Chapter 12. Extraglottic Devices for Ventilation and Oxygenation

A 57-year-old man was admitted for a laparoscopic appendectomy for acute appendicitis. He was otherwise healthy apart from essential hypertension, for which he took hydrochlorothiazide. He had fasted for more than 12 hours.

On examination, he was lying on a stretcher in a moderate amount of pain. He was hemodynamically stable. His height was 183 cm and his weight was 80 kg. His airway examination demonstrated a Mallampati score of II, mouth opening of 4.5 cm, thyromental distance of 6 cm, and good jaw protrusion. He had a full set of teeth, was not obese, and was estimated to be easy to ventilate with a bag and a mask. His cardiac and respiratory examinations were normal.

The patient was premedicated with intravenous midazolam 1 mg and, fentanyl 200 mcg, and this was followed by denitrogenation with 100% oxygen by facemask. As he did not have any indicators of a difficult airway, a decision was made to induce anesthesia with propofol 200 mg and rocuronium 50 mg. Bag-mask-ventilation (BMV) was established with an oral airway. Initial evaluation with direct laryngoscopy using a Macintosh laryngoscope showed a Cormack/Lehane Grade 3 view. The first attempt with direct laryngoscopy employing a tracheal introducer (bougie) resulted in an esophageal intubation. BMV was reestablished and a Glidescope was prepared. When the Glidescope was inserted, only the posterior arytenoids could be visualized, and several attempts with a styleted endotracheal tube and a tracheal introducer were unsuccessful (and were associated with a small amount of bleeding in the oropharynx).

At this point, the decision was made to attempt flexible bronchoscopy. Unfortunately, BMV became more difficult, the patient's oxygen saturation dropped into the low 80s, and it became necessary to insert nasal and oral pharyngeal airways and begin a two-hand and two-person BMV technique. A #4 Laryngeal Mask Airway Classic was rapidly prepared and inserted without complication, at which point it became possible to easily ventilate the patient. Sevoflurane was selected to maintain anesthesia, and to manage escalating tachycardia and hypertension. A 6.0 mm ID Microlaryngeal tracheal tube (MLT, [Covidien-Nellcor, Boulder, CO]) was loaded onto a flexible bronchoscope, which was then inserted through the LMA and into the glottic opening. The MLT was advanced into the trachea over the bronchoscope. After confirmation of correct placement by auscultation and capnograph recording, the decision was made to leave both the endotracheal tube and LMA in place for the duration of the procedure.

The surgery was uneventful and the patient emerged from anesthesia fully awake, warm, with adequate analgesia, and with no residual neuromuscular blockade. The difficult airway cart was brought to the room. However, the patient was extubated without complication, although he did complain of a sore throat in the post-anesthetic care unit, which gradually improved. He was later informed of the difficulty and provided with a notice to inform any subsequent practitioner of his difficult airway.

12.2.1 What Are Extraglottic Devices? Why Do We Need These Devices?

Difficulties in airway management are associated with significant morbidity and mortality,1 and it is crucial that practitioners responsible for airway management continue to refine existing skills, and acquire new knowledge and skills as they become available. Two decades ago, ventilation and oxygenation were achieved primarily via a facemask, or an endotracheal tube (ETT).

While BMV is seemingly simple to perform, it has limitations.2 Tracheal intubation has been considered to be the gold standard for providing effective ventilation, while at the same time providing protection from the aspiration of gastric contents. However, tracheal intubation is a skill that is not easily mastered3 and requires regular practice. Employing an extraglottic device (EGD) to successfully facilitate gas exchange may be a more easily acquired skill for the nonexpert airway practitioner.

In contrast to a mask placed on the face to provide bag-mask-ventilation (BMV), an EGD establishes a direct conduit for air to flow when placed in the periglottic area. The terminology has been somewhat confusing since some have referred to these devices as "supraglottic airway devices," although many have components that extend infraglottically (eg, the Combitube, the Laryngeal Tube [King LT in North America] and the EasyTube).4 Hence, we agree with Brimacombe that the term extraglottic devices, or EGDs, is the more appropriate terminology.

EGDs vary in size, shape, and material. Most have balloons, or cuffs, that upon inflation can provide a reasonably tight seal in the upper airway. As illustrated in the case presentation, these EGDs (including the LMA Classic™) have been used successfully as rescue airway devices. There is clear evidence of their effectiveness and safety in providing ventilation and oxygenation. During the last two decades, these devices have changed the landscape of contemporary airway management, securing a place in the most recent iteration of the American Society of Anesthesiologists' (ASA) Difficult Airway Management Algorithm.5

12.2.2 Do Manufacturing Standards Exist for EGDs to Ensure Patient Safety?

The American Society for Testing and Materials Standards (ASTM) Committee F29 on Anesthetic and Respiratory Equipment has proposed the establishment of standards related to EGDs used in human subjects. A task group has proposed the standardization of terminology, design, production, manufacturing, testing, labeling, and promotion. Devices produced according to the proposed ASTM standards will:

• Facilitate unobstructed access of respiratory gases to the glottic inlet by displacing tissue
• Not require a (external) facial seal to maintain airway patency
• Terminate in a 15/22 mm connector to facilitate positive pressure ventilation via an anesthetic breathing system
• Be capable of maintaining airway patency when the (15/22 mm) airway connector is open to ambient atmosphere
• Minimize the escape of airway gases to the atmosphere

12.2.3 What EGDs Are Commercially Available?

Many EGDs have been introduced.4 The best known are the Laryngeal Mask Airway Classic™ (LMA-C), ProSeal™ Laryngeal Mask Airway (PLMA), Laryngeal Mask Airway Fastrach™ (LMA-FT), and Combitube™ (CBT). A number of more recently developed EGDs such as the Laryngeal Tube™ (LT), CobraPLA™ (CPLA), Airway Management Device™ (AMD), LaryVent™ (LV), Cuffed Oropharyngeal Airway™ (COPA), PAxpress™ (PAX), Air-Q™ device, Ambu® AuraOnce Laryngeal Mask, Portex® Soft Seal Laryngeal Mask, and iGel™ are also gaining acceptance.

This is an evolving field with many new reusable and disposable EGDs introduced every year. This chapter will review the commonly used EGDs which also have sufficient information available in the literature, but it should not be considered an exhaustive review of all available devices. It should be emphasized that some devices (eg, the COPA and PAxpress™) are no longer being manufactured. The authors have elected to include them, as these devices have played a role in the evolution of EGDs; their limitations have informed the evolution of this class of devices.

12.3.1 What Is the LMA? When Was It Introduced?

The LMA (LMA North America Inc., San Diego, CA [Figure 12-1]) was designed in 1981 by Dr Archie Brain, as he searched for a device that was easier to use and more effective than the face mask, and less invasive than an ETT. The LMA is designed to cover the periglottic area and provide continuity of airflow between the environment and the lungs. The device has a wide-bore tube connecting to an oval inflatable cuff that seals around the larynx. It is currently available in eight different sizes for use in patients ranging from neonates to large adults. Typically, a #3 LMA is used in teenagers and small adult females, while #4, #5, and #6 are used in average and large size adults.

During the last two decades, more than 2500 published articles and an estimate of more than 200 million patient uses have provided sufficient evidence to demonstrate the safety and efficacy of the device in airway management.6,7 The LMA is now specified in the American Society of Anesthesiologists' Difficult Airway Management Algorithm.5 Moreover, the LMA has a role in emergency airway management during CPR, the transport of the critically ill patient, and in the intensive care unit.8,9 Although the LMA is a potentially useful device in situations in which tracheal intubation and mask ventilation are not possible (can't intubate, can't ventilate [CICV])5, it should never be used as a substitute for a surgical airway (see Chapters 2 and 40). While this device can provide adequate ventilation and oxygenation, it does not protect the airway from aspiration, and it does not easily allow for the removal of pulmonary secretions. Therefore, when employed as a rescue device, the LMA can only be considered a temporizing measure, until a more definitive and protective airway is secured.

12.3.2 What Is the Proper Way to Insert the LMA?

While many techniques have been suggested for the insertion of the device, including the midline approach, the lateral approach, and the thumb technique,10 the authors recommend the following steps:

1. To minimize the risk of down-folding the epiglottis, it is recommended that the cuff be completely deflated.

2. The LMA cuff should be well lubricated with a water-soluble lubricant.

3. Provided that there is no contraindication to moving the cervical spine, the patient's head and neck should be placed in a sniffing position. A head tilt will help to open the mouth.

