Laryngeal Mask Airway and the ASA Difficult Airway Algorithm (1996)

(Benumof) Professor of Anesthesia.Received from the Department of Anesthesiology, University of California San Diego Medical Center, San Diego, California. Submitted for publication May 10, 1995. Accepted for publication November 30, 1995.Address reprint requests to Dr. Benumof: Department of Anesthesiology, 8812, University of California, San Diego, 402 Dickinson Street, San Diego, California 92103.Shortly after the introduction of the American Society of Anesthesiologist's (ASA) difficult airway algorithm in 1991, [1,2]the United States Food and Drug Administration allowed the laryngeal mask airway (LMA) to be marketed in the United States, and it was immediately recognized as a major advance in airway management. [3]During these 5 yr, the literature on and the experience with the LMA has substantially increased. As a consequence, the role of the LMA both in the ASA algorithm on management of the difficult airway and in the management of the difficult airway in general has become more clearly defined. The most important understanding to emerge during this 5-yr period is that the LMA has worked well, with few complications, as a ventilatory device in patients whose tracheas cannot be intubated and/or whose lungs cannot be ventilated with conventional techniques, provided they do not have obvious periglottic pathology (massive cancer, hematoma, abscess, anaphylactic laryngeal edema). This article will sequentially, briefly review the original ASA difficult airway algorithm from a 1995 perspective, discuss the ways the LMA can be used, and conclude with a description of the multiple uses for the LMA within the ASA difficult airway algorithm. It must be noted that the ASA difficult airway algorithm can be changed only by a formal vote of approval by the House of Delegates of the ASA. Finally, it should be noted that a significant amount of the published information on the LMA is anecdotal, rather than from controlled clinical trials.(Figure 1) is a combination of two previous ways of depicting the ASA difficult airway algorithm, [1,2]i.e., the figure incorporates all previously approved ideas/concepts into one flow diagram. The algorithm begins with preoperative evaluation and recognition of the difficult airway. If a difficult airway is recognized, then it is logical to secure/guarantee the airway with awake tracheal intubation. For awake tracheal intubation to succeed, it is essential to prepare the patient properly. Once the patient is properly prepared, any one of a number of intubation techniques can achieve tracheal intubation (Figure 1), and the practitioner should make the choice based on their particular training, experience, and knowledge. Occasionally, awake tracheal intubation may fail because of lack of patient cooperation or equipment and/or operator limitations. Depending on the precise cause of failure of awake tracheal intubation, options include:(1) cancellation of surgery (patient may need further counseling regarding their degree of cooperation, different equipment/personnel obtained);(2) general anesthesia, if mask ventilation is considered likely to be easy;(3) regional anesthesia, if inadequate block can be followed by abrupt termination of surgery or awake tracheal intubation if necessary; and (4) creation of surgical airway, if surgery cannot be postponed and general anesthesia without endotracheal intubation is inappropriate. Rarely, creation of a surgical airway with the patient awake is the best first intubation choice (laryngeal/tracheal disruption, upper airway abscess, some mandibular-maxillary fractures).It is appropriate to attempt tracheal intubation after the induction of general anesthesia when a difficult airway is not recognized or a difficult airway is recognized but the patient is uncooperative and vigorously refuses awake tracheal intubation. With induction of general anesthesia in an uncooperative patient with a recognized difficult airway, one should consider the relative merits of preservation of spontaneous ventilation versus the use of muscle relaxants. In an elective case, positive-pressure ventilation via mask ordinarily will be employed before tracheal intubation, whereas in an emergency case with gastric contents present, positive-pressure ventilation via mask ordinarily will not be used before tracheal intubation. Tracheal intubation can be accomplished by any one of a number of choices. If a given intubation choice should fail, gas exchange should be controlled via mask ventilation. If the initial intubation choice was conventional laryngoscopy, the laryngoscopist should have a good idea of the degree of difficulty of laryngoscopy/intubation and should quickly (next attempt) make an optimal/best attempt at laryngoscopy. [4]Best attempt at laryngoscopy may be defined as being performed by an experienced endoscopist, with the patient in the optimal position, using optimal external laryngeal manipulation, and