The LMA is a supraglottic airway management device. A substantial body of literature, while supporting the wisdom of exercising caution when learning to use the supraglottic approach, provides ample evidence of a wide range of uses that go beyond those originally postulated.² For example, the LMA is becoming increasingly popular outside the operating room, as evidenced by its endorsement by the European Resuscitation Council and the American Heart Association.³ Its more exotic uses include the adoption of the Fastrach ILMA, which is the intubating form of the LMA, by the National Aeronautics and Space Administration (NASA) as part of its emergency medical kit for space travel. A literature search indicates that the later varieties of the LMA, including the FLMA, ILMA,⁴ and PLMA,⁵ may be more appropriate tools for specific uses than the original LMA.

More than 2000 scientific articles have described the impact of the LMA on modern anesthesia, and a full review is beyond the scope of a single chapter. Our aim instead is to provide an overview of the LMA’s uses worldwide. After a historical review and comments regarding the correct LMA insertion technique, we explore the principal uses of each LMA model, discuss possible problems, and offer suggestions for getting the best results from each device. We describe the evolution of the LMA’s use in patients with difficult-to-manage airways and provide the current recommendations for LMA use from the American Society of Anesthesiologists (ASA) difficult airway algorithm.⁶

II History and Development

In 1988, the definitive device, now referred to as the LMA Classic, was released commercially in the United Kingdom. Although the LMA was rapidly adopted there, it was not until 1991 that the U.S. Food and Drug Administration permitted release of the device in the United States and then only with the stricture that “the LMA is not a replacement for the endotracheal tube.” Because the LMA was at that time a very unconventional way of managing the airway, this caution was understandable. Nevertheless, it resulted in a somewhat slower acceptance of the concept of “masking the larynx” in the United States than in the United Kingdom, where the LMA was purchased by every health authority within 2 years of its launch, resulting almost immediately in a reduction in ETT use (Fig. 22-2).

Figure 22-2 Harold Wood Hospital (England) data show the percentage of cases managed with an endotracheal tube (ETT) or laryngeal mask airway (LMA) from June 1986 through November 1991. Use of the ETT has significantly declined in favor of the LMA in the United Kingdom.

A From Idea to First Prototype

Brain is often asked how the idea of the LMA first arose. Like many before him, he thought that a supraglottic approach would be less traumatic than intubation and therefore more desirable, provided the method could be easier to control and more reliable than the face mask. Other inventors had mainly explored the oral and pharyngeal spaces above the larynx,⁷^–¹² but the LMA was the first device to encircle the periglottic tissues in the hypopharynx with a mask. The idea was conceived in early 1981, and later that year, Brain began providing dental anesthesia at the outpatient clinic of the Royal London Hospital. At that time, a device known as the Goldman dental nose piece was being used for airway maintenance during dental extractions in anesthetized patients. It was a reusable, vulcanized rubber mask that could be detached from its rigid base for cleaning (Fig. 22-3). The mask was designed to fit over the nose, leaving the mouth free for surgical access. Noticing a certain similarity between the contours around the nose and those around the glottis, Brain wondered if the Goldman mask could be modified to fit over the larynx. Placing a device over the larynx would short-circuit the upper airway passages, perhaps eliminating some of the problems associated with maintaining their patency under anesthesia.

Figure 22-3 The Goldman dental nose piece was used to develop the early cuffs for the laryngeal mask airway prototypes. The central portion of the mask was cut out to allow attachment of the tube.

Because the Goldman mask was scheduled to be discontinued in favor of a disposable version, Brain was able to obtain samples for experimentation. Using an acrylic adhesive, he glued a diagonally cut, 10-mm Portex ETT to the rubber mask’s attachment flange, which he had to draw across the mask aperture into the midline to form a base (Fig. 22-4). Figure 22-5 is a 1981 photograph of the inventor as he is about to insert one of the resulting prototypes into his anesthetized pharynx to test the validity of his hypothesis. In his diary, he recorded an absence of any complications, despite having repeated the experiment four times. This observation, combined with a broadly worded institutional review board approval, provided the justification for subsequent extensive clinical investigations, which occupied him for the next 7 years. During this time, he built many prototypes, which he used in approximately 7000 patients.¹³ He also kept extensive notes in private diaries to record his progress but published only a small number of cases, because he believed there was little point in presenting data concerning an invention that was not ready for production.

Figure 22-4 The early laryngeal mask airway (LMA) prototype was made of a Goldman dental nose piece modified to form a cuff (a) and a diagonally cut endotracheal tube (b). The two pieces were glued together to form the first LMA to be tested clinically.

Figure 22-5 Archie Brain, MD (1981), was the inventor of the laryngeal mask airway (LMA). He is shown about to insert one of the LMA prototypes into his anesthetized pharynx to test his hypothesis that a supraglottic device was effective, safe, and much less invasive than the endotracheal tube.

B Early Publications

The first article about the LMA, published in the British Journal of Anaesthesia in 1983, presented data from only 23 patients and received little attention.¹ A second description 2 years later in Anaesthesia was subtitled “Development and Trials of a New Type of Airway” and detailed the LMA’s use in 118 patients, although it also reported that Brain and colleagues had gained experience in more than 500 cases.¹⁴ On the basis of this experience and a case report published the previous year in Archives of Emergency Medicine,¹⁵ Brain and colleagues felt justified in concluding that “the laryngeal mask may have a valuable role to play in all types of inhalational anesthesia, while its proven value in some cases of difficult intubation indicates that it may contribute to the safety of general anesthesia.”¹⁴

In the same issue of Anaesthesia, Brain presented further evidence of the potential usefulness of the device in cases of difficult intubation, but there was still no response to these claims from the profession, perhaps because no product was available for independent assessment.¹⁶ However, he had given one of his prototypes to a visiting American anesthesiologist, Ronald Katz, a physician and chairman of the anesthesiology department at the University of California–Los Angeles. Katz provided the first independent description of the LMA based on his experience with this prototype, writing in Wellcome Trends in Anesthesiology in October 1985 and again in February 1986.^17,¹⁸ The second article provided the first published image—reproduced from one of the inventor’s transparencies—of the glottis seen fiberoptically through the LMA prototype and mentioned the potential of the device to overcome intubation problems. American awareness of the LMA preceded its availability in the United States by 6 years.

C From Handmade Models to Clinical Use

There were three reasons why the LMA took so long to become clinically available: the initial lack of commercial interest, which meant there were no models available for others to use; the solitary nature of the LMA’s development, which was carried out virtually single-handedly by a clinician who continued to work with largely homemade equipment until the first commercial prototypes were made in early 1988; and the complexity of the airway anatomy, which made it hard to design a device that was safe and effective. One advantage of the long development process was that the considerable clinical history that the inventor accumulated between 1981 and 1988 guided the development of the LMA, and the first factory-made models required little modification. They were produced in Gary, Indiana; tested by Brain; and then demonstrated to colleagues at the Royal East Sussex Hospital, Hastings, United Kingdom, in April 1988. Colin Alexander, the chairman of the anesthesiology department at the Royal East Sussex Hospital, immediately authorized the LMA’s use in his department and published his experience in a letter (“Use your Brain”) in Anaesthesia that year.¹⁹ He concluded that the device “should be considered whenever the indication for tracheal intubation does not include protection of the airway from gastric contents.” Meanwhile, a few colleagues who had been given prototypes by Brain (one person built his own) continued to explore the LMA’s use in known cases of difficult intubation, with encouraging results.¹³

Arguably, the most influential clinical study using Brain’s hand-built prototypes was not published until 1989, after the commercial form of the device had become available. Brodrick and colleagues studied 100 cases in which the patients breathed spontaneously.²⁰ Eighteen anesthesiologists took part in the study and recorded a “clear and unobstructed airway in 98% of cases,” but obstruction on initial placement of the LMA occurred in 10 cases and “appeared to be as a result of downfolding of the epiglottis.” A stainless steel introducer tool with a handle similar to that of the Fastrach ILMA and a blade fitting into a slot in the distal anterior end of the LMA’s mask had been designed to overcome this problem. An aperture in the blade into which the epiglottis fit caused the epiglottis to be drawn upward as the tool was removed from the patient’s pharynx. This insertion tool was used successfully in these cases, but fears that it could cause trauma led to it being abandoned in the commercial form of the LMA. Brodrick is often quoted in support of limiting the use of the LMA to spontaneously breathing patients. However, because the LMAs used by Nunn’s group were prototypes, only a size 3 device was available for use in 72 men and 28 women (weight not recorded). Given the possibility that the LMA’s size was less than optimal, it is not surprising that eight patients could not be ventilated using positive pressure without unacceptable leaks and that the mean leak pressure was 17 cm H₂O, similar to that recorded by Brain 6 years earlier.¹³

In addition to the information accumulated in his clinical work, study of the anatomy and physiology of the larynx and pharynx guided Brain throughout development of the LMA. As the work progressed, he struggled to achieve a balance in simplicity, efficacy, and safety. In designing a device that fit into the lower pharynx, measures favoring efficacy tended to counteract those favoring simplicity. Improving the seal, for example, required more complex construction to avoid potential trauma related to high mucosal pressures. Likewise, an effort to make the device easier to insert led to the development of an insertion tool, which was determined by Brain to be potentially unsafe and therefore abandoned, despite the efficacy it demonstrated.¹³ Ultimately, the solutions chosen were compromises. For example, Brain realized that seals with a leak pressure much higher than 20 cm H₂O were rarely necessary in practice and that an inadequate seal often could be overcome by using a more appropriately sized device, using a better fixation technique, or giving a more appropriate anesthetic. To make insertion of the LMA maximally reliable and minimally traumatic, a technique gradually evolved that was based on the swallowing mechanism. Unfortunately, he underestimated the difficulty of teaching others to master such a subtle technique, which is virtually impossible to learn without direct, hands-on demonstration and guidance.²¹ As a result, many articles in the LMA literature suggest variant insertion methods, most of which had already been tried and rejected by Brain for being unreliable or traumatic.

