properly. Alternatively, the SGA can be inserted in an awake or sedated patient after proper topical anesthesia has been established.
Although careful placement, cuff inflation, and adaptation time improve the seal, leakage often occurs at greater than 20 cm H2O airway pressure with a first-generation SGA, such as the cLMA. Obesity, a head-down tilt, abdominal insufflation, airway obstruction, or any other conditions necessitating ventilation with high airway pressures increase the risk of hypoventilation, gastric insufflation, and regurgitation.
The SGAs are particularly well suited for the lightly anesthetized, spontaneously breathing ambulatory surgery patient. Compared with face mask or endotracheal anesthesia, there seems to be less need for an anesthetic plane deeper than that required for the surgery itself.54 Patients instrumented with an SGA tolerate a lighter depth of anesthesia with less chance of coughing, breath holding, stridor, or laryngeal spasm compared with patients whose tracheas have been intubated.55 Increasing anesthetic depth usually manages episodes of movement, tachypnea, or hyperpnea. Finally, patients tolerate a return to consciousness and can follow commands while an inflated SGA is still in place. Positive pressure ventilation can be applied through the SGA45; however, the tidal volume, respiratory rate, and inspiratory/expiratory ratio should be adjusted to avoid high airway pressures. Newer anesthesia ventilators that synchronize breaths or provide pressure support to a spontaneously breathing patient are practical for the patient with an SGA in place.
Using an SGA in an unfavorable setting increases the likelihood of unfortunate results. The devices do not protect as effectively as an ETT against pulmonary aspiration of gastric contents.56-58 In low-risk populations, the incidence of aspiration with the laryngeal mask is reported to be similar to that of mask anesthesia and very close to that of endotracheal intubation.59 Application of cricoid pressure impedes placement of the SGA.60 Reported, but rare, complications include 12th cranial nerve paralysis,61 unilateral hypoglossal nerve paralysis,62 and transient bilateral vocal cord paralysis.63
Laryngeal Mask Airway ProSeal
Pulmonary aspiration of regurgitant gastric material has long been a concern with the use of SGAs. Modifications were made to the cLMA design in 2000 to produce the LMA ProSeal (pLMA). The pLMA is a reusable, cuffed laryngeal mask with an integrated gastric drainage tube and posterior dorsal cuff. The gastric drainage tube exits the tip of the mask cuff and is designed to lie over the esophageal inlet. In addition to the gastric drainage tube, the pLMA makes use of a posterior dorsal cuff for sizes 3 and above. The posterior cuff of the pLMA is designed for greater seal pressure than the cLMA. Greater seal pressure makes the pLMA attractive for applications that require high-pressure ventilation, such as laparoscopic procedures or the care of obese patients.64
The pLMA can be inserted using a special introducer or in a manner similar to a cLMA. A reliable technique for pLMA insertion uses a gastric drainage tube such as a Salem Sump™ as a guide to ensure proper positioning while minimizing the risk of pLMA folding. First, the gastric tube is advanced through the pLMA drainage tube, and the gastric tube is inserted into the patient’s esophagus, either blindly or under direct visualization with a laryngoscope. The pLMA is then advanced over the gastric tube and into the patient’s hypopharynx.65 In a similar technique, a gum elastic bougie is inserted in the esophagus with the pLMA drainage tube advanced over its proximal end.66
After the pLMA has been inserted, proper positioning is confirmed with a four-step process. First, ventilation is confirmed by appropriate chest rise and CO2 presence on the capnograph. Second, the leak pressure is measured by closing the automatic pressure-limiting valve and slowly increasing the pressure in the breathing circuit until a leak is heard or 25 cm H2O pressure is reached. Third, a small amount of water-soluble lubricant or a thin film of soap is applied to the proximal end of the drainage tube.67,68 When properly positioned, the meniscus will move slightly during respiration, reflecting normal variation in esophageal pressure. A kinked or folded device will have a motionless meniscus. If the tip of the device is not positioned properly in the proximal esophagus, gas will travel from the respiratory part of the device up the gastric drainage tube, displacing the lubricant proximally or causing the soap film to form a visible bubble. The fourth and final step involves passage of a lubricated suction catheter or gastric drainage tube, 14 French or smaller, through the gastric drainage lumen of the device. Easy passage through the gastric drainage port demonstrates that the device is not folded, and that the gastric drainage port is patent.
The suprasternal notch test is also assessed for drainage tube patency.69,70 In the suprasternal notch test, the patient’s airway is palpated at the suprasternal notch while observing for corresponding movement of the lubricant placed in the proximal drainage tube. The lubricant should be displaced slightly by the pressure transmitted from the suprasternal notch to a patent drainage tube. No movement might indicate an obstructed, and therefore nonfunctional, drainage lumen. Alternatively, the smooth passage of an orogastric tube through the drainage tube past the level of the pLMA mask also confirms patency.
Flexible Laryngeal Mask Airway
The flexible LMA (fMLA; LMA Company North America, San Diego, CA) is helpful when access to intraoral structures is desired or space is limited by the patient’s face. The fLMA has enjoyed use in dental surgery, otolaryngologic procedures such as tonsillectomy, and even ophthalmologic procedures.71
Intubating LMA (Fastrach iLMA)
The Fastrach intubating LMA (iLMA; LMA North America, San Diego, CA) is designed to assist with ventilation and intubation. In a series of 254 patients with difficult-to-manage airways, 96.5% of patients had successful blind intubation via the iLMA. The remaining patients were intubated using a fiber-optic scope placed through the iLMA.72 Patients have been intubated through the iLMA using a variety of ETTs.73-75 Please refer to the section on tracheal intubation for a discussion of intubation through the iLMA.
Laryngeal Mask Airway Supreme
The LMA Supreme® (sLMA), a single-use supraglottic device with features of the pLMA (gastric port and integrated bite block) and of the LMA Fastrach (curved shaft), was introduced in 2007. Limited studies of the sLMA appear to show ease of use and function similar to that of the pLMA.76,77 Leak pressure for the sLMA has been reported to be higher than that observed with the cLMA, but lower than that with the pLMA.78 The sLMA has also been used to assist tracheal intubation, but because of its narrow-caliber lumen, an exchange catheter is needed for removal of the sLMA before tracheal intubation.79
The LMA Classic Excel® (eLMA) looks like a standard cLMA but has been modified for use as an adjunct to tracheal intubation via the device. The eLMA has a removable 15-mm adapter to accommodate up to a 7.5 tracheal tube via the ventilating shaft. In addition, the eLMA trades the aperture bars of a cLMA for an epiglottic elevating bar similar to the one found in the Fastrach iLMA. The eLMA, currently manufactured as a reusable device, is not available as a single-use device.
As the LMA has grown in popularity and its design has been modified, there has been no shortage of novel SGAs introduced by other manufacturers.
The laryngeal tube (LT) uses a double-cuff system fed by a single inflation line. The larger proximal cuff is a pharyngeal cuff; the second and smaller distal cuff is designed to rest in the proximal esophagus. Ventilation occurs via a shaft that terminates between the two cuffs near the laryngeal inlet. The original LT has a single lumen, but the Laryngeal Tube Suction™ (LTS) adds access to a second esophageal lumen and drainage tube. The LT has been used successfully in the prehospital setting to establish ventilation in cases of difficult intubation in the field.80 Insertion success of the LT may also be higher in the prehospital setting than alternative SGAs.81
The i-gel® airway is unique in that it does not have an inflatable cuff. The i-gel relies on a soft thermoplastic elastomer material for its mask. The i-gel mask becomes pliable when warmed by a patient’s body temperature and forms a seal. The i-gel’s broad ventilating shaft prevents rotation of the device, and there is an integrated drainage tube for gastric venting. The i-gel has been used as a rescue airway in the setting of in-hospital cardiac arrest with some success.82 The i-gel also has been used in pediatric anesthesia practice with high success rates and infrequent complications, similar to the pediatric versions of the pLMA and cLMA.83
Air-Q/Intubating Laryngeal Airway
The air-Q® (single use and reusable) family of SGAs is designed to facilitate endotracheal intubation and provide ease of ventilation. Currently, there are three varieties: the original air-Q, air-Q Blocker (includes separate drainage lumen with optional blocker), and the air-Qsp (self-pressurized mask bowl). The air-Q’s cuffed mask bowl is attached to a ventilating shaft. With the original air-Q and air-Q Blocker, the cuff is inflated using a pilot balloon and inflation channel, which is not possible with the air-Qsp. All air-Q devices have removable 15-mm adapters for introduction of a tracheal tube. The air-Q family of devices lacks aperture or epiglottic elevating bars. The air-Q has been used successfully as an aid to fiber-optic tracheal intubation in pediatric patients and for awake placement followed by asleep fiber-optic tracheal intubation in a series of morbidly obese adults.84,85
COMPLICATIONS OF NON-INTUBATED AIRWAY MANAGEMENT
Improperly conducted or monitored airway management can result in hypercapnia, hypoxic organ damage, or both, although supplemental oxygen and pulse oximetry reduce the incidence of the latter.1 Hypercapnia is nearly always well tolerated; however, there are rare situations (Box 32-3) in which hypercapnia causes morbidity.
Laryngeal spasm is an abnormal airway reflex of a sustained, disinhibited glottic closure precipitated by instrumentation, fluid irritation, or ill-timed stimulation of the larynx or other body parts (eg, moving or examining the patient in a light plane of anesthesia) in the setting of insufficient anesthetic depth. The anesthesiologist should consider a wide variety of causes (Box 32-7) when treating a patient whose lungs are difficult to ventilate (Box 32-11).
BOX 32-11 Progression of Steps to Manage Difficulty in Ventilating a Patient’s Lungs
Confirm that the machine’s selector valve is set to “bag” and that the reservoir bag is not twisted.
Deliver 100% oxygen.
Without exceeding 25 cm H2O, increase airway pressure while intensifying jaw thrust and observing for ventilation or gastric distension.
If blood pressure is adequate and if awakening the patient is unnecessary, deepen anesthesia with a rapid-acting intravenous drug (eg, thiopental, propofol).
If depth of anesthesia is judged adequate, insert an oro- or nasopharyngeal airway or an SGA.
Consider whether it would be safest to awaken the patient.
Administer 5 to 20 mg of intravenous succinylcholine.
Consider the wisdom of a full dose of relaxant to facilitate tracheal intubation.
Consider using an alternative extraglottic airway, such as a Combitube™.
Consider establishing a transcricothyroid or surgical airway.
SGA, supraglottic airway.
Aspiration of regurgitant material is a rare but serious complication of deep sedation and general anesthesia. Although anesthesia deep enough to obliterate airway reflexes eliminates active vomiting, passive regurgitation is possible at any time during the care of an anesthetized or critically ill patient. Repeated inspiratory efforts against an obstructed airway and gastric distension with fluid, food, or air or other gases are predisposing factors to regurgitation.86,87 During regurgitation, liquids should be removed from the pharynx by rapidly lowering the patient’s head, turning it to the side, and suctioning with a rigid-tip (eg, Yankauer) catheter. Subsequent pulmonary aspiration of fluid, solid, or acid may result in bronchospasm and oxygen desaturation, tracheobronchial obstruction, or chemical pneumonitis. Although the ASA closed-claims studies indicated that aspiration is rare in modern anesthetic practice, the consequences are dire enough to consider the possibility of aspiration in every patient and to plan and prepare for it.1
Using a face mask with straps presents the risk of traumatic pressure to the eyes or branches of the facial nerve. Upper airway laceration caused by an oral- or nasopharyngeal airway may precipitate mucosal bleeding sufficiently severe to render laryngoscopy impossible.
AIRWAY MANAGEMENT WITH TRACHEAL INTUBATION
Tracheal intubation is undertaken for reasons of physiology, pathology, or convenience (Box 32-12). Reflecting an appreciation for the consequences of hypoventilation, hypoxia, and aspiration or because of a desire to free the anesthesiologist’s hands for other tasks, the prevalence of tracheal intubation during anesthesia increased until the introduction of the LMA in the 1980s, after which the proportion of anesthetics with endotracheal intubation was reduced.
BOX 32-12 Indications for Tracheal Intubation Anesthesia
Control of the airway is maximal.
Airway is unobstructed and leak free for prolonged ventilation.
Aspiration risk is minimized.
High peak airway pressures can be used for ventilation.
Resuscitation of a moribund patient is facilitated.
Complex diagnostic and therapeutic matters can receive attention.
It has preemptive utility if it is feared that ventilation and intubation may later become impossible.
