The Laryngeal Mask Airway in Emergency Airway Management
By Charles G. Durbin, Jr., MD, FCCM
Designed by archie brain in the early 1980s and introduced into clinical practice shortly thereafter, the laryngeal mask airway (LMA) has become an indispensable part of anesthesia practice. This odd appearing device is the first appliance specifically created to completely bypass the most common cause of airway obstructionocclusion of the pharynx by the tongue. It is so effective in this regard that it is now recommended as the airway adjuvant of choice when an unexpected difficult or impossible intubation is encountered in the course of delivering anesthesia. It has virtually replaced anesthesia by face mask in elective general anesthesia in cases of short duration, due to its effectiveness in maintaining an open airway and its ease of use. It also frees the user’s hands for other tasks.
The LMA is spreading to areas outside the operating theater because it is more effective in inexperienced hands than mask ventilation. It also is more helpful than other devices in patients with difficult airways. This latter group includes the very young and morbidly obese patients in whom tracheal intubation is often difficult or impossible.
In this review, details of the device, suggestions for its use, its limitations, and some concerns will be presented.
The LMA consists of a large bore airway tube with a standard 15 mm male connector, an oval shaped cuff that rests against the lateral walls of the hypopharnyx, and a pilot tube with a one-way valve used to inflate the cuff (See Figure 1). The angle of the cuff and the curve of the tube are made to conform to the axes of the oral pharynx and the glottic opening (See Figure 2). The tip of the mask seats in the inferior recess of the hypopharynx superior to the esophageal sphincter. The upper border rests against the base of the tongue. The hypopharynx is freely distensible and cuff inflation volume is adjusted to allow positive pressure ventilation.
Figure 1
LMA
The laryngeal mask airway (LMA)
The LMA is not a substitute for a cuffed endotracheal tube. It does not prevent aspiration or allow ventilation with high airway pressures. It may reduce the amount of oral material aspirated into the lung by acting like a shield or umbrella over the larynx. Peak manual ventilation pressures to about 20 cm H2O are usually possible with the LMA properly seated. If high ventilation pressures are necessary, such as with interstitial fibrosis or ARDS, two-person facemask ventilation may be more effective than an LMA prior to placement of an endotracheal tube.
Using the LMA
The LMA is available in custom sizes to fit all patients, as listed in Table 1. Since there is only a rough relationship between body weight, age, and hypopharnygeal size, several sizes should be available for use in any situation. Placement of the device is quite stimulating, and the individual must be without reflexes or vomiting may occur. This requirement is not different from placement of other airway adjuvants such as oro- and nasopharyngeal airways. Nasopharyngeal airways are usually better tolerated in patients who are not totally comatose and are the initial airway tool of choice in this patient group.
Table 1
LMA sizes
Size DescriptioWeight Maximum Cuff Volume
1 Neonates/infants 0-6.5 kg 4 mL 2 Infants and Childre5-20 kg 10 mL 2 .5 Small Childre20-30 kg 14 mL
3 Large Children/ Over 30 kg 20 mL Small Adults
4 Normal Adults 30 mL 5 Large Adults 40 mL
Insertion of the LMA is simple and easy to learn. The cuff is deflated into a saucer shape, the mouth opened, and the device is inserted over the center of the tongue and advanced with an index finger down into the pharynx. It is advanced until further movement is impeded. The cuff is inflated, and the tube moves back out of the mouth a small amount. This backward movement is a sign of proper tube seating in the hypopharnyx. Ventilation is attempted and breath sounds confirmed. If ventilation fails, the device should be reinserted. Failure to seat correctly is usually related to failure to enter the pharynx or a back-folding of the cuff tip. This is often corrected on reinsertion. Head position is not critical, although slight extension may facilitate correct entry into the pharynx. A black stripe in the center of the tube helps maintain correct orientation of the mask over the larynx. If after two tries, ventilation fails, a different size tube may be needed or the technique abandoned in favor of mask ventilation. If breath sounds are heard but the ventilation leak is too large, additional air may be placed in the cuff.
Figure 2
LMAin place
Diagram of LMA in place, showing relationship to oral pharynx and glottic opening.
LMA Success After Minimal Training
A major advantage of the LMA is the success and rapidity with which its use can be taught to emergency personnel. In one study, nurses and medical students who were inexperienced in airway management were given brief instruction in manual ventilation (bag-mask ventilation), insertion and use of the LMA, and practice with both techniques under supervision in two anesthetized patients. Their ability to ventilate with both techniques was then tested in 10 patients. Ventilation was more quickly established with the LMA (15.8 vs 27.3 seconds) and more frequently successful than with an oropharnygeal airway (87% vs 47% maintained oxygen saturation above 90%).