perhaps a single change in each of laryngoscope blade type and size. [4,5]If conventional laryngoscopy fails after a best attempt, there are acceptable alternative approaches that do not require use of a conventional laryngoscope (Figure 1). Repeated conventional laryngoscopy can cause laryngeal trauma (edema, bleeding), which may result in the loss of the ability to ventilate via mask. A best attempt at ventilation via a conventional mask, defined as a two-person effort using appropriately sized oropharyngeal and nasopharyngeal airways, should be made before abandoning mask ventilation.If the ability to ventilate via mask is lost, and it already has been demonstrated that the trachea cannot be intubated, a true emergency exists, and gas exchange must be restored immediately. The four acceptable responses to the "cannot ventilate, cannot intubate" situation are insertion of an LMA, [3,6]insertion of a Combitube, [7],* institution of transtracheal jet ventilation, [8]and creation of a surgical airway (if personnel, equipment, lighting, and positioning are appropriate). Finally, those caring for the patient must guarantee communication of this difficult airway experience to future care-takers. [9].The LMA may be used to provide a routine airway for use during general anesthesia or, less frequently, as a conduit for tracheal intubation. Before describing the multiple places that these two uses of the LMA have in the ASA difficult airway algorithm, it is appropriate to briefly review these independent functions of the LMA.Provided the depth of anesthesia is appropriate and adequate, the LMA makes a routine airway during general anesthesia in 95–100% of patients in which LMA use is deemed appropriate. [10]Compared with ventilation via mask, the LMA has been found to be a superior device during three widely different settings/conditions (routine outpatient procedures not requiring intubation, [11]neonatal resuscitation, [12]use by inexperienced personnel [13]). First and, from the perspective of user frequency, most importantly, a randomized prospective study compared the quality of the airway with the LMA with that of a standard face mask/oropharyngeal airway system. [11]Smith and White found that problems associated with airway management (difficulties in maintaining an airway and SpO2< 95%) were more common in patients in the face mask group than in the LMA group. Certainly one can expect the LMA to be superior to a face mask if the facial contours of the patient are not suited to the standard mask, [14]such as the edentulous patient with invaginated cheeks. [15]Other advantages of the LMA are related to the fact the mandible does not need to be supported, and therefore, the anesthesiologist's hands are not occupied, fatigue is less likely, and remote observation is possible. Many authors have found that the stimulation related to insertion of the LMA is approximately the same as that for an oropharyngeal airway. [6]In addition, the LMA has some advantages over a tracheal tube as a routine airway; these include rapid insertion in the hands of both anesthesiologists and nonanesthesiologists and less in situ stimulation. [6].Second, although the American Heart Association recommends that positive pressure, when indicated, be administered by bag-and-mask, [16]this can be difficult to do effectively in small neonates, [17]even for anesthesiologists. In a recent study, in all of 21 newborn infants weighing 3.4+/-0.6 kg (mean+/-SD) who required resuscitation, trained neonatologists were able to easily insert a size-1 LMA in < 12 s on the first attempt and obtain a clinically patent airway with LMA leak and peak airway pressures of 22 and 37 cm H2O, respectively. [12]All resuscitations were successful, and there were no complications related to the use of the LMA. [12]Although the LMA was not directly compared with bag-and-mask ventilation, these results are impressive. The authors commented that a randomized prospective study is underway to determine whether these good airway results with the LMA can be obtained by other medical personnel performing neonatal resuscitation. [12].Third, nursing personnel who had a 30-min instructional course with the LMA and face mask and some practice on a mannequin could achieve larger tidal volumes (435 ml, range 385–485 ml) in patients with the LMA compared to anesthesiologists (328 ml, range 277–378 ml) or nurses using a face mask (239 ml, range 170–309 ml). [13]Thus, when ventilation via mask is appropriate, inexperienced operators appear to have better ventilation capability with the LMA than with a face mask.One of the reasons the LMA works well as a routine airway is that exact positioning is not crucial for a clinically acceptable/patent airway. The usual fit of the LMA around the larynx, as assessed by using flexible fiberoptic endoscopy, [18–20]radiologic investigation, [21]and nuclear magnetic resonance imaging, [22]is variable. One definition of appropriate position of the LMA consists of the