Ventilation is possible during thoracoabdominal surgery.
Lung isolation is facilitated.
The anesthesiologist can be distant from the patient’s head.
A patient’s position can be prone, sitting, lateral, or head down.
It facilitates administration of medication (eg, anesthetic gases, bronchodilators, nitric oxide).
Blood and secretions are kept out of the trachea during airway surgery. Critical care
It establishes airway patency.
It protects against pulmonary aspiration.
It facilitates tracheobronchial toilet.
It provides a route for airway positive pressure ventilation modes.
Most ETTs are disposable and made of clear, bioinert polyvinyl chloride (PVC) that molds to the contour of the airway after softening at body temperature. Lengths are marked in centimeters, while internal and external diameters are indicated in millimeters. Implantation testing in animals has shown these materials to be nonirritating by the standards of the American Society for Testing and Materials’ Committee F-29 on Anesthetic and Respiratory Equipment.
Although the resistance of a small ETT can impair the ventilatory weaning of a critically ill patient, it generally is not necessary in the operating room to use the largest possible tube. In many cases, a 7.0- or 7.5-mm internal diameter ETT is chosen for female patients, and an 8.0-mm ETT is used for men. Good judgment dictates even smaller tubes for patients with airway edema (eg, preeclamptic individuals) or for nasal or blind intubation. Pediatric ETT sizes can be selected by an age-related formula and tested for leaks in situ.
Historically, cuffed tubes were not used in children younger than 8 years because classical teaching describes the infant airway as funnel shaped, with the smallest diameter at a circular cricoid ring. There was concern with older cuffed ETTs that cuff trauma to the mucosa at the cricoid ring could cause postextubation airway obstruction. Thus, conventional practice was to use an appropriate size round, uncuffed tube that allowed a small air leak but caused minimal trauma. Early cuffed ETTs that suited pediatric laryngotracheal dimensions were poorly designed.88 Cuffs of varying lengths and distances from the end of the cuff to the tip of the tube sometimes made it difficult to properly position the cuff below the vocal cords while keeping the tip above the carina. Older, bulky ETT cuffs often required using a smaller diameter ETT (downsizing by 0.5 mm), thus increasing the patient’s work of breathing.
New evidence shows that in children the glottis or subglottic area has the smallest diameter; the larynx is not really funnel shaped; and the cricoid is ellipsoidal, not round.15,89 Functionally, the cricoid is still the smallest area of the airway because it is cartilaginous and less distensible than the other structures, such as the subglottis and glottis.
Many pediatric anesthesiologists now routinely use cuffed ETTs in children younger than 8 years, but the use of cuffed tubes in premature infants and neonates is still controversial. Studies show cuffed ETTs are safe and beneficial in children.90-92 Advantages to cuffed ETTs include accurate capnography, less anesthetic agent, and fewer direct laryngoscopies to exchange tubes for the most effective size.90-93 There is no increased risk of croup or stridor after the use of cuffed ETTs in the operating room setting.90,91 One study showed fewer sore throats with cuffed ETTs.94 Excessive air leaks with uncuffed tubes may make ventilation difficult when respiratory compliance changes during a procedure. The cuff of the microthin, polyurethane, low-pressure, high-volume MICROCUFF* (Halyard Health, Alpharetta, GA) adds only 10 μm to the outer radius of the ETT, making downsizing unnecessary. There is no distal opening on the wall or side of the ETT, which allows the cuff to be positioned close to the tip of the tube. This makes it easier to place the cuff below the larynx without inadvertently intubating the bronchus.
Cutting ETTs renders them less obtrusive and easier to handle. For adults, a length of 26 cm should be sufficient for oral tubes, and 29 cm can be used for nasal tubes. The 15-mm adapter is affixed by wiping it with alcohol and twisting it firmly into place in the ETT.
High-volume cuffs contact the trachea over a broad area, minimizing the pressure on the mucosa and improving the seal, which may help minimize aspiration risk. The pressure in the cuff is estimated by squeezing the pilot balloon, or pressure is set to less than 25 cm H2O when measured by a manometer. With longer periods of intubation, cuff overinflation is prevented by periodically measuring pressure or by deflating the cuff until a leak is heard and then reinflating the cuff until the leak is sealed, adding 1 mL of air for a margin of safety. When nitrous oxide is used, the cuff merits periodic checks to detect overinflation. If nitrous oxide diffuses into the cuff, high pressures may injure the tracheal mucosa.
The standard ETT has a bevel that opens toward the patient’s left when the concavity of the tube’s curve faces anteriorly. This bevel facilitates passing the tube through the vocal cords. The Murphy eye is an opening in the tip of the tube opposite the bevel that protects against obstruction. A variety of ETTs are available for specific applications (Table 32-3; Figures 32-16 and 32-17). During laser surgery in the airway, PVC tubes can burn rapidly, causing injury and producing hydrochloric acid and other pulmonary toxins. To minimize the risk of an airway fire during laser surgery, the use of a specially made laser-resistant tube is recommended. The cuffs of these metal or silicone ETTs should be filled with blue-tinted saline for prompt recognition of a torn cuff.95
Varieties of tracheal tubes. Shown from left to right are the armored laryngectomy tube, laser tube, and laryngeal mask airway flexible nondisposable tube used for Fastrach intubation.
Varieties of tracheal tubes. From left to right are a standard tube for oral or nasal intubation; a preformed tube for nasotracheal use (Ring-Adair-Elwyn [RAE]; Mallinckrodt, Inc, Boulder, CO); a preformed tube for orotracheal use (Mallinckrodt Inc).
Table 32-3Special Tracheal Tubes and Their Applications ||Download (.pdf) Table 32-3 Special Tracheal Tubes and Their Applications
|Description ||Use |
|Embedded wire (armored or anode) ||Minimizes chance of kinking |
|Endotrol with an intrinsic cable to flex the tip ||Facilitates entry into the glottis |
|J-shaped laryngectomy ||Fits into a tracheal stoma without entering a bronchus |
|Laser adapted ||Minimizes chance of ignition |
|Lumen containing ||Sample airway gas or medicate the airway (eg, with lidocaine) |
|Microlaryngeal 4- to 6-mm inner diameter with adult length and cuff (MLT) ||Traverse a narrowed stretch of the airway |
|Preformed oral or nasal (Ring-Adair-Elvyn or RAE) ||Avoid the surgical field during head and neck procedures |
|Uncuffed ||Prevent subcricoid edema in patients younger than 8 years |
|Double lumen ||Lung separation |
|Univent bronchial blocker ||Lung separation |
Direct laryngoscopes are instruments designed to create a line of sight for passage of an ETT by displacing the tongue and epiglottis anteriorly.96 A battery-operated bulb may sit near the tip of the blade or in the handle itself, in which case illumination is directed by a fiber-optic bundle to the laryngeal structures. Blade-mounted bulbs operate erratically if their contacts become corroded.
Laryngoscope blades are classified as semicritical devices that require high-level disinfection or steam sterilization. New information about cross infection suggests that both blades and handles may be sources of infection, but there is no consensus on cleaning requirements. Therefore, high-level processing for the entire laryngoscope should be considered.97
The issue of contamination may be addressed by using disposable blades with or without disposable handles. There are multiple disposable devices made of high-grade plastic or metal on the market. Both plastic and metal blades have high laryngoscopic success levels, but metal blades have a slightly lower failure rate.
Although innumerable laryngoscope blade designs have been developed, two remain the most popular: the straight Miller, which lifts the epiglottis directly, and the curved Macintosh, which does so with traction on the glossoepiglottic and hyoepiglottic ligaments (Figure 32-18).
From top to bottom: straight blade (Miller), curved (Macintosh) blade, laryngoscope battery handle.
Rigid video laryngoscopes (VLs) are devices that have a small video camera and light source incorporated into a rigid metal or plastic blade. The real-time image from the camera is displayed on a video screen and can be recorded for later viewing, teaching, or research. VLs are designed to improve the view of the larynx to ease tracheal intubation. Because they do not rely on a straight line of sight, the user can “see around the corner” of the natural airway, obviating the need for alignment of the oral, pharyngeal, and laryngeal axes.98 This view facilitates visualization of the glottic opening with minimal force against the airway structures.
A viewing angle of up to 80° is possible compared with the 15° viewing angle of direct laryngoscopy.99 This extended viewing angle may be helpful in difficult intubations in patients with limited neck mobility, cervical spine immobilization, retrognathia, or reduced thyromental or interincisor distance.100 Use of VLs in anticipated and unanticipated difficult airways is supported by current literature.101 Step 3 of the ASA Practice Guidelines now suggests anesthesia providers consider video laryngoscopy as an initial technique for management of the difficult airway.20 In addition to facilitating laryngoscopy and orotracheal intubation, VLs can be used for awake, nasotracheal, or fiber-optic intubation; confirmation of proper tracheal tube placement; and placement of a transesophageal echocardiography probe.
Views of the glottis are generally better with VLs than with direct laryngoscopy. A better view, however, does not always translate into easy tracheal intubation. Tracheal intubation is difficult when the glottic view is obstructed by secretions, blood, gastric contents, fogging of the lens, or most commonly, the inability to advance the ETT through the larynx or into the trachea. Difficult ETT manipulation under indirect visualization has been shown to account for increased time to intubation, oxygen desaturation, hemodynamic instability, and the potential for airway trauma.102
Since 2001, several VLs have been introduced, which can be divided into two groups: non–channel-guided VLs and channel-guided VLs.
NON–CHANNEL-GUIDED VIDEO LARYNGOSCOPES
Examples of non–channel-guided VLs include the GlideScope® (Verathon, Inc, Bothell, WA); the McGRATH® Series 5 (Aircraft Medical, Edinburgh, UK); the McGRATH® MAC (Aircraft Medical); and the STORZ C-MAC® (Karl Storz, Tuttlingen, Germany) (Figures 32-19, 32-20, 32-21).
GlideScope®. [Used with permission from Verathon Inc., Bothell, WA.]
McGRATH® Series 5. [Used with permission from LMA North America, Inc., San Diego, CA.]
STORZ C-MAC®. [© 2015 Photo Courtesy of KARL STORZ Endoscopy-America, Inc., El Segundo, CA.]
The GlideScope was introduced in 2001, and since then multiple blade styles and sizes have been developed. Reusable and disposable blades exist, with choices suitable for intubation of the neonate, child, and adult. Options now include titanium low-profile blades and Macintosh-style blades. The high-angle blades have a steep 60° curvature, which improves the view of the glottis because the tongue is not displaced anteriorly (Figure 32-19). The maximum thickness of the largest original reusable and disposable blade is less than 15 mm, allowing use in a patient with an interincisor distance of 2 cm.103 The newer low-profile titanium blade is only 11 mm thick, further increasing clinical applications.104 The camera lens, heated to prevent fogging, requires no other preparation before use.
Tracheal intubation with the GlideScope generally requires use of a preloaded, specially curved stylet.105 The GlideRite® Rigid Stylet, curved to follow the 60° angulation of the blade, or a standard stylet can be used. If a standard stylet is used, the ETT and stylet should be bent to approximate the angle of the convex side of the GlideScope blade to facilitate advancement of the ETT into the trachea.103
The primary advantage of the GlideScope over direct laryngoscopy is an equal or improved glottic view in both normal and difficult airways. In patients with an anticipated difficult airway, the GlideScope increased the percentage of Cormack-Lehane grades 1 and 2 views compared with views with direct laryngoscopy.9,89 The GlideScope can be useful when direct laryngoscopy fails.106 However, no device has been shown to be superior to any other in all cases as direct laryngoscopy may rescue attempted intubation with a VL as well.106
Because views are improved without aligning the oral, pharyngeal, and laryngeal axes, less cervical manipulation is required. Cervical spine motion was reduced 50% during GlideScope intubation compared with direct laryngoscopy.106,107 The GlideScope can accommodate any size and type of ETT, and ratings for time to intubation and “ease of use” were better with both experienced and inexperienced users in simulated difficult airways.108
The McGrath MAC (Aircraft Medical) is a thin-profile, Macintosh-style device. It is portable with a 2.5-cm LCD screen attached to the handle, into which can fit a proprietary lithium battery pack lasting up to 250 hours. The device can be used for both direct and indirect visualization, making it versatile and easy to use for those familiar with direct laryngoscopy. Disposable blades come in Macintosh-style sizes 2, 3, and 4. The highly angulated X blade was introduced in 2013, further extending the clinical applications of this device.109
The device has been successfully used for routine and difficult intubations.110 The use has been for patients with decreased cervical spine mobility,111 for double-lumen tube placement,112 and in the critical care setting.113
The McGrath Series 5 was the first device from Aircraft Medical, introduced in January 2006 (Figure 32-20). This VL has a reusable CameraStick handle, which incorporates a small camera and light source. A sterile, transparent, single-use blade with a 60° angle covers the Camera-Stick. The camera image is displayed on a screen that tilts for viewing and is located on the handle. Within the handle is a single AA battery, which provides 60 minutes of operating time.
