Chapter 36. Airway Management

1. Tracheal intubation can be accomplished using several techniques, including direct visual (rigid) laryngoscopy, video laryngoscopy, indirect visual (fiberoptic) laryngoscopy, guided blind (retrograde), and complete blind (eg, intubation through supraglottic airway [SGA] or blind nasal) intubation. Each technique has its preferred indication, risks, and benefits.

2. 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.

3. General anesthesia and muscle relaxants facilitate tracheal intubation. A rapid-acting muscle relaxant is used during rapid-sequence induction and intubation.

4. During general anesthesia, airway management without tracheal intubation has become well-accepted common practice since the introduction of SGA devices. As with any technique, it is incumbent upon the physician to determine what technique is most appropriate given the clinical scenario.

5. 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.

6. Awake intubation should be encouraged, taught, and practiced regularly to help maintain comfort and skill with the technique.

7. The availability of a difficult airway cart should be assured for every anesthetizing location.

8. Many major anesthetic complications are frequently associated with airway mismanagement, including inadequate ventilation or oxygenation and unrecognized esophageal intubation.

9. 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.

10. For patients in whom the upper airway is obstructed, establishing emergency ventilation with a supraglottic device (eg, laryngeal mask airway), esophageal device (eg, Combitube), cricothyrotomy, or transtracheal jet ventilation is a must and should be applied as soon as possible to prevent brain injury and death.

11. Trauma to laryngeal structures can leave patients with vocal cord paralysis and serious voice dysfunction.

12. Many airway disasters have been reported after patient extubation. A well-planned and prepared extubation is a must 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 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

Mastery of the airway demands familiarity with normal and variant anatomy and the alterations caused by sedation, anesthesia, and abnormal states.

The Pharynx

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 (Fig. 36-1). 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 (Fig. 36-2). 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

Nasopharynx and Nose

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 3 turbinates on each lateral wall (Fig. 36-3). 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.

Oropharynx and Mouth

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 (Fig. 36-4). Mandibular mobility depends in turn on the hinging and gliding motions of the temporomandibular joint. For successful rigid laryngoscopy, the tongue is displaced anteriorly for visualization of the larynx.

Laryngopharynx and Larynx

The epiglottis, thyroid, and cricoid cartilages and 6 smaller, paired cartilages (arytenoid, corniculate, cuneiform) shape the larynx (Fig. 36-5). 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 (Fig. 36-6).3 A properly positioned 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.

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 (Fig. 36-7). 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 for "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.

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 for "ladle") cartilages with superior, anterior, and lateral projections. The superior projections support the corniculate (Latin for "little horn") cartilages, and the anterior and lateral projections attach, respectively, to the vocal cords and various intrinsic laryngeal muscles (Fig. 36-5). Corniculate and cuneiform cartilages embedded in the aryepiglottic fold form 2 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. During phonation, the aryepiglottic folds and glottis are asymmetric. 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.

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; in contrast, face mask positive pressure may expand the piriform recesses and compress the aryepiglottic folds, compounding laryngeal closure.

The Lower Airway

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 fiberoptic 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 36-1).12,14

A difficult airway can present as difficult mask ventilation, difficult rigid laryngoscopic intubation, or both. The major task during preoperative airway evaluation is to identify patients at risk for a "cannot intubate, cannot ventilate" situation, which is caused by congenital or acquired anatomic variations or by abnormal afflictions of the upper and lower airway (Box 36-1).15-17 The variations or abnormalities are found by reviewing old records, 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.An 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, abnormal neck anatomy, sleep apnea, and a history of snoring.18,19 Special attention should be paid to syndromes associated with a problematic airway. Details of the airway evaluation appear in Chapter 10.

Part of developing an airway management plan is to determine whether or not the patient is best served by a supraglottic airway (SGA) or an ETT. One also needs to determine if the airway should be instrumented while the patient is awake or after induction of the anesthetic. Despite a thorough evaluation of the airway, anatomic variants such as supraepiglottic cysts20 or lingual tonsillar hypertrophy21,22 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.

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. Since 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.23 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 until the PaCO2 decreases 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 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. Inhalation inductions, popular for children, have some merit in adults when the ability to ventilate the patient's lungs after induction of anesthesia is uncertain.23 If worsening of airway obstruction is encountered during inhalation induction, the anesthetic can be turned off with the hope that the patient will awaken.

Hypoventilation

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 increments in FIO2 can maintain close to normal arterial O2 saturation despite profound hypoventilation (Fig. 36-8).

During apnea, arterial oxygenation can be sustained by apneic oxygenation.24 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 36-2).

Denitrogenation

Because it is impossible to ensure the ability to ventilate the lungs of a patient about to receive general anesthesia, proper preanesthetic denitrogenation is recommended. Eighty percent of the average 2.5-L adult functional residual capacity (FRC) that starts out as N2 is replaced with O2.25 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.

