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Difficult Airway Management: The LMA Option
By Michael W. Neft, DNP, MHA, CRNA, CCRN, is an Assistant Professor, Nurse Anesthesia Program, University of Pittsburgh School of Nursing
By Leslie A. Hoffman, PhD, RN is Professor and Chair, Department of Acute/Tertiary Care, University of Pittsburgh School of Nursing, is Associate Editor for Critical Care Alert.
Drs. Neft and Hoffman report no financial relationship to this field of study.
Difficult intubations are usually the result of a difficult airway, sometimes anticipated and sometimes not. The key to being successful with both an anticipated and unanticipated difficult airway is to have a variety of airway management skills that one can rely on. The focus of this essay is on one alternative approach to airway management the laryngeal mask airway (LMA).
When assessing an airway for level of difficulty, multiple anatomic factors should be considered. Primary considerations include the width of the oral opening (at least 3 finger-breadths is optimal) and how easily one can view the tonsillar pillars, uvula, and soft palate. Other considerations include whether the thyromental distance (at least four finger-breadths), hyomental distance (at least three finger-breadths), cervical range of motion (atlanto-occipital 35°), and temporo-mandibular joint motion (should be smooth to palpation without clicking or freezing in one position) are optimal or at least within range. If any of these are a concern, it is wise to have alternative equipment available.
Laryngeal Mask Airways
The LMA was introduced by Brain in 1988 with the goal of replacing the face mask during general anesthesia cases, thus avoiding more invasive methods of airway control.1 The LMA forms an end-to-end seal with the larynx, as opposed to the endotracheal tube, which forms a sleeve-like junction with the trachea.1 It is intended to be placed into the "pocket-like" hypopharynx, with its distal end wedged against the upper esophageal sphincter.2Several issues had to be overcome before the device was ready for use. These modifications, including design features that were intended to prevent epiglottic down-folding, reduce the likelihood of trauma and avoid gastrointestinal (e.g., retching and vomiting) and respiratory (e.g., coughing and bucking) rejection-type reflexes.1
The insertion technique developed for the LMA resembles the swallowing reflex.1 The operator's index finger assists with insertion of the device in a cranio-posterior fashion. The epiglottis and arytenoids are only slightly disturbed by manipulation of the head and neck (this helps to create a space behind the larynx). Tight laryngeal mask deflation is used to form the LMA into a flat, thin wedge-shaped object which helps in placing it correctly on the first attempt. In our experience, it is best to adhere scrupulously to the protocol advocated by Brain for insertion of an LMA. Some practitioners are able to seat the device successfully with variations to his protocol. However, if something unexpected happens, it is more difficult to defend a practice that deviates from the published protocol.
There are several distinct advantages when electing to use an LMA. The hands can be freed for other tasks. It can be used as a bridge to intubation in the case of an unanticipated difficult airway in the operating room, the general hospital, and even in the pre-hospital setting. It serves as a good "rescue device" in the "can't intubate/can't ventilate" patient.3 One potential example of the latter is the morbidly obese patient. Combes et al found that the intubating LMA was easier to insert in obese vs lean patients.4 Additionally, these researchers found that failed blind tracheal intubation attempts and airway adjustment maneuvers were decreased when the intubating LMA was used in obese patients.4 There are several additional advantages. The LMA can be inserted blindly. However, this is also a disadvantage because one cannot see where it is going or whether it is being placed properly. It is a very forgiving device because poor or incorrect use can still result in reasonable function.1 Finally, it does not compromise the function of the larynx as with an endotracheal tube.
There are also several disadvantages to use of an LMA. A patent airway can be compromised if the device is removed before return of protective reflexes, e.g., obstruction or laryngospasm can occur. It does not protect against aspiration. It is inserted blindly which raises the potential of improper positioning. If the patient's anesthetic level is light or the patient begins to regain consciousness after some sort of medical crisis, he or she can experience laryngospasm with the device in place. Laryngospasm can occur because an LMA, unlike an endotracheal tube, is not placed between the vocal cords.