Similar to other VLs, the McGrath Series 5 has been shown to improve glottic views in both routine and difficult airways. Compared with direct laryngoscopy with a Macintosh blade, the McGrath improved Cormack-Lehane views by 2 to 3 grades in more than 90% of patients.102 Similar to the GlideScope, the McGrath Series 5 requires a stylet to facilitate intubation. This requirement may pose difficulties with ETT manipulation, leading to multiple intubation attempts, airway trauma, or failed tracheal intubation. As with the GlideScope, the blade and stylet can be withdrawn slightly, and the handle can be rotated caudally to advance the tube through the vocal cords without abutting the anterior tracheal wall.
Both the McGrath MAC and McGrath Series 5 are portable and completely immersible for ease of disinfection. The MAC has a long battery life and can be used for both direct and indirect visualization.
The C-MAC was introduced in 2003. Its steel Macintosh-style blades are available in sizes 2, 3, and 4 and a highly angled D blade114 (Figure 32-19). The thin profile (14-mm MAC 4 and 12-mm D blade) allows use in patients with small oral apertures. The C-MAC incorporates a digital video camera and a high-power light-emitting diode located laterally in the distal third of the blade. The image from the camera is displayed on a lightweight, portable, color LCD monitor and can be recorded as a single image or a video stream. The monitor houses a rechargeable lithium ion battery with approximately 2 working hours.115
CHANNEL-GUIDED VIDEO LARYNGOSCOPES
Examples of channel-guided VLs include the Pentax AWS®-S100 (Pentax Medical Company, Montvale, NJ); Airtraq™ (Prodol Meditec, SA, Guecho Vizcaya, Spain); and King Vision® (Ambu, Inc, Ballerup, Denmark) (Figures 32-22 and 32-23). These VLs have highly curved blades with a channel to hold the ETT during laryngoscopy and guide it during intubation.
Pentax AWS. [Used with permission from Pentax, Ballerup, Denmark.]
Airtraq. [Courtesy of Airtraq, LLC, Fenton, MO.]
The Pentax AWS, a battery-operated, channel-guided VL, was introduced in Japan in 2006. It has a handle with a 2.4-in LCD screen and a 12-cm image tube with a camera and light source116 (Figure 32-22). The lighter AWS-S200 is the successor to the AWS-S100 and runs for about 1 hour on two AA batteries. There are now multiple PBlade sizes appropriate for use in neonates up to obese adults. The thinner-blade PBlade (M-ITL-TL) is designed for patients with micrognathia or limited oral opening. A channel allows passage of a 4.0-mm catheter to suction the oral cavity during intubation.
The tube channel accommodates an ETT with a 6.0- to 8.0-mm inner diameter. The standard PBlade (18 mm thick) is larger than the blades of other VLs. It is used only if a patient’s mouth opening is larger than 2.5 cm. However, newer blades have widened the device’s clinical application to include infants and children.117,118 Typically, the blade is inserted under the epiglottis and used like a Miller blade. A distinct feature of the Pentax AWS is a target symbol on the monitor that highlights the intended path of the ETT as it advances from the tube channel. This target mark is aligned with the glottic opening, and the ETT is advanced into the trachea. Because the monitor is attached to the handle and the ETT is preloaded and directed toward the target symbol, the operator does not have to look away while advancing the ETT, which may lower risk for airway trauma.
The Airtraq is an optical, channel-guided VL with disposable and reusable components (Figure 32-23). The blade has two separate tracks: the optical channel and the tube channel. The optical channel contains a series of lenses, a prism, and a viewfinder at the proximal portion of the device. The image can be viewed many ways: The operator can look in the eyepiece; a smartphone can be placed in an adaptor for the viewfinder; the device can be attached to most endoscopy cameras, or the device can work with a Wi-Fi–enabled camera, which transmits the image to a smartphone or computer.119 There is a rechargeable battery-operated LED at the tip of the blade for illumination up to 90 minutes. The Airtraq comes in four sizes for orotracheal intubation with ETTs from 2.5 to 8.5 mm inner diameter. The Airtraq has special blades for nasotracheal and endobronchial intubation and can accommodate double-lumen tubes from 35 to 41 French.
The Airtraq blade containing the ETT is inserted midline into the oropharynx while the airway structures are visualized through the viewfinder. The blade tip is directed either into the vallecula (Macintosh style) or to the epiglottis (Miller style). The blade is manipulated in all planes until the vocal cords are in the center of the viewfinder, at which time the ETT is advanced through the channel into the trachea. If advancement is difficult, the Airtraq is rotated slightly out of the airway and lifted anteriorly. If these maneuvers fail, the operator can try reducing cervical extension.120 When ETT placement in the trachea is confirmed, the Airtraq blade is tilted laterally away from the ETT and removed.
The Airtraq has advantages in routine and difficult laryngoscopy.121 Compared with direct laryngoscopy, the Airtraq improves glottic views; facilitates first-attempt tracheal intubations; and lowers the incidence of oxygen desaturation, airway trauma, and hemodynamic instability. The Airtraq is easy to master for both novice and experienced anesthetists. It reduces cervical spine motion but causes less dental compression than other VLs and the Macintosh blade.122,123 Hemodynamic stability with use of the Airtraq versus the Macintosh blade may be attributed to less force needed to elevate the mandible during laryngoscopy. Constant visualization of the glottis and alignment of the preloaded ETT with the trachea cause less trauma to the vocal cords.123 Data for pediatric patients show that the device can be safely used in children, but improvement in facilitating intubation as determined by first-pass success and time to intubation remains debated.124,125 Differences in outcome may depend on age of the population studied. But, case reports of the use of the Airtraq for children with difficult airways exist.126,127
The King Vision (Ambu Inc., Ballerup, Denmark) is a portable system with a 2.4-in. thin-film transistor LCD screen. Blades slide over the end of this battery-powered reusable device that serves as handle and screen. Both an 18-mm thick channeled and 13-mm thick nonchanneled blade are available. The channeled blades can accommodate size 6.0 to 8.0 ETTs. Intubation with the nonchanneled blade requires a styleted ETT similar to other nonchanneled devices. The original blades housed a camera at the tip of the blade that projected images onto the screen. The newer aBlade system incorporates a reusable, detachable aBlade video adapter with a camera at its end that snaps onto the device. Then, aBlades (same sizes as original) slide over this imager. Removing the camera from the blade decreases the cost of each disposable piece, making it more affordable. The video can be fed to other monitors if desired.128 Initial studies suggested that, similar to other VLs, glottic visualization is very good. Studies in the operating room and prehospital settings showed good success rates.129-132 Awake intubation and use of the King Vision in patients with limited oral aperture has been reported.133,134
Because of the position of the tongue and epiglottis, a glottic opening not exposed by routine laryngoscopy appears to hide anteriorly. Stylets are blunt-tipped, malleable tools used to give a different shape to the ETT to facilitate tracheal intubation. Stylets are lubricated and inserted in the ETT but are not intended to protrude from the tube (the distal tip of the stylet is positioned inside the ETT). The tip of the ETT and stylet are bent about 5 cm from the end to achieve a “hockey stick” shape. The ETT is passed beneath the epiglottis, and an assistant removes the stylet as the ETT enters the trachea. Excessively stiff, carelessly placed, or improperly used stylets can cause life-threatening complications. A stylet that is used repeatedly may fracture during intubation.
Introducers, exemplified by the angle-tipped Eschmann gum elastic bougie, can be used to facilitate tracheal intubation. Longer and less rigid than stylets, introducers facilitate difficult intubation. Introducers should be used when a portion of the larynx is visualized (grade 3 or better Cormack-Lehane view). Passed through the tracheal tube, with a laryngoscope blade in place, the tip is guided into the trachea, and the ETT is threaded over it.
A soft, flexible introducer can serve as a tracheal tube exchanger and guide the blind insertion of a new tube if an exchange of tubes is necessary. Dedicated tube changers include models with a hollow center and Luer lock or 15-mm male adapters at the proximal end for insufflating oxygen until a new tube can be placed. Even if the glottic opening cannot be visualized, it may be helpful to use a rigid laryngoscope to create open space in the hypopharynx, thereby facilitating the passage of the ETT over the tube changer or stylet into the trachea. An ETT is less likely to hang up on the arytenoid cartilage if its internal diameter is not much larger than the introducer.
Tracheal intubation usually is performed after induction of anesthesia and muscle paralysis but is also easily accomplished in conscious patients. In some patients, muscle relaxants are avoided, and intubation is performed during general anesthesia with the patient breathing spontaneously. Visualization of the glottic structures ensures the greatest likelihood of successful tracheal intubation. Tracheal intubation is optimally undertaken after careful setup in an operating room or critical care area with an appropriately stocked cart (Box 32-13). A portable cart with advanced airway equipment should be readily available in case difficulty is encountered.20 Alternative techniques of intubation and ventilation may be lifesaving when suboptimal circumstances prevent visualized tracheal intubation.
BOX 32-13 Preparation for Tracheal Intubation
Assemble and confirm functionality of:
Equipment for face mask ventilation
Face masks of various sizes
Source of positive pressure oxygen
Tongue blade and oro- or nasopharyngeal airways
Appropriate size endotracheal tube (including smaller sizes in case of difficulty)
Intubating stylet or introducers
Stiff (tonsil-style) suction device
Position and environment
Access to patient’s head
Elevate bed so the patient’s forehead is at the level of the anesthesiologist’s xiphoid
Occipital elevation (sniffing position)
Injectable for nerve blocks
Spray for pharynx, larynx, and trachea
Ointment for tongue
Intravenous access for
Sedation or anesthetic induction
Intubating (Magill) forceps
Backup equipment for unanticipated difficult intubation or ventilation (difficult airway cart)
An ETT can be passed orotracheally, nasotracheally, or through a tracheostomy. Although passage of an ETT through a mature tracheostomy requires no special instruments, intubating through the mouth or nose can be extremely difficult or impossible.
Many techniques exist to assist routine and difficult tracheal intubation (Box 32-14).3,12,86 They vary in their level of sophistication, invasiveness, tendency for blood and secretions to obviate visualization, and potential for major complications. In developing an airway strategy, the anesthesiologist considers the risks and utility of each available technique and has alternative plans ready to execute in case of unexpected failure to intubate or ventilate the patient’s lungs. The ideals against which a technique may be judged are summarized in Box 32-15.
BOX 32-14 Techniques of Tracheal Intubation Visualized
Rigid laryngoscope (direct)
Flexible intubating scope (also known as a fiber-optic scope) (indirect)
Video laryngoscope (indirect) Guided blind
Retrograde wire Blind nasal
Combination of techniques Blind nasal
BOX 32-15 Desired Features of an Intubation Technique Primary
Performed with visual guidance
High success rate in those with a difficult airway
Useful for upper and lower airway problems
Useful for oral and nasal intubations
Can ventilate during intubation
Topical anesthesia can be applied
Devoid of technique-specific complications
Head and neck manipulations are not crucial for success
Useful in combination with other techniques
Blood and secretions do not interfere with its use Secondary
Avoids dental trauma
Equipment easily cleaned and stored
Easily learned and mastered
RIGID DIRECT LARYNGOSCOPY
Rigid laryngoscopy retains its popularity because of its simplicity, speed, high success rate, and good visualization.12,30,86 In adults, it is critical to elevate the back of the head on a pad to flex the neck so that the atlanto-occipital extension will align the pharynx with the mouth and larynx (Figure 32-24). If the patient has been given a muscle relaxant, a neuromuscular blockade “twitch” monitor is the best way to ensure complete neuromuscular blockade. Although succinylcholine provides the most rapid onset of relaxation, the effect of nondepolarizing relaxants can be hastened by using either large doses or the priming principle.
Intubating position during rigid laryngoscopy. A. Supine patient without a headrest. B. Head elevation and neck flexion bring the pharyngeal and laryngeal axes into line. C. Extension of head at atlanto-occipital joint aligns the oral axis with the other two axes. [Reproduced with permission from Longnecker DE, Murphy FL: Introduction to Anesthesia, 9th ed. Philadelphia: WB Saunders; 1996.]