Because it may make the difference between life and death for the patient, proper denitrogenation (Box 36-3) should be a top priority for an anesthesiologist preparing to induce a general anesthetic.25,26

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 gases). 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.

Clinical Observation

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 36-2).12,23

Pulse Oximetry

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.27 Pulse oximetry is not sensitive to hypoventilation if FIO2 is high and it gives late notification of esophageal intubation after denitrogenation.28

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

Capnometry, using one of several detection methods, continuously displays the waveform of PETco2 sampled at the patient end of the breathing circuit. When the tidal volume is large enough, alveolar gas reaches the CO2 sampling site and the displayed PETco2 closely approximates PaCO2, 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 36-4). In most patients, 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.

An important application of capnometry is confirmation of the position of an intratracheal tube by the appearance of stable CO2 concentrations in sequential breaths immediately after intubation. This application is mandated by the American Society of Anesthesiologists (ASA) Standards for Basic Anesthetic Monitoring.29,30 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.

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.12,23,31

Face Mask Ventilation

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 semi-lateral 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 2 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, obviating the need for a pad.

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.

Achieving a Seal

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 (Fig. 36-9), 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.

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 makes a better seal and minimizes hand fatigue for the anesthesia provider. (Box 36-5) Concern about excessive apparatus dead space in patients with tiny tidal volumes led Rendel-Baker and Soucek to develop pediatric masks without a cushion and made from molds of infants' faces. In contrast with the racial and ethnic variability displayed in later life, infants share impressive uniformity of facial contours. Their full cheeks can be pulled up and around the rims of these masks. Undue submandibular pressure by the anesthesiologist's fingers tends to worsen airway obstruction. 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.

Beards or broad mustaches may hinder a good mask seal to make controlled ventilation simply impossible. For edentulous patients who are too alert to tolerate an 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.12,23

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 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.

Pharyngeal Airways

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 36-6).2,3 If a careful assessment suggests simple supraglottic obstruction, insertion of pharyngeal airway to separate soft tissues from the posterior pharyngeal wall is a logical next step (Fig. 36-10). Success confirms that the soft tissue had been obstructing the airway, but persisting or worsening obstruction is often indicative of active closure of the larynx. Active closure may be relieved by administering muscle relaxants or deepening anesthesia with IV 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.

Until the arrival of the LMA and esophageal devices, oropharyngeal or nasopharyngeal airways were the best ways to relieve simple supraglottic obstructions. They remain inexpensive, safe, and generally effective.23,31 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. Displacing the tongue into the hypopharynx is avoided by drawing it anteriorly with a tongue blade held in the left hand while the right hand opens the mouth and inserts the oropharyngeal airway.

The onset of soft tissue relaxation and airway obstruction usually heralds depression of cough and gag reflexes sufficient to tolerate pharyngeal stimulation. Swallowing or gagging triggered by a tongue blade or airway touching the base of the tongue suggests waiting until the patient is more deeply anesthetized; the stimulus itself often restores airway patency. Coughing and breath holding after uneventful placement of an oropharyngeal airway suggests airway irritation by anesthetic vapors. Approaches to coughing and breath holding include turning down the vaporizer and temporarily abandoning attempts at positive-pressure ventilation or deepening the depth of anesthesia with IV 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 36-7), 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.

Supraglottic Airways

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) (Fig. 36-11). These and other supraglottic devices have achieved great popularity for addressing simple, SGA obstruction in a variety of contexts.32,33 Their unique capabilities (Boxes 36-8 and 36-9), relative ease of use, and low incidence of serious complications enssure SGAs a place in the anesthesiologist's armamentarium.34-41 Several studies have indicated that trained but inexperienced resuscitators are more likely to be successful ventilating with an LMA than intubating the trachea with direct laryngoscopy.42

Becoming adept at proper SGA insertion requires consideration of a patient's anatomy, patience, and practice.43 Even when using 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 LMA should be deflated with finger pressure on the dorsal aspect of the cuff so that the totally flattened cuff curves away from the aperture (Fig. 36-12). A water-soluble lubricant should be applied to the dorsal surface of the cuff and kept from drying. The recommended technique for LMA placement is summarized in Fig. 36-13.44 When the epiglottis is dragged downward, the aperture bars of the LMA prevent impaction of epiglottis into the LMA and possible obstruction (Fig. 36-11).

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 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 20 cm H2O airway pressure with the classic LMA. 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.

