Chapter 19. Laryngeal Mask Airways

The laryngeal mask airway (LMA) is a device that fills the gap in airway management between that of endotracheal (ET) intubation and the use of a face mask. It was introduced in the United Kingdom in 1983 by British anesthesiologist A. I. J. Brain. His goal was to develop an airway apparatus that could rapidly overcome an obstructed airway, is simple to use, and is atraumatic to insert. In 1991, the LMA was approved for use in the United States by the Food and Drug Administration.

The LMA was designed primarily as a means of providing ventilatory support while avoiding the fundamental disadvantage of the need to visualize and penetrate the vocal cords with an ET tube.1 The LMA is introduced into the hypopharynx without direct visualization. It forms a low-pressure seal around the laryngeal inlet and permits positive-pressure ventilation. With the introduction of the LMA ProSeal, pressures of up to 30 cmH2O may be administered safely (A.I.J. Brain, M.D., personal communication). Once inserted, the LMA may be used as a conduit for fiberoptically guided ET intubation or to place an ET tube blindly.2 The LMA has come to be viewed as a viable method of airway management, with over 800 articles and case reports describing the advantages and disadvantages of the device.3 A more recent Medline search for articles involving the use of LMAs yielded over 3500 results.

Many disadvantages of the standard LMA became apparent with widespread use of the device. More than 10 years after its introduction, Dr. Brain and colleagues began to work on a new airway system with better intubation characteristics than the standard LMA. The intubating laryngeal mask airway (ILMA) was developed through the aid of analysis of magnetic resonance images of the human pharynx and laboratory testing of ET tubes.4 The new and more “anatomically correct” ILMA effects more precise placement. The design of the ILMA also avoids head and neck manipulation and insertion of the intubator's fingers into the patient's mouth, both of which occur during the placement of the standard LMA.4,5

There are approximately nine different models of the LMA. The term “laryngeal mask airway” is specific to one brand of laryngeal mask devices produced by LMA North America, San Diego, CA. Several other manufactures also make laryngeal mask devices. Some of these will also be described in this chapter. The LMA Classic (LMA-C) is the original and most commonly used version. The LMA Classic Excel (LMA-CE) is more durable than the original LMA-C and can be reused up to 60 times. The LMA Unique (LMA-U) is a single-use disposable version of the LMA-C. The LMA Flexible is a wire-reinforced version of the LMA that is more flexible than the original version and resists kinking. It is used by Anesthesiologists for patients undergoing head and neck procedures. It is not used in the Emergency Department. The LMA Fastrach is a modified version of the LMA that allows ET intubation through the unit. It is also referred to as the ILMA. It allows ventilation during intubation attempts. Its advantages include the following: no manipulation of the head and neck is required, it can accommodate up to a size 8 ET tube, it facilitates one-handed insertion, it can be inserted from the patient's side or from above the head, and it can be used in conjunction with fiberoptic intubation. The LMA ProSeal (LMA-PS) features a cuff deflator, modified cuff design, dual tubes, and a bite block. Similar to the LMA-PS, the LMA Supreme (LMA-S) has a built-in drain tube and a bite block. However, the LMA-S is intended for a single-use and has a more curved airway tube than the LMA-PS. The LMA CTrach (LMA-CT) includes an insertion site for an ET tube and allows for direct visualization of the larynx using built-in fiberoptics. The Ambu laryngeal mask (Ambu LM) has an airway tube that is curved more acutely than the LMA-Cs. This curve follows the anatomy of the upper airway and allows for easier insertion without having to manipulate the head or neck.

The standard LMA, ILMA, LMA-PS, LMA-CT, or Ambu LM may be available in the Emergency Department. The techniques for inserting these devices are discussed in this chapter. The anatomic differences between these devices produce subtle differences in their insertion methods. The indications, contraindications, assessment, and complications associated with these devices are largely identical.

The anatomy of the airway is briefly reviewed (Figure 19-1). Refer to Chapter 6 for the complete details of the airway anatomy. The oral cavity is bounded by the hard and soft palate above and the anterior portion of the tongue and the reflection of its mucosa onto the floor of the mouth below. Posteriorly, the mouth opens into the oropharynx through the oropharyngeal isthmus. The pharynx is a U-shaped tube extending from the base of the skull to the level of the cricoid cartilage, at which point it becomes continuous with the esophagus.6 The larynx extends from its oblique opening bordered by the aryepiglottic folds, the tip of the epiglottis, and the posterior commissure to the base of the cricoid cartilage.6 The esophagus lies posterior to the airway. When inflated and properly positioned, the tip of the device will lie in the esophagus at the level of the upper esophageal sphincter and directly posterior to the cricoid cartilage (Figure 19-2).

The indications for the use of an LMA device parallel the general indications for active airway management. These include the correction of hypoxemia or hypercarbia, the provision of controlled hyperventilation, the provision of a secure airway in the presence of obstruction, and the provision of airway access for pulmonary hygiene and bronchoscopy. An LMA may aid in supporting airways that are difficult to manage as well as being an invaluable aid to blind and fiberoptic intubation. The success rate of correct placement in inexperienced hands approaches 90%.7 This makes the LMA superbly suited for use by medical personnel who have had only a minimal amount of training in airway management.