The left hand grasps the open laryngoscope with the fifth finger just above the blade. Although simply extending the neck adequately opens some mouths, the best access is achieved by pushing on the right mandibular premolar with the right thumb while stabilizing the maxillary teeth with the third finger. With barrel-chested or obese patients, extra elevation of the head and shoulders or directing the laryngoscope handle to the left (rather than keeping it in a sagittal plane) prevents interference from the chest while inserting the blade in the mouth. The laryngoscope blade can then be slid along the right side of the tongue so that its flange displaces the tongue leftward. When it passes the right fauces, the blade is directed medially to the epiglottis, a key landmark. The tip of a curved blade, placed in the midline of the glossoepiglottic reflection, will maximally lift the epiglottis to expose the glottis. Straight blades are slid beneath the epiglottis to lift it directly (Figure 32-25). Elevation of the tongue and epiglottis is accomplished with the left hand pulling up and away from the anesthesiologist, keeping the left elbow close to the anesthesiologist’s side. The laryngoscope is not rotated or “levered” as the maxillary teeth can easily be injured. The view of the glottis may be improved by applying the right thumb and index finger to the thyroid cartilage for lateral or backward, upward, and rightward pressure (the BURP maneuver).86 Initiated by the laryngoscopist, laryngeal pressure can be maintained by an assistant during intubation. In small children, the relatively large occiput eliminates the need for a pad, and the more cephalad glottis increases the importance of laryngeal pressure.14
A. The straight blade is placed under the epiglottis to lift the epiglottis up to expose the glottis. B. The curved blade is positioned in the vallecula during rigid laryngoscopy. [Reproduced with permission from Longnecker DE, Murphy FL: Introduction to Anesthesia, 9th ed. Philadelphia: WB Saunders; 1996.]
Common preventable causes of difficult laryngoscopy include improper positioning of the head, inadequate opening of the mouth, selecting the wrong blade, letting the tongue hang over the right side of the blade, applying rotational force rather than translational force, and obscuring the line of vision with the ETT during its insertion. If the epiglottis is not seen, the blade may have been inserted too far. Slowly backing out the laryngoscope may bring the epiglottis into view. Conversely, selecting too short a blade prevents the tip from reaching the glossoepiglottic reflection.
Particular situations may call for either a straight or a curved blade. With its effective flange and its panoramic exposure of the anatomic features, the Macintosh curved blade is recommended for those learning intubation. It retracts large tongues and the prominent lips of edentulous patients. Because a curved blade does not touch the sensitive laryngeal surface of the epiglottis, it is well suited for intubation in conscious patients. In patients with micrognathia, a floppy epiglottis, or an anteriorly hidden glottis, the straight blade can lift the epiglottis for a superior view of the larynx. The Miller straight blade, with its small cross section, is especially useful when positioned in the right corner of the mouth in patients with prominent maxillary teeth or limited temporomandibular mobility.
Nasotracheal intubation guided by rigid laryngoscopy may be indicated in oral and maxillofacial surgery and in the intensive care setting. Introduced through the right corner of the mouth so laryngoscopic visualization is not blocked, a Magill intubating forceps directs the ETT tip to the glottis while an assistant advances the tube on command.86,135 The nasally inserted tube may hang up on the anterior laryngeal structures, requiring rotation of the tube or flexion of the neck or occipitocervical junction to facilitate the ETT entering the trachea.
Intubation of the Conscious Patient
In patients with a difficult airway or at high risk of aspiration, serious consideration should be given to securing the airway before inducing anesthesia.2,3 Intubation in a conscious patient is usually the best choice when risks of aspiration and difficult airway factors coexist. To ensure maximum cooperation, preanesthetic preparation includes an explanation of the procedure to the patient before premedication.
Sedation to an extent that may cause apnea or airway obstruction is contraindicated. Opioid-induced analgesia and depression of airway reflexes increase the risk of aspirating gastric contents but facilitate oropharyngeal instrumentation while providing a patient who is cooperative enough to follow commands. Protective reflexes remain more active when a benzodiazepine is used, but the patient may be less cooperative, reacting more vigorously to instrumentation. A combination of carefully titrated fentanyl in 25- to 50-μg aliquots up to 1.5 μg/kg and midazolam in 0.5- to 1.0-mg doses up to 30 μg/kg has been used successfully.136 To ensure that these synergistic drugs have reached their peak effect, 3 to 5 minutes should elapse between doses. Continually asking the patient to take deep breaths helps assess the patient’s responsiveness, thereby avoiding oversedation and hypoxemia.
Glycopyrrolate, 0.2 to 0.3 mg IV, minimizes secretions and improves the effectiveness of topical anesthetics.137 Patients may benefit from medications that increase gastric fluid pH (oral sodium citrate or famotidine) or enhance gastric emptying, such as metoclopramide.
Topical anesthesia is achieved by an oropharyngeal spray of 4% lidocaine and translaryngeal injection of 3 mL of 4% lidocaine. Topical anesthesia with lidocaine begins to work within 30 seconds after its application and is fully effective within 2 minutes but lasts only 20 to 30 minutes. For nasotracheal intubation, 4% cocaine or a 3-mL mixture of 4% lidocaine with 1 mL of 1% phenylephrine provides anesthesia while shrinking mucosae.138 Use of lidocaine jelly before application of other anesthetics to normal mucosa increases patient satisfaction.139
During rigid laryngoscopy in a conscious patient, the anesthesiologist continually instructs and reassures the patient while proceeding gently. Time may be required to spray more topical anesthetic on the tongue base or epiglottis. Laryngeal pressure by an assistant is particularly helpful, and a lingual nerve block may decrease refractory gagging.
Rapid-Sequence Induction and Intubation
In patients at high risk of aspiration without indication of difficult laryngoscopy or intubation, rapid-sequence induction (RSI) should be considered. Preoxygenation, avoidance of mask ventilation, and compression of the cricoid cartilage (Sellick maneuver; Figure 32-26) to resist passive regurgitation of gastric contents into the oropharynx are elements of a traditional RSI.4,30,86 Anesthesia begins with an injection of propofol or thiopental, immediately followed by succinylcholine. Intubation proceeds as soon as muscle relaxation is confirmed. An assistant maintains cricoid pressure from the onset of hypnosis until tracheal intubation is confirmed, and the cuff is inflated. Some providers mask ventilate with low inflation pressure during RSI. While not part of a traditional RSI, doing so helps maintain oxygen saturation and will inform clinical decision-making if intubation is discovered to be difficult. Other induction agents and nondepolarizing muscle relaxants are alternatives for induction.
Proper application of cricoid pressure during rapid-sequence induction and intubation to prevent passive regurgitation of gastric contents.
Cricoid pressure, as described by Sellick, should be firm enough to prevent the esophagus from slipping laterally but not so firm that it obstructs ventilation.4,140,141 This pressure may be difficult to attain as described because the 30-N (6.7-lb) force currently recommended may obstruct the view of the larynx.142 Application of cricoid pressure is a safe and effective maneuver, with only one reported case of esophageal rupture after vomiting. Complete anesthesia and paralysis, confirmed with a blockade monitor, eliminates any chance of active vomiting. With this knowledge, the anesthesiologist can be confident in having the assistant maintain cricoid pressure until the position of the tube in the trachea is certain.
If intubation fails, the risk of asphyxia may exceed the risk of aspiration. Mask ventilation with maintained cricoid pressure was described in 1961 by Sellick.4 If mask ventilation proves difficult, the patient may be placed in a 5° head-down tilt or kept in a flat supine position while cricoid pressure is slowly decreased until it is released. If mask ventilation is improved, the possibility of airway obstruction caused by improperly applied cricoid pressure35,140 should be considered, and intubation may proceed without cricoid pressure. If mask ventilation is impossible, previously unsuspected pathology (eg, hypertrophic lingual tonsils) should be considered. If a SGA is needed for rescue breathing, cricoid pressure may prevent proper positioning of these devices. Cricoid pressure should be released if the rescue breathing device is not working properly.
Anything that increases the intragastric-to-esophageal pressure gradient increases the risk of regurgitation of stomach contents. Factors that elevate this pressure gradient include inflation of the stomach with air, a steep head-down position, high intra-abdominal pressure, and spontaneous respiratory efforts against a fully or partially obstructed airway (this lowers the intraesophageal pressure). Airway pressures below 15 cm H2O during mask ventilation rarely inflate the stomach, but in adults not subjected to cricoid pressure, the minimum airway pressure required to push air into the stomach is reported to be 20 cm H2O.
In infants and children, correct application of cricoid pressure prevents gastric gas insufflation during mask ventilation with an airway pressure up to 40 cm H2O.143 Complete airway obstruction is one of the complications of improperly applied cricoid pressure. This is more likely in infants and children because of their more pliable trachea and laryngeal cartilages.
To perform video laryngoscopy with a non–channel-guided VL, the blade is inserted into the midline of the oropharynx under direct visualization until the tip of the blade is past the posterior tongue. Performing this under direct vision helps prevent damage to the soft palate or palatoglossal arch.144 When the device is past the tongue, attention is directed to the video screen, and the blade is advanced midline until a glottic view is achieved. Blades may come to rest in the vallecula or underneath the epiglottis. A Cormack-Lehane grade 2 glottic view is acceptable because if additional anterior force is applied to the blade, the larynx may be directed farther anterior, impeding passage of the ETT into the trachea.144 After the glottis is visualized, the operator’s attention is directed away from the video screen to the oropharynx, and the ETT is inserted under direct visualization until its tip is past the posterior tongue, paying careful attention not to injure the soft palate or palatoglossal arch with the ETT. The operator then looks at the video monitor while directing the tip of the ETT into the vestibule of the larynx and then advances the tube over the stylet, through the vocal cords, and into the trachea.
As the ETT passes over the stylet, its trajectory becomes less parallel to the axis of the trachea, occasionally causing the tip of the ETT to impact the anterior tracheal wall. This problem can be addressed in three ways. The ETT may be loaded on the stylet with “reverse camber” orienting the natural curve of the tube posteriorly. The tube then passes off the stylet parallel to the axis of the trachea. The operator may also spin or “corkscrew” the ETT as it passes off the stylet to minimize the impact of the ETT with the anterior tracheal wall. Finally, an ETT with no curve such as the Parker Tube (Parker Medical, Highlands Ranch, CO) or the Verathon GlideRite tube may be used.
Although highly angulated VLs such as the GlideScope may offer improved glottic views, advancement of the ETT into the trachea still can be difficult. Difficult advancement may prolong intubation times; increase the number of intubation attempts; and lead to failed intubation, oxygen desaturation, hemodynamic instability, and trauma to the soft palate and palatoglossal arch.98,105,144-146 If intubation is difficult, the blade can be withdrawn 2 to 3 cm, and lifting force can be reduced to lessen the anterior displacement of the larynx and improve the alignment of the axes of the larynx, trachea, and ETT.91,92
Video laryngoscopes with a conventional, or not highly angulated, shape such as the McGrath MAC and the STORZ C-MAC can be used as direct or indirect laryngoscopes. As with a Macintosh blade, advancement of the ETT into the trachea does not routinely require a stylet. The C-MAC improved glottic views and facilitated successful tracheal intubation when attempts with direct laryngoscopy failed.115 Compared with the GlideScope, Airtraq, and Macintosh blade in airway simulations, the C-MAC had the highest ratings for ease of use, provided the best glottic view (along with the Airtraq), and needed the shortest time for intubation.98 The STORZ C-MAC resulted in more successful first attempt intubations than direct laryngoscopy in patients with predictors of airway difficulty.147 The STORZ D-blade has a unique shape and works with the C-MAC platform. More curved than other C-MAC blades, the D-blade lets the user “see around the corner” of the tongue. Although this blade improves visualization of the larynx in some settings, it may require intubation techniques similar to those for the GlideScope system.
CHANNEL-GUIDED VIDEO LARYNGOSCOPES
With channel-guided VLs such as the Airtraq, Pentax AWS, or King Vision, the view of the glottis is indirect, obviating the need for alignment of the oral, pharyngeal, and laryngeal axes.98 A well-lubricated ETT is positioned in the tube channel of the blade, with only the tip visible on the LCD screen. The blade is inserted midline into the oropharynx under direct visualization until its tip is past the posterior tongue, preventing damage to the soft palate and palatoglossal arch. When it is past the tongue, the blade is kept midline, and attention is turned to the video display. After the glottic opening is observed on the monitor, the device is lifted up, and the ETT is advanced into the trachea. If the ETT abuts the epiglottis or arytenoids, the manufacturers recommend rotating the devices back (ie, out of the mouth) and lifting them anteriorly before readvancing the ETT.