Despite these difficulties, the history of the LMA since its first commercial launch is essentially a story of steady expansion in use around the world. Availability, cost, and user education have governed the speed at which the various forms of the LMA have been accepted. Figure 22-2 demonstrates data collected by the anesthesiology department of Harold Wood Hospital, a typical general hospital near London, on the influence of the LMA Classic in the first 3 years of its availability and on the use of the ETT and the face mask. The dip in the curve representing LMA use indicates a period when it was commercially unavailable. These data show that use of the ETT almost immediately declined in favor of the new method of airway management, and they illustrate the rapid growth of LMA use in the United Kingdom. They also cast some doubt on the widely held view that the popularity of the LMA in the United Kingdom has been due to the more frequent use of the face mask there than in the United States.

As new models of the LMA have become available, countries with different anesthesia traditions have responded to them with various degrees of enthusiasm. In all cases, however, use of the LMA has steadily increased (personal communication, LMA International SA, March 2004).

III Laryngeal Mask Airway Insertion Technique

The LMA occupies a potential space that is shared by the respiratory and alimentary tracts, which are subject to the control and coordination of several complex reflexes. Although anesthesiologists do not need a detailed knowledge of the specific reflexes to use the LMA, they do need to understand the basic concept behind the recommended insertion technique, which ensures the greatest success and results in the fewest complications. Physiologically, the alimentary tract is capable of accepting (i.e., swallowing) or rejecting (i.e., vomiting) liquids or solids in the form of food. In contrast, the respiratory tract mobilizes defensive responses (e.g., coughing, laryngospasm, bronchospasm) only when invaded by liquids or solids (e.g., an ETT). When inserted correctly, the LMA does not stimulate the respiratory tract defenses because the device forms an end-to-end seal against the periglottic tissues.

Investigations using magnetic resonance imaging (MRI) to assess the effect of the LMA on the anatomy of the airway may help to explain the reliability of the device. A study by Shorten and coworkers of 46 adults requiring sagittal MRI views of the head and neck compared the anatomic differences in awake, sedated, and anesthetized patients.²² With an LMA in place, the epiglottic angle was more than twice as great with respect to the posterior pharyngeal wall in the anesthetized group as it was in the sedated or awake group. This had no apparent effect on ventilatory function in most patients, probably due to the depth of the LMA bowl, which the inventor found to be a critical dimension when experimenting with different design ideas during the 1980s. The recommended standard insertion technique evolved slowly as Brain gained experience, and it was not until he had been inserting LMAs for almost 10 years that he realized that his technique was becoming more and more similar to the physiologic act of swallowing food. When he realized this, it was a simple matter to study this mechanism more closely and make allowances for the fact that in the anesthetized patient, this reflex is partially or completely abolished. The following key points emerged:

1. Correct mask deflation is important. The purpose of chewing food is to form a soft, atraumatic paste that can easily be passed through the pharynx and esophagus. At the onset of swallowing, this paste (i.e., food bolus) is pressed by the tongue into the hard palate. The pressure generated is distributed widely over the palatal surface, so there is no localized high-pressure point, which would give the sensation of a sharp object and lead to rejection instead of swallowing. Brain realized that to imitate the sensation of a soft food bolus, he needed to deflate the mask so that it presented an elastic, hollow shape. When this shape was pressed into the dome of the palate, the hollow form would need to be inverted. The pressure required by inserting the finger to achieve this would cause the outer rim of the mask to act like a gentle spring, producing the desired effect of spreading pressure smoothly over the entire posterior surface of the mask. This spring effect cannot be achieved without deflating the mask to a vacuum pressure of about −40 cm H₂O. Only in this way was it possible to prevent the pointed distal end of the mask bowl from transmitting an irritating localized pressure point as it was pressed into the oropharyngeal curve. Partial mask inflation could not achieve this aim, however, because the soft distal end of the mask rolled backward, allowing the pointed tip of the mask bowl to scratch the palatal surface. Deflating the mask such that it followed the curvature of the palate had the same disadvantage, because it made the pointed end even more prominent. Inserting a fully inflated mask introduced excessive bulk, which created the possibility of tearing the cuff against the teeth and was physiologically equivalent to swallowing too large a bolus of food, which could lead to the rejection reflex.

2. The deflated mask must be lubricated if the oral cavity is not already wet. There is a parallel with swallowing because lubrication is a key part of deglutition. Because the mask is slid against the palate, it makes sense to apply a bolus of lubricant to the distal hollowed posterior surface of the mask immediately before insertion. Water-soluble jelly is a good substitute for oral secretions. It is not necessary or desirable to spread the lubricant over the whole surface of the mask before insertion.

3. Flatten the mask against the hard palate. Initially during swallowing, the tongue flattens the softened food bolus against the hard palate; during the first step in LMA insertion, the mask, correctly prepared to impart a sensation similar to that of a soft food bolus, is flattened by pressing it against the hard palate. Placing the index finger on the airway tube at its junction with the mask under the deflated proximal rim of the cuff is the best way to impart the necessary force.

4. Cranioposterior movement of the index finger. In swallowing, the bolus of food is advanced into the pharynx, esophagus, and stomach through precise coordination of several muscle groups, beginning with the tongue. During LMA insertion, the clinician must use her or his index finger to advance the mask in the cranioposterior direction, imitating the action of the tongue. This allows a completely deflated tip to slide smoothly along the hard palate, soft palate, and posterior pharyngeal wall while minimizing the contact of the mask with anterior structures such as the base of the tongue, epiglottis, and laryngeal inlet. The finger must continue to push in a cranioposterior direction even though the anatomy forces the mask and the finger to move caudally. The finger must never consciously be directed caudally and should be inserted to its fullest extent until resistance is felt as the mask tip enters the upper esophageal sphincter (UES). It is anatomically impossible to perform this action correctly without extending the proximal metacarpophalangeal joint of the index finger and flexing the wrist.

5. Widening the oropharyngeal angle is the first role of the nondominant hand. Cadaveric work demonstrates that if the head of the supine subject is pushed by the supinated hand in a caudal direction, head extension, neck flexion, and mouth opening are simultaneously achieved. This maneuver widens the oropharyngeal angle to greater than 90 degrees in the normal subject and draws the larynx away from the posterior pharyngeal wall. Both effects facilitate LMA insertion. The nondominant hand should therefore maintain firm caudal pressure on the occiput from the start of insertion until the mask has passed behind the tongue.

6. Removal of the index finger is the second role of the nondominant hand. To prevent the mask sliding out of position after it is fully inserted, the nondominant hand should move from behind the head to grasp the proximal end of the LMA before the index finger is removed. As the index finger is removed, the mask is held steady, or if it has not been fully inserted, it can be pressed further into position by the nondominant hand.

7. The mask is inflated. As the mask is inflated, its increased bulk and the relatively large radius of the airway tube cause it to slide cranially. It can be shown anatomically that this results in loss of contact between the mask tip and the UES. However, the LMA should not be held in place during inflation because this can result in the distal end of the mask stretching the UES. All LMAs should be inflated to a pressure of less than 60 cm H₂O; pressures above this have been found to cause discomfort in awake volunteers.

8. Device fixation restores stability of the seal against the UES. The distal end of the tube is again pressed into the curve of the hard palate to reestablish firm contact between the proximal end of the device and the UES. While this pressure is maintained, adhesive tape is applied to the maxilla on one side of the patient’s face and passed over and under the tube in a single loop before fixing to the opposite maxilla. This form of fixation ensures stability of the device and is likely to afford maximum protection in the event of unexpected regurgitation, and it reduces the incidence of gastric insufflation during PPV.*

IV Classic Laryngeal Mask Airway

A Basic Uses

1 Indications for Use

Indications for LMA use have evolved since its invention. Although it has long been accepted that success rates for establishing an airway with the LMA tend to be high, even in relatively unskilled hands, it is equally clear that there is more to the art of using the LMA than getting it into place. Indications have steadily expanded as the device’s popularity has spread. Just as complications tend to diminish with increasing user experience, so the more confident and more adept user seems to find applications for the LMA that might previously have seemed inappropriate. Using the LMA for airway maintenance during atrial septal defect repair in children, for example, would no doubt strike many American anesthesiologists as highly unconventional, just as it would have alarmed the inventor had it been suggested he try this in 1988.²⁴

The problem of defining indications for the LMA is perhaps best resolved by recommending that, as with any skill, it is best to start at a simple level and progress gradually to more complex uses. What are appropriate basic uses for the LMA? Broadly speaking, any nonemergency case requiring general anesthesia in a patient in the supine position who has an ASA classification of I (ASA I) or II and in whom the surgeon is performing a routine, short procedure that does not involve the alimentary or respiratory tract would constitute an appropriate basic use. In practice, such cases are likely to be found in the ambulatory setting and include simple orthopedic, urologic, superficial, or gynecologic procedures. Although it involves external manipulation of the bowel, inguinal canal surgery also falls within this category.

2 Inherent Teaching Difficulties: A Vicious Circle

The learning curve for correct LMA insertion extends beyond the often cited 10 to 15 uses by one or two orders of magnitude.²⁵ For the anesthesiologist who is just starting to get used to the LMA, an important advantage of confining its use to simple cases is that they represent the greater part of the surgical caseload in many locations, and there are many opportunities for learning and practice. Most anesthesiology residents, however, start out in a teaching hospital, where the caseload tends to be weighted more heavily toward long and complex procedures for which LMA use would be inappropriate in any but the most experienced hands. For this reason, it is common to hear experienced U.K. and U.S. consultant anesthesiologists complain that newly appointed colleagues, who have spent the greater part of their training years in teaching hospitals, appear to have only the most rudimentary concept of LMA use. It is, unfortunately, the same academic colleagues who carry out many of the studies that make up the core of evidence-based knowledge for the LMA. This represents a vicious circle that is not easy to break, particularly at a time when there is increasing pressure on the medical profession to justify all clinical activity by reference to proven techniques. A suggested way out of this impasse is outlined subsequently.

3 Graduating from Simple to Specialized Uses of the Laryngeal Mask Airway

The safety of the patient must be the guiding principle when deciding whether someone is qualified to perform specialized uses of the LMA. A clinician whose first-time insertion success rate is 90% or less should not be considered adequately trained to progress beyond the simplest procedures in ASA I patients. Davies and colleagues reported a success rate of 94% in the first 10 cases in which naval medical trainees used the LMA for the first time in ASA I anesthetized patients.²⁶ The insertion success rate depends on the types of cases routinely encountered, and the preceding generalization applies to clinicians in an average peripheral hospital that performs a broad range of common procedures.