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.45 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.46 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 LMA36; 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 support ventilators 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.47-49 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.50 Application of cricoid pressure impedes placement of the LMA.51 Reported but rare complications include 12th cranial nerve paralysis,52 unilateral hypoglossal nerve paralysis,53 and transient bilateral vocal cord paralysis.54

Laryngeal Mask Airway Proseal

Pulmonary aspiration of regurgitant gastric material has long been a concern with the use of devices such as the LMA. 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 doral 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 also 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.55

The pLMA can be inserted using a special introducer or in a manner similar to a classic LMA. A very 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 the pLMA's 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.56 In a similar technique, a gum elastic bougie is inserted in the esophagus with the pLMA drainage tube advanced over its proximal end.57

After the pLMA has been inserted, proper positioning is confirmed with a 4-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.58,59 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 Fr 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.60,61 In the suprasternal notch test, the patient's airway is palpated at the suprasternal notch while observing for a 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.62

Intubating LMA (Fastrach iLMA)

The Fastrach intubating LMA (iLMA; LMA North America, San Diego, CA) is designed to assist with ventilation and intubation. In 1 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 fiberoptic scope placed through the iLMA.63 Patients have been intubated through the iLMA using a variety of ETTs.64-66 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.67,68

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.

Laryngeal Tube

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 is provided by a shaft that terminates between the 2 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 newest addition to the LT family is the Gastro-Laryngeal Tube. Upper endoscopy is possible via its large esophageal lumen while ventilation is maintained with the ventilating lumen.

Cobra PLA

The Cobra Perilaryngeal Airway (PLA) is another device that makes use of a pharyngeal cuff. The Cobra PLA has a soft plastic, wedge-shaped mask that lies distal to a large pharyngeal cuff. The mask does not contain an inflatable cuff and has many small, flexible bars covering its distal orifice. A Cobra PLA Plus measures temperature with an integrated probe, and there is a channel for distal gas sampling.

i-gel

The i-gel airway is unique in that it does not have inflatable cuffs. 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.

Air Q/Intubating Laryngeal Airway

The air Q (single use) and Intubating Laryngeal Airway (ILA, reusable) are SGAs designed to facilitate endotracheal intubation. Both devices use a cuffed mask bowl attached to a ventilating shaft. Both have removable 15-mm adapters for introduction of an ETT introduction and predate the eLMA in this design feature. The air Q and the ILA lack aperture or epiglottic elevating bars.

Esophageal–Tracheal Airway

The esophageal–tracheal Combitube (Fig. 36-14) is intended for establishing emergency ventilation when there is simple, supraglottic obstruction or when the operator cannot ventilate with a face mask or intubate the trachea.69-73 This device differs from the earlier esophageal obturator airway because the lungs can be ventilated whether the device enters the esophagus or the trachea.

When the lubricated Combitube is passed through the pharynx of a comatose or anesthetized patient, a neutral position or slight flexion of the neck generally directs the device to follow the posterior pharyngeal wall into the esophagus. Approximately 4% to 6 % of the time, the Combitube enters the trachea. A large 100-mL balloon seals the oropharynx, and a smaller one seals the esophagus. Two lumens protrude from the end of the Combitube. The one continuous with the inserted tip is used to ventilate if the tip has entered the trachea. More commonly, the other lumen that opens into multiple pharyngeal fenestration is used to ventilate the patient's lungs. Lifesaving ventilation has been provided by this device.74 Rusch has introduced the Easytube (Teleflex Medical, Research Triangle Park, NC), a latex-free alternative to the Combitube.

Complications of Nonintubated 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 36-2) 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 36-6) when treating a patient whose lungs are difficult to ventilate (Box 36-10).

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 gasses are predisposing factors to regurgitation.75,76 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-tipped (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 indicate 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 may precipitate mucosal bleeding sufficiently severe to render laryngoscopy impossible.

Tracheal intubation is undertaken for reasons of physiology, pathology, or convenience (Box 36-11). 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.

Visualization of the pharyngeal and 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 36-12). Alternative techniques of intubation and ventilation may be lifesaving when suboptimal circumstances prevent visualized tracheal intubation.

Endotracheal Tubes

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, and internal 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. During laser surgery in the airway, PVC tubes can burn rapidly, producing hydrochloric acid and other pulmonary toxins. To minimize the risk of an airway fire during laser surgery, the use of tubes made of metal, metal-wrapped red rubber, or silicone is recommended.77

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) or for nasal or blind intubation. Pediatric ETT sizes can be selected by an age-related formula and tested for leaks in situ. Cuffs often are not traditionally used until children have reached the age of 8 or 9 years, when the cricoid ring ceases to be the narrowest, edema-prone portion of the airway. Cutting ETTs renders them less obtrusive and easier to handle, but 26 cm of length should be sufficient for adult oral tubes, allowing 3 cm more for nasal tubes. One can firmly affix the 15-mm adapter 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 helps minimize aspiration risk. The pressure in the cuff is estimated by squeezing the pilot balloon, or it is set to be 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 injecting an additional 1 cc of air after an audible air leak has been sealed. A cuff initially inflated with air merits periodic checks to detect overinflation when nitrous oxide is used during an anesthetic because if nitrous oxide enters the cuff, high pressures may result, injuring 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. The Murphy eye is a fenestration in the tip of the tube opposite the bevel that is added to protect against obstruction. A variety of ETTs are available for specific applications (Table 36-3; Figs. 36-15 and 36-16).