4. In order to have clear access to the glottic opening and minimize down-folding of the epiglottis, it is recommended that the practitioner perform a jaw lift using the thumb and index finger of the nondominant hand. This lifts the tongue and epiglottis away from the posterior pharyngeal wall to facilitate placement of the LMA. The LMA should be inserted into the mouth with the index finger placed at the mask-tube junction, pressing the cuff against the hard palate, and advancing the LMA into the oropharynx following the natural curve of the posterior pharyngeal wall. The dimensions and design of the device allow the tip of the LMA to wedge into the hypopharynx. A definite resistance should be felt when the tip of the LMA enters the hypopharynx. Occasionally, resistance is encountered during insertion because of backward folding of the cuff also called 'tip roll'. Sweeping a finger behind the cuff to redirect it inferiorly into the laryngopharynx can usually overcome this problem.11

5. Following placement, the cuff should be inflated with the minimal volume of air necessary to achieve an adequate seal. However, this just-seal volume may not be adequate to seal the hypopharynx from the esophagus.10 Therefore, most practitioners commonly inflate the cuff with more volume. In general, approximately 20 mL is required for #3, 30 mL for #4, and 40 mL for #5 LMA. Seal characteristics may be improved by ensuring that the LMA is secured in the midline of the mouth, and the head and neck placed in a neutral position.

6. The LMA should be fixed in position by taping it to the face, or by attaching it to the anesthesia breathing circuit.12

12.3.3 What Is the Proper Way to Remove the LMA?

In its normal position, the LMA is less stimulating than an ETT and is generally well tolerated by most patients on emergence. Many studies have compared removal under deep anesthesia versus while awake. Although airway obstruction appears to be less frequent if the device is removed with the patient awake, this technique is associated with more coughing, laryngospasm, biting, and hypersalivation.13 While much controversy remains, it is the opinion of the authors that, in adults, the LMA should be removed awake. This is particularly true if mask ventilation is expected to be difficult. Many pediatric airway practitioners prefer removal under deep anesthesia, as children are more prone to laryngospasm.

It is unclear whether the LMA should be removed with the cuff deflated or inflated. Some recommend an inflated cuff because of its capacity to remove secretions that accumulate above the device from the oral cavity.14 Others argue that the cuff should be deflated to minimize trauma and damage to the cuff itself. Brimacombe recommends the removal of the LMA with the cuff partially deflated.13

12.3.4 What Are the Advantages and Disadvantages of Using the LMA as Opposed to an Endotracheal Tube?

Brimacombe conducted a meta-analysis of randomized prospective trials involving 2440 patients comparing the LMA with other forms of airway management, including tracheal intubation.15 He reported many advantages of the LMA including rapidity and ease of placement, particularly for inexperienced operators; improved hemodynamic stability on induction and during emergence; minimal rise in intraocular pressure following insertion; reduced anesthetic requirements for airway tolerance; lower frequency of coughing during emergence; improved oxygen saturation during emergence; and a lower incidence of sore throat in adults.

An additional advantage of the LMA is its utility as a rescue device and during resuscitation.16 Further, studies have shown that the LMA has less impact on mucociliary clearance than an ETT, and may reduce the risk of retention of secretions, atelectasis, and pulmonary infection.17

The major disadvantage of the LMA is its inability to seal the larynx and protect against aspiration, gastric insufflation, and air leak with positive pressure ventilation.15 The mask is designed in such a way that the distal end of the device is intended to become wedged into the upper esophageal sphincter. However, in reality, the distal end may lie anywhere from the nasopharynx to the hypopharynx.

The magnitude of potential gastric insufflation probably depends on the airway pressure generated and the position of the LMA. However, very large series have shown that positive pressure ventilation with the LMA is both safe and effective, with no episodes of gastric dilatation in 11,910 LMA anesthetics under both spontaneous and positive pressure ventilation.18

According to a meta-analysis involving 547 LMA publications, the incidence of gastric aspiration associated with the use of the laryngeal mask airway is rare (0.02%),19 and most of these cases had predisposing risk factors for pulmonary aspiration. However, fatal aspiration of gastric content has recently been reported,20 and so proper assessment for aspiration risk prior to the use of the LMA is imperative. Most airway practitioners hesitate appropriately to use the LMA in patients with a history of hiatal hernia, gastroesophageal reflux, in obstetrical patients, or in patients with a bowel obstruction. Careful placement of the device, and vigilance at emergence of anesthesia, may attenuate the risk of gastric aspiration.

12.3.5 Is It Safe to Use the LMA for Positive Pressure Ventilation?

Over the last two decades, the use of a face mask to facilitate the administration of anesthesia has largely been replaced by the LMA. Originally felt to be most appropriate for nonparalyzed patients with spontaneous ventilation, a survey done in the United Kingdom in the mid 1990s showed that 5236 of 11,910 patients (44%) underwent positive pressure ventilation (PPV) through the LMA.18 While a few studies have reported the successful use of the LMA for PPV in a variety of patient populations and procedures,21-23 they involved mostly small numbers of patients, with few large prospective randomized trials.24 Recently, Bernardini et al compared the risk of pulmonary aspiration in a study involving 65,712 patients with positive pressure ventilation via an ETT (30,082 procedures) compared to an LMA (35,630 procedures).25 Although three pulmonary aspirations occurred in the LMA group compared to seven with the ETT, there were no deaths related to these pulmonary aspirations. The investigators concluded that, while there was a selection bias related to contraindications and exclusions to the use of the LMA in their study group, the use of a laryngeal mask airway was not associated with an increased risk of pulmonary aspiration, compared with an ETT in this selected population.

Based on the current evidence, the LMA appears to be effective and probably safe for positive pressure ventilation in patients with normal airway resistance and compliance, and normal tidal volumes. However, gastroesophageal insufflation may occur when the LMA is used in conjunction with, and in the presence of, decreased pulmonary or chest wall compliance.26,27

Pressure-controlled ventilation (PCV) rather than volume-controlled ventilation (VCV) may provide effective mechanical ventilation in patients with high airway pressure, or reduced lung compliance, while at the same time minimizing the risk of gastric insufflation with the LMA.28 It must be reemphasized that, although rare, cases of serious and even fatal gastric aspiration associated with the use of LMA have been reported.20,29-31 Because of the potential for serious complications, more evidence with studies involving a large number of patients may be needed to confirm the safety of the use of the LMA for PPV.24

12.3.6 How Are LMAs Used Appropriately in Clinical Practice?

Since its introduction in 1988, the LMA has been used in more than 200 million patients worldwide7 and it has largely replaced the ETT and face mask for patients undergoing simple and uncomplicated surgical procedures. The extensive use of the LMA is a reflection of its overwhelming effectiveness and safety in a variety of age groups and surgical procedures. The LMA has also been shown to be effective and safe for elective caesarean section in nonobese parturients, though its use for this indication is controversial.32

A meta-analysis of currently available data shows that the LMA is safe and effective for pediatric airway management.33 Furthermore, the LMA has been used successfully in the management of large numbers of difficult pediatric airways associated with a variety of congenital anomalies.

The LMA was approved for resuscitation by the European Resuscitation Council in 1996,34 and the American Heart Association in 2000.35 However, the possibility of gastric insufflation, related to high peak airway pressure, continues to be a concern in these patient populations, similar to those managed with BMV.

Brimacombe summarized the current evidence with respect to the use of the LMA in the management of the difficult and failed airway.36 With the exception of airway pathology that may interfere with the LMA placement or seal, there is a considerable body of evidence to support the use of the LMA in both predicted and unpredicted difficult airways.5

The LMA also provides a conduit for tracheal intubation using either a blind technique, a transillumination technique (using the Trachlight™ without the stylet),37,38 or a flexible bronchoscope (FB). Intubation success rates through the LMA have been found to be similar for patients with both normal and abnormal airways.39

The flexible laryngeal mask airway (FLMA) was specifically designed for use in ear, nose, and throat; head and neck; and dental surgery. It has been used for adenotonsillectomy,40 laser pharyngoplasty,41 and dental extraction.42 The device consists of a Classic LMA bowl connected to a floppy, a wire-reinforced tube with a slightly narrower bore than the LMA Classic™. The long, flexible, narrow bore tube provides better surgical access to the oropharyngeal cavity than the standard laryngeal mask airway. The technique for placement of the FLMA is similar to that for the LMA.

The reusable LMA Classic™ is the original LMA. Variations on the original include:

• LMA Fastrach™, also known as the Intubating LMA (ILMA), and also available in a disposable form (Figure 12-2)
• LMA Flexible™, similar in design to the Classic, but incorporating a nonkinkable, wire-reinforced tube
• LMA ProSeal™, a device that has improved seal characteristics and incorporates a gastric drainage capability (Figures 12-3, 12-4, and 12-5)
• LMA Unique™, a single-use device virtually identical to the Classic (Figure 12-6)
• LMA Supreme™, a new disposable device that incorporates the insertion advantages of the Fastrach™, with the seal characteristics of the ProSeal™ (Figure 12-7)

12.4.1 What Is the LMA Fastrach™, or Intubating LMA, and Why Was It Developed?

While it is possible to intubate the trachea through an LMA, success rates are variable. Accordingly, an Intubating LMA (LMA Fastrach™, or Intubating LMA (ILMA), LMA North America Inc., San Diego, CA [Figure 12-2]) was designed by Dr Brain. The device has a rigid metal-curved airway tube with a guiding handle, an epiglottis-elevating bar, a deeper bowl, and ramp that directs an ETT up and into the larynx. The device is easy to use, is associated with high success rates of intubation, and has received widespread acceptance. The ILMA is a reusable device which can be cleaned and sterilized using an autoclave. A disposable device has also been recently introduced.