Those who wish to gain greater expertise in the use of the LMA, but whose practice is based in specialized centers that lack suitable simple cases, can consider the practice of inserting an LMA routinely at the start of a case and then switching to the preferred airway technique before the surgery. Brain found this to be a useful strategy in the teaching hospital environment. Its justification is that the skills acquired could be life-saving in the event of an airway emergency. If the LMA has been inserted successfully and the patient subsequently proves impossible to intubate, the clinician has an already proven way of at least maintaining oxygenation while other strategies are considered. Alternatively, if the clinician has been unable to use the LMA successfully in a certain patient, time is not wasted in trying to use it after a subsequent failed intubation in this patient.

B Specialized Uses

1 Procedures Outside the Operating Room

a Radiology and Magnetic Resonance Imaging

The potential advantages of the LMA in investigative imaging were first described in a letter to Anaesthesia from Glasgow, Scotland, in 1990.²⁷ The investigators pointed out that the LMA permitted hands-free control of the airway in patients who needed to be kept immobile for prolonged periods, a situation often necessitating general anesthesia in restless or young patients. To improve its performance and durability, the LMA’s valve later was fitted with a small, stainless steel spring, which unfortunately interfered with MRI of the head and neck. However, LMAs equipped with valves made of nonferrous material were subsequently made available for use in this situation. Stevens and Burden, in a letter to Anaesthesia in 1994, commented that they had used the LMA Classic with the modified, nonmetallic valve in more than 500 small children undergoing MRI and that it had proved safe and reliable.²⁸ They also presented an MRI image demonstrating that the FLMA could not be used for investigations involving the head and neck because the tube contained a wire, which obliterated the image of the surrounding area.

Goudsouzian and associates were the first Americans to report the efficacy of the LMA during MRI, using the images obtained during investigations in 28 children to comment on the position of the device when inserted by residents in training.²⁹ Despite poor user skills (21% of attempts resulted in a failure to insert, 21% of the cases required more than one insertion attempt, 82% had a downward deflection of the epiglottis, and 7% had oropharyngeal misplacement), satisfactory ventilatory parameters were maintained in all of the children. The safety of the LMA, even in less than fully skilled hands, is a powerful argument for its use in areas remote from the operating room. Van Obbergh and colleagues, working in Brussels, Belgium, presented results from somewhat more experienced users.³⁰ The LMA was used during MRI in 100 consecutive procedures in children that were carried out using propofol. The position of the LMA was not recorded, but only 16% of the cases required more than one insertion attempt, there were no failures to insert, and oxygen saturation values of 99.1% or above were maintained in all of the children. Ventilation was manually assisted using an Ayre T-piece.

b Radiation Therapy

Grebenik and coworkers were the first to describe the use of the LMA in pediatric radiation therapy in their study of 25 children who underwent a total of 312 courses of radiation therapy under anesthesia.³¹ The children were between 3 weeks and 3 years old, and eight of them were anesthetized once daily for 20 or more consecutive days. In each case, the LMA was left in place until the protective reflexes returned. The absence of complications suggests that the LMA may be appropriate for procedures requiring frequent, repeated use of anesthetics in children.

A major advantage of the LMA over the ETT in children receiving radiation therapy on a daily basis during a 4- to 6-week course of treatment is that the LMA does not invade the trachea. The risk of tracheal ulcerations, granulation tissue, and subsequent tracheal stenosis associated with repeated intubations with an ETT is eliminated. The LMA causes much less stimulation than does an ETT; anesthesia requirements for the LMA are significantly lower. For example, at the University of Texas M.D. Anderson Cancer Center in Houston, all children undergoing radiation therapy receive an intravenous infusion of propofol as the sole anesthetic agent during their treatment. The LMA is frequently used for airway management, and spontaneous respiration is preserved (Fig. 22-6). This allows more rapid turnover of patients and more efficient use of the radiation therapy suite.

Figure 22-6 Use of the laryngeal mask airway (LMA) in a child undergoing a series of radiation treatments at the University of Texas M.D. Anderson Cancer Center in Houston. A, Propofol is used to induce general anesthesia, and after the LMA is inserted, the child is placed in a prone position. B, Continuous intravenous infusion of propofol is used as the sole anesthetic agent during radiation treatment while the child is breathing spontaneously through the LMA. This allows more rapid turnover of patients and more efficient use of the radiation therapy suite.

c Diagnostic and Short Therapeutic Procedures in Children

The LMA can be very useful during short diagnostic, therapeutic, and minor surgical procedures performed in children in the hospital’s procedure room or in the operating room. These procedures include spinal puncture with or without intrathecal therapy, bone marrow aspirations, insertion or removal of a central line or a Port-a-Cath, and minor biopsies (Fig. 22-7). Most children tolerate these procedures well under deep intravenous sedation with propofol and local anesthesia with maintenance of spontaneous respiration. However, some children develop respiratory depression or airway obstruction during deep sedation. In those children, the LMA can be an excellent and much less invasive alternative to endotracheal intubation, resulting in a clear airway without resorting to general anesthesia and muscle relaxation.

Figure 22-7 Lumbar spinal tap and intrathecal therapy performed on a small child at the University of Texas M.D. Anderson Cancer Center in Houston. Continuous infusion of propofol is used to achieve deep sedation. The laryngeal mask airway (LMA) is used to maintain the open airway, and the child is allowed to breathe spontaneously. The LMA is less invasive than the tracheal tube, and less medication is required to tolerate the device.

d Cardiology

The LMA can be useful in patients undergoing transesophageal echocardiography (TEE). TEE is an invasive procedure, and many patients experience significant discomfort or are unable to tolerate TEE under topical anesthesia. In the cardiology clinic setting, TEE is usually performed with topical anesthesia consisting of spraying the oropharynx with a local anesthetic (e.g., 4% lidocaine or 20% benzocaine), with or without sedation.^32,³³ However, a significant number of patients experience discomfort during the procedure, and many cannot tolerate the insertion of the probe, even after sedation.^34,³⁵ Because topical anesthesia and light sedation do not completely abolish the gag reflex, deep sedation or general anesthesia may be necessary for patients with highly sensitive reflexes in the upper airway and pharynx. A possible solution for patients who cannot tolerate the insertion of the TEE probe with topical anesthesia and light sedation is deep sedation with propofol. The LMA can be used to maintain the airway in patients undergoing TEE examination during deep sedation with propofol.³⁶ The LMA can easily be inserted with the TEE probe in place, and the presence of the LMA does not interfere with the manipulation of the probe (Fig. 22-8).

Figure 22-8 Use of the laryngeal mask airway (LMA) during transesophageal echocardiography (TEE) at the University of Texas M.D. Anderson Cancer Center in Houston. The LMA is inserted after TEE placement. A, The LMA does not interfere with TEE examination. B, Fiberoptic view through the LMA shows the TEE probe (arrowhead) inside the LMA bowl.

The LMA can be a better alternative than endotracheal intubation in patients undergoing cardioversion in whom face mask ventilation is difficult or inadequate. The minimal hemodynamic stimulation associated with insertion of the LMA, which contrasts with a significant hemodynamic response during endotracheal intubation, offers a great advantage in patients with cardiovascular disease.³⁷

2 Head and Neck Surgery

Most of the applications of the LMA in procedures involving the head and neck are done with the FLMA. However, a unique advantage of using the LMA Classic in these patients is the access to the larynx that the device allows (Fig. 22-9), which is particularly useful for diagnostic evaluation of the larynx and trachea and during neodymium:yttrium-aluminum-garnet (Nd:YAG) laser surgery. It is difficult to manage the airway using an ETT in patients who require Nd:YAG laser treatment of lesions located in the vocal cords or the proximal part of the trachea because the ETT limits access to these lesions. There also is a high risk of a laser-induced airway fire when an ETT is used. In contrast, the LMA provides an unobstructed view of the surgical field and virtually eliminates the risk of airway fire (Fig. 22-10).

Figure 22-9 View of the larynx through a fiberscope placed coaxially through the optimally positioned laryngeal mask airway. The epiglottis is not downfolded, and the tip of the mask lies behind the larynx, occluding the upper esophageal sphincter.

Figure 22-10 Fiberoptic view through the laryngeal mask airway of the left vocal cord lesion (arrow). This type of lesion would be very difficult to treat with the Nd:YAG laser if an endotracheal tube were used.

Head and neck surgery is associated with the risk of bruising or otherwise traumatizing nerves that control the motor functions of the larynx. The LMA can be useful in evaluating the function of the vocal cords at the conclusion of neck dissection and thyroid and parathyroid surgery.³⁸ While the patient is still under general anesthesia, the LMA is inserted behind the ETT and inflated. The anesthesiologist then removes the ETT, and the patient is allowed to breathe spontaneously. As the patient emerges from general anesthesia, a fiberoptic bronchoscope (FOB) is inserted through the lumen of the LMA to observe the function of the vocal cords. At M.D. Anderson Cancer Center, this technique has become an important diagnostic tool to detect the functional status of the nerves providing motor function to the larynx and has allowed the anesthesiologists and surgeons to make more informed decisions about the postoperative airway management of their patients. Similarly, patients undergoing brainstem surgery in the area that involves the lower cranial nerves, which control the pharynx and larynx, can be evaluated fiberoptically through the LMA in the intensive care unit. This helps the intensivist and the surgeon determine whether the patient will be able to maintain her or his airway postoperatively (Fig. 22-11).

Figure 22-11 A child was admitted to the intensive care unit after brainstem surgery at the University of Texas M.D. Anderson Cancer Center in Houston. Using deep sedation with propofol, the laryngeal mask airway (LMA) was inserted behind the endotracheal tube (ETT). After successful LMA insertion, the ETT was removed to allow visualization of the vocal cords and evaluation of their function in a spontaneously breathing child. This helped the intensivist and the surgeon determine whether the patient would be able to maintain the airway postoperatively.