Types of LMA
Multiple types of LMA are currently available, each with specific design advantages. The LMA Classic (cLMA), which is reusable, is the prototype designed by Brain. Two variations are available a cLMA with a flexible arm (LMA Flexible) and a cLMA with a rigid arm bent at a 90° angle. The LMA Flexible has a thin-walled, wire-reinforced, small diameter barrel that allows the LMA Flexible to be manipulated for facial, dental, or ear nose and throat (ENT) procedures, so that the surgical site is relatively unobstructed. The LMA Classic has been further developed into the intubating LMA (also known as the ILMA),3 the ProSeal LMA, the LMA Unique (a disposable version of the LMA Classic),5the Soft-Seal Laryngeal Mask,5 the Fastrach LMA, and the LMA Supreme.5 The ILMA was designed to facilitate blind or fiberoptic-guided intubation.4
Combes et al compared outcomes in 50 morbidly obese and 50 lean patients (mean BMI, 42 kg/m2 and 27 kg/m2, respectively).4 The LMA was successfully inserted and adequate ventilation achieved through the LMA in all 100 patients. Success rates for intubation were similar in the obese and lean groups (96% and 94%, respectively). Notably, the numbers of failed tracheal attempts and airway adjustment maneuvers were significantly reduced in obese patients. They concluded that the ILMA may be an airway rescue device of choice due to the ability to both ventilate and intubate as demonstrated in their study.
The LMA Supreme has four chief advantages over the other types. The first advantage is that its barrel (also known as the air tube) is bent at an anatomic angle (90°), which sometimes decreases the need for the practitioner to put the hands in the patient's mouth. Some practitioners feel that the 90° angle assists in placing the device correctly on the first attempt. The second advantage is the presence of a gastric drainage port. This port allows for the passage of a gastric tube (blindly) that can be attached to suction or it can be used to permit passage of regurgitated gastric contents. The third advantage is the presence of an integral bite block. The fourth advantage is that this device is allows higher seal pressures than the LMA Classic or the LMA Unique.
The ProSeal LMA was also developed by Brain.6 One advantage of this device is that the seal is more effective so that peak airway pressures of 40-60 cm H2O pressure can be used if mechanical ventilation is attempted with the device.2,6 The ability to use increased pressures to ventilate the patient results from the presence of a "second posterior cuff."2 The device also has a bite block built into it and an incorporated gastric drainage tube. The latter characteristic is the ProSeal's main advantage over other LMAs.
The Soft-Seal LM was developed as another alternative to the LMA Classic when only re-usable LMAs were available. Studies demonstrate that the Soft-Seal LM provides an adequate airway and similar clinical performance in spontaneously breathing patients when compared with the LMA Classic.7 The Soft-Seal Laryngeal Mask has decreased permeability to nitrous oxide, a characteristic that acts to decrease the amount of air that enters the cuff with a consequent increase in cuff pressure and, therefore, pressure within the hypopharynx. The Soft-Seal Laryngeal Mask has aperture bars and it is easier to access the larynx with a fiberoptic bronchoscope.
The Fastrach LMA was designed to improve the success of blind intubations through a laryngeal mask. It is especially helpful in "can't intubate/can't ventilate" situations and can also be used with patients who have a known difficult airway. One of its advantages is that control of the airway can be maintained throughout the intubation process. Another advantage is the epiglottic elevating bar in the mask aperture, which elevates the epiglottis as the endotracheal tube is passed through, and a ramp, which directs the tube centrally and anteriorly to reduce the risk of arytenoid trauma or esophageal placement.8 The C-Trach intubation device, a variation of this type of LMA, allows the intubating clinician to see the endotracheal tube pass through the vocal cords via video screen that is attached to the Fastrach.
The clinical situation usually dictates which LMA one chooses. In an emergency, any LMA is usable because ventilation can be achieved with any of them. Otherwise, the following situations would dictate what type of LMA one would use.
The LMA is a versatile instrument that has the distinct advantage of being easy to learn to use. A "can't intubate/can't ventilate" situation often can be easily overcome with an LMA. Because of its utility in emergency situations, it is a versatile device whose insertion technique should be mastered by all who might be expected to manage an airway in a life-threatening crisis.