epiglottis and esophagus outside and the laryngeal opening within the rim of the LMA and is obtained only 45–60% of the time. [18–22]When the epiglottis is within the proximal rim of the LMA, the tip of the epiglottis is slightly downfolded toward the larynx 50–90% of the time, and the lateral aryepiglottic folds are infolded toward the larynx half the time. [18–22]The slight downfolding means that the proximal anterior surface and tip of the epiglottis are against the upper half of the aperture bars, which is, in essence, close to the normal anatomic position. Consequently, visualization of the epiglottis against the aperture bars (e.g., fiberoptically) causes a partial obstruction to the laryngeal view but not necessarily to gas flow. It is not surprising that, in 94–99% of adult [18,23]and pediatric patients, [19,20,24–27]there is no difficulty with ventilation, and the airway is ultimately judged to be clinically acceptable (although proper position may require two insertion attempts; see below). In fact, there are reports in which x-rays revealed the mask to be in the oral cavity or bending completely backward, neither of which had been detected clinically. [28,29]Finally, the distal rim of the LMA usually is wedged in the hypopharynx, but in 0–7% of cases, the esophagus may be seen inside the distal rim, and in some cases, the distal rim may be directly opposite the glottis. [30–32].The use of the LMA for routine airway management can be associated with a number of problems. These problems consist of clinically unacceptable nonpatent airway, the requirement for multiple insertion attempts in a small percentage of patients, aspiration of gastric contents, and suboptimal positive-pressure ventilation. The exact incidence of each of these problems, to some extent, must depend on insertion technique and skill. [33]Inadequate anesthesia may cause all of these problems, and therefore, a basic requirement for the safe use of the LMA is an adequate depth of anesthesia. [10]The most serious problem is that, in 0.4–6% of anatomically normal patients, placement of the LMA is clinically inadequate because of backfolding of the distal cuff, occlusion of the glottis by the distal cuff, complete backfolding of the epiglottis, or 90–180 degrees C rotation of the mask around the long axis. [11,18,19,23–27,34,35]The results of the report with a 6% incidence of a wholly inadequate airway with the LMA may have been related to the fact that the anesthesiologists participating in the study were second- and third-year residents [11]and thus somewhat inexperienced.The most common causes of poor LMA placement are inadequate anesthesia/relaxation (pharyngeal muscle and/or laryngeal spasm), [10]failure to negotiate the 90 degrees turn from the posterior pharynx to the hypopharynx, and choice of wrong LMA size. In 2–33% of LMA placements, more than one attempt is required, whether by residents or experienced practitioners, adult or pediatric patients. [11,22–29,34,36]Correct placement may be more difficult in patients with a small mouth, a large tongue and/or tonsils, and a posteriorly placed larynx (blocks the advancement of the tip of the LMA into the hypopharynx). Obviously, in view of these placement considerations, the use of the LMA is relatively contraindicated in patients with major local pathology in the pharynx and larynx such as tumor, abscess, edema, and/or hematoma.For two reasons, the LMA is also relatively contraindicated as a routine airway in patients who have a risk of regurgitation and/or active vomiting of gastric contents or have a large amount of blood present in the upper airway. First, the LMA does not provide an airtight seal around the larynx (usual pop-off pressures are 15–20 cm H2O), and therefore, the larynx/trachea may communicate with a fluid-filled pharynx and esophagus. Second, as described above, in 0–7% of patients, the esophagus is included within the rim of the LMA, [30–32]and in these instances, the esophagus may be directly exposed to positive-pressure ventilation. Thus, it is not surprising that studies using gastrointestinal tracers have found a large (up to 25%) but variable incidence of patients with gastrointestinal tracer within the LMA. [31,37,38]The variability in findings probably is related to a variable depth of anesthesia and/or intensity of surgical and, therefore, in and muscle of clinically obvious and serious vomiting and aspiration have been were to be associated with inadequate anesthesia two with change in position the These few cases, from two large prospective an incidence of aspiration of with the LMA in is to that found for elective anesthesia outpatient anesthesia using the face mask or tracheal tube of gastric have been incidence of aspiration with the LMA has been to and found to be to that for outpatient anesthesia with the face mask and tracheal general of aspiration risk with the LMA has been usual LMA is 15–20 cm In and patients whose lungs were being ventilated via an LMA, peak