3 Pulmonary Medicine and Thoracic Surgery

a Bronchoscopy in Children and Adults

Physicians in the fields of thoracic surgery and pulmonary medicine have shown interest in the LMA because of the unique access it provides to the larynx and respiratory tree. Diagnostic fiberoptic laryngoscopy and FOB can be performed readily through the LMA in patients under general anesthesia or under topical anesthesia with sedation.³⁹^–⁴¹ Maekawa and colleagues, in a 1991 letter to Anesthesiology describing the use of a size 1 LMA as a conduit for FOB with a 3.6-mm flexible endoscope in two children (ages 2 and 8 months), listed four advantages. First, the LMA tube is much larger (5-mm internal diameter) than the corresponding ETT, permitting the use of a larger bronchoscope, which gives a better view than that obtained through the 2- to 2.5-mm bronchoscope normally required to fit through the ETT in this age group. Second, the use of the LMA permitted examination of the larynx, including vocal cord movement and the part of the trachea normally occupied by the ETT. Third, the larger-diameter LMA airway tube permits easy ventilation, which permits uninterrupted observation. Fourth, not using an ETT may be valuable in cases of laryngeal or tracheal stenosis that may be made worse by the passage of the ETT.⁴²

In a letter to Anesthesiology, Theroux and associates described the use of the size 1 LMA as a conduit for intubation in a 2.5-kg baby with Schwarz-Jampel syndrome who could not be intubated by other means.⁴³ The uncuffed ETT was advanced over a 2.2-mm bronchoscope, which was easily passed into the trachea through the LMA. In 1997, Mizikov and coworkers reported their experience of using FOB through the LMA in 45 children: 15 diagnostic cases, 22 cases of lavage, 7 cases of foreign body removal, and 1 case of electrocoagulation of an adenoma.⁴⁴ Total intravenous anesthesia and PPV were used in all cases. Patients’ ages ranged from neonatal to 15 years. They used the Olympus BF3C20 bronchoscope (3.6-mm diameter) with the size 1 LMA, and the Olympus BFP30 (5-mm diameter) was used with the size 2 LMA. The epiglottis was within the mask in 96.5% of cases but was not associated with significant airway obstruction in any case.

b Laser Surgery of the Trachea

In 1992, Slinger and colleagues provided a detailed account of a difficult case of palliative laser resection of a severely obstructing distal tracheal mass.⁴⁵ The airway was initially managed using a size 4 LMA, through which a 6-mm Olympus FOB was passed by a swivel connector to apply the laser. Spontaneous ventilation with propofol-isoflurane anesthesia was used. After 120 minutes, 50% of the tracheal lumen had been restored, at which point it was decided to convert to rigid bronchoscopy so that the surgeon could remove larger pieces of tissue by forceps, thereby facilitating the procedure. The physicians repeated this approach in two less severe cases without complications. They pointed out that the laser is not likely to burn the silicone LMA tube if it is switched on only when in the trachea. However, they stressed that use of the rigid bronchoscope remained the gold standard for such cases.

c Tracheobronchial Stent Placement

Another advantage of using the LMA in patients with pathology involving the tracheobronchial tree is evident during stent placement using fiberoptic guidance.⁴⁶ The LMA’s shaft permits use of a 6-mm FOB and provides a larger cross-sectional area than does a 9-mm ETT, which is usually employed during stent placement. The LMA allows better ventilation during stent placement than does an ETT in patients who already have compromised respiratory function. In patients who have an obstruction high in the trachea, the LMA is much better than an ETT because it allows placement of the stent without the risk of extubating the patient (Fig. 22-12).

Figure 22-12 Fiberoptic view of the tracheal stent (arrow) placed high in the trachea (1.5 cm below the vocal cords) through the laryngeal mask airway (LMA). The LMA’s shaft permits use of a 6-mm fiberoptic bronchoscope and provides a bigger cross-sectional area than a 9-mm endotracheal tube (ETT), allowing better ventilation during stent placement than the ETT in patients who already have compromised respiratory functions.

4 Neurosurgery

The hemodynamic stability associated with LMA use may be beneficial during induction in patients undergoing neurosurgical repair of an intracranial aneurysm and in patients with increased intracranial pressure. Silva and Brimacombe reported that hypertension, coughing, and bucking, all of which are common during emergence from general anesthesia with an ETT, were prevented in neurosurgical patients by replacing the ETT with the LMA at the end of the procedure.⁴⁷ The insertion and use of the LMA in patients under general anesthesia have been associated with minimal changes in intracranial pressure.⁴⁸ This characteristic may be particularly useful during ventriculoperitoneal shunt placement in children, adults, and patients who have suffered a traumatic brain injury.

Other uses for the LMA in neurosurgical patients include awake craniotomy and stereotactic procedures in children and adults. In an awake craniotomy, eloquent areas of the brain are mapped and monitored intraoperatively by stimulating the cerebral cortex with an electrical current. This direct electrical stimulation of the cerebral cortex greatly increases the risk of focal or generalized seizures. Airway management using a face mask and endotracheal intubation during generalized seizures can be very difficult because the patient is usually lying on her or his side, giving the anesthesiologist limited access to the airway, and the patient’s head is fixed by metal pins and a frame to provide a stable surgical field and allow the use of modern intraoperative image guidance. However, an experienced and skilled anesthesiologist can easily insert the LMA into such patients, allowing ventilation and oxygenation in this potentially difficult clinical situation (Fig. 22-13).⁴⁹

Figure 22-13 Insertion of the ProSeal laryngeal mask airway (PLMA) into a patient undergoing craniotomy with awake intraoperative speech mapping. The anesthesiologist is facing the patient and uses his thumb to insert the PLMA into the patient.

Stereotactic biopsies can be performed in children using the LMA. Anesthesia is induced with propofol in the radiology suite, and the LMA is inserted (Fig. 22-14). Local anesthetic is then injected to anesthetize the skin before pins for the stereotactic frame are applied. During continuous infusion of propofol, an MRI is obtained while the child breathes spontaneously through the LMA. While asleep, the child is transported to the operating room for the stereotactic biopsy. This technique provides optimal comfort for the children and excellent operating conditions for the radiologists and surgeons.

Figure 22-14 A young child undergoing stereotactic biopsy at the University of Texas M.D. Anderson Cancer Center in Houston. Anesthesia is induced with propofol in the radiology suite, and the laryngeal mask airway is inserted.

V Flexible Laryngeal Mask Airway

Many operations, particularly procedures performed on the head and neck, require the anesthesiologist and surgeon to share access to the airway. Traditionally, special ETTs that have a spiral coil built into them to increase the flexibility of the tube and to prevent kinking have been used to allow the surgeon to manipulate the ETT during surgery to gain access to the operating field. To make an LMA specifically for head and neck procedures, a similar spiral coil was incorporated into the LMA’s shaft, creating the FLMA (Fig. 22-15), which was introduced into clinical practice in 1994. The FLMA has since been used successfully in patients undergoing a variety of head and neck procedures.

Figure 22-15 The flexible laryngeal mask airway (FLMA), which was introduced into clinical practice in 1994, has a spiral coil built into the shaft to increase the flexibility of the tube and to prevent kinking. This allows the surgeon to manipulate the FLMA’s shaft during the surgery and to have good access to the operating field. The FLMA has been used successfully in patients undergoing a variety of head, neck, eye, and oral operations.

A Tonsillectomy and Adenoidectomy

Several investigators have reported the successful use of the FLMA during tonsillectomies and adenoidectomies. The main advantages of using the FLMA for these procedures are better tolerance of the FLMA by the patients, fewer adverse airway events during emergence and on extubation, and less blood soiling of the airway because of the shielding of the larynx by the LMA’s cuff. Williams and Bailey reported that when the FLMA was used in children during adenotonsillectomies,^50,⁵¹ there was little soiling of the trachea with blood. In contrast, when an uncuffed ETT was used, blood was almost always present in the trachea, causing coughing on emergence. At the end of surgery, there were also fewer episodes of airway obstruction in the FLMA group than in the ETT patients. This is probably because the FLMA was better tolerated by the patients, allowing extubation when the airway reflexes were less obtunded and the patients were able to maintain an open airway. Fiani and coworkers demonstrated in a randomized study of patients undergoing elective tonsillectomies that fewer complications such as laryngospasm, bleeding, bronchospasm, and desaturation occurred in the FLMA group than in the ETT group.⁵²

The FLMA is useful during ear and nose surgery, such as tympanoplasty, myringoplasty, rhinoplasty, septoplasty, and nasal polypectomy.^50,⁵³^–⁵⁸ As reported by Watcha and colleagues, the LMA provided better oxygen saturation and better surgical conditions in pediatric patients undergoing myringoplasties than did the face mask.⁵⁹ Although in other studies the FLMA and the ETT were equally effective in adult patients undergoing nasal surgery, there was less blood in the trachea and fewer airway events during emergence in the FLMA group.^54,⁵⁹

B Dental and Oral Surgery

The FLMA has been useful during dental procedures and oral surgery in children and adults (Fig. 22-16).^60,⁶¹ For example, George and Sanders,⁶² in a comparison of the FLMA with the nasal mask during dental procedures in children, reported significantly fewer instances of airway obstruction, oxygen desaturation, and cardiac dysrhythmias in children in the FLMA group. Other oral surgeries in which the FLMA has been used successfully include repair of a cleft palate,⁶³^–⁶⁵ glossopexy,⁶⁶ removal of a tongue tumor,⁶⁷ and fixation of mandibular fractures after failed endotracheal intubation.⁶⁸

Figure 22-16 The flexible laryngeal mask airway (FLMA) was used in a patient undergoing oral surgery. Because the FLMA causes less hemodynamic stimulation than the endotracheal tube, it is safer to use in patients with severe atherosclerotic heart disease.