Airway control also facilitates emergent radiographic investigations, for example, computed tomography (CT) or magnetic resonance imaging (MRI) scans without motion artifact.6 The standard LMA contains no ferromagnetic components and is a suitable alternative to an ET tube in many situations. It is ideal for use in patients emergently requiring diagnostic MRI scans. Use of the LMA does not require a metal laryngoscope, which is contraindicated if a patient requires airway management in the MRI suite.

LMA devices may be used in the event of a failed ET intubation. They have a role in securing the airway presumptively in patients with an “anteriorly” situated larynx, a situation whereby direct laryngoscopy and ET intubation are historically difficult. In emergent situations, the LMA is a safe alternative to the esophageal obturator airway, King tube, Combitube, and EasyTube. The LMA has also proved to be useful in burn patients requiring repeated dressing changes, especially of the face. Finally, the LMA may well be the airway technique of choice for professional singers who require short-term airway management since there is less likelihood of causing vocal cord or laryngeal nerve injury with this approach.7

However, in all its uses, there is a conspicuous absence of airway protection from aspiration. The LMA-PS and LMA-S are being marketed as superior to the LMA-C for use in nonfasting patients. These versions feature an improved laryngeal seal for permitting positive-pressure ventilation at pressures up to 30 cmH2O and a drain tube in tandem with the airway tube. The drain tube facilitates blind insertion of a gastric tube for decompressing the stomach. An introducer aids insertion of the LMA-PS while obviating the need to introduce fingers into the patient's mouth.

There are no absolute contraindications to the use of LMAs. However, there are several relative contraindications. These devices should not be used in individuals who are at an increased risk of regurgitation or aspiration unless the benefit of securing an airway outweighs the risk of aspiration (e.g., when other techniques for securing the airway have failed).8 This is supported by uncontrolled studies using fiberoptic bronchoscopy, which have shown that the esophagus is visible within the LMA mask in 6% to 9% of patients.7 Patients at high risk for aspiration include those with previous upper gastrointestinal surgery, known or symptomatic hiatal hernia, gastroesophageal reflux disease, women more than 10 weeks pregnant, patients with intestinal ileus or peptic ulcer disease, obese patients, or those individuals who are not fasted.5,9,10

In emergent situations where cricoid pressure is needed to prevent active or passive regurgitation of stomach contents prior to airway placement, the LMA is not an appropriate airway device. It will not prevent subsequent aspiration of stomach contents as efficiently as will a cuffed ET tube. The act of placing an LMA after the application of cricoid pressure (i.e., the Sellick maneuver) has been shown to have a significantly high failure rate.7 The LMA-PS and LMA-S feature dual tubes (i.e., airway and drain) as well as a modified cuff designed to provide separation of the respiratory and alimentary tracts. As a result, they may prove invaluable in negating this “Achilles' heel” of the standard LMA.

These devices should not be used in individuals with severe respiratory diseases.2,9,10 Specifically, individuals with airway obstruction at or below the larynx and those with low pulmonary compliance or high airway resistance (e.g., morbid obesity, bronchospasm, pulmonary edema, pulmonary fibrosis, or thoracic trauma) are not appropriate candidates for LMAs. The only possible exception is that it can be inserted as a temporary airway rescue device in preparation of another method of ET intubation or a surgical airway.

Patients must be able to assume the “sniffing” position, analogous to that of individuals positioned for direct laryngoscopy prior to ET intubation. Patients who cannot passively or actively extend their head and flex their neck are not candidates for the LMA-C, LMA-CE, LMA-U, or LMA-S. The ILMA, LMA-CT, LMA-PS with an introducer, or the Ambu LM are more appropriate for these patients. Patients should not receive these devices if they cannot open their mouth at least 1.5 cm due to anatomic limitations (e.g., ankylosing spondylitis, severe rheumatoid arthritis, cervical spine instability, etc.).7 This is one situation where blind nasotracheal intubation or fiberoptically guided nasotracheal tube placement has an advantage over the LMAs.

Finally, the LMA is relatively contraindicated in cases of pharyngeal pathology. This includes but is not limited to abscesses, caustic ingestions, hematomas, and tissue disruptions. These processes make the use of the LMA difficult. The device may rupture abscesses and hematomas, causing the patient to aspirate. The use of an LMA after a caustic ingestion can result in perforation of the eroded upper esophageal or hypopharyngeal walls from the pressure of the inflated cuff.

• LMAs, various types and sizes
• ET tubes
• Water-soluble lubricant
• Syringes, 10 and 20 mL
• Oxygen source, tubing, and regulator
• Face masks
• Bag-valve device
• Pulse oximeter
• Cardiac monitor
• Noninvasive blood pressure monitor
• Advanced Cardiac Life Support (ACLS) medications
• Advanced airway equipment
• Surgical airway equipment

LMA Classic (LMA-C) and Unique (LMA-U)

The standard LMA preceded the ILMA by more than a decade. The prototype of the LMA was constructed by forming a shallow mask with an inflatable rubber cuff joined to a tube communicating with the lumen of the mask at an angle.1,2 The modern LMA is made of flexible silicone, is completely latex-free, and has a more tapered appearance. It has a variably sized, internally ridged tube fused at a 30° angle to a spoon-shaped mask with a flexible rim.