12.4.2 How Is Tracheal Intubation Performed Using the ILMA?

Tracheal intubation through the ILMA can be achieved blindly. To facilitate the insertion of an ETT through the ILMA, the following steps are recommended:

1. Lubricate the posterior side of the ILMA and the ETT (including the connector of the tracheal tube) with a water-soluble lubricant. Ensure that the ETT slides easily through the ILMA.

2. With the patient in a sniffing position, open the airway by using a head tilt. It should be emphasized that the insertion of an ILMA may be difficult if the interincisor gap is less than 20 mm.

3. Grasp the metal handle of the ILMA and insert the device straight back over the tongue to the back of the oropharynx. Then advance the cuff into the hypopharynx following the palatopharyngeal curve by rotating the device using the metal handle and maintaining gentle pressure against the palate. Once in place, inflate the cuff to achieve a seal for manual ventilation. The metal handle may be used to manipulate the device to achieve a seal to ensure adequate ventilation and oxygenation. The device should be gently rotated in the sagittal plane (commonly known as the first Chandy maneuver) to establish optimally unobstructed ventilation.43

4. While a number of ETTs, including the Mallinckrodt Hi-Lo PVC tube, can be used for tracheal intubation, the dedicated wire-reinforced silicone-tipped tracheal tube (TT) supplied with the ILMA has been shown to give the highest success rates.44 With the black vertical line on the tube facing the operator, insert the tube into the metal lumen of the ILMA until the horizontal black line on the tracheal tube meets the proximal end of the ILMA metal tube (Figure 12-2). At this point, the tip of the TT is just emerging from beneath the epiglottis-elevating bar. Resistance will be felt as the TT elevates this bar exiting the distal end of the ILMA, and entering the patient's glottis.

5. Tracheal placement is confirmed in the usual manner. Manipulation of the ILMA by lifting the device from the posterior pharyngeal wall using the metal handle (the second Chandy maneuver) may enhance successful passage in the event of failure. This manuever helps to prevent the TT from colliding with the arytenoids and minimizes the angle between the aperture of the ILMA and the glottis.45

Some evidence suggests that the ILMA in situ produces sufficient pressure on the posterior hypopharyngeal wall to potentially compromise mucosal blood flow.46 For this reason, except perhaps in an airway rescue or resuscitation situation, it is recommended that the device be withdrawn over the TT. A stabilizing rod is provided with the ILMA to hold the TT in position while the ILMA is withdrawn.

Many investigators have studied the effectiveness of the blind intubating technique through the ILMA. The reported mean (range) first-time and overall success rate is 73% (53-100) and 90% (44-100), respectively.46 Several factors that decrease success rates of blind intubation through the ILMA technique have been identified: the use of a #3 ILMA, instead of #4 or #5 ILMA, for adult male patients; the application of cricoid pressure; lifting the ILMA handle; the use of a collar; and an inexperienced practitioner.

12.4.3 What Other Techniques Have Been Described to Enhance Success Rates for Tracheal Intubation through the ILMA?

Several studies have been published evaluating the effectiveness of a laryngoscope to assist ILMA intubation. The overall success rate appears to be no better than the blind technique. Light-guided techniques employing a flexible lightwand (Trachlight™) have also been investigated, and have demonstrated improved success rates.47,48 Lightwand-guided intubation through the ILMA has a first-time and overall success rate of 84% and 99%, respectively.46 Recently, Wong et al49 reported the successful use of the Trachlight-assisted Fastrach intubation in a patient with a difficult airway secondary to the Hallermann-Streiff syndrome. In out-of-hospital tracheal intubation by an emergency physician, Dimitriou et al has shown that a flexible lightwand-guided tracheal intubation through the ILMA had a high success rate, with no failures in 37 patients.50

Pandit et al51 found that bronchoscopic-guided intubation had a higher success rate (95%) through the ILMA than through the LMA (80%), although the time to intubation was longer with the flexible bronchoscope (FB)-assisted technique, compared to the blind technique (74 seconds vs 49 seconds). Overall, in a range of studies, flexible bronchoscope-guided intubation through the ILMA has a first time and overall success rate of 87% and 96%, respectively. However, following a failed blind technique, flexible bronchoscope-guided intubation through the ILMA has a success rate of only 86%.46

Agro et al52 reported the use of a shorter fiberoptic device, Shikani Seeing Eye Stylet™, (Clarus Medical, Minneapolis, MN, USA) to facilitate a Fastrach intubation. Although tracheal intubation was successful, the investigators commented that the major limitation of the Shikani device was its inability to control the direction of the tip of the device.

Using the Patil Intubation Guide (Anesthesia Associates Inc., San Marcos, CA, USA), a whistle diaphragm to detect breath sounds, Osborn successfully intubated the trachea through the ILMA under topical anesthesia in a patient with a recent cervical spine fusion.53 In 2005, a case series was published describing the successful use of the airway whistle with the ILMA in four patients with known difficult airways.54

12.4.4 What Are the Indications for the ILMA?

The ILMA alone does not prevent the aspiration of gastric contents and may produce hypopharyngeal mucosal ischemia if it is left in place for a prolonged duration. Therefore, its role in routine airway management may be limited. However, when used as a temporizing measure, it is a highly effective device in the emergency environment, as an adjunct to failed or difficult BMV, and as a rescue device in the failed airway. Brain has suggested that the ILMA may not be indicated when the patient is anticipated to be an easy intubation (easy direct laryngoscopy), but may be of considerable benefit when the glottis is high and anterior (difficult direct laryngoscopy). Furthermore, recent studies have confirmed earlier findings that ventilation and intubation through the LMA Fastrach™ can be successfully achieved in obese patients with BMI greater than 30.55,56

With respect to emergency medical services (EMS) and prehospital care, the importance of early and effective airway control is universally acknowledged. Tracheal intubation under direct laryngoscopy is associated with a number of practical problems in prehospital trauma and there is evidence to suggest that the ILMA may play an important role in the prehospital setting, in securing the airway of trauma patients with a head injury.57,58

In a recent study by Gercek et al,59 the degree of cervical spine movement of three common methods of tracheal intubation in patients with C-spine injuries (direct laryngoscopy [DL], ILMA, and FB) were compared using real-time, three-dimensional ultra-sonography in healthy elective surgical patients with manual in-line immobilization. They showed that manual in-line immobilization reduced the cervical spine range of motion during different intubation procedures to a limited extent: the least diminution (ie, the greatest C-spine movement) occurred with DL (with an overall flexion/extension range of 17.57 degrees), versus significantly less c-spine movement with ILMA use (overall flexion/extension range of 4.60 degrees), and FB use (overall flexion/extension range of 3.61 degrees—oral, 5.88 degrees—nasal). Furthermore, the mean (± SD) total time required for intubation was shortest for the ILMA (16.5 ± 9.76 seconds), followed by DL (27.25 ± 8.56 seconds), and the longest for both FB techniques (oral: 52.91 ± 56.27 seconds, nasal: 82.32 ± 54.06 seconds).

The prime role of the ILMA lies in managing the airway of patients with a difficult or a failed airway. From a retrospective study involving 254 patients with difficult airways, including patients with either Cormack/Lehane Grade 4 views, immobilized cervical spines, stereotactic frames, or airways distorted by surgery or radiation therapy, the clinical experience with the ILMA (both elective and emergency use) has been largely positive.45,60

The Difficult Airway Society (UK) guidelines for management of the unanticipated difficult tracheal intubation in the nonobstetric adult patient without upper airway obstruction now include the ILMA.61

The LMA C-trach™ was a modification of the ILMA (Fastrach™) fitted with a fiberoptic camera to allow continuous visualization of the airway. When compared to the ILMA, it was shown to have a higher first attempt success rate, but a longer insertion time.62 This device is no longer available on the market, largely due to its cost.

12.5.1 What Is the PLMA? How Does It Differ from the LMA?

The PLMA (Intavent Orthofix, Maidenhead, UK [Figure 12-3]) is a laryngeal mask variant that incorporates several modifications to the LMA:

• An esophageal conduit is incorporated to provide access to the esophagus and the gastrointestinal tract to minimize the risk of aspiration. This incorporated conduit renders a dual tube look to the device.
• A second cuff on the dorsal aspect of the PLMA is intended to enhance the seal characteristics of the device.
• The PLMA lacks mask aperture bars, and (like the ILMA) has a deeper bowl which makes the migration of the epiglottis into the distal lumen of the device less likely.
• The PLMA also has a flexible wire-reinforced airway tube to improve flexibility and minimize kinking, and a bite-block to reduce the danger of bite-induced airway obstruction, or tube damage.