Another study demonstrated the superiority of the LMA over endotracheal intubation in the hands of emergency personnel. Seven experienced paramedics and 12 respiratory therapists trained in endotracheal intubation placed both the laryngeal mask airway and endotracheal tube on the same patient in random sequence. They were evaluated for speed, difficulty, and effectiveness. The mean time to ventilate successfully with the LMA was significantly less than that with the endotracheal tube (38.9 seconds vs 206.1 seconds). The average number of attempts was 1.0 for the LMA and 2.2 for the endotracheal tube. No one failed to place the LMA while ten of 19 (52.6%) failed to successfully perform endotracheal intubation.
An obvious use of the LMA is during cardiac arrest. Some experience in this role suggests it is superior to other techniques in establishing an airway and can be used for tracheal drug delivery but may have a slightly higher incidence of gastric regurgitation than ventilation with a facemask.
The LMA and the Difficult Airway
The LMA fills an important niche in management of the difficult airway. Reports abound of its successful use in patients in whom intubation was impossible. Patients with airway edema and tumors have been resuscitated with the LMA when other techniques, including intubation, have failed. The Difficult Airway Algorithm proposed by the American Society of Anesthesiologists suggests use of the LMA as an alternative to surgical intervention (e.g., cricothyroidotomy) when ventilation and intubation fail.
In addition to the uses mentioned above, the LMA can be useful in guiding blind or fiberoptic placement of a cuffed endotracheal tube. About 90% of the time, a small endotracheal tube will pass blindly into the trachea through the LMA. The size of the tube that can be placed is noted in Table 2. A long tube must be used, and the standard connector must be removed if the LMA is to be removed and the tube left in place. LMAs have also been used to maintain the airway and as a guide for fiberoptic assistance to percutaneous dilational tracheostomy.
Table 2
Size of Tube
LMA Size Fiberoptic Scope Size Maxium Endotracheal Tube Size
1 2.7 mm 3.5 2 3.5 mm 4.5 2 5 4.0 mm 5.0 3 5.0 mm 6.0 cuffed 4 5.0 mm 6.0 cuffed 5 5.0 mm 7.0 cuffed
Concerns with the LMA
There are some concerns related to LMA use. The initial devices were hand made in England, non-disposable, and expensive. They can now be purchased in the United States from Gensia, Inc., 9360 Towne Centre Drive, San Deigo, CA 92121-3030 (800-788-7999). A single LMA costs about $200, and a complete set runs well over $1000. After use, the LMA must be mechanically washed with a mild soap solution and autoclaved at 134°C. The cuff must be completely evacuated or it will rupture during the sterilization process. Glutaraldehyde should not be used as it is quite toxic to the laryngeal mucosa.
LMAs have been resterilized between 100-200 times. If marked discoloration of the mask or failure of the pilot tube and cuff to hold pressure occurs, the tube must be discarded. Shorter life spans occur if the cuff is torn on sharp teeth during use, and under field use the device may be accidentally discarded.
A single-use LMA has recently been introduced. Currently only available in adult sizes3, 4, and 5these devices sell for about $36.00 each. They are made of polyvinylchloride and will not tolerate heat or gas resterilization. The availability of a disposable device makes emergency use more practical. The cost of providing LMAs in peripheral locations is thus more acceptable.
Other than the possibility of regurgitation, sore throat and vocal cord dysfunction have been reported after the use of the LMA. Compared to endotracheal intubation during elective general anesthesia, dysphagia was more common after use of the LMA and was related to the length of surgery, while dysphonia was more frequent following intubation. Most of the reported complications have been self-limited and have resolved over time. Considering the demonstrated life-saving benefits, use of the LMA in emergency situations overrides its potential problems.
References
1. Alexander R, et al. Anesthesia 1993;48(3):231-234.
2. Reinhart DJ, et al. Ann Emerg Med 1994;24(2): 260-263.
3. Anonymous. Anesthesia 1994;49(1):3-7.
4. Dimitriou V, et al. Anesthesiology 1997;86(4): 1011-1012.
5. Martin SE, et al. J Trauma 1997;42(2):333-336.
6. Benumof JL, et al. Anesthesiology 1996;84(3):686-699.
7. Zagnoev M, et al. Anesth Analg 1994;78(4):813-814.
8. Rosenberg MK, et al. Anesth Analg 1996;83(6): 1335-1336.
9. Cros AM, et al. Anesthesiology 1997;86(2):498-500.
10. Rieger A, et al. J Clin Anesth 1997;9(1):42-47.
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