The LMA-C is a disposable unit that can be used multiple times. It must be sterilized between uses following specific manufacturer recommendations. The LMA-U is similar in construct to the LMA-C. However, the LMA-U is a single-use device. These LMAs are designed to conform to the contours of the hypopharynx, with the lumen facing the glottic opening (Figure 19-2).

They consist of an airway tube, an inflation line, and a mask (Figure 19-3). Overall, they resemble a giant spoon. The airway tube has a large bore and is clear, like an ET tube.2 The proximal end contains a standard 15 mm airway adapter that can connect to a bag-valve device or a ventilator. A black line along the posterior border is used as a marker for proper positioning. The distal end of the airway tube connects to the mask.

The mask is elliptical in shape (Figure 19-4). The outer rim of the mask contains an inflatable cuff. When inflated and properly positioned, the tip of the LMA will lie in the esophagus at the level of the upper esophageal sphincter and directly posterior to the cricoid cartilage (Figure 19-2). The lateral edges of the mask rest in the pyriform fossae. The upper edge rests against the base of the tongue. The LMA provides a seal against the upper esophageal sphincter, aryepiglottic folds, and distal epiglottis so as to direct air into the trachea and avoid insufflation of the stomach (Figure 19-2).2,3

The distal end of the airway tube opens into the mask. This opening is covered by two vertical aperture-bars that prevent the epiglottis from obstructing the lumen of the airway tube (Figure 19-4). The aperture bars should be cut off prior to inserting the LMA if an ET tube is to be inserted through the LMA.

The inflation line is used to inflate and deflate the cuff (Figure 19-4). The distal end of the inflation line attaches to the upper border of the cuff. The proximal end contains an inflation port and balloon, similar to an ET tube. An air-filled syringe attaches to the inflation port to inflate the cuff.

The correct size of the LMA is based on the patient's weight and is crucial to ensure a proper seal and reduce complications (Table 19-1).8 The distal end assumes a different shape when the cuff is inflated and deflated. The distal end is pentagon-shaped when deflated (Figure 19-4A). It is oval-shaped when inflated (Figure 19-4B).

LMA Classic Excel (LMA-CE)

Although similar in construct to the standard LMA, the LMA-CE has been designed as an “enhanced” version of the LMA-C (Figure 19-5). The airway tube has been reinforced, allowing the LMA-CE to be used up to 60 times. It must be sterilized between uses following specific manufacturer recommendations. The inflatable cuff is made of soft silicone to minimize throat stimulation and irritation. The LMA-CE is available in three sizes (Table 19-2).

Several modifications have been made in order to facilitate ET intubation with the aid of a fiberoptic bronchoscope. Proximally, the airway tube has a 15 mm connector that can be easily removed to allow for access. The airway tube has been designed to accommodate up to a 7.0 cuffed ET tube. It is short enough that the cuff of the ET tube can pass through the LMA-CE and beyond the vocal cords. The mask aperture includes a vertically oriented epiglottic elevating bar, also known as the EEB (Figure 19-5). The EEB is free at the caudal end and fixed at the cephalad end, effectively creating a hinge mechanism. An ET tube passed through the mask aperture swings the EEB backward and elevates the epiglottis away from the path of the advancing ET tube.

LMA Fastrach (ILMA)

The LMA Fastrach is also known as the intubating LMA or ILMA (Figures 19-6 & 19-7). The form of the ILMA was derived from head and neck sagittal MRI studies in 50 normal subjects whose heads were held in a neutral position. The convex radius of the curve of the silicone-covered steel tube represents a value close to the best-fit curve derived from the MRI studies.4 The new prototype consists of an anatomically curved steel tube connected to standard LMA cuff sizes 3, 4, and 5.5,9

The ILMA has several significant modifications that make it different from the LMA-C (Figures 19-6 & 19-7). It is available in a reusable stainless steel version and a plastic single-use disposable version (Figure 19-6A). Both versions are available in three sizes (Table 19-3). The airway tube is stainless steel covered with silicone rubber. The proximal end has a handle fused to the airway tube to facilitate insertion, manipulation, and removal of the ILMA. It is curved to follow the curve of the hypopharynx and position the mask aperture over the glottic aperture. It has a larger diameter (13 mm vs. 9 mm) than the LMA.9 This allows the ILMA to accommodate a cuffed ET tube with an inner diameter up to 9.0 mm.5,11 It is significantly shorter (14.5 vs. 20 cm) than the LMA-C.9

The mask of the ILMA is similar to that of the LMA with two major modifications. The ILMA contains a ramp inside the distal airway tube as it meets the mask and continues into the mask aperture. It is designed to direct the ET tube into the center of the aperture and into the patient's airway. It also has a large, single, and stiff EEB designed to lift the epiglottis out of the way of the advancing ET tube (Figures 19-6B & 19-7).