Laryngoscopes

These instruments are designed to create a line of sight for passage of the ETT by displacing the tongue and epiglottis anteriorly.77 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 fiberoptic bundle to the laryngeal structures. Blade-mounted bulbs operate erratically if their contacts are not corrosion free.

Laryngoscope blades require a high level of disinfection to kill vegetative organisms but do not necessarily need to be sterilized. They should be soaked and brushed clean in an enzyme detergent before disinfection. Autoclaving or soaking in glutaraldehyde will corrode the contact between the bulb and blade over time. Gas sterilization is effective but time consuming. Disposable plastic covers keep handles and blades free of saliva and blood and minimize cross-contamination.

Although innumerable laryngoscope blade designs have been developed, the 2 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 (Fig. 36-17).

Stylets

Because of the position of the tongue and epiglottis, a glottic opening not exposed by routine laryngoscopy seems to hide anteriorly. Stylets are blunt-tipped, flexible 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

Introducers exemplified by the angle-tipped Eschmann gum elastic bougie can guide an ETT into the trachea. Longer and less rigid than stylets, introducers facilitate difficult intubation. Passed through the tracheal tube, the tip is guided into the trachea, and the ETT is threaded over it.

A soft, flexible introducer can serve as 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 Luer lock or 15-mm male adapters at the proximal end for oxygenating with jet ventilation 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 least likely to get stuck on the epiglottis or aryepiglottic folds 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 done during general anesthesia with the patient breathing spontaneously.

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 36-13).3,12,75 They vary in their level of sophistication, invasiveness, tendency for blood and secretions to obviate visualization, and potential for major complications. In selecting a technique, the anesthesiologist weighs risks against the likelihood of success, keeping in mind a backup plan to deal with unexpected failure. Expertise may vary depending on when the anesthesiologist trained. For example, whereas recent American trainees may not have extensive experience in blind nasal intubation, those of an earlier vintage may be less comfortable with fiberoptic techniques. The ideals against which a technique may be judged are summarized in Box 36-14. Fiberoptic bronchoscopy scores high as a technique to manage difficult airways. Its shortcomings include its size, cost, relatively fragile nature, and susceptibility to obliteration of the view by blood and secretions. Compact, battery-powered light sources for bronchoscopes have proven advantageous when portability, compact size, and low weight are important.

Disposable, single-use bronchoscope availability removes 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.

Rigid Direct Laryngoscopy

Rigid laryngoscopy retains its popularity because of its simplicity, high success rate, and good visualization.12,23,75 In adults, it is critical to elevate the occiput on a pad to flex the neck so that the atlanto-occipital extension will align the pharynx with the mouth and larynx (Fig. 36-18). If the patient has been given muscle relaxants, a neuromuscular blockade 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.

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 sternum 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 (Fig. 36-19). 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. Rotating the laryngoscope or "levering" the device is to be avoided 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).75 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

Common avoidable causes of difficult laryngoscopy include improper positioning of the head, inadequate opening of the mouth, selecting the wrong blade, allowing the tongue to hang over the right side of the blade, applying leverage rather than traction, 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, placing the esophagus at the end of the laryngoscope. 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 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 avoids contact with 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 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 used in oral and maxillofacial surgery and in the intensive care setting. Introduced through the right corner of the mouth so as not to block laryngoscopic visualization, a Magill intubating forceps directs the ETT tip to the glottis while an assistant advances the tube on command.75,78 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 in 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 the choice when both risk 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 fentanyl and midazolam (≤1.5 mcg/kg and 30 mcg/kg in divided doses) has been used successfully.79 In ensuring 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, avoiding oversedation and hypoxemia.

Glycopyrrolate, 0.2 to 0.3 mg IV, minimizes secretions and improves the effectiveness of topical anesthetics.80 Patients may benefit from medications that increase gastric fluid pH or enhance gastric emptying.

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.81 Use of lidocaine jelly before application of other anesthetics to normal mucosa increases patient satisfaction.82

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 lingual nerve block may decrease refractory gagging.

Rapid-Sequence Induction and Intubation

Preoxygenation, avoidance of mask ventilation, and compression of the cricoid cartilage (Sellick maneuver; Fig. 36-20) to resist passive regurgitation of gastric contents into the oropharynx are elements of a traditional rapid-sequence induction.4,23,75 Anesthesia begins with a rapid-sequence injection of propofol or thiopental followed by succinylcholine and intubation 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. Other induction agents and nondepolarizing muscle relaxants are alternatives for induction.