The drainage conduit traverses the bowl of the cuff on its way to the upper esophagus, in an effort to reduce the risk of gastric insufflation when positive pressure is applied to the airway. Standard gastric tubes (≤18 French [Fr] gauge) can be accommodated by the conduit to facilitate gastric decompression. An accessory vent under the drainage tube is intended to prevent the pooling of secretions and can act as an accessory ventilation port.63

Employing moderate force to advance the laryngeal cuff forward into the periglottic tissues may improve the airway seal. The dual-tube arrangement seems to reduce the incidence of accidental device rotation during anesthesia. This feature enhances the ability to secure the device in position, giving greater confidence for use in longer procedures.

12.5.2 How Is the PLMA Placed?

The technique of insertion of the PLMA is similar to that of the LMA. While there is no randomized controlled study comparing the placement technique of the PLMA, with or without a muscle relaxant, it has recently been shown that successful placement of the PLMA requires deeper anesthesia when compared with the LMA.64,65

Three insertion techniques for the PLMA have been advocated:

1. The Introducer-Assisted Insertion Technique: Prior to its placement, the PLMA is loaded onto an introducer by placing the distal end of a metal introducer in an insertion strap on the PLMA (Figure 12-4). The airway tube is folded around the introducer and fitted into a proximal matching slot. The head and neck of the patient should be placed in a sniffing position. Following the placement of the PLMA, the introducer is removed as the PLMA is held in position.

2. The Digital Technique: Similar to the LMA, the digital technique involves the placement of the index finger under the insertion strap during the insertion of the PLMA. Rotating the PLMA 90 degrees in the mouth until resistance is felt at the hypopharynx was found to be more successful and associated with a decrease in blood staining on the device, and in the incidence of sore throat.66

3. The Tracheal Introducer-Guided Insertion Technique: This is probably the most reliable technique to optimally place the tip of the PLMA cuff in the hypopharynx.67 A well-lubricated tracheal introducer (eg, an Eschmann tracheal introducer) is placed into the esophagus under direct vision with a laryngoscope. The PLMA is guided into position by placing the tracheal introducer through the esophageal conduit (Figure 12-5). While this technique enjoys a high success rate, it is time-consuming, and probably more stimulating and traumatic.

In a recent study, Eschertzhuber et al68 compared these three insertion techniques in patients with simulated difficult laryngoscopy using a rigid neck collar. Insertion was more frequently successful with the Eschmann tracheal introducer technique (ETI) at the first attempt (ETI—100%, digital—64%, introducer-assisted technique—61%). The time taken for successful placement was similar among groups on the first attempt. However, it was shorter for the ETI technique after three attempts (ETI 31 ± 8 seconds, digital 49 ± 28 seconds, introducer-assisted technique 54 ± 37 seconds).

Proper placement of the PLMA can be confirmed by a number of techniques. Air leak through the drainage tube at low airway pressures suggests malposition of the PLMA. Although air leaks are ordinarily easily detected by auscultation, or by feeling air exiting the drainage tube, a small volume leak is probably best detected by the soap bubble test.69 Three other tests have been suggested to check the patency of the drainage tube, including passing a gastric tube through the drainage tube; passing an FB through the drainage tube; and performing a suprasternal notch tap while observing a soap bubble, or lubricant, at the proximal end of the drainage tube.70

12.5.3 What Are the Advantages of the PLMA, Compared to the LMA?

In principle, the PLMA would be expected to reduce the aspiration risk when compared to the LMA. Laboratory (and cadaver) evidence are supportive of the theoretical efficacy of the PLMA.71 However, clinical evidence is lacking, largely because the incidence of aspiration of gastric contents with the LMA is so low (0.02%), and a randomized controlled clinical trial with a large patient population is needed. Aspiration of gastric contents has been reported with the PLMA,72 and malposition of the PLMA has been identified as a cause of the aspiration.73

The design of the PLMA cuff significantly improves airway seal when compared to the LMA. The larger, softer, wedge-shaped PLMA cuff enables the anterior cuff to better adapt to the shape of the pharynx.74 Most believe that pressure exerted on the pharyngeal mucosa by the cuffs of LMAs is the cause of sore throat seen with the device. Compared to the LMA, PLMA intracuff pressures are lower and airway seal pressure higher for any given intracuff volume.75 Moreover, pressure exerted on the hypopharyngeal mucosa has been found to be below that considered critical for mucosal perfusion.

Perhaps the greatest limitation of the use of the LMA in small children is that the seal is often inadequate for positive pressure ventilation, even at high intracuff pressures. This does not appear to be as significant a limitation when the PLMA is used in these patients. In a series of studies comparing the PLMA to the LMA in children of various ages, Goldmann et al showed that the first-time insertion of the PLMA was more successful, was associated with a seal sufficient to permit maximal tidal volume with positive pressure ventilation, produced less gastric insufflation, and provided an improved bronchoscopic laryngeal view compared to the LMA.76-79 Another comparison study between PLMA and LMA in neonates and infants showed similar success rates, but higher tidal volumes and leak pressures for the PLMA.80 A larger study by Lopez-Gil of children aged 1 to 16 showed equivalence of ease of insertion, endoscopic confirmed position and mucosal trauma between the PLMA and LMA, but better sealing pressures and less gastric insufflations with the PLMA.81 Finally, Goldmann et al demonstrated that positive end-expiratory pressure (PEEP) could safely be applied using the PLMA in children.82

12.5.4 What Are the Disadvantages of the PLMA?

It is generally felt that the PLMA is more difficult to place than the LMA. The success rate for first-time PLMA insertion is lower than the first-time insertion success rate for the LMA (average success rate of 85% with a range from 81% to 100% for the PLMA vs average success rate of 93% with a range of 89% to 100% for LMA).74 It is possible that the insertion difficulty may in part be related to the larger, deeper, and softer cuff of the PLMA. Although the learning curve for the insertion of the PLMA has not been studied, it has been suggested that 20 to 30 insertions of the PLMA are required before competency is achieved.74

12.5.5 What Are the Potential Clinical Uses of the PLMA?

The improved airway seal characteristics and touted lower risk of gastric aspiration of the PLMA compared to the LMA has expanded its applicability to surgical procedures that would not have been considered safe had an LMA been employed. These procedures include laparoscopy,83 open abdominal surgery, surgery in patients with obesity, and in patients with gastroesophageal reflux.74 A recent study by Hohlreider et al demonstrated less postoperative nausea, vomiting, airway morbidity, and analgesic requirements for the PLMA than the tracheal tube in females undergoing breast and gynaecological surgery.84

The PLMA has been used to provide ventilation and oxygenation in patients with a history of difficult laryngoscopic intubation.85,86 Recently, a number of investigators reported the successful use of the PLMA to rescue a failed airway in obstetrical patients after a failed intubation.71,87-89

A number of studies, involving volunteers under general anesthesia90 and manikins have shown that the PLMA may play an important role in airway management in the trauma setting. Although supported by laboratory evidence,91 there are no clinical case reports of the use of the PLMA in the trauma setting. As well, the role of the PLMA shows favorable promise for CPR, but needs further investigation.

12.5.6 What Is the LMA Supreme™ and What Is Its Clinical Utility Compared the PLMA?

The LMA Supreme™ (Intavent Orthofix, Maidenhead, UK) is a new, single-use, latex-free, LMA device with a drainage tube (Figure 12-7). It was designed to combine the desirable features of both the Intubating LMA (ease of insertion, because of the rigid anatomically shaped airway tube made of medical-grade polyvinyl chloride) and the PLMA™ (higher seal pressures and gastric access).92 The cuff of the LMA Supreme (LMAS) is designed to provide higher seal pressures than the LMA Classic or Unique. In an early clinical study involving 70 patients, Ali et al93 reported that the LMAS is superior to the LMA Classic because of its ease of insertion, with low cuff pressure and high oropharyngeal leakage pressure. However, several recent clinical studies comparing the LMAS and PLMA reported conflicting findings.92,94,95 While studies conducted by Verghese92 and Hosten95 reported that both LMAS and PLMA had similar leak pressures, Lee et al94 found that the oropharyngeal leak pressure and the maximum achievable tidal volume are lower with the LMAS than with the PLMA. However, there was no difference in the efficacy in ventilation and safety between the LMAS and PLMA in these studies.

Because of the ease and speed of successful insertion, higher glottic seal pressures, and ability to access gastric contents, Verghese et al92 suggested that the LMAS may have a role in airway management in cardiopulmonary resuscitation (CPR), and in the cannot intubate, cannot ventilate scenario currently recommended for the LMA Classic.5

12.6.1 What Is CBT and How Does It Differ from the LMA?

The Combitube (CBT) (Tyco-Healthcare-Kendall-Sheridan, Mansfield, MA [Figure 12-8]) is an easily inserted and highly efficacious EGD. It is specified in the ASA Difficult Airway Algorithm as a primary rescue device in CICV situations.5 It also has been used successfully during CPR and in trauma patients.