C Ophthalmologic Procedures

Patients with increased intraocular pressure who are undergoing intraocular procedures are frequently at higher risk for injury from sudden pressure changes during laryngoscopy and endotracheal intubation.⁶⁹ Coughing and bucking on the ETT during emergence from general anesthesia can be detrimental and may cause suture rupture.⁷⁰ The benefits of using the FLMA for eye surgery include less change in the intraocular pressure during induction and emergence from general anesthesia and less hemodynamic stimulation.^71,⁷² The FLMA has been particularly useful during cataract surgery, trabeculectomy, and vitroretinal surgery.⁷³ Use of the device has also benefited children undergoing strabismus repair, gonioscopy, nasolacrimal duct probing, eyelid repair, scleral and conjunctival procedures, and foreign body removal.⁷⁴

VI Laryngeal Mask Airway Use in Patients with Difficult-to-Manage Airways

One of the most important tasks of an anesthesiologist is to provide ventilation and oxygenation for the patient during surgery. This requires establishing and maintaining a patent airway during the course of anesthesia. As reported in 1990 in a closed claims study published by the ASA, airway-related problems were among the leading causes of major morbidity and mortality directly related to anesthesia.⁷⁵ This study laid the groundwork for the development of the ASA difficult airway algorithm, which established pathways for the care of patients with difficult-to-manage airways.⁷⁶ Although the algorithm provides an organized approach to airway management based on preoperative findings, it does not constitute a foolproof system. Many patients still prove difficult to intubate by means of conventional laryngoscopy, even when the preoperative interview and physical examination do not yield any signs of potential difficulty. Airway swelling may ensue quickly after multiple intubation attempts. Although face mask ventilation in these patients might have been adequate initially, it may soon become difficult, creating the very dangerous and potentially life-threatening situation of inadequate oxygenation.

During the past 10 years, the LMA has received much attention because it can be effective in patients who are difficult to intubate by conventional laryngoscopy and difficult to ventilate with a face mask. The success of the LMA in these patients results from its design. The LMA fits into the potential space of the pharynx much like a hand fits into a glove. In contrast to rigid laryngoscopy, insertion of the LMA does not rely on direct visualization of the larynx. Many factors that are associated with difficult rigid laryngoscopy (e.g., Mallampati class III and IV, Cormack-Lehane grade 3 and 4 views) do not affect the insertion of and ventilation through the LMA.^77,⁷⁸

A Classic Laryngeal Mask Airway

The potential of the LMA for the emergency and nonemergency management of patients with difficult airways was appreciated shortly after its invention. In February 1983, an early prototype was used successfully by Brain in a 114-kg man undergoing laparotomy who could not be intubated. However, the first publication describing the LMA as a possible solution to airway management problems in emergency situations did not appear in the scientific literature until 1984.⁷⁹ By 1985, the LMA had been used successfully in five adults in whom difficult intubation was anticipated, and in October 1987, it was used for the first time in cases of failed pediatric intubation.¹³ In 1989, Allison and McCrory used fiberoptic guidance for endotracheal intubations,⁸⁰ and in 1991, McCrirrick and Pracilio first reported an awake intubation through the LMA.⁸¹ Numerous case reports appeared describing airway management with the LMA in several clinical situations, including adult and pediatric patients with cervical spine pathology, including cervical spine instability^12,⁸¹^–⁸⁴; morbid obesity⁸⁵; micrognathia and macrognathia^86,⁸⁷; Klippel-Feil syndrome⁸⁸; Treacher Collins syndrome⁸⁹; Pierre Robin syndrome⁹⁰; Goldenhar’s syndrome⁹¹; Hurler’s syndrome⁹²; Down syndrome⁹³; or unexpected failed intubation associated with difficult face mask ventilation.^94,⁹⁵

A major step in recognizing the LMA’s potential in the management of airway emergencies took place in 1993, when it was incorporated into the Practice Guidelines for Management of the Difficult Airway by the ASA Task Force on Management of the Difficult Airway.⁷⁶ Not enough data were available then to appreciate fully the LMA’s role in difficult airway situations. By 1996, the reported experience with the LMA had substantially increased, and Jonathan Benumof, who participated in the development of the ASA algorithm, assessed the LMA’s potential in a difficult airway scenario.⁹⁶ His recommendations were that the LMA should be considered as originally recommended in the emergency pathway of the algorithm and in four additional situations: during awake intubation as an aid to endotracheal intubation, as a definite airway in nonemergency situations, as an aid to tracheal intubation in anesthetized patients, and as an aid to tracheal intubation after the airway is established in emergency situations. In his review, Benumof concluded, “With multiple uses and multiple places of use, the LMA is an important option within the ASA difficult airway algorithm. More importantly, the clinical record of LMA use in ‘cannot intubate, cannot ventilate’ situations has been excellent, and in patients whose lungs cannot be ventilated because of the supraglottic obstruction and whose trachea cannot be intubated due to unfavorable anatomy (but not periglottic pathology), the LMA should be immediately available and considered as the first treatment of choice.”⁹⁶ In 2003, Benumof’s recommendations fully materialized in the Practice Guidelines for Management of the Difficult Airway that was updated by the ASA Task Force on Management of the Difficult Airway.⁶ Essentially, depending on the user’s level of expertise, the LMA can be used in any place in the algorithm.

B Fastrach Intubating Laryngeal Mask Airway

In 1983, while developing the LMA, Brain conducted a fiberoptic investigation that revealed the LMA’s potential as a guide for endotracheal intubation. The same year, he developed a prototype LMA and used it to intubate blindly three patients using a 9-mm ETT (Fig. 22-17). However, the development of an intubating LMA was not revisited by Brain until 1994. In response to clinicians’ growing demands for a device that had the same ventilatory properties as the LMA Classic but would serve as a better conduit for intubation, he designed the Fastrach ILMA (LMA North America, San Diego, CA), which was introduced in 1997 (Fig. 22-18).

Figure 22-17 A prototype of the intubating laryngeal mask was built and used by Archie Brain in 1983. It was used to blindly intubate three patients who had a history of difficult intubation with a 9-mm-ID tracheal tube.

Figure 22-18 The intubating laryngeal mask airway (ILMA) was introduced in 1997. It consists of the mask, which has the same shape as the LMA Classic, and the 13-mm internal diameter, stainless steel shaft, which can accommodate an endotracheal tube with an internal diameter up to 8.5 mm.

The ILMA is designed to facilitate blind or fiberoptically guided endotracheal intubations without the need to move the cervical spine during intubation. Available only in adult sizes, the ILMA consists of an anatomically curved, stainless steel tube with a 13-mm internal diameter that is connected firmly at its distal end to the laryngeal mask. The angle of the metal shaft was carefully designed using measurements from sagittal MRI images to fit well into the oral and pharyngeal space while keeping the head and neck in a neutral position. Proximally, the metal shaft forms a standard 15-mm connector for the anesthesia circuit, and a rigid guiding handle serves to insert the device, eliminating the need to insert fingers into the mouth, and to stabilize and direct the device during intubation attempts. The two bars at the aperture of the LMA Classic have been replaced in the ILMA by a single, movable epiglottic elevating bar that pushes the epiglottis out of the way and allows smooth and unobstructed passage of the ETT as it emerges from the distal end of the ILMA’s metal shaft (Fig. 22-19). This shaft can accommodate an ETT up to 8.5 mm in diameter. The shaft of the ILMA is shorter than that of the LMA Classic, eliminating the need for longer ETTs in patients with long necks.

Figure 22-19 Fiberoptic view of intubation through the intubating laryngeal mask airway (ILMA). A, Epiglottic elevating bar (EEB) as seen from inside the shaft. B, The tip of the endotracheal tube (ETT), as it advances through the LMA Fastrach, pushes the EEB upward. C, This movement of the EEB lifts the epiglottis out of the way. D, It also provides a clear passage for the ETT through the vocal cords.

The ILMA was first described by Brain and coworkers in 1997 in the British Journal of Anaesthesia.⁹⁷ In the same issue, there were two separate reports by Brain and Kapila and their colleagues^98,⁹⁹ of early clinical experience with the ILMA. Unfortunately, Kapila’s report described results obtained 3 years earlier using a more primitive prototype of the ILMA and created some confusion regarding the technique of intubation through the device. At the same time, early versions of the ILMA instruction manual included recommendations for use based on these early prototypes. Subsequently, the results from a large study that evaluated the effectiveness of the ILMA in patients with different types of difficult-to-manage airways rendered most of these earlier recommendations irrelevant by demonstrating that the only technique that improved the rate of blind intubation through the ILMA was Chandy’s maneuver (Chandy Verghese, Royal Berkshire Hospital, Reading, England, personal communication, January 1998).¹⁰⁰

Chandy’s maneuver consists of two steps that are performed sequentially. The first step, which is important for establishing optimal ventilation, is to rotate the ILMA slightly in the sagittal plane using the metal handle until the least resistance to bag ventilation is achieved. The second step of Chandy’s maneuver is performed just before blind intubation and consists of using the metal handle to lift slightly (but not tilt) the ILMA away from the posterior pharyngeal wall. This facilitates the smooth passage of the ETT into the trachea (Fig. 22-20). Ferson and colleagues assessed the effectiveness of the ILMA in 254 patients, including patients with Cormack-Lehane grade 4 views, immobilized cervical spines, and airways distorted by tumors, surgery, or radiation therapy and patients wearing stereotactic frames.¹⁰⁰ Insertion of the ILMA was accomplished in three attempts or fewer in all patients. The overall success rates for blind and fiberoptically guided intubations were 97% and 100%, respectively. This represents the largest analysis examining the use of the ILMA in patients with difficult-to-manage airways and demonstrates that the ILMA may be a particularly valuable tool in the emergency or elective airway management of patients in whom other techniques have failed and in the treatment of patients with immobilized cervical spines.

Figure 22-20 Chandy’s maneuver consists of two steps that are performed sequentially. A, The first step is important for establishing optimal ventilation. The intubating laryngeal mask airway (ILMA) is rotated slightly in the sagittal plane using the metal handle until the least resistance to bag ventilation is achieved. B, The second step is performed just before blind intubation. The metal handle is used to lift slightly (but not tilt) the ILMA away from the posterior pharyngeal wall. This facilitates the smooth passage of the endotracheal tube (ETT) into the trachea.