The ILMA was designed to be used with a wire-reinforced cuffed silicone ET tube with an 8.0 mm inner diameter (Figure 19-8).5 The ILMA ET tube is available in 6.0, 6.5, 7.0, 7.5, and 8.0 mm sizes. The molded tip allows atraumatic insertion through the vocal cords. It has a transverse block line along its posterior surface. This line serves as a marker to let the intubator know when the tip of the ET tube is positioned at the EEB. This occurs when the ET tube is inserted through the ILMA, and the transverse bar is located at the proximal end of the airway tube. While it is ideal to use the wire-reinforced silicone ILMA ET tube, a standard ET tube may also be used.

LMA CTrach (LMA-CT)

The LMA-CT is basically an ILMA with built-in fiberoptics that allow direct visualization of airway anatomy (Figure 19-9). Two fiberoptic channels lie along the lateral edges of the airway tube. These channels merge and exit under the EEB. The properly positioned LMA-CT fiberoptics project an image of the laryngeal inlet directly in front of the mask aperture. A portable color display, the LMA CTrach Viewer, attaches magnetically to the top of the LMA-CT airway tube. This allows the intubator to monitor the passage of the ET tube through the vocal cords. The LMA-CT Viewer lies just above the patient's chin and in line with the actual airway anatomy, making intubation easier from a hand-eye coordination standpoint. Images may be recorded and downloaded onto a computer for later documentation and teaching purposes.

LMA ProSeal (LMA-PS)

The LMA-PS has been designed to be inserted manually or with the aid of a metal introducer (Figure 19-10). The use of the introducer obviates the need for the intubator to place their fingers in the patient's mouth. The LMA-PS has been modified to allow for ventilation at higher airway pressures. A combination of a softer silicone cuff, an additional rear cuff in larger sizes, and a deeper bowl mask permit higher seal pressures up to 30 cmH2O. This is approximately 50% higher than with the LMA-C. The LMA-PS provides a tighter seal without increasing mucosal pressure or the risk of complications. It is a reusable device that is available in numerous sizes (Table 19-4).

The LMA-PS features a dual tube (i.e., drain tube and airway tube) system that decreases the risk of rotational dislodgement of the device. The drain tube communicates with the upper esophageal sphincter, allowing for blind insertion of an orogastric tube and for venting of gastric gases and liquids. The drain tube is positioned in the cuff to prevent the epiglottis from blocking the airway tube. The LMA-PS has been designed to decrease the risk of aspiration. Despite this, the manufacturer cautions that the LMA-PS does not provide complete protection against aspiration.

LMA Supreme (LMA-S)

The LMA-S, like the LMA-PS, is a dual tube system that provides some separation of the respiratory and digestive tracts. The LMA-S is a single-use device and has an airway tube that is more curved and anatomically shaped (Figure 19-11). It has a more rigid airway tube than the LMA-PS, thus it requires no digital or metal introducer for placement. It can be used for the blind passage of an orogastric tube. The drain tube can help monitor correct positioning of the LMS-S. Gases will audibly leak from the drain tube if the LMA-S does not have a tight airway seal. The LMA-S incorporates a bite block. It is available in numerous sizes (Table 19-5).

Ambu Laryngeal Mask (Ambu LM)

The Ambu LM (Ambu Inc., Glen Burnie, MD) consists of an airway tube, spoon-shaped mask, and inflatable cuff similar to the LMA-C (Figure 19-12). However, the airway tube of the Ambu LM is bent into a smooth curve of approximately 90° to conform to the anatomy of the upper airway and to facilitate easier insertion. Because of this anatomically correct curve, the device can be placed without manipulating the patient's head or neck. The airway tube is D-shaped and easier to grip than other tubes. The distal tip of the Ambu LM is reinforced so that the cuff does not fold over during insertion.

King Laryngeal Airway Device (King LAD)

The King LAD (King Systems, Noblesville, IN) is a disposable, single-use, silicone device similar to the LMA-C. It is available in two styles (Figure 19-13), and a wide range of sizes in each style. The standard model has a curved airway tube while the flexible model has a straight and easily bendable airway tube.

Air-Q Masked Laryngeal Airway (Air-Q)

The Air-Q Masked Laryngeal Airway or Air-Q (Mercury Medical, Clearwater, FL) is another commonly used device (Figure 19-14A). It is available in a full range of sizes (Table 19-6). The airway tube shape and mask inlet have a different shape than the LMAs. An ET tube can be inserted through the Air-Q similar to the ILMA.

The Air-Q Blocker Masked Laryngeal Airway or Air-Q Blocker (Mercury Medical, Clearwater, FL) has been modified from the Air-Q to include a soft guide tube along side of the airway tube (Figure 19-14B). A lubricated suction catheter or nasogastric tube (up to size 18 French) can be inserted and directed into the posterior pharynx and esophagus to suction secretions. A proprietary suction catheter with an inflatable balloon near the distal end can be inserted through the guide tube (Figure 19-14B). The inflated balloon blocks the upper esophagus to prevent aspiration. The tip of this catheter has multiple holes to allow esophageal venting while the balloon prevents aspiration. The Air-Q Blocker is available in three sizes (Table 19-6).