Cricoid pressure, as described by Sellick, should be firm enough to prevent the esophagus from slipping laterally but not so firm as to obstruct ventilation.4,83,84 This pressure may be difficult to attain as described because the 30-Newton force currently recommended may obstruct the view of the larynx.85 Application of cricoid pressure is a safe and effective maneuver, with only 1 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 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 by Sellick in 1961.4 If mask ventilation proves difficult, the patient may be placed in a 5-degree 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 pressure28,83 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 an LMA or other supraglottic or extraglottic airway is needed for rescue breathing, it is important to remember that 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, appropriate application of cricoid pressure prevents gastric gas insufflation during mask ventilation with an airway pressure up to 40 cm H2O.86 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.

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.87 This facilitates visualization of the glottic opening with minimal force against the airway structures.

A viewing angle of up to 80 degrees is possible compared with the 15-degree viewing angle of direct laryngoscopy.88 This extended viewing angle may be helpful in difficult intubations secondary to limited neck mobility, cervical spine immobilization, retrognathia, or reduced thyromental or interincisor distance.89 In addition to facilitating laryngoscopy and orotracheal intubation, VLs can be used for awake, nasotracheal or fiberoptic 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 an 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.90

Since 2001, several VLs have been introduced, which can be divided into 2 groups: non–channel-guided VLs and channel-guided VLs.

Non–Channel-Guided Videolaryngoscopes

Non–channel-guided VLs include the GlideScope (Verathon Inc, Bothell, WA), the McGrath Series 5 (Aircraft Medical, Edinburgh, UK), and the Storz C-MAC (Karl Storz, Tuttlingen, Germany). These devices are similar to a Macintosh blade in shape and in use; a view of the glottis is obtained before the introduction of the ETT (Figs. 36-21, 36-22, and 36-23).

To perform videolaryngoscopy 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.91 When the device is past the tongue, attention is directed to the video screen and the blade is advanced midline until a Cormack-Lehane grade II view is achieved. A grade II glottic view is acceptable because if additional anterior force is applied to the blade, the larynx may be directed further anterior, impeding passage of the ETT into the trachea.91 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 advancing 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 3 ways. The ETT may be loaded on the stylet with "reverse camber" orienting the natural curve of the tube posteriorly. This allows the tube to pass off the stylet in direction 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 Glideright tube may be used.

Glidescope

The GlideScope was introduced in 2001. The blade, available in 3 sizes, has a steep 60-degree curvature, which improves the view of the glottis because the tongue is not displaced anteriorly. (Fig. 36-21) The maximum thickness of the largest blade is less than 15 mm, allowing use in a patient with an interincisor distance of 2 cm.91 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.92 The GlideRite Rigid Stylet, curved to follow the 60-degree 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.91

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 anticipated difficult airways, the GlideScope increased the percentage of Cormack-Lehane grade I to II views compared with views with direct laryngoscopy.89,93

Because the improved views are attained without aligning the oral, pharyngeal, and laryngeal axes, less cervical manipulation is required. Cervical spine motion was reduced 50% during GlideScope intubation compared with cervical spine motion during direct laryngoscopy.94 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.95

Although 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.87,89,92,93,96,97 If difficult intubation is encountered, the blade can be withdrawn 2 to 3 cm and the stylet 3 to 5 cm to lessen the anterior displacement of the larynx. Withdrawal improves the alignment of the axes of the larynx, trachea, and ETT.91,92

McGrath Laryngoscope

The McGrath Series 5 (Aircraft Medical, Edinburgh, UK) was introduced in January 2006 (Fig. 36-22). This VL has a reusable CameraStick handle, which incorporates a small camera and light source. A sterile, transparent, single-use blade with a 60-degree angle covers the CameraStick. 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.90 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.

Storz C-MAC

The C-MAC was introduced in 2003. It has a Macintosh-shaped steel blade with a slim 14-mm profile, can be equipped with a suction catheter, and is available in 3 sizes98 (Fig. 36-23). 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 for approximately 2 working hours.98

The C-MAC differs from other VLs because it can be used as a direct or indirect laryngoscope. 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.98 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.87 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 Videolaryngoscopes

The channel-guided VLs include the Pentax AWS-100 (Pentax Medical Company, Montvale NJ) and the Airtraq (Prodol Meditec, SA, Guecho Vizcaya, Spain) (Figs. 36-24 and 36-25). These VLs have highly curved blades with a channel to hold the ETT during laryngoscopy and guide it during intubation.

With channel-guided VLs, view of the glottis is indirect, obviating the need for alignment of the oral, pharyngeal, and laryngeal axes.87 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. The Pentax AWS PBlade is inserted under the epiglottis and used like a Miller blade. The Airtraq blade may be placed in either the vallecula (Macintosh style) or under the epiglottis (Miller style). 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.

Pentax AWS

The Pentax AWS, a battery-operated, channel-guided VL, was introduced in Japan in 2006. It has a handle with a 2.4-in LDC screen; a 12-cm image tube with a camera and light source; and a disposable rigid blade, the PBlade99 (Fig. 36-24).