The ILMA can be used as an intubating tool in patients with normal airways. In a study conducted by Brain and colleagues, the hemodynamic response to the ILMA was similar to the response to the LMA Classic; in patients with compromised cardiovascular systems the ILMA could be a less stimulating alternative to rigid laryngoscopy for intubation of the trachea.^98,¹⁰¹ Using the ILMA in patients with normal airways allows clinicians to develop good skills and familiarity with the device before using it in emergency situations.

VII ProSeal Laryngeal Mask Airway

The PLMA (LMA North America, San Diego, CA) (Fig. 22-21) was designed by Brain with the principal objective of providing a separate conduit to permit gastric fluids to bypass the glottis. He thought such a device was needed because even in fasted patients, the anesthesiologist can never be completely certain that the stomach is empty. The PLMA permits access to the stomach using standard gastric tubes, provides a more reliable seal around the glottis, reduces the leakage of inspired gases into the stomach, provides a more comfortable fit within the pharynx, facilitates the use of mechanical ventilation, and permits the diagnosis of incorrect LMA placement.

Figure 22-21 The ProSeal laryngeal mask airway (PLMA) was designed to separate the respiratory and gastrointestinal tracts and to provide a better seal around the glottis and allow positive-pressure ventilation in a more reliable manner than the LMA Classic.

The LMA Classic may or may not block the esophagus, depending on how precisely it is positioned in the hypopharynx. Realizing this, Brain developed insertion and fixation techniques to ensure correct positioning, but these recommendations are widely ignored or unknown to most users, who continue to choose their own favored insertion techniques and methods of fixation. It therefore comes as no surprise that there are cases of aspiration in the LMA literature, although they are rare.¹⁰² In the PLMA, the drain tube opening at the distal tip of the mask ensures that if the tip is not correctly placed against the UES, inflation of the reservoir bag causes some of the gas to be diverted back up the drain tube, providing measurable evidence of inadequate device placement. The PLMA instruction manual further details the diagnostic functions made possible by the drain tube.¹⁰³

PLMA, which will soon be available in the same range of sizes as the LMA Classic (excluding size 6), has several important differences. The adult sizes are fitted with a posterior extension to the cuff that expands to a relatively small degree when inflated within the confined space of the pharynx, as demonstrated radiologically (Fig. 22-22). Similar images in which the cuff is inflated excessively demonstrate that the presence of the posterior cuff, although probably increasing the seal pressure by about 10%, introduces two dangers that must be guarded against. One is the possibility of herniating the cuff bowl forward toward the glottis, thereby causing partial or complete blockage of the delicate drain tube and compromising the airway (Fig. 22-23). Second, overinflation may cause the mask to slide proximally, reducing the efficacy of its seal against the UES. If the drain tube is blocked and its opening is simultaneously moved away from contact with the UES, the major advantages of the device are lost because there is no longer any guarantee that a seal exists against the UES, although the seal may appear to be excellent. The PLMA is therefore a more sophisticated device than the LMA Classic, and instructions for its use must be followed carefully.

Figure 22-22 Lateral neck radiograph with the ProSeal laryngeal mask airway (PLMA) in place. When inflated correctly with a pressure up to 60 cm H₂O, the posterior cuff of the mask expands only slightly (white arrow). This ensures the patency of the gastric drain tube (black arrow).

Figure 22-23 Lateral neck radiograph with the ProSeal laryngeal mask airway (PLMA) in place. If the cuff is inflated with excessive volume, exceeding a pressure of 60 cm H₂O, the gastric drain tube can be partially or completely occluded (black arrow) by the bowl of the mask that is pushed toward the glottis by the overinflated cuff (white double arrow).

Pediatric sizes of the PLMA feature the drain tube but no posterior cuff. The relatively larger airway and drain tube configuration required for optimal functioning in the pediatric anatomy result in a wider device angle when viewed laterally. If a posterior cuff were added, the angle would become critically large, causing the device to slide proximally out of the pharynx as it is inflated. Halaseh and colleagues reported their experience with the PLMA in 3000 elective cesarean sections in a single center and using a method of insertion that allowed a rapid establishment of a patent airway together with gastric drainage.¹⁰⁴

VIII Supreme Laryngeal Mask Airway

After several years of continuous research, Brain designed the LMA Supreme (Intavent, Direct, Maidenhead, United Kingdom) as a single-use laryngeal mask airway device with gastric access. The intent was to combine some of the desirable features of the ILMA, such as ease of insertion, without the need for the insertion of the fingers into the oropharynx, and the PLMA, which offers higher seal pressures with a gastric tube access to permit drainage from and access to the stomach, and it provides confirmatory evidence of correct or incorrect device placement.

The LMA Supreme has a manifold with an integral bite block, an anatomically shaped airway tube enclosing a drain tube, a redesigned inflatable cuff (through which the drain tube passes), and a cuff inflation line with pilot balloon (Figs. 22-24 and 22-25). The LMA Supreme manifold and integral bite block is at the proximal end of the device. Two tubes project from the manifold. The standard 15-mm diameter airway tube is designed to be connected to the airway circuit. The narrower tube is the proximal end of the drain tube.^104,¹⁰⁵

Figure 22-24 The LMA Supreme has a manifold with an integral bite block, an anatomically shaped airway tube enclosing a drain tube, a modified cuff through which the drain tube passes, and a cuff inflation line with pilot balloon.

Figure 22-25 The LMA Supreme manifold and integral bite block is at the proximal end of the device. Two tubes project from the manifold. The 15-mm-diameter airway tube is designed to be connected to the airway circuit. The narrower tube is the proximal end of the drain tube.

The fixation tab is a rectangular structure molded onto the manifold at right angles, and it projects over the patient’s upper lip. It is designed to facilitate easy insertion and fixation of the LMA Supreme after insertion and inflation of its cuff. The fixation tab was found in early pilot studies to act as a visual guide to correct size selection. After fixation of the device and inflation of the cuff to a pressure of 60 cm H₂O, the fixation tab should be 1.5 to 2 cm from the upper lip. If the fixation tab is less than this distance, the size chosen may be too small, and if it is more than 3.0 cm from the upper lip, the size chosen may be too large (see Figs. 22-24 and 22-25).

Extending distally from the manifold is the flattened, semirigid airway tube, which has an elliptical cross section and an integral bite block at its proximal end. The airway tube ends distally at the laryngeal inlet. The elliptical shape of the airway tube is intended to facilitate insertion in patients with reduced interdental space without requiring the insertion of fingers into the mouth. After it is in place, the flattened shape and stiffness of the airway tube also helps to minimize accidental rotation. The airway tube is much stiffer than that of the PLMA, but it is intended to bend with movements of the head and neck, unlike the completely rigid metallic airway tube of the ILMA. Patented lateral grooves on the airway tube of the LMA Supreme prevent it from kinking and occluding when bent, no matter how much it is flexed (see Figs. 22-24 and 22-25).

The drain tube runs from its rigid proximal end on the manifold through the middle of the airway tube and continues along the posterior surface of the cuff to the distal end of the cuff. At the distal end, it terminates as a centrally placed orifice designed to face into the opening of the UES, when the device is correctly inserted. The drain tube equalizes the pressure at the UES and atmosphere. In addition to venting gastrointestinal gases and liquids, the drain tube also serves as a conduit for the passage of a well-lubricated gastric tube (up to 16 F) into the stomach. The drain tube functions as a continuous clinical monitoring tool during PPV, indicating whether the LMA Supreme is correctly positioned immediately after insertion and warning the user if the device becomes displaced from its optimal position during use. Incorrect positioning of the LMA Supreme results in a poor airway seal and an audible leak of delivered gases through the drain tube (see Figs. 22-24 and 22-25).

The modified shape and enlarged surface area of the inflatable cuff enhances the anatomic fit of the device into the pharynx, permitting higher glottic seal pressures than the LMA Classic and LMA Unique. The distal cuff is over-molded to strengthen the tip and prevent it from folding over during insertion. Two fin-shaped structures extend on either side of the drain tube where it passes through the bowl of the mask, designed to prevent the epiglottis from obstructing the airway (see Figs. 22-1 and 22-2). The cuff has a conventionally placed inflation line terminating in a pilot balloon and one-way valve for mask inflation and deflation.

The technique for LMA Supreme insertion described in the study by Balog and coworkers is similar to that recommended in the instruction manual.⁷⁴ The device was deflated to a vacuum using a 50-mL syringe and correctly shaped at the distal tip by compressing between finger and thumb during deflation to form a thin wedge. Insertion was performed with the head and neck in the semi-sniffing position. Complete extension is not required for successful insertion.^105,¹⁰⁶

In a prospective, descriptive study on the use of the LMA Supreme for airway management in 205 adult patients undergoing elective orthopedic surgery in the prone position, the investigators were able to demonstrate that first-pass success was achieved in 184 insertions.¹⁰⁷ Regurgitation of gastric contents through the LMA drainage tube was observed in 205 patients. There were no cases of clinically relevant aspiration. Sharma and colleagues concluded that the LMA Supreme was a useful device for airway management in patients anesthetized in the prone position and for possible airway management with PPV, with or without neuromuscular block.¹⁰⁷ No patient had to be turned to the supine position because of an airway problem during anesthesia. Brimacombe and coworkers demonstrated in 40 adult patients that maintenance of anesthesia is feasible in the prone position when the LMA Supreme was inserted by experienced users.¹⁰⁸

The PLMA and LMA Supreme offer the additional advantages of higher glottic seal pressures than the LMA Classic, providing a separate conduit for passive passage of gastric contents and allowing the passage of a lubricated gastric tube through the drain tube to access liquid and gaseous gastric contents. The advantages of a higher glottic seal pressure, easy access to the stomach,¹⁰⁵ ease of insertion in the supine, lateral, and prone positions, efficacy for PPV, and as a reliable and noninvasive airway during the recovery phase from general anesthesia support its use in this form of surgery.

In a well-designed, randomized, prospective study comparing the safety and efficacy of the LMA Supreme with the PLMA in elective ambulatory procedures, Seet and associates included 99 patients and concluded that although the LMA Supreme has lower oropharyngeal leak pressures than the PLMA, the first attempt insertion success rate was higher for the LMA Supreme.¹⁰⁹ It is a safe, efficacious, and easy to use disposable supraglottic airway device suitable for elective ambulatory procedures.¹⁰⁹ The higher first-attempt success rate may make the LMA Supreme a more suitable choice as an airway rescue device.