The CBT is a double-lumen airway, one of which is open at both ends, as with a normal ETT. The other consists of an open proximal lumen and a distal blocked lumen, which resembles an esophageal obturator airway.96-100 The device has two balloons designed to trap the glottis between them. An oropharyngeal balloon is designed to be positioned just behind the posterior part of the hard palate. Once inflated, this balloon presses the base of the tongue in a ventro-caudal direction and the soft palate in a dorso-cranial direction, sealing the oral and nasal airways from behind. Another smaller cuff seals the esophagus once inflated. Perforations between the two balloons in the distally blocked lumen permit the egress of air or oxygen when positive pressure ventilation is applied to a proximal port. Two circumferential rings printed on the proximal end of the tube indicate that the device has been inserted to the proper depth when the upper teeth or alveolar ridges are situated between these two marks. The CBT is available in two sizes: the CBT 37F SA (small adult), to be used in patients 4 to 6 ft in height (approximately 120 to 180 cm); and the CBT 41F, for patients taller than 6 ft (approximately >180 cm).

12.6.2 How Is the CBT Inserted?

Insertion is facilitated by bending the CBT between the balloons for a few seconds before insertion to mimic the curvature of the pharynx. It is made more pliable if heated to body temperature, perhaps attenuating its blunt trauma potential. Placement of the CBT is most readily performed with the patient's head placed in a neutral position,99 although some clinicians prefer slight extension or flexion. The classical sniffing position is usually not helpful. In the fully awake patient, sedation and topical anesthesia are necessary to ensure that the patient does not react to the insertion. To elevate the tongue and epiglottis, a jaw lift is performed by grasping the lower jaw with the thumb and forefinger. The CBT is inserted blindly along the surface of the tongue with initial gentle downward, curved, dorso-caudal movement, and then directed parallel to the patient's horizontal plane until the printed ring marks lie between the upper and lower teeth, or alveolar ridges in edentulous patients. After insertion, the oropharyngeal balloon of the CBT 37F is inflated with 85 mL of air through a blue pilot balloon. The corresponding filling volume for the CBT 41F is 100 mL. Then the distal balloon is inflated with approximately 10 mL of air.

With blind insertion, the CBT is successfully placed in the esophagus in more than 95% of cases. Ventilation is achieved via the longer blue connector (No. 1), leading to the blocked lumen which contains perforations at the level of the larynx, between the two balloons. The trachea is effectively ventilated because the nose, mouth, and esophagus are sealed by the two balloons. The second tracheoesophageal lumen of the CBT can be used for decompression of the esophagus and stomach, thereby minimizing the risk of aspiration.

Auscultation of breath sounds over the chest, the absence of gastric insufflation, end-tidal CO2 detection, and esophageal detection devices can all assist in the confirmation of correct positioning.101,102

Should the CBT enter the trachea on blind insertion, it can function like a standard ETT and there will be no need for inflation of the pharyngeal cuff. Ventilation can be achieved through the shorter, unobstructed clear tube (No. 2), leading to the tracheal lumen.

Although it is rare, ventilation may be impossible through either the proximal or distal lumen. This usually signifies that the CBT has been placed too deeply, with the obturator lumen positioned in the esophagus and the oropharyngeal balloon obstructing the entrance to the larynx. After deflation of the balloons, the CBT should be withdrawn approximately 2.0 to 3.0 cm. While the CBT may be inserted blindly, the use of a laryngoscope is recommended whenever possible.

12.6.3 What Are the Advantages of the CBT, Compared to the LMA?

The CBT was designed primarily for use in CPR.97,103 even by nonmedical personnel. It has been demonstrated to permit effective ventilation during routine surgery, as well as in the ICU.104 Most believe that the principal role of the CBT is in emergency airway control when tracheal intubation is not immediately possible.105-108 The CBT may be kept in situ for up to 8 hours and allows controlled mechanical ventilation at inflating pressures as high as 50 cm H2O (see aspiration potential below). The CBT can be replaced by deflation of the oropharyngeal balloon and insertion of an ETT either under direct laryngoscopy, or by indirect view using a flexible bronchoscope placed anterior, or lateral to the CBT.

Several case reports describe the successful use of the CBT in cases of unanticipated difficult airways.109-111 Thus, it is not surprising that the American Society of Anesthesiologists (ASA) task force on difficult airway management lists the CBT, along with the laryngeal mask airway as CICV rescue methods.5,112 Consequently, the CBT should be part of a portable kit for the management of difficult airways.

A major advantage of the CBT over conventional tracheal intubation is that the device can be inserted with the head and neck in a neutral position. Additionally, it requires only modest mouth opening for insertion, and its tubular profile permits insertion in situations that cannot be negotiated by more bulky devices. The CBT can be inserted from a variety of angles making it useful in awkward environments (eg, a patient who is trapped in a vehicle, see Chapter 16). The CBT may be of special benefit in patients with massive bleeding or regurgitation, when visualization of the vocal cords is impossible. While protection from aspiration is not absolute, the CBT may be more effective in this regard, due to much higher sealing pressures than the traditional LMA.113

12.6.4 What Are the Disadvantages of the CBT?

The CBT was not designed to replace other devices for routine surgery. While the esophageal cuff offers some protection against the reflux of gastric contents into the periglottic area, the level of protection against aspiration does not approach that of a cuffed ETT.

The suctioning of tracheal secretions is impossible when the CBT is in the esophageal position. To address the issue of secretions and suctioning, Krafft et al proposed a modification in the CBT in which the two anterior, proximal perforations of the CBT are replaced by a single, larger, ellipsoid-shaped hole that allows for fiberoptic access of the trachea, tracheal suctioning, and tube exchange over a guide wire.114 It should be noted that recently developed flexible bronchoscopes (eg, Storz, Tuttlingen, Germany) with a small outer diameter (3.0 mm OD) allow passage through the unmodified pharyngeal perforations.

Contraindications to the use of the CBT include: an intact gag reflex, airway obstruction by foreign bodies, tumors, or swelling, the presence of known esophageal disease, and the prior ingestion of caustic substances.

Complications associated with the use of CBT have been reported.115,116 In a retrospective study of 1139 patients requiring resuscitation using the CBT, four cases of subcutaneous emphysema, pneumomediastinum, and pneumoperitoneum associated with the CBT during prehospital management were reported.116 The reason for these complications appeared to be hyperinflation of the distal balloon (20-40 mL), although external chest compression and continuous positive-pressure ventilation may also have been factors. Other rare complications include transient cranial nerve dysfunction,117 esophageal rupture,118 and tongue engorgement.119

12.6.5 What Are the Potential Clinical Uses of the CBT?

The CBT is an easy-to-use, rapidly inserted emergency airway device that has performed satisfactorily in many circumstances. It is accepted as a primary rescue device in CICV situations, as well as for CPR, and in trauma patients. The CBT has been recommended in Practice Guidelines for Management of the Difficult Airway of the ASA.5 It has also been recommended in the Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiac Care of the American Heart Association (AHA). In 2000, the CBT was upgraded by the AHA as a class IIa device. Furthermore, the CBT may provide an element of protection in patients at risk for aspiration, and it may be of benefit for patients in whom manipulation of the cervical spine is hazardous or impossible. Successfully placed, the device is capable of facilitating adequate ventilation and oxygenation, and in most instances is as effective as endotracheal intubation.120

12.7.1 What Is a LT and How Does It Differ from LMA?

The laryngeal tube airway (VBM Medizintechnik, Sulz am Neckar, Germany [Figure 12-9]), also known as the King LT Airway® in North America, is an EGD that was introduced to the European market in 1999.121 It is similar in appearance and function to the CBT, and is available in three configurations (see below). The fundamental configuration of the LT is a silicone airway tube with ventilation outlet perforations lying between two cuffs, pharyngeal and esophageal. As opposed to the CBT, the LT has a single pilot balloon connected to both cuffs and a single 15 mm standard male adapter. The airway tube is short and "J" shaped with an average diameter of 1.5 cm leading to a blind tip. The device requires a mouth opening of at least 23 mm for its insertion. After device placement, the proximal cuff should lie in the hypopharynx and the distal cuff in the upper esophagus. Both cuffs are high volume-low pressure in design to establish an adequate seal, while minimizing the risk for ischemic mucosal damage. Two ventilation outlets are located between the two cuffs, in the anterior aspect of the tube. The proximal outlet is protected by a V-shaped deflection in the pharyngeal cuff, such that when with the cuff is inflated, soft tissue is deflected from this opening, helping to maintain a patency. There are two side holes near the distal outlet.

Even though the two cuffs are supplied by a single inflation pilot balloon apparatus, the design of the inflation system allows the pharyngeal cuff to fill first, stabilizing the position of the tube.121 Once the pharyngeal cuff has molded to the anatomy of the patient, the esophageal cuff inflates. The amount of air for cuff inflation is specific to tube size and is indicated on a syringe that is included in the package. Six sizes, suitable for neonates up to large adults, are available. Safe inflation of the dual cuffs may be enhanced with the aid of a cuff pressure gauge and ought to be limited to 60 cm H2O.