A meta-analysis comparing the Pentax AWS with direct laryngoscopy showed improved glottic visualization but no difference in tracheal intubation time or success rates in routine and difficult airways with the AWS. Less cervical spine motion is needed during its use.107,148 Novice operators using the AWS have a high success rate visualizing the larynx. Tracheal intubation was faster and more likely to be successful on the first attempt for novices using the AWS compared with Macintosh direct laryngoscopy.108
The Pentax AWS has been used for tracheal intubation of awake and sedated patients. When the glottic view is obtained on the monitor, lidocaine can be injected through the suction channel to anesthetize the airway, and the ETT can be advanced through the tube channel.149
As with other VLs, advancement of the ETT into the trachea may be problematic after the glottic view is obtained on the monitor. The ETT may impinge on the epiglottis or arytenoids, in which case a gum elastic bougie is used. The bougie is inserted through the ETT and directed into the glottic opening. When the bougie is in the trachea, the ETT can be advanced over the bougie through the glottis. The bougie also has proved useful when the PBlade is too short to reach the epiglottis or larynx.150
The introduction of VL has significantly changed difficult and routine airway management. All of the commercially available devices improve glottic visualization, even in the hands of novice operators. The user should understand the fundamental differences between direct and video laryngoscopy. Direct laryngoscopy requires a straight line of sight from the operator’s eye to the vocal cords. The line of sight may be difficult to establish, but once the vocal cords are seen, tracheal intubation is usually easily achieved. On the other hand, VLs make viewing the larynx easy even when the airway maintains its normal, highly curved architecture. Thus, viewing the cords is often easier with a VL than with direct laryngoscopy, but passage of the tube through the cords may be harder. As with any tool, its proper use and unique strengths and weaknesses must be understood.
Flexible Intubation Scope (Also Known as Fiber-optic) Intubation
A flexible bronchoscope has a handle and a long insertion cord with a maneuverable, flexible tip. Traditional flexible bronchoscopes have a delicate fiber-optic bundle that carries light from the handle to the tip and a separate cohesive bundle of glass fibers that transmit the image back to the eyepiece in the handle. Newer scopes incorporate video chips at the tip, and in some devices, LEDs provide the light source. Compact, battery-powered light sources for bronchoscopes have proven advantageous when portability, compact size, and low weight are important. Disposable, single-use bronchoscopes remove the concerns of high per-unit expense, allowing the devices to be strategically deployed throughout the hospital in areas such as intensive care units and emergency departments. These areas may not previously have been candidates for expensive but rarely used capital equipment. In addition, concerns about device breakage, sterilization, and reprocessing costs are removed with disposable devices.
A flexible intubation scope, also referred to as an FIS or fiberscope (Figure 32-27), can be used for routine or challenging intubations in patients with airway tumors, infections, or cervical spine fractures or fixation (Figure 32-28).3,137-142 Prior to the introduction of VLs, awake FIS intubation was the clear gold standard for anticipated difficult intubations. However, recent publications proposed the use of VLs for awake oral or nasal intubation in these patients.151,152 Acquiring or retaining skills with FIS intubation remains necessary as there may be cases where FIS intubation is the only option, such as in patients with a mouth opening less than 14 mm or when space-occupying lesions within the oropharynx are present.153 The FIS used in conjunction with VLs or SGAs may be advantageous in certain situations.154,155 Indications for flexible scope tracheal intubation are summarized in Box 32-16. Among the shortcomings are size, cost, relatively fragility, and susceptibility to obliteration of the view by blood and secretions.
Flexible intubation scope. Modern scopes have a video camera at the distal tip. The tower contains a light source, video processor, and monitor.
Advanced carcinoma of the larynx.
BOX 32-16 Indications for Flexible Intubation Scope (Fiber-optic) Intubation
Routine intubation (teaching and learning)
History of previous difficult intubation
Physical evidence of difficult intubation
Upper airway abnormality
Tracheal stenosis or compression
Minimization of neck movement
Unstable cervical spine
Vertebral artery insufficiency
High risk of dental damage
Poor, loose, or fragile teeth
Extensive dental restoration
Awake or sedated intubation
Flexible scope intubation can be accomplished nasally, orally, awake, or under general anesthesia. Because normal airway architecture is maintained, provided proper preparation, FIS intubation is easier in conscious patients: The tongue and epiglottis are less likely to obscure the vocal cords, and patients can assist by phonating or protruding the tongue. Haste is unnecessary in a breathing patient, and desaturation can be mitigated with oxygenation via a nasal cannula. The patient with a history of failed intubation, upper airway abnormality, or expected difficult intubation may benefit from an awake FIS intubation. Depending on the degree of anticipated difficulty and other patient characteristics, sedation may be acceptable or advantageous. Use of benzodiazepines, opioids, propofol, remifentanil, dexmedatomidine, and other medications has been described.156 Topical anesthesia can be achieved as described in the section on intubation of the conscious patient. Inhalation of nebulized lidocaine may minimize coughing. With experience, topical anesthesia of the larynx and trachea may be achieved by spraying local anesthetic through the working channel of the FIS as it is advanced. Alternatively, an epidural catheter can be threaded through the channel and local anesthetic administered through it to direct the anesthetic properly.
After applying topical anesthetic to the tongue and oropharynx, a special oropharyngeal airway is inserted to prevent biting on the FIS, to keep the instrument in the midline, and to restrain the tongue (Figure 32-29).3 The oropharynx is suctioned, and the lubricated ETT is placed over the FIS and slid as far proximal as possible. If the FIS is accidentally passed through the Murphy eye of the ETT, intubation will not be successful even after the FIS is guided into the trachea. The left thumb maneuvers the control lever on the handle, moving the tip anterior or posterior, and the right hand gently advances the tip of the scope into the oral cavity (Figure 32-30).
Ovassapian fiber-optic intubating airway. [Used with permission from Telefllex Inc., Durham, NC.]
Fiber-optic orotracheal intubation during sedation and topical anesthesia. A. After sedation and application of topical anesthesia, an Ovassapian intubating airway is placed, and the oropharynx is suctioned. B. The endotracheal tube is removed from a warm water bath, lubricated, and placed inside the airway. The flexible intubation scope (FIS) is advanced through the endotracheal tube into the oropharynx, under the epiglottis, and inside the trachea. Care should be exercised to avoid passing the FIS through the Murphy eye. C. The endotracheal tube is passed over the FIS into the trachea. The distance between carina and tip of the endotracheal tube is measured using the FIS before it is removed.
As the FIS is advanced toward the oropharynx, the soft palate and uvula come into view (Figure 32-31). With entry into the oropharynx, the tip is deflected anteriorly to expose the epiglottis and vocal cords. To separate a floppy epiglottis from the posterior pharyngeal wall, the head is extended at the atlanto-occipital joint, and tongue traction or jaw thrust is applied. In an obese patient or one with a difficult airway, the sitting position will improve airway patency and pulmonary physiology.
Endoscopic view during orotracheal intubation. A. As the flexible intubation scope (FIS) enters the intubating airway, the white laryngeal surface of the Ovassapian airway is seen at the top of the circle. The soft palate is visualized in the lower half of the image. B. When the tip of the FIS is advanced to the oropharynx, the epiglottis is in the center of the view. C. With the tip of the FIS passed beneath the tip of the epiglottis, the glottic opening is visualized. D. The tip of the FIS is located in the lower third of the trachea, revealing the carina.
After the glottis is exposed, it is maintained in the center of the field of view by fine manipulations of the control lever. The FIS is advanced into the midtrachea, as confirmed by a view of the carina and flat posterior wall. The ETT is slipped over the FIS and advanced with a twisting motion into the trachea, positioning the tip 3 to 4 cm above the carina.
In many patients, even though the FIS has entered the trachea, the ETT catches on laryngeal structures and cannot pass. In such a case, the ETT is pulled back and rotated 90° counterclockwise until the leading edge of the bevel is oriented anteriorly. The patient is instructed to inspire deeply, abducting the vocal cords, and the tube is readvanced over the FIS. In some patients, this maneuver may have to be repeated two or three times, particularly when a large discrepancy exists between the size of the FIS and the ETT. Passage of the tube over the FIS into the larynx can be facilitated by using a larger FIS,157 a special tube with tapered tip158 such as the tube used to intubate through the Fastrach LMA (Figure 32-32), or a Parker tube (Parker Medical, Highlands Ranch, CO). Laryngospasm also may prevent ETT advancement. Additional topical anesthesia applied through the FIS usually remedies this problem.
Endotracheal tubes over a 4.0-mm flexible bronchoscope. The tube designed for intubation through the Fastrach LMA (right) has a curved tip, which eases passage of the tube into the trachea.
Nasotracheal FIS Intubation
In the conscious patient, FIS nasotracheal intubation often is easier than an oral approach.3 Minimal pressure on the base of the tongue causes less gagging, and the patient cannot bite the tube. By creating a “straight shot,” passing the FIS through the nose facilitates locating the glottis and advancing the FIS and tube into the larynx. A warmed, softened, lubricated tube advanced into the pharynx through a nasal passage prepared with anesthetic, with or without a vasoconstrictor, serves as a channel to suction the pharynx and to find the glottis with an FIS. Laryngeal anesthesia and intubation proceed as described for the oral method. The gag reflex is minimized or eliminated during nasal intubation, so minimal or no oropharyngeal topical anesthesia is needed. If the tube does not easily pass from the nasopharynx to the posterior oropharynx, it is pulled back, rotated 90°, and reintroduced. If this maneuver fails, the ETT is withdrawn and a lubricated FIS is advanced from the nasopharynx to the posterior oropharynx. The ETT is then gently advanced over the FIS into the oropharynx.
Passing the tube too far into the oropharynx may direct the FIS into the esophagus or away from the midline, preventing laryngeal exposure. The oropharynx is suctioned thoroughly through the ETT before the lubricated FIS is inserted through it. In most patients, the epiglottis and vocal cords are seen immediately with minimal manipulation of the FIS tip. In heavily sedated or edentulous patients, the tongue and pharyngeal tissues may block exposure of the glottis, necessitating head extension, jaw thrust, or tongue traction. The FIS is advanced into the midtrachea followed by the ETT.
Flexible scope oral and nasal intubation in an anesthetized patient requires an assistant to monitor the patient and apply the jaw thrust.3 Intubation attempts are interrupted to ventilate the patient’s lungs as needed. With oral and nasal approaches, the ETT is loaded on the FIS before intubation is attempted. The FIS is then passed through the nostril or intubating airway into the mouth and advanced through the glottis into the trachea. The ETT then is advanced over the FIS into the trachea (Figure 32-33).
Fiber-optic orotracheal intubation during general anesthesia. A. The patient is paralyzed, the intubating airway is in place, and the oropharynx has been suctioned. The operator receives the flexible intubation scope (FIS) from an assistant and inserts the tip of the FIS inside the intubating airway. B. The assistant applies a jaw thrust as soon as the FIS has been passed to the operator. The operator looks at the monitor and advances the insertion cord through the airway and vocal cords into the trachea. The tube is rotated 45° to 90° counterclockwise if resistance is encountered during advancement through the vocal cords. Note the position of the endoscopist’s right hand.
Failed direct rigid or video laryngoscopic intubation during RSI leaves the patient vulnerable to aspiration. If the patient’s lungs can be ventilated via face mask, oral fiber-optic intubation with cricoid pressure is an effective technique that should be seriously considered. The ability to perform rapid fiber-optic intubation may prevent airway catastrophes. Repeated unsuccessful attempts at blind nasal intubation or at rigid laryngoscopy traumatize the airway, converting a manageable airway into one that is impossible to ventilate.
In RSI incorporating fiber-optic intubation, one assistant maintains cricoid pressure while another applies jaw thrust (Figure 32-34). Excessive cricoid compression may block the endoscopist’s view of the glottis by folding the epiglottis posteriorly. In this setting, it may be appropriate to gradually release cricoid pressure until the larynx is visualized.
Fiber-optically aided rapid-sequence induction and intubation. The first assistant on the right side of the operator applies cricoid pressure before induction of anesthesia. The second assistant on the left of the operator administers the induction agents, passes the flexible intubation scope (FIS) to the operator, and then applies jaw thrust.