The higher intracuff pressures demonstrated for the PLMA may be related to the cuff material. The PLMA is made from silicone, and the LMA Supreme is constructed from polyvinyl chloride.¹⁰⁶ Mucosal pressures are lower than pharyngeal perfusion pressure over the inflation range for the PLMA.¹¹⁰

Eschertzhuber and colleagues found a lower leak pressure with the size 4 LMA Supreme than with the size 4 PLMA in 93 healthy, female patients.¹⁰⁶ However, there was no significant difference in leak pressure with the LMA Supreme and PLMA in two other studies by Verghese and Ramaswamy¹⁰⁵ and Hosten and coworkers.¹¹¹ A literature review of the oropharyngeal leak pressure of the supreme LMA and the PLMA showed conflicting results. A prospective, randomized, crossover study of 36 female patients using a size 4 Supreme or the PLMA showed no difference in the oropharyngeal leak pressure (28.6 versus 28.5 cm H₂O, P = 0.91).¹⁰⁵ Hosten and associates conducted a prospective, randomized, controlled trial enrolling 60 patients (men and women) and comparing the Supreme with the Proseal.¹¹¹ Various LMA sizes (sizes 3 through 5) were used according to body weight. The leak pressures were also found to be similar for the Supreme and ProSeal groups at intracuff pressures of 60 cm H₂O (26.1 versus 26.9 cm H₂O).¹¹¹ However, muscle relaxants were given to 13 of 60 patients, which might have confused the results. The application of neuromuscular blocking agents can result in a decreased leak pressure of the PLMA and may have influenced the accuracy of measurement.¹¹² The lower oropharyngeal leak pressure for the LMA Supreme may be related to the less elastic properties of polyvinyl chloride.

Cuff pressures are not directly related to leak pressures. The materials play a major role in the compliance and elasticity of the device, as do the volume and elasticity of the patient’s oropharyngeal anatomy, but it is also essential that the device is correctly located in the hypopharynx and that it remains securely fixed in position. The fact that leak pressures have been found by some to be lower in the LMA Supreme may be due to material differences, but it could also reflect positioning and subsequent movement of the airway after insertion.¹¹³

IX Disposable Laryngeal Mask Airways

Infection is a perennial risk to health care workers and patients. The risk of infection in hospitals seems to be about as intractable a problem as iatrogenic disease. Newer antimicrobial agents encourage the emergence of resistant organisms just as more powerful therapeutic tools offer new opportunities for human error in their application. Although laryngeal masks have never been proved to be a source of infection transmission, the continuing uncertainty surrounding the size of the population of Creutzfeldt-Jakob disease carriers and the risk of transmission of the infectious agent through the tonsillar bed, together with the difficulties in ensuring effective device sterilization against small virus-like particles, have led to increased interest in disposable airway equipment, particularly in some European countries. The U.K. Department of Health required surgeons and anesthesiologists to use disposable equipment for tonsillectomies but reversed this decision when the use of poorly designed disposable surgical instruments was implicated in the death of a patient. In London’s main otolaryngologic hospital, the Royal Throat, Nose, and Ear Hospital, the reusable FLMA had for some years been used in approximately 90% of tonsillectomies (Paul Bailey, personal communication, March 2004), and substitution with the disposable ETT was believed to be a retrospective step. Accordingly, the Department of Health agreed to fund the cost of treating the reusable FLMA as a single-use item, pending the availability of a disposable version of the device.

The lessons learned from this experience were that we should be wary of rushing to embrace disposable forms of an established device until we are sure that their function is equivalent and that the avoidance of a theoretical risk of low probability (e.g., transmission of prion infection associated with tonsillectomy) should not take precedence over the avoidance of known risks (e.g., imposition of untried and unfamiliar equipment for an operation, the safety of which depends on skill, training, and well-established techniques).

All pediatric and adult sizes of the disposable LMA (LMA Unique; LMA North America) have been subjected to a rigorous series of tests to confirm that their function is equivalent to that of the reusable silicone device.^114,¹¹⁵ This has not been easy to accomplish because vinyl plastic materials lack the elasticity of silicone, and this tends to affect the insertion and seal characteristics of the LMA. It is likely that the plastic disposable LMAs will be found to be less appropriate for PPV than the LMA Classic. However, this limitation may be regarded as academic because the PLMA is specifically designed for use with positive pressure.

X Exchange Using the Aintree Intubation Catheter

When an LMA is placed after a difficult intubation or difficult ventilation by face mask, the anesthesiologist must determine whether the airway should be secured by an ETT for the surgical procedure. The Aintree intubating catheter (AIC, Cook Critical Care, Bloomington, IN) is a semirigid, 560-mm-long tube with internal and external diameters of 47 and 70 mm, respectively.^116,¹¹⁷ It was designed to enable fiberoptically guided intubation of the trachea through a supraglottic airway device. The technique permits fiberoptic instrumentation of the airway while oxygenation and ventilation take place around the fiberscope through the airway device. Use of the AIC through the LMA Classic and the PLMA have been reported when conventional tracheal intubation has failed.¹¹⁸^–¹²²

The PLMA may offer additional benefits over the LMA Classic when using the AIC because of its larger airway bowl and the absence of aperture bars at the distal end of the airway tube. The deeper bowl of the PLMA and the absence of bars may allow improved access to the larynx compared with the LMA Classic and improve passage of the AIC during insertion.^123,¹²⁴ The PLMA is not as easy to insert as the LMA Classic, and it has a slightly smaller internal diameter through which an AIC can easily pass.

Clinical studies have reported less than 30 intubations with the LMA Classic or the cuffed oropharyngeal airway (COPA). Both reports were executed by the inventors of the device and between them involved only three operators. On a manikin study comparing the use of AIC over the LMA Classic and the PLMA using the fiberscope, Blair and colleagues found no significant difference between the devices with regard to ease of advancement of the fiberscope or the view of the vocal cords with the AIC.¹²⁵ The study concluded that in a manikin, fiberoptically guided intubation through a PLMA was at least as easy and reliable as through the LMA Classic.¹²⁵ The technique of exchanging an LMA over an AIC has only been described in humans during difficult airway situations and found as case reports in the literature.

XI Problems and Controversies

The occurrence of problems and complications associated with the use of the LMA appears to be inversely proportional to the experience and skill level of the operator. Most adverse events associated with LMA are probably the result of incorrect use of the device or inappropriate selection of patients. Some of the advanced clinical applications of the device (e.g., PPV with the LMA) have been considered controversial. However, as their experience and skill with the LMA advance, many clinicians find it to be a very useful tool in situations that they had previously considered to be problematic. The skill level and experience of the clinician, not the type of application, should guide the use of the LMA. In the following sections, we address the controversies regarding the LMA’s use and discuss reported problems and complications and ways to manage them when they occur.

A Oropharyngolaryngeal Morbidity

Any foreign body that comes into contact with airway structures can cause complications. The LMA passes through and occupies anatomic areas from the oral cavity to the hypopharynx. Structures that are at high risk for injury from supraglottic airways, including the LMA, are mucous membranes, soft tissues of the pharynx and larynx, salivary glands, nerves and blood vessels of the neck, laryngeal cartilages, and bones of the neck. When injury occurs, it usually manifests in minor complaints such as a dry mouth or sore throat.¹²⁶ These problems usually resolve quickly and have no long-term sequelae. However, more serious complications, such as hypoglossal and lingual nerve palsy, trauma to the epiglottis and larynx, dysarthria, dysphonia, and tongue cyanosis related to vascular compression, have been reported.¹²⁷^–¹³³

1 Sore Throat

Sore throat, dry throat, pharyngeal erythema, and minor pharyngeal abrasions have been reported with the LMA. The published incidence of sore throat varies between 0% and 70%.^126,¹³² Initially, it was not clear why the incidence of sore throat varied so much. Factors that may affect the incidence include the insertion technique, duration of the procedure, type of lubricant, type of ventilation (i.e., spontaneous or controlled), and intracuff pressure.¹³⁴^–¹³⁷ Of these, the only variable that has been shown to reduce the incidence of sore throat reliably is lowering the intracuff pressure.¹³⁸ Overinflation of the LMA’s cuff is a common practice when the size of the device is too small for a given patient and the practitioner encounters a significant leak while attempting assisted ventilation or PPV. The overinflated cuff becomes stiff and exerts high local pressure on tissues, especially those surrounding bony structures, such as the hyoid bone and cervical spine. Nitrous oxide diffuses through the silicone walls of the LMA, increasing the pressure inside the cuff.¹³⁹ This can be remedied by monitoring the intracuff pressure and periodically withdrawing the gas from the LMA’s cuff. Based on Brain’s unpublished research in awake volunteers, the maximum pressure inside the LMA’s cuff should not exceed 60 cm H₂O because higher pressure causes discomfort, presumably because of stretching of the constrictor muscles. Appropriate LMA size selection combined with a good insertion technique and low intracuff pressure reduces significantly the incidence of postoperative sore throat.

2 Vascular Compression and Nerve Damage

Although rare, compression of the blood vessels of the tongue that leads to tongue cyanosis has been observed after LMA insertion.¹³⁰ This complication is likely to occur when the LMA is not inserted deeply enough or when the LMA’s cuff is overinflated. The blood vessels of the tongue or the lingual nerve can be compressed by malpositioning of the LMA’s shaft on the lateral side of the tongue, as found in cadaveric research. Similarly, if during LMA insertion the cuff is partially or fully inflated, the device frequently lies higher than when the correct insertion technique is used. Malpositioning of the LMA can compress the lingual or hypoglossal nerve, resulting in transient or prolonged nerve palsy. The hypoglossal nerve, which supplies all of the intrinsic and all but one of the extrinsic muscles of the tongue, is particularly vulnerable to injury at the point where the nerve loops anteriorly, close to the greater cornu of hyoid bone, and then runs along the lateral surface of the hyoglossal muscle and above the posterior border of the mylohyoid muscle before dividing into several branches that supply tongue muscles. To avoid these complications, the anesthesiologist should select the appropriate LMA size, use the standard insertion technique, and ensure that the intracuff pressure is no higher than 60 cm H₂O.