Since its introduction in 1999, the LT has undergone con-siderable changes in design. Presently, there are several versions of the laryngeal tube: standard reuseable laryngeal tube, single-use laryngeal tube (LT-D), laryngeal tube-Suction II, and single-use laryngeal tube-Suction II (LTS-D).122 Similar to the PLMA, the laryngeal tube- Suction has two lumens: one for ventilation and the other serves as a conduit to the esophagus and stomach.

12.7.2 How Is a LT Inserted?

An appropriately sized LT should be selected based on the patient's weight and height. Prior to insertion, the cuffs should be completely deflated and well lubricated. The device should be inserted with the patient's head and neck in a sniffing position.122 The head is extended on the neck with the nondominant hand, to open the mouth. The LT is then inserted blindly in the midline, with the tip pressed against the hard palate and then advanced along the palate into the hypopharynx until resistance is felt, at which point a proximal horizontal black line should be aligned with the front teeth. The device is usually easily inserted with insertion times comparable to those reported for the LMA.123 While a number of studies reported easier and faster insertion of the LT compared to the CBT by the prehospital care personnel and trainees, these studies used only manikins and not patients.124,125 Clinical studies are necessary to confirm these findings.

The device provides a patent airway in the majority of patients following the first insertion attempt and success does not require extensive training.126,127 Indicators of correct placement include end-tidal carbon dioxide detection, auscultation of bilateral breath sounds, absence of gastric insufflation, and adequate chest movement. Capnographic waveform analysis may be of particular use in confirming proper position of the LT. A brief period of positive pressure ventilation (PPV) may also confirm proper alignment of the LT and the absence of obstruction.

Correct placement of the LT may also be verified using a lightwand (Trachlight™). The Trachlight™ (without the internal stiff wire stylet) is inserted into the LT and advanced until a faint glow can be seen above the thyroid prominence. This indicates that the tip of the lightwand is just above the laryngeal inlet. The lightwand is then advanced further until a well-defined circumscribed glow is seen in the anterior neck, slightly below the thyroid prominence, indicating entrance into the glottis and correct positioning of the LT. Incorrect positioning would demonstrate a lateral glow, or a glow with a halo, indicating malpositioning of the ventilation orifice. The LT should be removed with the patient either deeply anesthetized, or totally awake. In an awake patient, the LT should be removed only when airway protective reflexes have completely returned.

12.7.3 What Are the Advantages of the LT, Compared to the LMA and the CBT?

Insertion of this device is relatively easy and successful in most patients on the first attempt. The soft tip minimizes mechanical trauma on insertion and high volume/low pressure cuffs provide a good seal and protection against mucosal ischemic damage. A single pilot balloon confers an element of simplicity and speed in emergency situations. Other advantages of LT include:

1. The adequacy of ventilation with the LT is comparable to that obtained with other EGDs. The ease of insertion and high quality of the seal achieved may confer a preferred role for the LT in airway management during cardiopulmonary resuscitation.126

2. The LT can be used successfully in children as young as 2 years old, with superior seal pressures and equivalent ease of insertion.128

3. The esophageal cuff of the laryngeal tube may provide an element of protection against the reflux of gastric contents into the periglottic area and the tube-Suction options permit gastric decompression. Both of these features may reduce the risk of aspiration, relative to the LMA Classic.129,130

4. Due to the form and length of the device, an unintended tracheal intubation should not occur.

12.7.4 What Are the Disadvantages of the LT?

1. Protection from aspiration is less than that offered by a cuffed ETT, and in high aspiration risk situations tracheal intubation remains necessary. While the newer laryngeal tube-Suction II, and single-use laryngeal tube-Suction II (LTS-D) may have the potential to provide some protection from aspiration, presently there are no clinical data available.

2. The intracuff pressure may increase by as much as 15 cm H2O within 30 minutes after its insertion if nitrous oxide is employed, due to the diffusion of this gas into the cuff. Manometric monitoring of the cuff pressure has been suggested.131

3. Position adjustments to ensure airflow continuity may be required more frequently in obese patients.132

Positive pressure ventilation through the LT may provide inadequate ventilation in patients who require high pulmonary inflation pressures.

1. The mouth opening required for LT insertion is at least 23 mm.

2. As with any EGD, the LT may not be effective in the presence of anatomic distortion of the upper airway, such as lesions of the epiglottis or laryngopharynx.

3. The LT is less effective than the LMA in children younger than 10 with respect to ease of ventilation and endoscopic view through the device.133

12.7.5 What Are the Potential Clinical Uses of the LT?

In anesthetic practice, the LT can be used in patients who are candidates for face mask or LMA-delivered anesthesia. It may also find a role in the failed airway, similar to that of the LMA and the CBT.

The dimension and position of the ventilation holes and the protection offered by the overhanging cuff block permits the insertion of a suction catheter, endotracheal tube exchange device, FB, or an Eschmann introducer, over which an ETT may be passed.134

12.8.1 What Is the LV and How Does It Differ from the LMA?

The LV (B+P Beatmungs-Produkte GmbH, Seelscheid, Germany) consists of a single tube with a standard male connector, two cuffs with a single pilot balloon, and a ventilation outlet. The superior cuff lies in the hypopharynx and the ventral part of the cuff contains the orifice for ventilation. The inferior cuff is smaller and should lie at the level of the upper esophageal sphincter. As with other EGDs, the insertion of the LV is a blind technique and appears to have a rapid learning curve, similar to that of the LT.

12.8.2 How Do You Insert the LV?

Prior to the use of the LV, the cuffs should be tested by inflating 50 mL of air. During insertion, the tip of the LV should be introduced along the posterior wall of pharynx and advanced until resistance is felt. The cuffs should then be inflated with 50 mL of air. If there is resistance to filling, the LV has been introduced too deeply and should be retracted 2 to 3 cm before reattempting cuff inflation.

12.8.3 What Are the Advantages of the LV, Compared to the LMA?

The advantages of the LV are similar to those of the LMA Unique, and LT, with comparable provision of ventilation and oxygenation, at least in early clinical experience.126,135

12.8.4 What Are the Disadvantages of the LV?

More complex handling, resulting in a significantly higher failure rate, and postoperative patient discomfort suggest that the LV may not be the first choice in routine anesthesia practice.135

12.8.5 What Are the Potential Clinical Uses of the LV?

The role and advantage of the LV are similar to those of the LT. The precise advantages have not yet been defined by clinical trials.

12.9.1 What Is the AMD and How Does It Differ from the LMA?

The AMD (Nagor Limited, Isle of Man; manufactured by Biosil Ltd, Cumbernauld, UK [Figure 12-10]) is a newly introduced EGD.136 The AMD consists of a clear silicone dual lumen tube that is concave ventrally with inflatable oropharyngeal and hypopharyngeal cuffs. An oval ventilation port is located in the ventral part of the device opposite the laryngeal inlet. The connector at the proximal end of the tube is Y-shaped incorporating two ports: one for anesthetic gas delivery and providing access for suction catheters, an FB or an Eschmann introducer; and the second for a channel into the esophagus for suction. When fully inflated, the upper cuff fills, elevating the tongue and epiglottis. The cuffs have independent inflation controls, which are color coded. The shape of the cuffs ensures correct orientation in the airway and prevents both lateral movement and rotation of the tube. The AMD is available in several sizes: 3.0 to 3.5 for patients weighing 30 to 60 kg, and size 4.0 to 5.0 for patients more than 60 kg.

12.9.2 How Is the AMD Inserted?

The insertion technique is similar to other EGDs. Both cuffs of the AMD should be well lubricated, the pharyngeal cuff should be fully deflated, and the esophageal cuff should have 5.0 to 9.0 mL of air. This closes the esophageal cuff channel through a unique constriction mechanism and permits atraumatic insertion. The AMD, held in the dominant hand, is inserted in the midline of the mouth in a caudal direction until it seats properly in the hypopharynx. The pharyngeal cuff is then inflated with 50 to 80 mL of air. Like all EGDs, proper placement should be confirmed after insertion.

12.9.3 What Are the Advantages of the AMD Compared to the LMA?

A key feature of this device lies in the access it provides to the esophagus when the esophageal cuff is partially deflated. A suction catheter can be introduced through the device without interrupting ventilation to aspirate the esophagus, and provides an element of protection against aspiration.

12.9.4 What Are the Disadvantages of the AMD?

Compared with other EGDs, the AMD device is somewhat difficult to insert and airway trauma is possible.136-138 Cook et al reported a first-time success rate of 66% in establishing an airway, with an average of 0.56 manipulations per patient and a primary failure rate of 11%.137 The AMD also had an increased incidence of loss of airway during anesthesia.139 While the AMD may provide protection against aspiration, presently there are no data to support the claim.

12.9.5 What Are the Potential Clinical Uses of the AMD?

While the dynamic relationship between the hypopharyngeal cuff and the esophageal suction port is interesting, the precise advantage of the AMD is difficult to define at this time.