In retrograde intubation, a guidewire is passed through a needle that has been percutaneously inserted through the cricothyroid membrane or between the first tracheal ring and the cricoid cartilage. The wire is delivered via the needle through the mouth or nose to serve as a guide for the ETT.159-165 Dedicated kits (Cook Retrograde Intubation Set, Bloomington, IN) are available for pediatric and adult use. This blind technique can be used in adults or children when blood, secretions, or anatomical distortion prevent visualization of the glottic structures or in patients with limited cervical spine mobility or small oral aperture, especially when other devices such as FISs are not available.166-168 Contraindications include unfavorable anatomy such as with morbid obesity, laryngotracheal disease, and coagulopathy. Although laryngotracheal disease is an indication for this procedure, severe stenosis may be worsened by the needle puncture or catheter placement.169
The supine patient is placed in the sniffing position. Then, the oropharynx, larynx, and trachea are topically anesthetized. A Touhy or other 18-gauge needle, attached to a syringe containing 2 mL of lidocaine 4%, is inserted into the larynx through the cricothyroid membrane in a slightly cephalad direction. Aspiration of air confirms correct placement of the needle, and local anesthetic is injected into the larynx. The guidewire is threaded through the needle into the pharynx, and the tip is delivered through the mouth. A guide is passed over the wire, through the mouth, through the vocal cords, and into the trachea. Before the wire is removed, the ETT is advanced over the guide into the trachea (Figure 32-35). Use of a ventilating bougie as a guide to aid in advancing the ETT into the larynx has been described.170,171
Retrograde intubation. A. A needle attached to a syringe filled with lidocaine is passed through the cricothyroid membrane into the larynx. Free aspiration of air confirms correct placement of the needle. Lidocaine is injected to provide topical anesthesia of the airway. B. The guidewire is passed into the needle, retrograde through the larynx, and up into the oropharynx. The guidewire is retrieved through the mouth using a hook or forceps. The endotracheal tube is advanced over the guidewire into the trachea. [Reproduced with permission from Ovassapian A: Fiberoptic Endoscopy and the Difficult Airway, 2nd ed. New York: Lippincott-Raven; 1996.]
An FIS loaded with an ETT may be advanced over the guidewire or next to the guidewire to assist retrograde intubation.159,161,163 A technique that involves passing the guidewire through the suction channel of the FIS has greatly improved the success rate of retrograde intubation.
If the larynx is entered through the cricotracheal membrane rather than the cricothyroid membrane, the ETT can be advanced farther into the larynx.165 In this method, the cricothyroid arteries that cross the cricothyroid membrane at its proximal section are avoided.
The most common complication in the retrograde technique is bleeding in and around the airway. Bleeding usually is minor and does not require special treatment. Other complications are trauma to the airway, pneumomediastinum, and failed intubation.172
Blind nasal intubation is a valuable technique in patients who are uncooperative, unable to open the mouth, or have a fair amount of secretions or blood in the airway.86,173-175 The nasal mucosa is prepared with cocaine or a mixture of vasoconstrictor and local anesthetic. If sedation is needed, ketamine has been used for sedation with spontaneous ventilation or to induce general anesthesia for blind nasal intubation.173
The head is placed in the sniffing position, and a lubricated ETT is advanced gently into the oropharynx. If resistance is encountered at the oropharynx, the tube is pulled back about 2 cm, rotated 90°, and readvanced. If the maneuver is unsuccessful, a suction catheter or a nasogastric tube passed through the ETT into the oropharynx serves as a guide. The intensity of breath sounds and bulging in the neck guide maneuvers.174 As the tube is advanced toward the larynx, the breath sounds become louder. To help pass through the cords, the patient is encouraged to breathe deeply and rapidly, and the tube is advanced swiftly during inspiration. Successful intubation is confirmed by continued breath sounds through the tube and the patient’s inability to phonate. Coughing is common when topical anesthesia is omitted.
If breath sounds stop being transmitted through the tube, the tube has not entered the trachea. It may be in the esophagus, vallecula, or one of the piriform recesses. A loss of breath sounds without resistance to passage indicates esophageal placement. In this case, the tube should be withdrawn and readvanced after further elevating and extending the patient’s head. Inflating the tracheal tube cuff with 15 mL of air may accomplish the identical end.175 The tube is advanced 1 to 3 cm before the cuff is deflated and advanced farther into the trachea. Entry into a piriform recess is corrected by withdrawal and rotation. Obstruction by the epiglottis necessitates neck flexion and jaw thrust or application of traction on the tongue.
Success rates between 86% and 97% have been reported for blind nasal intubation. Success rates in emergency room patients are approximately 90%.176 Blind nasal intubation is less successful when the larynx is distorted by a mass, edema, or scarring from previous surgery. Contraindications to blind nasal intubation include nasal pathology, coagulopathy, thrombocytopenia, severe midface trauma, or prior transsphenoidal surgery—after which an ETT may pass into the cranium.
Complications of blind nasal intubation include trauma to the nasopharyngeal mucosa, entry into the submucosal plane of the pharynx, dislodging nasal polyps, pushing foreign bodies into the larynx, and nasal bleeding.174,176 Difficulty advancing the tracheal tube into the oropharynx may be the result of a deviated septum, a turbinate spur, hypertrophied inferior turbinates, or nasopharyngeal lymph nodes. A smaller tube or use of the other nostril may remedy these problems.
INTUBATION THROUGH A SUPRAGLOTTIC AIRWAY
Supraglottic airway (SGA) devices can be used to facilitate tracheal intubation. This technique is useful in patients in whom cervical spine immobilization is important, where access to the airway is limited, and in the CICV secenario.177,178 Virtually all SGAs can be conduits for intubation. When using SGAs for this purpose, it is important to be familiar with appropriate device sizing and positioning. For example, if rescue intubation is attempted by passing an ETT blindly through a cLMA, the largest PVC ETT that will fit is a size 6.0 mm, and the distance from the LMA aperture bars to the vocal cords is 3.5 cm.179 If the length of a 6-mm ETT is limited to 26 cm, the cuff of the ETT will be positioned inside the larynx just millimeters beyond the vocal cords, which increases the possibility of a laryngeal nerve palsy.
To address these issues, several devices, such as the LMA Fastrach™ (LMA Northamerica, a Teleflex Company); air-Q® (Cookgas LLC; distributed by Mercury Medical); Ambu Aura-i™ (Ambu, Inc.); and i-gel (Intersurgical, Inc.) have been designed specifically to facilitate intubation. The LMA Fastrach can serve as a primary airway, but its main purpose is to provide a conduit for endotracheal intubation. In a series of patients with difficult-to-manage airways, blind endotracheal intubation with the LMA Fastrach was successful 96.5% of the time.72 Its stiff airway tube with metal handle, epiglottis lifting bar, and accompanying ETT, may be reasons for its success. The air-Q, Ambu Aura-i, and i-gel have larger-diameter air tubes, enabling larger ETTs to be inserted through the device.126 Tracheal intubation through a supraglottic device can be achieved blindly or with the aid of an FIS. In each case, either an appropriately-sized ETT can be inserted directly through the SGA or a guide to facilitate the threading of a larger ETT after SGA removal can be used.63,129,132,180
Correctly sized and functioning equipment should be available before initiating the procedure. The selected supraglottic device, lubricant, ETT, and an ETT stabilizer (also known as a “pusher”) should be available at a minimum. It is prudent to confirm that the chosen ETT fits through the SGA when the pilot balloon is deflated, and that the ETT connector can be removed readily from the ETT. The stabilizer can be the specific device made by the SGA manufacturer, such as for the LMA Fastrach or air-Q, or an additional ETT can act as a stabilizer if needed.
Blind intubation via an SGA proceeds in the following general sequence: The SGA is inserted, ability to ventilate is confirmed, the ETT is threaded through the SGA, and the ETT pilot balloon is inflated. The ETT is attached to the breathing circuit; CO2 and bilateral breath sounds are confirmed; and the pilot balloon on the ETT is deflated. The ETT connector is removed, and the ETT is “pushed” into the SGA as the SGA is removed slowly. The ETT then is stabilized as quickly as possible and the SGA fully removed. The ETT connector is replaced, the pilot balloon is inflated, and CO2 and breath sounds are again verified. Many devices can be used successfully for this blind technique. Studies consistently show that the LMA Fastrach has higher success rates.181,182
With proper SGA positioning, the aperture lies opposite the glottic inlet for blind insertion of an ETT or guide. SGA positioning can ensue as discussed in the section on supraglottic devices. One well-documented maneuver is the two-step Chandy maneuver to improve the position of the Fastrach before blind intubation.72 In the first step of the Chandy maneuver, the device’s metal handle is rotated in the sagittal plane until ventilation is optimized. In the second part of the Chandy maneuver, the Fastrach is lifted to displace it anteriorly away from the posterior pharyngeal wall. The second part of the Chandy maneuver is applied as the ETT is advanced through the device.72
Correct position is important for success during SGA-assisted endotracheal intubation, but the type of ETT is also a consideration. The manufacturer of the LMA Fastrach produces a reusable, reinforced ETT for use with the LMA Fastrach. This ETT is made of wire-reinforced silicone with a blunted tip, features that facilitate smooth passage into the trachea. Standard PVC ETTs can be used with the LMA Fastrach, but their rigid design and sharper bevel increase the risk of resistance or injury during blind intubation. Reverse loading of a standard ETT, so that the curve of the tube points posteriorly, has been reported to increase first-attempt success at blind intubation with the LMA Fastrach, although overall success was the same with a traditionally loaded standard ETT.75 Other devices, such as the air-Q, i-gel, and Ambu Aura-i are intended to be used with standard PVC ETTs. The tapered Parker Flex-Tip ETT has had high success rates with the Fastrach when rotated 180°.183
When time and resources allow, FIS assistance should be considered. Direct visualization of the glottis and trachea decreases the likelihood of airway trauma and increases the likelihood of successful intubation.184 One study of patients with a known or predicted difficult airway showed that using an FIS in conjunction with an intubating LMA produced a 100% success rate for tracheal intubation.72 Use of the Aintree catheter, guidewire plus airway exchange catheter (AEC), gum elastic bougie, and small ETT as guides has been described.79 The air-Q catheter has been used as an intubation conduit in children when other means of intubation have failed.185 The Aintree intubation catheter (Cook Critical Care, Bloomington, IN), which is 56 cm long with a 4.7-mm internal diameter, is specifically designed to facilitate intubation when an SGA is in place. An FIS is placed through the catheter. The FIS and catheter are then directed through the SGA into the trachea. The Aintree catheter is left in place, the FIS is removed, and then the SGA is removed over the catheter. The ETT is placed over the catheter into the trachea.
CRICOTHYROTOMY AND TRACHEOSTOMY
Surgical airway access through the anterior neck is indicated in patients with severe upper airway obstruction or failed tracheal intubation combined with impossible ventilation. In cricothyrotomy, the larynx is entered through the cricothyroid membrane to pass a small ETT or a special cricothyrotomy tube into the trachea. Cricothyrotomy is preferred to tracheostomy when an airway must be established promptly. Cricothyrotomy is faster, is easier to perform, and is farther away from the mediastinum than a tracheostomy. Several kits are available for percutaneous cricothyrotomy, including the Melker cricothyrotomy system (Cook Critical Care). Applying the Seldinger technique for cricothyrotomy is familiar for nonsurgeons treating a patient with a difficult airway.186 Cricothyrotomy usually is performed during emergency situations and under less-than-optimal conditions, which increases the chances for laryngeal injury. After the patient’s condition is stabilized, the wound and the larynx should be examined.
PERCUTANEOUS TRANSTRACHEAL OXYGENATION
Placement of a large-bore catheter through the cricothyroid membrane (needle cricothyrotomy) into the trachea gives rapid access to the airway and can be lifesaving when mask ventilation and tracheal intubation have failed.186-189 Percutaneous transtracheal jet ventilation is also an interim means of oxygenation during difficult intubation.188
The incidence of malfunctioning of thin-walled 16- or 14-gauge intravenous catheters caused by kinking or dislodgement is high and can cause major complications. Large population studies indicated that surgical cricothyroidotomy has a higher rate of success for surgeons, emergency physicians, and anesthesia providers in CICV scenarios.19
The Arndt emergency cricothyrotomy catheter set (Cook Critical Care) was developed to minimize the problems associated with emergency cricothyrotomy. The set has a 3-mm kink-resistant catheter with a 15-mm connector coaxially positioned over a Luer lock connector. A hollow, tapered-tip dilator assists the placement of the catheter into the trachea. After it is in place, the airway catheter and its 15-mm connector may be attached to the common gas outlet of the anesthesia machine or self-inflating resuscitating breathing bag (eg, Ambu bag) or directly to a jet ventilator through the Luer lock connector. The relatively large tracheal catheter is effective for high-pressure jet ventilation. Bag-valve manual ventilation delivers oxygen but is ineffective for ventilation, which will result in a progressive increase in CO2 concentration.