The Air-Q Self-Pressurizing Masked Laryngeal Airway or Air-Q SP (Mercury Medical, Clearwater, FL) is similar to the Air-Q except for one major structural change. The Air-Q SP has a self-pressurizing cuff that does not require a pilot balloon, a inflation line, or a syringe to inflate the cuff (Figure 19-14C). Positive-pressure ventilation provided by a bag-valve device or ventilator inflates and self-pressurizes the cuff. The Air-Q SP is available in a full range of sizes (Table 19-6).

The patient should be appropriately monitored with electrocardiography (ECG), end-tidal CO2 monitoring, noninvasive blood pressure cuff, and pulse oximetry. The patient preparation is exactly the same as that for orotracheal intubation. As for any situation where airway manipulation is to occur and the patient's protective airway reflexes are blunted or ablated, a fully functioning suction apparatus with a variety of catheters must be immediately available. Insertion of the LMA requires an anesthetic depth similar to that which allows placement and acceptance of an oropharyngeal airway.7 Successful placement of the standard LMA is much more likely if the patient is premedicated. In the case of the ILMA, the successful placement of the ET tube is highly dependent on adequate sedation and/or muscle relaxation. The optimal induction agent should produce jaw relaxation and attenuation of airway reflexes, permitting insertion of the LMA device within 30 to 60 seconds of loss of consciousness. A variety of induction agents may be used.

There is some controversy as to what physical examination findings represent the endpoint for judging when to insert the LMA. The consensus is that the first attempt at insertion should occur following the loss of the eyelash reflex (seventh cranial nerve) as when the jaw is relaxed.10,12 This typically occurs 30 to 60 seconds after administration of the ultra-short-acting induction agents. Some practitioners also rely on the onset of apnea and/or loss of response to verbal stimuli as signs of adequate depth of anesthesia.12

LMA Classic, Unique, and Classic Excel

Prior to insertion, carefully inspect the cuff for leaks with the cuff slightly overinflated. Completely deflate the cuff so that it forms a smooth wedge shape. The technique for inserting the LMA-C, LMA-U, and LMA-CE is rather simple (Figure 19-15). Lubricate the posterior surface of the LMA with a water-soluble lubricant. Care must be taken to avoid lubricating the anterior surface of the device, as the gel might obstruct the distal aperture or trickle into the larynx and provoke laryngospasm.7 Avoid using silicone-based lubricants that may degrade the cuff.8 Avoid lubricants containing lidocaine as they may provoke an allergic reaction or decrease laryngeal protective reflexes.8

Position the patient's head as for ET intubation in the sniffing position. Place the nondominant hand behind the patient's head to stabilize the occiput and slightly flex the neck (Figure 19-15A). Allow the patient's jaw to fall open. An assistant may be required to help open it.

Insert the LMA into the oral cavity with the aperture facing but not touching the tongue (Figure 19-15A). It is essential that the leading edge of the cuff be smooth, wrinkle-free, and shaped like a wedge. This facilitates passage of the cuff around the posterior pharyngeal curvature and into the hypopharynx while avoiding the epiglottis. Place the index and middle fingers of the dominant hand against the junction between the LMA and the cuff (Figure 19-15B). Advance the LMA in one smooth movement following the curvature of the pharynx until it enters the hypopharynx (Figure 19-15B). The fingers should lie almost horizontally when the LMA is properly positioned.13,14 Grasp and stabilize the airway tube with the nondominant hand, then remove the index and middle fingers of the intubating hand (Figure 19-15C). Slightly advance the LMA further downward until resistance is felt. At this point, it is important to not push further. If difficulty is encountered, a rotational movement of the tube, slight inflation of the cuff, a jaw-thrust maneuver, or, in rare cases, the use of a laryngoscope may be helpful.7

Inflate the cuff with the recommended volume of air (Figure 19-15D). Do not overinflate the cuff. Inflation usually causes a characteristic outward movement of the airway tube of up to 1.5 cm as the cuff centers itself around the laryngeal inlet. A slight forward movement of both the thyroid and cricoid cartilages will be noted. The longitudinal black line on the shaft of the tube should lie in the midline against the upper lip. Any deviation may indicate the wrong size device was used or misplacement of the cuff and a partial airway obstruction.7 When correctly positioned, the tip of the LMA cuff lies at the base of the hypopharynx against the upper esophageal sphincter, the sides lie in the pyriform fossae, and the upper border of the mask lies at the base of the tongue, pushing it forward.7 Even when grossly malpositioned, the mask may still create a useful airway.8 Secure the LMA like an ET tube.

LMA ProSeal

Prior to insertion, carefully inspect the cuff for leaks with the cuff slightly overinflated. Completely deflate the cuff so that it forms a smooth wedge shape. The LMA-PS features a cuff deflator, which is a compact, portable instrument for assuring complete removal of air without causing the silicone to wrinkle. Lubricate the posterior surface of the LMA with a water-soluble lubricant. Insert the LMA-PS like that described above for the LMA-C. The only difference is that the fingertip should be pushed into the introducer strap at the rear of the cuff.