12.10.1 What Is the CPLA and How Does It Differ from the LMA?

The CobraPLA (CPLA) (Engineered Medical Systems, Inc., Indianapolis, IN [Figure 12-11]) consists of a breathing tube with a circumferential inflatable cuff proximal to a ventilation outlet, a 15 mm standard adapter, and a distal widened cobra-shaped head designed to separate soft tissues and to allow ventilation of the trachea. Once in place, the cobra head lies in front of the laryngeal inlet. Internal to the cobra head, a ramp directs ventilation into the trachea. A soft grill shields the inferior aperture of the device in an attempt to deflect the epiglottis anteriorly. The bars of the grill are sufficiently flexible to permit an ETT to pass easily. The cuff is shaped such that it resides in the hypopharynx at the base of the tongue and, when inflated, raises the base of the tongue exposing the laryngeal inlet and affects an airway seal. The unique shape of the distal part of the device allows it to slide easily along the hard palate during insertion, and to move soft tissues away from the laryngeal inlet once in place.

The CPLA is available in eight sizes and it can be used in small children, including neonates.140 Size selection is governed by the weight of the patient. Generally, #3 is used in most female patients, #4 for most men, and #5 for larger men. When one is unsure which size is best, or when learning placement technique, selecting the lower size is recommended. In general, larger sizes require considerably higher cuff pressures to produce an acceptable seal compared to the smaller sizes.141

Recently, several modifications of the original design of the CPLA have been introduced.140 The second-generation CPLA has a distal curve in the breathing tube to avoid kinking, and softer material to facilitate insertion and minimize trauma. The Cobra PLUS has a temperature probe to measure core temperature and a gas sampling line for the three smallest pediatric sizes.

12.10.2 How Do You Insert the CPLA?

The CPLA is simple to insert, though some more difficulty is encountered in the obese.142 Prior to insertion, the pharyngeal cuff is fully deflated and folded back against the breathing tube. The back of the cobra head and cuff are lubricated, taking care that the lubricant does not obstruct the grille. The patient's head is placed in the sniffing position. A jaw lift is performed and the distal end of the CPLA is directed straight back through the mouth between the tongue and hard palate. Modest neck extension (without a jaw lift maneuver) may aid the passage of the device as it turns toward the glottis at the back of the mouth. Once the CPLA traverses the back of the mouth, it usually turns caudally toward the larynx with minimal resistance, as the flexible distal tip guides the device downward. The CPLA is properly seated above the glottis when modest resistance to further distal passage is encountered. Once inserted, the flexible tip lies behind the arytenoids, the cuff lies in the hypopharynx at the base of the tongue, and the ramp lifts the epiglottis. Then the cuff is inflated until the leak with positive pressure ventilation disappears. Indicators of correct placement are absence of leak on auscultation of the neck, bilateral breath sounds, absence of gastric insufflation, easily produced chest movement, and positive carbon dioxide detection. Exceeding a peak airway pressure of 25 cm H2O with positive pressure ventilation is not recommended, even when testing for ventilation and cuff seal, because of the risk of gastric insufflation.

If the CPLA is not inserted far enough, inflation of the cuff may cause the tongue to protrude from the mouth of the patient. In this situation, the cuff should be deflated and the device advanced further or a smaller sized CPLA selected. It is possible to advance the cobra head beyond the laryngeal inlet, in which case ventilation will not be possible. The CPLA should be removed awake with the airway protective reflexes intact.

12.10.3 What Are the Advantages of the CPLA, Compared to the LMA?

The tube of the CPLA has a larger lumen than most EGDs and may be particularly useful in directing flexible endoscope-assisted tracheal intubation,143,144 especially when larger ETTs are indicated. An ETT of 8.0 mm ID can be advanced through the sizes 4 to 6 CPLA.140 In addition, it has been made short enough that its removal after insertion of an ETT is greatly facilitated.

As with similar EGDs, a Trachlight™ with the rigid internal stylet removed can be used in lieu of an FB to facilitate tracheal intubation. Although less reliable, blind tracheal intubation through the CPLA using a generic ETT introducer (eg, the Eschmann introducer) may be possible.

Like many other EGDs, the insertion technique is simple and has been accomplished by personnel with little or no experience. Several small clinical studies reported that the CPLA has better airway sealing characteristics compared to the LMA.145,146 During gynecological laparoscopy, the CPLA provided similar insertion characteristics, but higher airway-sealing pressures than the LMA Classic.147 However, Park et al148 showed that gastric insufflation, or ventilatory difficulty, may occur following the change of the position of the head and neck when using the CobraPLA, as compared to PLMA. A number of reports have supported the use of the CPLA in the CICV situation, a factor related to the unique design of the device.140,142,149

Khan et al150 reported successful use of the CPLA for ventilation following failed attempts in placing an LMA in patients with face and neck contractures, as well as limited mouth opening.

12.10.4 What Are the Disadvantages of the CPLA?

In comparison with trials for the LMA Classic and LMA Unique, the CPLA took slightly longer to insert and macroscopic blood occurred more frequently on the CPLA, seen on up to 40% of the devices after removal.143,146,147 Although blood staining has been detected more frequently with the CPLA compared with other EGDs, there were no differences in airway morbidity.151 Therefore, the clinical significance of these findings is uncertain.

The CPLA is not appropriate for patients with low lung compliance or increased airway resistance. The major disadvantage of the device is that it does not protect against aspiration and does not secure the airway as effectively as an ETT.152 The mask aperture bars probably have no anatomical utility and predispose to herniation of the pharyngeal structures on insertion and while in situ.151

Although it is rare, aspiration associated with use of the CPLA has been reported.152,153 In fact, Cook et al152 terminated the CPLA evaluation study after two cases of serious pulmonary aspiration with the use of the CPLA, suggesting that the CPLA should be avoided in patients at risk of aspiration.

12.11.1 What Is the SLIPA and How Does It Differ from the LMA?

The SLIPA (SLIPA Med, Cape Town, South Africa [Figure 12-12]) is a disposable EGD. It is designed for airway management during controlled ventilation.154,155 The peculiar shape of the device provides a seal without the use of an inflatable cuff.

The body of the SLIPA is shaped like a hollow boot with toe, bridge, and heel prominences, designed to engage the mucosal lining of the patient's pharynx. Its hollow configuration and shape permit the entrapment of secretions, blood, or gastric contents in the device, theoretically reducing the risk of aspiration. The device is formed from soft plastic material, flexible enough to allow easy insertion. The hollow chamber flattens to facilitate insertion. After placement, the toe should sit in the hypopharynx. The bridge, with its two lateral bulges, fits into the pyriform fossae, displacing tissue away from the posterior pharyngeal wall. The heel of the chamber anchors the SLIPA in position by sliding over the soft palate and into the nasopharyngeal opening. Toward the toe side of the bridge are smaller lateral bulges that coincide with the inferior cornus of the hyoid bone designed to relieve pressure on relevant nervous tissue, such as the superior laryngeal branch of the vagus.

12.11.2 How Is the SLIPA Inserted?

The SLIPA is inserted similarly to the LMA. The patient's head and neck should be placed in a sniffing position. Held in the dominant hand, the SLIPA is inserted in the midline of the mouth, pressed against hard palate, and advanced until resistance is felt. A jaw lift may facilitate placement. The crescent shape of the toe minimizes the risk of downward folding of the epiglottis, which may lead to airway obstruction. The toe of the device slips easily into the esophagus, where it creates a seal. After placement, the SLIPA returns to its preinsertion shape.

12.11.3 What Are the Advantages and Disadvantages of the SLIPA, Compared to the LMA?

Although there is a theoretical lower risk of gastric insufflation relative to the LMA, this has not been shown in studies. In one small study, Lange et al found that there was actually a higher rate of gastric insufflations with SLIPA compared to LMA (19% vs 3%).156

12.11.4 What Are the Potential Clinical Uses of the SLIPA Device?

Based on the current available evidence, the SLIPA appears to have comparable efficacy and complications as the LMA, and may be used as a primary airway device for short surgical procedures.140 While the SLIPA may have a potential lower risk of aspiration in the presence of PPV, there are few clinical trials in this regard.

12.12.1 What Was the COPA and How Did It Differ from the LMA?

The COPA (Mallinckrodt Medical, Athlone, Ireland [Figure 12-13]) was first described in 1992 by Greenberg,157 and was intended for use during anesthesia in spontaneously breathing patients. The device is a modified Guedel airway, with an inflatable distal cuff, and a proximal 15 mm connector. The flange at the proximal end is fitted with two posts for securing a strap, used to stabilize the device in the mouth against the upper teeth or gums. The device is no longer manufactured and is presented for historical purposes only. The COPA was available in four sizes: 8, 9, 10, and 11 (the numbers refer to the length of the shaft of the device, ie, the distance in centimeters between the flange and the distal tip).

12.12.2 How Was the COPA Inserted?

The COPA was inserted in the same fashion as a Guedel airway, with a rotating movement.