In the event of total upper airway obstruction, percutaneous transtracheal jet ventilation requires that an exit airway be established. The technique can cause barotrauma, including pneumothorax; pneumomediastinum; or injury to the larynx, trachea, and esophagus. Inadequate time for exhalation or inability of gas to escape can lead to “breath stacking” or pulmonary tamponade. The resultant impairment of venous return can lead to hypotension and even pulseless electrical activity similar to that seen with a tension pneumothorax. It is prudent to practice the technique first on a mannequin and then during controlled patient care conditions before applying it to emergency situations.
CARE AFTER TRACHEAL INTUBATION
CONFIRMATION OF TRACHEAL INTUBATION
While visually observing the position of the ETT between the vocal cords after passage is a reliable indicator of tracheal intubation, it is not sufficient to meet the standard of care. Immediately after intubation, the cuff is inflated, and the anesthesiologist should observe the sequential rise and fall of the chest while auscultating over each midaxillary line and the epigastrium for assurance that the trachea, not the esophagus or bronchi, has been intubated.190 Because breath sounds have misled even skilled clinicians, the intraoperative monitoring standards of the ASA mandate that tracheal intubation be confirmed by detecting consistent levels of exhaled CO2 in successive breaths.36 CO2 can be sampled while the esophagus is ventilated, but its exhaled concentration declines after a few breaths.30 During circulatory shock, exhaled CO2 levels may be low despite proper tracheal tube position. If there is no sustained CO2 and the patient has a perfusing rhythm, the tracheal tube is removed, and the lungs are ventilated by face mask or SGA, particularly if the risk of aspirating gastric contents is low.
The self-inflating bulb (Ambu TubeChek B, Ambu, Inc., Glen Burnie, MD) relies on anatomy rather than the physiology of CO2 in exhaled gases. The device is similar to a “turkey baster” used in many kitchens. The bulb is collapsed and applied to the end of the ETT. The device will reinflate within 5 seconds if the tube is in the trachea but should remain collapsed if the tube is in the esophagus (Figure 32-36).191,192
Left, self-inflating bulb fitted with a standard 15-mm adapter used as an esophageal detector device. Middle, disposable CO2 detector showing the green color change to yellow color (right) with CO2 exposure.
The ideal position for the tip of an ETT is 3 to 4 cm above the carina. For an average-size woman, the ETT should be taped with the teeth at the 21-cm mark. For most men, 23 cm at the upper incisors is the appropriate depth. Nasotracheal tubes should be inserted 3 cm deeper.
MAINTAINING THE TRACHEAL TUBE
To avoid tracheal mucosal ischemia, many clinicians inflate the cuff until there is a small audible leak at peak airway pressure. During prolonged intubation, regular checks are conducted to prevent overinflation. Tracheal tubes usually are secured with adhesive tape. Tincture of benzoin, Mastisol (Ferndale Pharma Group, Ferndale, MI), or other skin adhesives may improve stability. Special ETT holders are often used for ICU patients who are expected to be intubated for more than a few hours. An oropharyngeal airway or roll of gauze sponges placed between the teeth keeps the patient from biting the tube. Nasotracheal tubes should be taped securely without putting pressure on the nares. The position of the tube is verified each time the patient’s position changes.
DEVELOPING AN AIRWAY STRATEGY AND THE AMERICAN SOCIETY OF ANESTHESIOLOGISTS’ DIFFICULT AIRWAY ALGORITHM
One of the major recommendations of the NAP4 study is for anesthesia providers to prepare for airway management with a strategy rather than a plan. An example of a plan might be “tracheal intubation via direct laryngoscopy after induction of general anesthesia.” A strategy would include a coordinated, logical sequence of plans that aims to achieve good gas exchange and prevent aspiration of gastric contents.19
The vast majority of difficult airway cases are unexpected. A prospective study of over 188,000 patients in Denmark showed that 93% of difficult intubations and 94% of difficult face mask ventilation encounters were unanticipated.193 A strategy must include backup plans for unanticipated difficult intubation and ventilation for every patient, even if clinical indicators do not suggest that the airway will be difficult to manage.
The lungs of patients who are difficult to intubate often can be ventilated by face mask. When intubation has failed but ventilation is adequate, the anesthesiologist should weigh the available options to ensure that each new maneuver represents a logical, substantive change from steps that have failed. Approximately 1 in every 250 patients will have combined difficult face mask ventilation and difficult direct laryngsoscopy.194
Repeated rigid laryngoscopy causes bleeding and rapidly evolving airway edema that frustrates subsequent attempts and may render mask ventilation impossible.19,177 It is therefore essential to anticipate patients at risk for difficult intubation or mask ventilation so they can benefit from a controlled awake or sedated intubation. Proper preparation includes optimal positioning, thorough denitrogenation, glycopyrrolate pretreatment, and the presence of proper tools and personnel. Only two or three rigid laryngoscopy attempts generally are indicated before changing techniques.2,3,20 A simple algorithm for tracheal intubation after two attempts at direct laryngoscopy with a Macintosh blade and fiber-optic intubation had a 99.96% success rate when both techniques were incorporated in daily use.195 Allowing an anesthetized patient to awaken or maintaining or resuming spontaneous ventilation may be the wisest course. Experienced assistance is invaluable.
Morbidity and mortality surrounding airway management prompted the ASA to convene the Difficult Airway Task Force to develop a management algorithm, which was most recently updated in 2013 (Figure 32-37).20 Subsequent to the publication of the ASA guidelines, other organizations have published guidelines for airway management.196
The American Society of Anesthesiologists’ difficult airway algorithm. [Reproduced with permission from Apfelbaum JL1, Hagberg CA, Caplan RA, et al: Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology. 2013 Feb;118(2):251-270.]
Key features of the ASA guidelines include an assessment of the likelihood and impact of particular patient factors, including difficulty in any one of the following areas: patient cooperation or obtaining consent, mask ventilation, SGA placement, laryngoscopy, intubation or surgical airway access. The guidelines suggest that the provider “actively pursue opportunities to deliver supplemental oxygen throughout the process of difficult airway management.” This can be accomplished with nasal cannula, face mask, or blow-by or via a surgical cannula.
The guidelines state that four management choices be made before initiating the anesthetic: Should the airway be secured with the patient awake or after induction of general anesthesia? Should the initial technique be noninvasive, or should it include invasive elements? Should video-assisted laryngoscopy be used as the initial approach to intubation. Finally, should spontaneous ventilation be maintained or abolished? If problems are encountered after the induction of general anesthesia, the algorithm distinguishes between difficult ventilation (life threatening) and difficult intubation (rarely life threatening). The 2013 version of the guidelines suggests that an SGA be used as the first device to establish or maintain ventilation and oxygenation if face mask ventilation is inadequate.
Because any patient may unexpectedly prove difficult to intubate or ventilate, proper denitrogenation before inducing general anesthesia should be routine. Maintaining the skills and techniques of ventilation without tracheal intubation and mastering a variety of methods for tracheal intubation are a must for every anesthesiologist.2,3 Each anesthetizing location should have rapid access to a difficult airway cart, including equipment to deal with a CICV scenario.
Because the ASA algorithm focuses only on management of the difficult airway, the airway approach algorithm was developed in 2004 to assist anesthesia providers in determining where their patients fit in the ASA algorithm197 (Figure 32-38). It includes consideration of whether the airway needs to be managed, whether the stomach is empty, if the patient will tolerate an apneic period, and the likelihood of successful tracheal intubation and SGA use.
The airway approach algorithm. This algorithm is used to determine if the patient is appropriate for airway management before or after induction of general anesthesia.
In 2013, a cognitive aid for airway management called the vortex approach was developed.198 Its website (http://vortexapproach.org/) has excellent educational resources for the novice and expert airway manager. The vortex approach consists of a figure with three zones: Zone 1 (green) applies when the current plan is working and the patient is doing well. Zone 2 (blue) applies when airway management is not going well, and oxygenation or ventilation is inadequate. In this zone, the provider should move rapidly through the three parts of the zone, alternating between attempts at face mask ventilation, SGA use, and tracheal intubation. To prevent repeating the same technique with each successive attempt, one or more of the following variables should be modified: device size or type (eg, changing from Miller to Macintosh blade or moving from direct to video laryngoscopy); using adjuncts such as a tube introducer; manipulating the patient’s larynx or head position; applying suction or supplemental oxygen; and administering neuromuscular blockers. No more than three attempts at each technique should be made, and at least one attempt should be by the most experienced available clinician. If the patient becomes significantly hypoxemic and ventilation is not possible, then zone 3 is entered, and an emergency surgical airway is secured. If ventilation is adequate and the trachea is not intubated after three attempts, a decision must be made to awaken the patient, perform the procedure without tracheal intubation, or secure the airway using a surgical technique (Figure 32-39).
The vortex approach to airway management. [Reproduced with permission from Chrimes N: The Vortex: a universal ‘high-acuity implementation tool’ for emergency airway management. Br J Anaesth. 2016; 117 Suppl 1: i20-i27. (vortexapproach.org ©Nicholas Chrimes, 2013, 2016).]
A 2005 closed-claims analysis showed that since the introduction of the ASA practice guidelines for management of difficult airways in 1993, there has been a reduction in airway-related claims associated with the induction of anesthesia. There has, however, been no change in the rate of claims for airway misadventures during the maintenance, emergence, or recovery from anesthesia.199 The NAP4 study similarly revealed that about one-third of respiratory events take place during or after extubation (Box 32-17).19
BOX 32-17 Complications Related to Extubation During extubation
Hypertension, tachycardia, arrhythmias, electrocardiographic ST segment changes
Coughing, breath holding, cyanosis
Difficult extubation Postextubation
Soft tissue obstruction
Edema of stenotic trachea
Vocal cord malfunction
Dysfunctional vocal cords (paradoxical adduction during inspiration)
Negative pressure pulmonary edema
Aspiration of gastric contents
Dislocation of arytenoid
The Difficult Airway Society extubation guidelines propose four simple steps to extubation: plan, prepare, perform, and provide postextubation care.22 Planning for extubation includes strategizing about how and when to extubate. Preparing for extubation requires an assessment of readiness for extubation. Extubation itself can then be performed under the best circumstances, and postextubation care can be provided with appropriate vigilance. A plan for extubation should be developed after determining if the patient is at “low risk” or “high risk” for extubation. High-risk factors include difficult intubation or airway management at induction; significant changes to the airway (eg, edema) caused by or occurring during the surgery; restricted postoperative airway access; and other general risk related to cardiac and pulmonary physiology, such as OSA.22
When determining if the patient meets extubation criteria, the anesthesiologist should consider whether bag-mask ventilation may be difficult or impossible and if there is a leak around the deflated ETT cuff (positive cuff leak). In some settings, the larynx is visualized with direct laryngoscopy (DL) or VL prior to extubation to assess the airway for edema, inflammation, and ease of reintubation should it become necessary. Reversal of neuromuscular blockade must be assessed prior to extubation. When these tests indicate readiness for extubation is optimized, extubation can proceed.
When neuromuscular blocking agents are used for surgery, full reversal must be verified prior to extubation. Residual paralysis is linked to an increased risk of postoperative respiratory events.200 A train-of-four (TOF) ratio at least greater than 0.9 is desirable prior to extubation.200,201 When a TOF ratio is less than 0.9, pharyngeal coordination and hypoxic ventilatory drive are impaired, and aspiration risk is increased.202-204 Unfortunately, visual and tactile measures of TOF correlate poorly with the actual TOF ratio. Clinical tests such as a 5s head lift do not necessarily correlate with a TOF greater than 9.0. Electromyelographs are accurate but large and expensive. The acceleromyograph is not widely available in clinical practice but more accurately measures the TOF.201 Thus, when using clinical signs or visual analysis of a twitch monitor, the anesthesiologist must understand these limitations. In very high-risk patients, more accurate monitors may be indicated.205 Complete reversal is more likely when an anticholinesterase is administered 15-20 minutes before extubation when a TOF of 4 twitches is evident prior to administration of reversal.