An alternative method of insertion involves a metal introducer. When using the introducer, head and/or neck manipulation may not be required. Place a properly sized introducer into the strap. Fold the tubes around the convex surface of the introducer and fit the proximal end of the airway tube into the matching slot. Insert the LMA-PS into the oral cavity with the aperture facing, but not touching, the tongue. The back of the mask must remain in constant contact with the hard palate. Rotate the LMA-PS inward in one smooth movement following the curvature of the introducer until it enters the hypopharynx and resistance is felt. Grasp and stabilize the airway tube with the nondominant hand. Remove the introducer. Inflate the cuff and secure the LMA-PS. The LMA-PS includes a built-in bite block.

LMA Supreme

Prior to insertion, carefully inspect the cuff for leaks with the cuff slightly overinflated. Completely deflate the cuff so that it forms a smooth wedge shape. Lubricate the posterior surface of the LMA-S with a water-soluble lubricant. Position the patient's head in a semi-sniffing position. The neutral position or a full “sniffing” position may preclude proper placement of the LMA-S.

Insert the LMA-S. Grasp the LMA-S by the connector end. Insert the LMA-S into the oral cavity with the aperture facing, but not touching, the tongue. Briefly rub the mask tip across the palate in order to lubricate the area. Rotate the LMA-S inward in one smooth movement following the curvature of the pharynx until it enters the hypopharynx and resistance is felt. Directing the distal tip toward the right or left side of the throat may facilitate placement. Grasp and stabilize the airway tube with the nondominant hand. Inflate the cuff and secure the LMA.

LMA Fastrach (ILMA)

The technique for inserting the ILMA is not very different from that for the standard LMA. It involves a one-handed rotational movement in the sagittal plane with the patients head supported to achieve a neutral position.5 The ILMA may be inserted from above the patient's head (like the LMA) or standing to the side of the patient's head. It may be inserted with the right or left hand.

Prior to insertion, slightly overinflate the cuff and check it for leaks. Completely deflate the cuff. Lubricate the posterior surface of the airway tube and the mask liberally. Grasp the ILMA by its handle. Place the patient in the sniffing position if no contraindications exist. Open the patient's mouth with the nondominant hand. Position the ILMA over the patient with the tip of the mask in the patient's mouth (Figure 19-16A). Slowly insert the mask while the posterior aspect of the mask remains in constant contact with the hard palate. When the entire mask is inside the patient's mouth and against the hard palate, rotate the ILMA inward along the natural curve of the hard palate and pharynx (Figure 19-16B). The airway tube should maintain constant contact with the upper central incisors as the unit is advanced. Stop advancing the unit when resistance is felt. This signifies that the tip of the mask is in the upper esophagus (Figure 19-16B).

Inflate the cuff with the recommended volume of air (Figure 19-16C). Inflation usually causes a characteristic outward movement of the airway tube, up to 1.5 cm, as the cuff centers itself around the laryngeal inlet. A slight forward movement of the thyroid and cricoid cartilages will be noted. The airway tube should lie in the midline against the upper central incisors. Any deviation may indicate the misplacement of the cuff and a partial airway obstruction. When correctly positioned, the tip of the ILMA cuff lies at the base of the hypopharynx against the upper esophageal sphincter, the sides lie in the pyriform fossae, and the upper border of the mask lies at the base of the tongue, pushing it forward.

Confirm proper placement of the ILMA. Have an assistant attach a bag-valve device to the proximal end of the airway tube and ventilate the patient. Observe the upper chest rise, auscultate bilateral breath sounds, and observe end-tidal CO2 monitoring to confirm proper placement. An anterior movement, or bulging, of the cricoid and thyroid cartilages during or after cuff inflation also indicates correct positioning of the ILMA.1

Insert an ET tube. Lubricate the wire-reinforced silicone ET tube (or a standard ET tube) liberally. Insert the silicone ET tube into the ILMA until the transverse black line on its posterior surface is at the proximal end of the airway tube (Figure 19-16D). At this point, the tip of the silicone tube will be just inside the distal end of the airway tube. If necessary, an assistant can connect a bag-valve device to the silicone ET tube and ventilate the patient. Make sure that the longitudinal black line on the posterior surface of the silicone ET tube is facing upward.

Slowly and gently advance the silicone ET tube 1.5 cm beyond the transverse black line. If no resistance is felt, the tip of the silicone tube is just past the vocal cords. Continue to advance the silicone ET tube an additional 4 cm (Figure 19-16E). The patient can be ventilated by an assistant during this procedure if necessary. Inflate the cuff of the silicone ET tube and ventilate the patient through the silicone ET tube (Figure 19-16F). Confirm proper tube placement by the auscultation of breath sounds, observation of chest rise, and end-tidal CO2 monitoring.

The ILMA should now be withdrawn. Deflate the cuff of the ILMA. Have an assistant remove the bag-valve device and the 15 mm adapter on the proximal end of the silicone ET tube. Withdraw the ILMA by gently reversing the ILMA over the silicone ET tube (Figure 19-16G). Simultaneously apply slight pressure to the proximal end of the silicone ET tube so that it does not become dislodged (Figure 19-16G). When the mask begins to exit the patient's mouth, stop withdrawing the ILMA. Grasp the silicone ET tube firmly at the patient's mouth and hold it securely. Withdraw the ILMA in a smooth curved motion (Figure 19-16H). Reattach the standard respiratory connector, ventilate the patient, and reconfirm proper placement of the silicone ET tube.