pressures of and cm leak of not to from to and of to from to the LMA is relatively contraindicated it is that positive proximal airway pressures cm will be required to ventilate the lungs or of and/or airway because the LMA may become or may at any time, the LMA is relatively contraindicated as the ventilatory device tracheal intubation cannot be accomplished (e.g., when the patient is when the of the is from the or when the for difficult intubation is the must be used to from the LMA against the risk of this relative are reports to the of using the LMA as an airway for the of an endotracheal tube or an tracheal or for the of a flexible fiberoptic may be over the or fiberoptic view of the LMA usually around the larynx, it is obvious that, when the LMA has a position of the time, see any of the has some of It is likely that the the degree of of the LMA over the larynx, the less the of of intubation. In addition, the insertion of a an already LMA may result in tracheal intubation is an LMA in a large of patients to have normal there is a failure on the first attempt and a failure with an there is an failure with an the may with change in and from the position to degrees of and use of further the of an the LMA into the trachea for two First, when is before the LMA is the the tip of the LMA from the of the both the and and of the and in with pressure, the LMA may be wedged in the hypopharynx, but it can only the cm of the the and is cm more proximal than obstruction to the of the LMA by perhaps by or of see may has in widely variable in the LMA from a of of of the LMA, the more proximal than of the LMA should further the of intubation the the into and of the of an LMA in a by the of causes the of the laryngeal aperture to approximately degrees around the of the LMA distal (Figure likely that it be more difficult for a device to an aperture that is in a degrees the to the insertion than an aperture that is in the to the insertion to the trachea with an or of which are may result in periglottic In to a LMA may be and in the of of an the LMA is in most may be over the and the of the and LMA and a may be over the and the of the LMA. If a larger is the LMA and the or may be for a larger over a jet the that fit all LMA and the that fit these If a or is used with the or the lungs can be ventilated around the but within the by the the of a the distal and proximal of the are to the and ventilatory (Figure With a the for ventilation around the to a are three problems with an over an the of the LMA. First, in patients with a long the of the be or the the of the of LMA to the of the with the and the these two the the tip of the the of the With the and and the the tip of the only and in a normal sized the cannot be in the trachea more than cm of to tip is approximately 5 These with the that the the of the LMA and the is cm in and cm in the of the of the LMA the of the that can be the LMA. In some who require large tidal a may not of flow adequate for ventilation (e.g., those with A change to a use of a tube which and a but long does not for of the LMA over the without for these three problems to which of the three problems they and to the of the patient the of the LMA and the With to a standard inside a LMA, one that all three problems is to change the and LMA for a larger by using a tube is insertion of the LMA into the patient with the into the LMA that the tip of the is the aperture bars (Figure of an a the and the of the LMA into the trachea may ventilate around the or but within the of the and of the over the into the trachea the of the is against the of the LMA (Figure the insert the tube into the to the appropriate both the and the LMA over the tube insert the larger over the to the and the tube from the larger The to this is that a tube has and of larger to the tube into the from jet for the three problems associated with a standard inside a LMA is to use a LMA LMA, of which of a larger and, with the LMA, of the LMA. of these two of the LMA are to the problem of a long standard in situ is to use the This insertion of the of the tube but does not the problems of an in situ tube or of the LMA over this and the long is not to the problem of a long standard in situ is to the of the LMA and advance the LMA and The LMA will approximately cm of depth but does not of the other two to the standard LMA combination is to the proximal of the with a long as a can be used as a tube after into the This technique from the same of a standard tube and these are not for the problem of the LMA from a is to the by without the to of the or by the tip of an that has an less than the of the into the proximal of the is to a the of the into the both the and the LMA, and the over the the small outside and of the can it as an the that has been the LMA is of adequate there is no or to the LMA and there is to the LMA in the of the case, the patient may be of the the LMA in This two important First, on a well upper airway device is already in Second, a for is immediately