EXTUBATING THE PATIENT AT LOW RISK
Extubation of an easily intubated patient who did not undergo airway surgery is performed as soon as extubation criteria are met (Box 32-18).12,30,86 The Difficult Airway Society recommends the sequence outlined in Box 32-18 for “low-risk” extubation22:
BOX 32-18 Tracheal Extubation in Low-Risk Patients Criteria for extubation:
No ongoing indication to keep the patient intubated.
Spontaneous ventilation is adequate.
Muscle relaxant is fully reversed.
Airway reflexes are recovered.
Patient follows commands. Sequence for low-risk extubation in an awake patient:
Preoxygenate with 100% oxygen.
Suction as appropriate.
Insert a bite block (eg, rolled gauze).
Position the patient appropriately.
Antagonize neuromuscular blockade.
Establish regular breathing.
Ensure adequate spontaneous ventilation.
Minimize head and neck movements.
Wait until awake (eye opening/obeying commands).
Apply positive pressure, deflate the cuff, and remove tube.
Provide 100% oxygen.
Check airway patency and adequacy of breathing.
Continue oxygen supplementation until recovery is complete.
Breath holding and coughing elevate pulse, blood pressure, intracranial pressure, and intraocular pressure (Box 32-17).143,144 Intravenous lidocaine and esmolol are popular adjuncts to minimize coughing and the cardiovascular responses to laryngeal stimulation by the ETT during emergence from anesthesia.45,145
Extubation of the trachea during deep anesthesia minimizes the cardiovascular response,206,207 although ventilatory depression, upper airway obstruction, and difficulty with mask ventilation may be problematic. In patients who were difficult to intubate or in those at high risk of aspiration, extubation during deep anesthesia usually is contraindicated. Asthmatic patients whose symptoms are well controlled tolerate conscious extubation.
Laryngospasm and airway obstruction are common after extubation, especially in children.208 Management of laryngospasm includes prevention, recognition, and treatment. Prevention includes ensuring the appropriate level of anesthetic for deep extubation, refraining from airway preemptive suctioning, and offering heightened vigilance in high-risk patients (those undergoing ear, nose, and throat surgery or those with asthma or gastroesophageal reflux disease). Administration of intravenous magnesium, lidocaine, or atropine may help prevent laryngospasm, but clear supportive data are lacking.209 Although a patient with mild laryngeal spasm may have stridor, a severe episode results in complete airway obstruction and silence. The clinician may see diaphragm movement with suprasternal retractions and absence of mask misting or end-tidal CO2.
To manage laryngeal spasm, all triggering stimuli, such as moving the patient by other operating room staff, must cease. Oropharyngeal blood and secretions are suctioned, and any component of supraglottic obstruction should be managed. A Guedel airway or nasal trumpet can be inserted gently. Continuous positive pressure with a well-sealed mask is applied with 100% oxygen, and jaw thrust is applied. If the patient continues to decompensate, administration of an intravenous agent such as propofol 0.5 mg/kg is given to deepen the anesthetic.209 If the spasm continues, intravenous succinylcholine, 0.1 mg/kg, relieves the spasm, making mask ventilation possible without causing complete paralysis and apnea.210 On rare occasions, reintubation may be necessary.
Laryngeal edema should be suspected when inspiratory stridor develops within 30 to 60 minutes after extubation.211 Laryngeal edema caused by intubation is uncommon in adults. Overhydration, prolonged Trendelenburg position, or an allergic reaction to medications given before or during surgery should be considered causes. Maintaining the patient in a head-up position; providing humidified oxygen, inhaled racemic epinephrine, or intravenous dexamethasone; and reintubation are options for management.
Acute pulmonary edema may complicate tracheal extubation when severe airway obstruction coexists with vigorous spontaneous attempts at inspiration.212-214 Negative intrathoracic pressure and associated hypoxemia contribute to the development of pulmonary edema. Relieving the obstruction and administering supplemental oxygen resolves the congestion. Tracheomalacia caused by long-standing and severe compression, such as may be caused by a goiter, may obstruct the airway after extubation.215
EXTUBATION OF THE DIFFICULT AIRWAY OF HIGH-RISK PATIENTS
Patients who are difficult to intubate, who have had major head and neck operations, or in whom airway access is restricted are at high risk after extubation. Should emergent reintubation be required, these patients are likely to be hypoxic, hypercarbic, and uncooperative, with gastric distension from failed ventilatory attempts or previous application of a continuous positive airway pressure device (Box 32-19).216-218 Proper timing of extubation, equipment availability, use of advanced maneuvers, and the presence of a skilled anesthesiologist are vital for safe extubation of these patients. If the safety of extubation is tenuous, then postponing extubation or placement of a tracheostomy should be considered.
BOX 32-19 Characteristics of the Patient at High Risk During and After Extubation
Known difficult airway
Uncooperative, combative patient
Blood and secretions
Cervical immobilization or instability
Head and neck dressing
Inadequate operator experience
Difficult mask ventilation
Risk of aspiration
Poor oxygenation and ventilation
Poor topical anesthesia as a result of secretions
Residual nondepolarizing neuromuscular blocker or reversal agent
Occurrence during transportation
Unavailability of equipment
Extubation may proceed more easily if patients are extubated when fully awake and after edema or hematoma has resolved. The presence of a leak around a deflated ETT cuff usually predicts that glottic edema will not complicate extubation in adult patients. Under most circumstances, the patient should be extubated after a negative result on a cuff leak test.103
Extubation is facilitated in high-risk patients by the Bailey maneuver, extubation over an AEC, or use of a remifentanil infusion.22 An AEC or gum elastic bougie may be left in the trachea to facilitate reintubation.219-223 As discussed elsewhere, AECs are long, thin tubes with a hollow center and Luer lock or 15-mm male adapters at the proximal end for oxygenating. An airway circuit, self-inflating resuscitation bag, (eg, an Ambu bag), or jet ventilation can be used to provide oxygen and some degree of ventilation to the patient.219-221 The AEC should be threaded through the ETT before extubation. Care should be taken not to hit the carina as this area is highly innervated, and stimulation can cause bronchospasm, laryngospasm, and severe coughing. After extubation, the AEC is taped in place to prevent migration into the bronchus. For adults, a depth of 21 cm at the lip or 27 cm at the nares is usually appropriate. Most patients tolerate the device well. It is left in place until concern for the need to reintubate is gone. Reintubation over an AEC has a high level of success. Direct laryngoscopy or VL can improve success because the catheter is straighter, improving intubation geometry, and the operator can observe if the tube is encountering resistance.224-226
In the Bailey maneuver, an ETT is exchanged for an SGA while the patient is deeply anesthetized.227 This maneuver can reduce the risk of airway obstruction during a deep extubation. If the anesthesiologist is confident that the subglottic larynx will not be obstructed, an LMA or similar device may be placed in the hypopharynx before extubation to reduce the risk of upper airway obstruction and serve as bridge to full extubation228,229 (Figure 32-40).
Endoscopic view from inside a supraglottic airway showing an endotracheal tube (ETT) passing into the larynx. This view reflects proper position prior for supraglottic airway (SGA)–assisted extubation of the trachea.
There are several options for placement of the SGA: It can be placed cephalad to the existing ETT, railroaded over the ETT, or over an exchange catheter placed through the ETT prior to extubation. Then the AEC can be used as a guide to facilitate subsequent SGA insertion.230 At the end of the procedure, the oropharynx is suctioned, and the ETT is removed. Ventilation through the SGA is confirmed. The patient can now be awakened with less risk of airway obstruction, coughing, bucking, hypertension, and tachycardia. The basic steps of SGA exchange are described in Box 32-20.22
BOX 32-20 Sequence for SGA Exchange in “At-Risk” Extubation
Administer 100% oxygen.
Avoid airway stimulation: either deep anesthesia or neuromuscular blockade is essential.
Perform laryngoscopy and suction under direct vision.
Insert a deflated supraglottic airway (SGA) behind the tracheal tube.
Ensure SGA placement with the tip in its correct position.
Inflate cuff of SGA.
Deflate tracheal tube cuff and remove tube while maintaining positive pressure.
Continue oxygen delivery via SGA.
Insert a bite block.
Sit the patient upright.
Allow undisturbed emergence from anesthesia.
Remifentanil can attenuate the hemodynamic response or coughing and bucking response as the patient is extubated. Opioids have cough suppressant effects and can blunt the cardiovascular response to extubation. Remifentinil is short acting and thus can be titrated to allow for an awake and responsive patient with minimal respiratory depression. An intraoperative infusion can be continued through extubation or an infusion can be started just to facilitate extubation. At the end of the procedure, volatile agents and other sedatives should be turned off. Enough time should be given for sedative hypnotic agents to wear off. Once patients open their eyes spontaneously (without stimulation), spontaneous ventilation is established. The infusion is decreased until the respiratory rate is adequate.22
Iatrogenic causes and mechanical failure on rare occasion can render extubation difficult or impossible.223,231-234 Extubation may be difficult in patients with laryngeal abnormalities or those biting the ETT. Difficult extubation has been reported when the ETT tube cuff folds below the vocal cords or from laryngeal edema after a difficult intubation. The tracheal tube has been accidentally secured in the airway with surgical wires, sutures, and screws.231
FOLLOW-UP OF A DIFFICULT AIRWAY
For safe airway management in the future, patients with proven difficult airways should be identified and informed of the difficulty. Immediate application of a temporary wristband, flagging the medical record, and signs near the patient’s bed alert health care providers to the special requirements of these patients.
A statement with pertinent airway management information regarding difficulty encountered with face mask, supraglottic device placement, or intubation should be written. A copy is given to the patient, with a copy filed in the patient’s medical record. For future reference and availability of information for other health care organizations, the patient with a difficult airway can be enrolled in the Medic Alert Difficult Airway/Intubation Registry.235
The clinician should follow up with the patient regarding possible complications of difficult airway management, including edema and aspiration. The patient should be advised to seek medical attention if symptoms of complications occur, such as fever, sore throat, chest pain, swelling of the face and neck, and difficulty swallowing.20
COMPLICATIONS OF AIRWAY MANAGEMENT
The difficulties and complications of tracheal intubation arise from the act of intubation itself, maintenance of the ETT, or extubation (Box 32-21).6,226-241 A closed-claims analysis found that the larynx, pharynx, and esophagus are the most common sites of airway injuries. Pharyngoesophageal perforation injuries were the most severe. Early signs of perforation were found in only 51% of the claims. The authors of the analysis recommended extended observation of patients in whom tracheal intubation has been difficult. Patients should be instructed to watch for signs and symptoms of retropharyngeal abscess, mediastinitis, or both.238
BOX 32-21 Complications of Tracheal Intubation Physiologic responses to laryngotracheal stimulation
Tachycardia, hypertension, myocardial ischemia
Bronchospasm and bronchorrhea
Intraocular hypertension or extrusion of vitreous humor Trauma
Abrasion of the cornea
Lacerations of lips, gums, tongue, or pharynx
Perforation of pharyngeal or esophageal mucosa
Chipping or avulsion of teeth or dental appliances
Persisting subluxation of the mandible
Laryngotracheal penetration with subcutaneous emphysema
Injury to the vocal cords and arytenoid cartilages Tube malposition
Prolonged or failed intubation
Bronchial intubation Airway foreign bodies
Stylet During tracheal tube maintenance
Changes in position With extubation
Physiologic responses (same as previous)
Difficult or impossible extubation
Negative pressure pulmonary edema Common sequelae of a mild nature and lasting less than 48 hours
Sore throat Complications of prolonged intubation
Vocal cord granuloma
Vocal cord paralysis
The patient’s airway may be injured by overinflation of the cuff of an SGA or ETT. The mechanism is thought to be hypoperfusion of the mucosa of the larynx or pharynx. The most common side effect of cuff overinflation is a sore throat, but more serious complications, including injuries to the hypoglossal, lingual, and recurrent laryngeal nerve, have been described.239 For this reason, it is recommended to keep the cuff pressure in an SGA less than 60 cm H2O (44 mm Hg), while the pressure in an ETT cuff should be maintained at less than 25-30 cm H2O (18-22 mm Hg).
While VLs are popular for airway management, they are associated with some unique airway injuries. Both direct and video laryngoscopy can cause dental damage. It appears that the rate of damage to the soft palate, palatoglossal arch, and posterior pharynx may be higher with VL than with DL.115 This may be prevented if the operator looks directly in the patient’s mouth rather than at the video monitor while the ETT is inserted. Once the tip of the tube disappears from view behind the tongue, the operator’s attention is directed to the monitor as the trachea is intubated.
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