Some physicians prefer to use a “pusher” to prevent accidental extubation while the ILMA is being withdrawn. Cut a 25 cm length from a second silicone ET tube. Insert this into the ILMA as it is being removed. Apply slight pressure so it pushes against the first ET tube and prevents it from moving proximally. When the ILMA exits the patient's mouth, remove the ILMA and pusher as a unit. Secure and assess the proper positioning of the ET tube, as mentioned previously.

LMA CTrach (LMA-CT)

The technique for inserting the LMA-CT is similar to that for the ILMA. The LMA-CT may be inserted from above the patient's head like the LMA-C or standing to the side of their head. Place the patient in the neutral position to avoid head extension. The manufacturer recommends only using the LMA-CT with straight, wire-reinforced cuffed silicone ET tubes with a 6.0 to 8.0 mm inner diameter. Standard curved plastic ET tubes may lead to an increased incidence of laryngeal trauma.

Insert the LMA-CT using the technique described for the ILMA. Inflate the cuff with the recommended volume of air and confirm proper placement of the ILMA. Have an assistant attach a bag-valve device to the proximal end of the airway tube and ventilate the patient. Observe the upper chest rise, auscultate bilateral breath sounds, and observe end-tidal CO2 monitoring to confirm proper placement.

Attach the Viewer by placing the Viewer's socket onto the magnetic latch connector on the LMA-CT. Turn on the Viewer to visualize the glottis. Lubricate the wire-reinforced silicone ET tube. Grasp the LMA-CT by its handle and pass the ET tube back-and-forth through the airway tube several times in order to lubricate the entire airway tube. Do not pass the lubricated silicone ET tube beyond the transverse black line on its posterior surface in order to avoid obscuring the fiberoptics with lubricant. Make sure that the longitudinal black line on the posterior surface of the silicone ET tube is facing upward.

Slowly and gently advance the silicone ET tube 1.5 cm beyond the transverse black line. Gripping the handle and lifting a few millimeters optimize the alignment of the silicone ET tube and the trachea. As the silicone ET tube passes the mask aperture, the EEB will be seen to rise on the Viewer display. Continue to advance the silicone ET tube through the vocal cords. The patient can be ventilated by an assistant during this procedure if necessary. Detach the Viewer. Then, inflate the cuff of the silicone ET tube and ventilate the patient through the silicone ET tube. Confirm proper tube placement by the auscultation of breath sounds, observation of chest rise, and end-tidal CO2 monitoring. Withdraw the LMA-CT similar to the technique described for the ILMA.

Other Laryngeal Mask Devices

The Ambu Laryngeal Mask (Ambu LM), King Laryngeal Airway Device (King LAD), and the Air-Q Masked Laryngeal Airway (Air-Q) can be inserted and secured similar to the LMA. An ET tube can be inserted through all the Air-Q models similar to the ILMA.

It is generally held that difficulty in insertion of the standard LMA occurs most frequently at the point where the tip of the mask passes just behind the tongue as it changes direction toward the hypopharynx.15 Most of the suggested alternative methods for inserting the LMA involve the negotiation of direction change from the pharynx to the hypopharynx. Some authors suggest that a partially inflated mask is easier to place in the correct position.15 Others employ a jaw-thrust maneuver. After adequate jaw relaxation has been established, the mask is positioned firmly and flatly against the hard palate, as recommended. Perform the jaw-thrust maneuver with the nondominant hand while firmly thrusting the mask into place with the dominant hand, in one motion.16 The jaw-thrust creates a space in the hypopharynx for the mask. In rare cases, the use of a laryngoscope may help facilitate LMA placement, though this reduces the inherent simplicity of the technique of LMA insertion.

One study of the LMA-PS showed that a 90° rotation would improve rates of successful placement.17 This technique was also associated with a lower incidence of mucosal bleeding and sore throat. After preparing the LMA-PS and the patient as usual, insert the device until the entire cuff is inside the mouth. Rotate the LMA-PS 90° counterclockwise and advance until resistance is felt. Once the LMA-PS is in the hypopharynx, straighten it out.

Given that there is less experience with the ILMA, few alternative methods of insertion exist. However, one must remember that the metal handle on the tip of the ILMA tube may be used to modify the position of the cuff within the hypopharynx.9 Pulling back on the metal handle toward the intubator rotates the tube caudally in the sagittal plane. Pushing on the metal handle away from the intubator rotates the tube cephalad in the sagittal plane.

Successful placement of an LMA device is most accurately demonstrated by auscultation of bilateral breath sounds, chest wall movement, and end-tidal CO2 monitoring.5,9 One may also gain a sense of accuracy of placement during insertion. During observation of the front of the neck while inserting an LMA, one may see a bulging of the tissues overlying the larynx. Visualization of this bulge, in addition to increased resistance to forward motion of the mask, indicates that the device is in the correct position.1 A chest radiograph should be obtained if an ET tube has been placed through an LMA.