The tube channel can accommodate an ETT with a 6.0 to 8.5 mm ID. The PBlade comes in only 1 size (18 mm thick) and is larger than the blades of other VLs. It is used only if a patient's mouth opening is larger than 2.5 cm. 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.

Studies comparing the AWS with direct laryngoscopy show improved glottic visualization and tracheal intubation and less cervical spine motion in routine and difficult airways with the AWS.94,99 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.95

The Pentax AWS has been used for awake intubation of the trachea. 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.100

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.101

Airtraq

The Airtraq is a single-use, channel-guided VL with a viewfinder and disposable blade (Fig. 36-25). The blade has 2 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. There is an optional video camera, which can be attached to the viewfinder to transmit the image to a monitor, and a rechargeable battery-operated LED at the tip of the blade for illumination up to 90 minutes. The antifog system for the lenses is activated by the LED for 30 to 60 seconds before use to warm the lens. The Airtraq comes in 4 sizes for orotracheal intubation with ETTs from 2.5 to 8.5 mm ID. The Airtraq has special blades for nasotracheal and endobronchial intubation and can accommodate double-lumen tubes from 35 to 41 Fr.

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.102 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. Compared with direct laryngoscopy, it 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.103,104

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.104

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 VL. 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.

Fiberoptic Intubation

A flexible fiberoptic bronchoscope (ie, a fiberscope) (Fig. 36-26) can be used for routine or challenging intubations in patients with airway tumors, infections, or cervical spine fractures or fixation (Fig. 36-27).3,105-110 Indications for fiberoptic tracheal intubation are summarized in Box 36-15.

Because normal airway architecture is maintained, fiberoptic 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. The patient with a history of failed intubation, upper airway abnormality, or expected difficult intubation may benefit from an awake fiberoptic intubation. Proper topical anesthesia and sedation ease the task. With experience, topical anesthesia of the larynx and trachea may be achieved by spraying local anesthetic through the working channel of the fiberscope. Inhalation of nebulized lidocaine may minimize coughing.

Oral Fiberoptic Approach

After applying topical anesthetic to the tongue and oropharynx, a special oropharyngeal airway is inserted to prevent biting on the fiberscope, to keep the instrument in the midline, and to restrain the tongue (Fig. 36-28).3 The oropharynx is suctioned, and the lubricated ETT is placed 4 or 5 cm inside the airway. The fourth and fifth fingers of the right hand stabilize the ETT while the index finger and thumb feed the fiberscope through it (Fig. 36-29). If the fiberscope is accidentally passed through the Murphy eye of the ETT, intubation will not be successful even after the fiberscope is guided into the trachea.

As the fiberscope is advanced toward the oropharynx, the soft palate and uvula come into view (Fig. 36-30). 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 are applied. In an obese patient or one with a difficult airway, the sitting position will improve airway patency and pulmonary physiology.

After the glottis is exposed, it is maintained in the center of the field of view by fine manipulations of the control lever. The fiberscope is advanced into the midtrachea, as confirmed by a view of the carina and flat posterior wall. The ETT is slipped over the fiberscope 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 fiberscope 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 degrees 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 fiberscope. In some patients, this maneuver may have to be repeated 2 or 3 times, particularly when a large discrepancy exists between the size of the fiberscope and the ETT. Passage of the tube over the fiberscope into the larynx can be facilitated by using a larger fiberscope,111 a special tube with tapered tip112 such as the tube used to intubate through the Fastrach LMA (Fig. 36-31), or a Parker tube (Parker Medical, Highlands Ranch, CO). Laryngospasm also may prevent ETT advancement. Additional topical anesthesia applied through the fiberscope usually remedies this problem.

Nasal Approach

In the conscious patient, fiberoptic 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 fiberscope through the nose facilitates locating the glottis and advancing the fiberscope 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 a fiberscope. Laryngeal anesthesia and intubation proceed as described for the oral approach. 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 degrees, and reintroduced. If this maneuver fails, the ETT is withdrawn and a lubricated fiberscope is advanced from the nasopharynx to the posterior oropharynx. The ETT is then gently advanced over the fiberscope into the oropharynx.

Passing the tube too far into the oropharynx may direct the fiberscope into the esophagus or away from the midline, preventing laryngeal exposure. The oropharynx is suctioned thoroughly through the ETT before the lubricated fiberscope is inserted through it. In most patients, the epiglottis and vocal cords are seen immediately with minimal manipulation of the fiberscope 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 fiberscope is advanced into the mid trachea followed by the ETT.

Asleep Fiberoptic Intubation

Fiberoptic oral and nasal intubation in an anesthetized patient requires an assistant to monitor the patient and apply 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 fiberscope before intubation is attempted. The fiberscope 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 fiberscope into the trachea (Fig. 36-32).