B Risk of Aspiration

Aspiration during general anesthesia has an overall incidence of 1.4 to 6.5 per 10,000 cases and a mortality rate of 5%.¹⁴⁰^–¹⁴³ In a study of 215,488 anesthesia cases, Warner and coworkers reported that the incidence of aspiration was 2.6 per 10,000 patients undergoing elective surgery and 11 per 10,000 patients undergoing emergency procedures.¹⁴⁴ The mortality rate was 0.14 per 10,000 patients with an ASA physical status classifications III through V. The study by Warner and colleagues did not include patients whose airways were managed using the LMA.¹⁴⁴

The LMA does not reliably protect against aspiration and should not be used electively in patients who are at high risk for this complication. However, most users do not adhere to the recommended insertion or fixation techniques when using the LMA, which are designed to optimize the seal of the distal end of the device against the UES. Nonetheless, a meta-analysis of the literature on the LMA by Brimacombe and Berry revealed that the overall incidence of pulmonary aspiration with the LMA is approximately 2 per 10,000 patients.¹⁴⁵ Eighteen cases of suspected pulmonary aspiration during LMA use have been found by meta-analysis, and only 10 of these were confirmed radiographically. In only three patients did the aspiration warrant ventilatory support, which lasted 1 to 7 days. None of the patients who aspirated through the LMA suffered any long-term effects. Most of these patients had one or more factors predisposing them to aspiration, including emergency surgery in an unfasted patient, a difficult airway, obesity, a steep Trendelenburg position with intra-abdominal insufflation, and previous gastric surgery. Although the meta-analysis study contained only reports published through September 1993, a subsequent analysis of 11,910 LMA anesthesia cases by Verghese and Brimacombe yielded an even smaller incidence of aspiration (0.84 per 10,000).¹⁴⁶

A study by Bernadini and Natalini compared the risk of pulmonary aspiration in patients whose lungs were mechanically ventilated through an LMA airway (35,630 procedures) or ETT (30,082 procedures).¹⁴⁷ Three cases of pulmonary aspiration occurred with the LMA and seven with the ETT. No deaths were related to pulmonary aspiration. The incidence and outcome of pulmonary aspiration detected in this study were similar to those previously reported. The adjusted odds ratio (OR) for pulmonary aspiration with the LMA was determined to be 1.06 (95% confidence interval [CI], 0.20 to 5.62). Unplanned surgery (OR = 30.5; 95% CI, 8.6 to 108.9) and male sex (OR = 8.6, 95% CI, 1.1 to 68) were associated with an increased risk of aspiration and age younger than 14 years with a reduced risk (OR = 0.21; 95% CI, 0.07 to 0.64). There were contraindications and exclusions to the use of the LMA, but in this selected population, use of an LMA was not associated with an increased risk of pulmonary aspiration compared with an ETT.

Even allowing that critical events in anesthesia are frequently under-reported, the absence of admissions to intensive care units for ventilatory support indicates that aspiration with the LMA is rare. Nevertheless, the anesthesiologist must always be meticulous about selecting patients appropriately, using the correct insertion technique to obtain the optimal LMA position, paying attention to the appropriate depth of anesthesia, and maintaining constant vigilance during surgery. If regurgitation or aspiration occurs despite all of these measures, the following plan of action should be implemented:

1. Do not attempt to remove the LMA because a significant amount of regurgitant fluid may be trapped behind its cuff. The cuff shields and protects the larynx from the trapped fluid, and removing the LMA may worsen the situation.

2. Temporarily disconnect the circuit to allow drainage of the fluid while tilting the patient’s head down and to the side.

3. Suction the LMA, and administer 100% oxygen to the patient.

4. Ventilate the patient manually using low gas flows and small tidal volumes to minimize the risk of forcing fluid from the trachea into the small bronchi.

5. Use a large FOB to evaluate the tracheobronchial tree, and suction any remaining fluid.

6. If aspiration below the vocal cords is confirmed, consider intubating the patient with an ETT, and institute appropriate treatment protocols.

The risk of aspiration with an LMA is likely to be significantly reduced with the PLMA, which incorporates a drainage tube into the LMA design, warns of an inadequate UES seal, and permits more reliable PPV than does the LMA Classic.

C Positive-Pressure Ventilation

When the first independent trial of the LMA was carried out, only a size 3 was available, and the correct fixation technique for ensuring an adequate seal against the UES had not been developed.¹⁴⁸ When used in large patients, the device was not very reliable for applying PPV. Because the LMA concept was new, it was prudent for clinicians initially to limit the use of the LMA to patients who were breathing spontaneously. Even now, PPV should be considered an advanced use of the LMA, and clinicians should practice and gain experience using the LMA in patients who are breathing spontaneously before attempting controlled ventilation. However, after the LMA was introduced commercially in a range of sizes, first for adults and then for children, many LMA users found that after they became experienced, the LMA could be effective during PPV.⁷³ Devitt and colleagues compared the effectiveness of the LMA with that of the ETT in 48 patients and demonstrated that PPV (range, 15 to 30 cm H₂O) through the LMA was adequate and comparable to that achieved through the ETT.¹⁴⁹ Epstein and associates studied the effectiveness of the LMA with controlled ventilation in children 3 months to 17 years old and concluded that the device performed effectively and reliably.¹⁵⁰ In another study, Epstein and coworkers established that the airway seal pressures (25.9 to 31.2 cm H₂O) were well maintained with the LMA in children.¹⁵¹

Two large clinical studies of more than 7000 patients led by Verghese and Van Damme established that the LMA was as effective as the ETT for controlled ventilation.^114,¹⁵² Van Damme’s study also assessed the airway seal pressures and demonstrated that at 15 cm H₂O or less pressure, leaks occurred with the LMA in only 2.7% of patients. Subsequently, Verghese reported his experience of using the LMA successfully in 5236 patients undergoing a variety of surgical procedures under general anesthesia and PPV.¹⁴⁷

The following principles should be considered when using the LMA with PPV:

1. Selection of patients: Most patients with normal lung compliance who have fasted can be mechanically ventilated effectively with the LMA.

2. Size selection: Select the largest LMA size appropriate for the patient, which prevents a tendency to compensate for inadequate seal pressure by overinflating the cuff.

3. Insertion technique: Carefully follow the correct insertion technique to ensure optimal positioning of the LMA in the airway.

4. Fixation technique: Use the correct method of taping the LMA. This ensures proper contact between the LMA’s tip and the esophagus and prevents gastric insufflation.

5. Auscultation: Always auscultate over the stomach to ensure that gastric insufflation is not taking place.

6. Ventilatory parameters: Limit tidal volumes to 8 mL/kg, and control the end-tidal carbon dioxide by adjusting the respiratory rate.

7. Treatment of inadequate tidal volume: Maintain an adequate level of anesthesia for the particular surgical procedure.

If leaking occurs when using the LMA for PPV, investigate the cause, and try to correct the situation. If the device has been correctly fixed in place and remains correctly inflated, the problem usually is caused by the need for more relaxant or deeper anesthesia.

D Use for Prolonged Procedures

The maximum duration for which the LMA can be safely used is not well established, but a limit of 2 hours was suggested soon after the LMA became widely available for clinical use.⁸² This recommendation was based on the possible increased risk of aspiration or pharyngeal morbidity. Subsequent reports demonstrated that in the hands of experienced users, the LMA can be safely used during procedures lasting up to 8 hours.^153,¹⁵⁴ In rare circumstances, the LMA has been used in the intensive care arena to provide effective respiratory support for 10 to 24 hours with no evidence of adverse effects.¹⁵⁵ The PLMA, which is designed for PPV and has a gastric drainage tube to minimize the risk of aspiration, may be best suited for prolonged procedures.¹⁵⁶ Regardless of the model used, clinicians must remain vigilant and provide adequate anesthesia to their patients, minimizing the risks of complications. If nitrous oxide is administered to the patient, the anesthesiologist should remember that this gas diffuses into the LMA’s cuff, increasing intracuff pressure. During prolonged LMA use, close monitoring of the intracuff pressure is recommended. To minimize the risk of mucosal ischemia associated with high intracuff pressures, hourly removal of a few milliliters of air from the cuff is considered a prudent practice.¹⁵⁷

E Use in Nonsupine Positions

Use of the LMA in patients in other than the supine position should be considered an advanced technique.¹⁵⁸^–¹⁶³ An alternative plan is necessary in case the device dislodges from its original position during the procedure. Because of the risk of LMA dislodgment in patients in nonsupine positions, consider inducing general anesthesia and inserting the LMA after the patient has been positioned for the procedure. This ensures the feasibility of inserting the LMA at any time during the procedure. If insertion cannot be performed successfully, reconsider whether the LMA should be used in that patient. The LMA insertion technique in patients in the lateral or prone position is significantly different from the insertion technique in supine patients. Using a thumb to insert the LMA may be the most useful method in patients positioned prone or laterally.¹⁶⁴ An advantage of using the LMA in patients in the prone position is that they are able to position themselves comfortably before induction of general anesthesia, potentially reducing the incidence of back problems.¹⁶⁵

F Device Problems

Before its clinical release, the LMA was subjected to rigorous testing to ensure compliance with the medical industry standards. However, some complications have been reported, including separation of the LMA cuff from the shaft,^166,¹⁶⁷ fragmentation of the device inside the patient,¹⁶⁸ kinking of the LMA’s shaft,¹⁶⁹ and failure to inflate or deflate the cuff.^170,¹⁷¹ Most of these complications are related to use of the device beyond the manufacturer’s recommendations and to use of the wrong chemicals for sterilization and coating the device with silicone lubricants, which are not recommended for the LMA. Strict adherence to the manufacturer’s instructions for cleaning, sterilization, and use should always be followed, including not exceeding the recommended 40 uses per device. Instructions from the manufacturer’s manual should be followed if a malfunction occurs. With the introduction of the disposable LMA models, the number of device problems linked to overuse and wrong sterilization techniques may be eliminated, but all LMAs should be inspected and tested before use to ensure optimal performance and safety.