12.12.3 What Are the Advantages of the COPA, Compared to the LMA?

Agrò et al158 demonstrated the ability of the COPA to guide an ETT into the trachea employing a light-guided technique with a lightwand. After confirming proper placement, the lightwand was removed and a tube exchange catheter (TE) was inserted through the COPA into the trachea. The patients were then paralyzed and ventilation through the TE reconfirmed. The COPA was removed leaving the TE in situ for the ETT to be guided into place. This combined technique was successful in 6 out of 10 patients.

12.12.4 What Were the Disadvantages of the COPA?

The COPA was contraindicated in patients at risk for aspiration. Compared to the LMA, the COPA appeared to have a higher incidence of postoperative sore throat, as well as jaw and neck pain.159 The COPA required more airway manipulations than the LMA in order to maintain patency.160

12.12.5 What Were the Potential Clinical Uses of the COPA?

The simplicity of the COPA was its most compelling feature, enhancing its utility in many environments. It is smaller than most other devices suggesting it might be particularly useful in patients with restricted mouth opening. The COPA could be used to assist with the placement of an ETT, although the success rates were low.

12.13.1 What Was the PAX and How Does It Differ from the LMA?

Like the COPA, this device is no longer manufactured. The PAX (Vital Signs, Totowa, NJ) was an EGD invented by Douglas Mongeon of Orange Park Acres, California. The PAX was made from polyvinyl chloride and was intended for single use. It consisted of a single curved tube with an inflatable cuff to be positioned in the proximal pharynx, and a noninflatable, gilled, conical tip at the distal end. The tip forms a no-pressure seal in the hypopharynx that was designed to minimize gastric insufflation and regurgitation. Between the cuff and tip on the inner curve was a rectangular vent that faced anteriorly toward the glottic inlet. The distal half of the vent had three vertical gills to prevent epiglottic intrusion and device obstruction. The internal diameter of the airway tube was about 12 mm. The maximum recommended cuff inflation volume was 60 mL. There was only one size for adults weighing greater than 41 kg.

12.13.2 How Was the PAX Inserted?

Prior to insertion, the cuff was deflated and lubricated. During insertion, the PAX was held in the dominant hand like a pen. The mouth was opened with the nondominant hand and the PAX advanced into the pharynx until resistance was felt. The cuff was then inflated with the pilot balloon until a seal sufficient to permit ventilation was achieved, or the maximum cuff inflation volume reached.

12.13.3 What Were the Advantages of the PAX, Compared to the LMA?

The insertion success rate for the PAX was high and it was an effective ventilatory device, with a low risk of gastric insufflation.161 Mondello et al162 evaluated the PAX in 91 patients undergoing surgery and demonstrated that the device provided safe and effective airway control during mechanical ventilation in all but one case.

12.13.4 What Were the Disadvantages of the PAX?

This device was associated with a relatively high incidence of mucosal trauma. Further, mucosal pressures with the device in place may exceed pharyngeal perfusion pressure.

The PAX had a moderately high failure rate when lightwand-guided intubation was attempted and produced more marked changes in hemodynamic variables when compared with those produced by the LMA.163

12.14.1 What Is the iGel and How Does It Differ from the LMA?

The iGel (Intersurgical Ltd., Wokingham, UK) is a single-use extraglottic device that is made of a thermoplastic elastomer gel. It has a noninflatable cuff which can anatomically seal the pharyngeal, laryngeal, and perilaryngeal structures with a minimal risk of compression trauma. The device has an elliptical cross-sectional–shaped tube with a slight curve longitudinally to facilitate insertion and minimize axial rotation once it is placed (Figure 12-14). It also has an independent gastric drainage tube and an integral bite block. It is single use and available in sizes 3 to 5. A size 4 is recommended by the manufacturers for patients between 50 and 90 kg, making it the most common size for the normal adult population.

12.14.2 How Is the iGel Inserted?

With the patient's head and neck placed in a sniffing position, the well-lubricated iGel is placed in the mouth and passed along the posterior pharynx until resistance is felt.164 Insertion does not require an introducer or placement of the finger into the mouth, as the device is simply pushed into place. A 45-degree twist can be employed to facilitate insertion. The cuff does not require the inflation of air following placement.

12.14.3 What Are the Advantages of the iGel, Compared to the LMA?

The insertion process requires one fewer step, as there is no air required for cuff inflation. The elastomer gel may provide a more efficient seal around the larynx after warming to body temperature.165 In addition, the gel-filled cuff may potentially cause less direct trauma or pressure damage to the oropharyngeal mucosa. Unfortunately, at present, there are no clinical data to confirm this potential advantage.

The iGel has a gastric drainage tube which may offer added protection against the aspiration of regurgitated stomach contents. Two separate case reports have confirmed that this drainage tube provided protection against aspiration.165,166 However, in a case series of 280 patients reported by Gibbison et al,167 three patients had regurgitation while using the iGel. Although the iGel completely protected the airway from aspiration of regurgitated stomach contents in two of these patients, it did not provide complete protection in the third patient. The investigators concluded that the efficacy of the drainage tube has not been confirmed, and further study is required to determine the safety profile of the device.

12.14.4 What Are the Disadvantages of the iGel?

In a clinical evaluation study with 100 patients, Gatward et al168 found that the airway seal offered by the iGel is inferior to other EGDs, such as the PLMA. In a cadaver study, Schmidbauer et al169 showed that both the LMA Proseal and LMA Classic provided a better seal of the esophagus than the iGel airway. If there is a leak around the iGel, it may have to be replaced with a different size, since there is no option of adding or withdrawing air from the cuff.

The drainage tube of the iGel is significantly smaller than the drainage tube of the PLMA. For instance, a 12 Fr gauge catheter can be inserted through the size 4 iGel compared to a 16 Fr catheter for a size 4 PLMA.168 It is unknown if the smaller drainage tube is adequate to provide equivalent protection of aspiration, compared with other EGDs with a larger drainage tube.

12.14.5 What Are the Clinical Uses of the iGel?

Compared with seven other extraglottic airway devices (Airway Management Device™, CobraPLA™, Combitube™, Laryngeal Tube, Laryngeal Tube Disposable (LTD), Laryngeal Tube Suction II (LTS II), and the SLIPA™), the iGel has been shown to perform the best for ease of insertion into the airway during training on manikins by 10 anesthesiologists.170

In a clinical evaluation study involving 100 patients, Gatward et al168 reported that the iGel was successfully inserted in all patients and allowed effective controlled ventilation in 98%. The investigators also commented that, while the airway seal offered by the iGel may be inferior to other EGDs, such as the PLMA, it is still sufficient for controlled ventilation in the vast majority of patients. Rates of failure, manipulations required, and complications were also very low for the iGel in that study. In another prospective observational study with 71 patients, Richez et al171 confirmed the efficacy and safety of the iGel airway device.

The iGel has been successfully used to provide ventilation in patients with a difficult airway in a number of case reports. Michalek et al172 reported successful placement of the iGel under general anesthesia in two uncooperative patients with an anticipated difficult intubation (Hunter and Waardenburg syndromes). Oxygenation and ventilation were maintained using the iGel which was then used as a conduit for tracheal intubation using a pediatric flexible bronchoscope (FB).

Joshi et al173 reported the use of the iGel as an airway rescue in a patient with scleroderma and predicted difficult intubation. Under general anesthesia, ventilation was difficult with a bag-mask, the LMA Classic, and the LMA Proseal but ventilation was achieved easily with a size 4 iGel. Others have also reported the use of the iGel as a rescue airway device.174

While these are encouraging results, more clinical studies with larger patient populations are needed to confirm these findings.

During the last two decades, EGDs, such as the Laryngeal Mask Airway™ and the Combitube™, have been shown to be effective and safe devices for delivering effective oxygenation and ventilation. In addition, many studies have shown that these devices can be used successfully to rescue patients with a failed airway. These devices are now recommended by authorities such as the American Society of Anesthesiologists (ASA) (Difficult Airway Management Algorithm) and the Difficult Airway Society (UK) for this indication.

The major disadvantage of all EGDs is their inability to completely seal the larynx and protect against aspiration. In addition, poor seal by any of these devices can lead to air leak on positive pressure ventilation and gastric insufflation. Newer designs of EGD, such as the Intubating LMA (or LMA Fastrach™), LMA Proseal™, LMA Supreme™, and the King LTS-D have been developed to attempt to address these concerns.

As a result of the widespread acceptance and popularity of the original LMA, many newly designed, reusable, and disposable EGD devices have been introduced. Although many preliminary clinical studies have demonstrated the efficacy and safety of these devices, most of them involved only a small number of patients. More clinical studies with larger patient populations are needed to confirm these findings. Finally, these devices are not only effective airway management and airway rescue devices, but they can be used and learned easily, in contrast to bag-mask-ventilation and endotracheal intubation. It is entirely reasonable to expect that these devices will supplant BMV as a rescue airway maneuver.