Failed direct rigid laryngoscopic intubation during a rapid-sequence induction leaves the patient vulnerable to aspiration. If the patient's lungs can be ventilated via face mask, oral fiberoptic intubation with cricoid pressure is an effective technique that should be seriously considered. The ability to perform rapid fiberoptic intubation may prevent airway catastrophes. Repeated unsuccessful attempts at blind nasal intubation or rigid laryngoscopy traumatize the airway, converting a manageable airway into one that is impossible to ventilate.

In a rapid-sequence induction incorporating fiberoptic intubation, 1 assistant maintains cricoid pressure while another applies jaw thrust (Fig. 36-33). 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.

Retrograde Intubation

In retrograde intubation, a guidewire is passed through a needle that has been percutaneously inserted into the larynx. The wire is delivered through the mouth or nose to serve as a guide for the ETT.113-119 Dedicated kits (Cook Retrograde Intubation Set, Bloomington, IN) are available for pediatric and adult use.

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 the 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 (Fig. 36-34).

A fiberscope loaded with an ETT may be advanced over the guidewire or next to the guidewire to assist retrograde intubation.113,115,117 A technique that involves passing the guidewire through the suction channel of the fiberscope 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.119 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.120

Blind Nasal Intubation

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.75,121-123 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.121

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 degrees, 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.122 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.123 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%.124 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.122,124 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 Laryngeal Mask Airway

The LMA can be used to manage a "cannot intubate, cannot ventilate" situation or to facilitate tracheal intubation.125-132 There are 3 distinct techniques for tracheal intubation through a classic or unique LMA: blind passage of a 6.0-mm inner diameter or smaller ETT,131 blind insertion of a guide to facilitate the threading of a large ETT after LMA removal,130 or fiberoptic-assisted tracheal intubation through the LMA.63,129,132 With perfect LMA position, the aperture lies opposite the glottic inlet for blind insertion of an ETT or guide. When the epiglottis partially blocks the laryngeal inlet, fiberoptic assistance is needed. 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 LMA is in place. A fiberoptic bronchoscope is placed through the catheter. The fiberscope and catheter are then directed through the LMA into the trachea. Leaving the Aintree catheter in place, the fiberoptic scope is removed, and then the LMA is removed over the catheter. The trachea is intubated over the catheter.

If rescue intubation is attempted by passing an ETT blindly through a classic LMA, it is important to remember that the distance from LMA aperture bars to the vocal cords is 3.5 cm.133 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.

The LMA Fastrach is an SGA device designed to aid endotracheal intubation. It can serve as a primary airway, but its primary purpose is to serve as a conduit for endotracheal intubation. Blind endotracheal intubation with the LMA Fastrach is successful 96.5% of the time. One study of high-risk airway patients showed that using a flexible fiberoptic bronchoscope in conjunction with an intubating LMA produced a 100% success rate for tracheal intubation.63

Properly positioning the LMA Fastrach facilitates introduction of an ETT into the trachea, but suboptimal positioning can result in failure. The Chandy maneuver is a 2-step technique used to improve position of the Fastrach before using it for blind intubation.63 The first step of the Chandy maneuver uses the device's metal handle for rotation 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.63

Correct position is important for success during LMA Fastrach–assisted endotracheal intubation, but the type of ETT is also a consideration. The manufacturer produces a reusable, reinforced ETT for use with the LMA Fastrach. The Fastrach ETT is made of silicone with a blunted tip, features that help with its smooth introduction 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. A comparison of the manufacturer's ETTs and standard PVC ETTs during blind intubation via the Fastrach showed better success with the silicone Fastrach ETT even when the standard ETTs were rotated on advancement to avoid bevel impact on glottic structures.64 Another study evaluating Fastrach-assisted blind endotracheal intubation found similar success rates with the manufacturer's silicone ETT and a warmed PVC ETT.65 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.66 The unique ability to establish ventilation in an unanticipated difficult mask ventilation, coupled with a mechanism to definitively secure the airway, makes the LMA Fastrach a strong addition to the airway management arsenal.

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. Cricothyrotomy involves entering the larynx 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, 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, Bloomington, IN). Applying the Seldinger technique for cricothyrotomy is familiar for nonsurgeons treating a patient with a difficult airway.134 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 Ventilation

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.135-137 Percutaneous transtracheal jet ventilation is also an interim means of oxygenation during difficult intubation.136

The incidence of malfunctioning of thin-walled 16- or 14-gauge IV catheters caused by kinking or dislodgement is high and can cause major complications. This problem is more likely to happen with an awake, struggling patient. The Arndt emergency cricothyrotomy catheter set (Cook Critical Care, Bloomingdale, IN) may minimize these problems. The set features 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, self-inflating resuscitating breathing bag (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 with a progressive increase in CO2 concentration.

Rupture of the lungs may produce a pneumomediastinum, pneumothorax, or other serious complications. 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.