The LMA does not protect against aspiration as well as an ET tube. It should be replaced with an ET tube or a surgical airway. The method of securing the airway with a device other than an LMA will be determined by the patient's condition, if they have a “difficult airway,” available equipment, and experience of the Emergency Physician.

There are numerous documented complications associated with the use of LMAs. One of the most obvious of these, and potentially the most devastating, is the failure to place the device successfully or to obtain a satisfactory laryngeal seal. Fortunately, even in inexperienced hands, the incidence of failure to achieve satisfactory ventilation is quite low. One large study, a retrospective review of 11,910 surgical cases where the standard LMA was used, noted an overall success rate of 99.81%.18 Success rates have been classified as success on one single attempt and overall success. The overall success rate allows up to three attempts to be considered for successful placement. One investigator claimed a 99.5% single-attempt success rate in a retrospective analysis of 1500 cases.10 Most studies imply correct LMA placement in 88% to 90% of first attempts.7 Several studies have found success rates of 90% to 99% for ILMAs. Success rates appear to be higher if a wire-reinforced silicone ET tube is used rather than a standard ET tube.19,20 Besides failure, there are other complications, which may be divided into minor complications and major complications.

Minor Complications

Minor complications are those that may result in significant patient morbidity but usually are not associated with mortality or extremely deleterious outcomes. Stomach inflation can occur during positive-pressure ventilation at pressures greater than 20 cmH2O for the standard LMA. Cuff herniation secondary to overinflation may result in failure of the cuff to seal effectively. Partial airway obstruction may occur in up to 10% of adults and 25% to 50% of pediatric patients when standard LMA cuffs are examined by fiberoptic bronchoscopy.7 Trapping of the epiglottis in the distal aperture of the LMA may result in edema of the epiglottis. Air leaks around the cuff can occur during positive-pressure ventilation at pressures greater than 20 cmH2O for the standard LMA and 30 cmH2O for the LMA-PS. Forceful attempts to pass the LMA around the posterior pharyngeal curvature can result in uvular bruising.7 Lingual nerve injury, tongue numbness, parotid gland swelling, and hypoglossal nerve palsy are sometimes noted. Unilateral vocal cord paralysis can occur secondary to traumatic insertion. Bilateral vocal cord paralysis has not been reported. Dental trauma may occur during the insertion or during maintenance of the airway.

Major Complications

Major complications are those from which significant patient morbidity may be expected, including patient mortality. Fortunately, as regards the LMA, major complications are exceedingly rare. In a report of 11,910 surgical cases where the standard LMA was used, there were a total of 18 critical events related to the LMA, for an overall incidence of 0.15%.18 These events included regurgitation of stomach contents (0.03%), vomiting of stomach contents (0.017%), pulmonary aspiration (0.009%), laryngospasm (0.07%), bronchospasm (0.025%), cardiac dysrhythmias (0.09%), and cardiac arrest (0.06%). While there appears to be a higher incidence of critical events when the device is used for controlled ventilation and positive-pressure ventilation, the incidence has not proved to be statistically significant.

In general, the complication rate (defined as events not attributable to the patient's underlying condition or to surgical or other interventions) should be equivalent to that seen during placement of either a Guedel or Berman type oropharyngeal airway. Referring to standard anesthesiology textbooks, one realizes that the complication rate in each of the aforementioned categories when using the LMA is significantly lower than that occurring during direct laryngoscopy and ET intubation, potentially due to the intense autonomic nervous system stimulation occurring with the latter procedures.

A major advancement in airway management was made with the introduction of the LMA. It is superior to a face mask in that it prevents supraglottic obstruction and reduces the likelihood of gastric insufflations.2 However, it does not provide protection from aspiration. The LMA-PS and LMA-S, with their dual tube system, may help decrease the risk of aspiration.

The standard LMA has clearly earned a valuable place in the armamentarium of clinicians who provide airway management. The technique is easy to learn, easy to teach, and requires no specialized equipment. The LMA causes minimal autonomic nervous system activation and less of a response from the cardiovascular system than with direct laryngoscopy. The LMA is not associated with a risk of esophageal or endobronchial intubation. Both, however, are possible complications following use of the ILMA. The LMA has minimal effects on the intraocular pressure response to airway manipulation. The LMA may be of use in cases of suspected cervical spine injury.

The use of an LMA in place of a face mask avoids many risks, such as injury to the eyes, supraorbital and facial nerves, nose, and lips. There is less risk of hand fatigue than with the bag-valve-mask device. The LMA provides a safer and more secure airway in children and adults than does a face mask, with fewer episodes of hypoxemia as detected by pulse oximetry.7

The introduction of the ILMA more than a decade after the standard LMA further defined and expanded the role of this apparatus in airway management. It allows for precise ET tube placement, therefore ensuring airway protection. It is anatomically designed to ensure more accurate placement of the cuff. Given the ease of placement of the ILMA without the need for the rescuer to be positioned behind the head, there may be a significant place for the ILMA in future airway management algorithms.4 The advent of the LMA-CT allows for direct fiberoptic visualization of the vocal cords prior to intubation.