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 mid-axillary line and the epigastrium for assurance that the trachea, not the esophagus or bronchi, has been intubated.138 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.29,30 CO2 can be sampled while the esophagus is ventilated, but its exhaled concentration declines after a few breaths (Fig. 36-35).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 mask, 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. (Fig. 36-36).139,140

The ideal position for the tip of an ETT is 3 to 4 cm above the carina. For an average-sized 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. 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.

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. Repeated rigid laryngoscopy causes bleeding and rapidly evolving airway edema that frustrates subsequent attempts and may render mask ventilation impossible.125 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 2 or 3 rigid laryngoscopy attempts generally are indicated before changing techniques.2,3,125 A simple algorithm for tracheal intubation after 2 attempts at direct laryngoscopy with a Macintosh blade and fiberoptic intubation had a 99.96% success rate when both techniques were incorporated in daily use.141 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 (Fig. 36-37).125 Subsequent to the publication of the ASA guidelines, other organizations have published guidelines for airway management.142

Key features of the ASA guidelines include 3 management choices made before the 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 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). In the 2003 revision of the guidelines, the LMA was mentioned as a means to establish or maintain ventilation and oxygenation and to facilitate intubation.

Because any patient may unexpectedly prove difficult to intubate or ventilate, proper denitrogenation before inducing general anesthesia should be routine. Maintaining skills at 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 cannot intubate, cannot ventilate scenario.

The Routine Airway

Extubation of an easily intubated patient who did not undergo airway surgery is performed as soon as extubation criteria are met (Box 36-16).12,23,75 Breath holding and coughing elevate pulse, blood pressure, intracranial pressure, and intraocular pressure (Box 36-17).143,144 IV 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,146,147 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. Even properly treated patients with asthma tolerate conscious extubation.

Laryngospasm and airway obstruction are common after extubation, especially in children.148 Although a patient with mild laryngeal spasm may have stridor, a severe episode results in complete airway obstruction and silence. To manage laryngeal spasm, positive pressure is applied with oxygen, oropharyngeal secretions are suctioned, and jaw thrust is applied. In patients with severe episodes, IV succinylcholine, 0.1 mg/kg, relieves the spasm for mask ventilation without causing apnea.149 On rare occasions, reintubation may be necessary.

Laryngeal edema should be suspected when postextubation inspiratory stridor develops within 30 to 60 minutes after extubation.150 Laryngeal edema caused by intubation is uncommon in adults. Overhydration, prolonged Trendelenburg position, and an allergic reaction to medications given before or during surgery should be considered. Management includes maintaining the head-up position, providing humidified oxygen, inhaled racemic epinephrine, IV dexamethasone, and possible reintubation.

Acute pulmonary edema may complicate tracheal extubation when severe airway obstruction coexists with vigorous spontaneous attempts at inspiration.151,152 The negative intrathoracic pressure and possibly associated hypoxemia contribute to the development of pulmonary edema. Management consists of relieving the obstruction and administering supplemental oxygen while the congestion resolves. Tracheomalacia caused by thyroid disease may obstruct the airway after extubation.153

The Difficult Airway

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 been no change, however, in the rate of claims for airway misadventures during the maintenance, emergence, or recovery from an anesthetic. The authors call for the development of additional management strategies during these phases.154

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. Proper timing of extubation, equipment availability, and the presence of a skilled anesthesiologist are vital for safe extubation of these patients. Should emergent reintubation be required, these patients are likely to be hypoxic, hypercarbic, and uncooperative, with gastric distension from failed ventilatory attempts or prior application of a continuous positive airway pressure device (Box 36-18).127,155,156

Extubation may proceed more easily if these 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 cuff leak test result.78 If the patient does not have a leak around a deflated cuff or if other risk factors are present, consideration should be given to extubating or over an introducer, fiberscope, or jet stylet.157-162 A jet stylet, airway exchange catheter, or bougie may be left in the trachea to facilitate reintubation.157-161 If reintubation fails, the hollow device can be used to oxygenate and ventilate the patient's lungs.157-159 The jet stylet can be positioned in the lower trachea using the centimeter markings along its length. Side holes placed along its distal 5 cm prevent tissue trauma from catheter whip during jet ventilation.158 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 extubation163,164 (Fig. 36-38).

The Difficult Extubation

Iatrogenic causes and mechanical failure on rare occasion can render extubation difficult or impossible.161,165-168 Extubation may be difficult in patients with laryngeal abnormalities and those biting the ETT. Difficult extubation with a deflated cuff has been reported when the ETT tube cuff folds below the vocal cords or from laryngeal edema after a difficult intubation. Persistent fixation of the tracheal tube with surgical wires, sutures, and screws also has been reported.165

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 or flagging the medical record alerts health care providers to the special requirements of these patients.

A written statement with pertinent airway management information 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.169

The difficulties and complications of tracheal intubation arise from the act of intubation itself, maintenance of the ETT, or extubation (Box 36-19).6,170-175 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 recommend 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.172

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