if If this airway management is used may the of the LMA should be the is in the laryngeal mask airway, as a ventilatory device and/or can be placed into the ASA difficult airway algorithm in places (Figure with on the awake intubation of the algorithm as a conduit for fiberoptic tracheal intubation, on the of the as a ventilatory by which to do the case or as a conduit for fiberoptic tracheal intubation, and (4) on the emergency as both a ventilatory device and as a conduit for fiberoptic tracheal are of using the LMA in properly awake patients as a conduit for fiberoptic intubation (Figure technique is when the preoperative evaluation the patient should be intubated awake for First, awake tracheal intubation can be performed by techniques in a properly awake the of conventional laryngoscopy and insertion of an LMA is a relatively that results in relative lack of stimulation in an LMA the amount of that an awake patient The of the insertion of the LMA. the LMA is in good position, the of the LMA is usually well toward the larynx, and visualization of the laryngeal aperture with an is and perhaps most importantly, with the patient no options are and risk if there is difficulty in the LMA or the placement of the LMA into an awake patient also the LMA to be used as a means of airway in patients whose are difficult but who do not require endotracheal intubation. The of the is by of failure to and ventilate the LMA after the induction of general anesthesia in patients with difficult a patient general anesthesia who cannot be intubated but whose lungs can be ventilated via mask, one of the options in the ASA difficult airway algorithm is to provide anesthesia via mask. these the LMA is an alternative to mask ventilation. First, the LMA may provide a better airway, with to ventilation and than a conventional mask and oropharyngeal airway system. use of the LMA the anesthesiologist's hands for other the LMA will provide a conduit for fiberoptic intubation of use of the LMA as a ventilatory device during in patients whose trachea could not be intubated are a patient patent an adult patient to the is a patient in must be may with placement of the LMA. the patient who can be ventilated via conventional mask is placement of the LMA have and vomiting and alternative of maintaining in a patient at risk for aspiration and failure to properly insert the LMA during is to as the distal tip of the LMA the this the of LMA placement risk of Once the LMA is in it probably does not with the of LMA works as well as a conduit for tracheal intubation (Figure in the patient as it does in the awake patient because the LMA of the tongue to the which is the other airway intubation as the and do not well in patients. As in the awake use of an as an will guarantee a degree of the and the of the LMA are usually well toward the laryngeal the intubation usually less than s in and patients. The same and and positioning an LMA in the of the LMA works well as a routine device in most patients, those with a or and/or a or is not surprising that the LMA has been found to be a emergency device in patients whose lungs could not be ventilated using a and conventional mask and whose trachea could not be patients include patients emergency patients with a other adult patients. all of these patients, there was no or periglottic pathology hematoma, obstruction to mask ventilation was (e.g., and difficulty with intubation was to (e.g., failure to the and laryngeal have been no reports of failure to or ventilate the LMA in patients in a "cannot ventilate, cannot intubate" it is that this a Consequently, in such a insertion of the LMA is a to quickly when local pathology in the pharynx or larynx a of proper placement and/or gas The reasons the LMA is a first choice over transtracheal jet ventilation in the situation are that the of anesthesiologists are with the LMA and the LMA is and, compared to transtracheal jet ventilation, has less trauma As the LMA should be a "cannot ventilate, cannot intubate" situation may In the United of anesthesiologists using the LMA as the first for the "cannot ventilate, cannot intubate" insertion of the LMA does not gas exchange transtracheal jet ventilation should be immediately or a surgical airway immediately the LMA does some gas a of airway should be obtained as quickly as spontaneous ventilation, tracheal intubation surgical because of the risk of aspiration as well as the need for positive-pressure ventilation.If gas exchange is obtained by insertion of the LMA in a "cannot ventilate, cannot intubate" has been obtained to use the LMA as a conduit for tracheal intubation. The of the LMA as a conduit for tracheal intubation after a "cannot ventilate, cannot intubate" situation is the same as that after a "cannot can situation If adequate ventilation is the LMA, it is that the of the LMA the larynx and tracheal intubation will be Many of the patients in were intubated the LMA. Thus, if the conventional intubation difficulty was to and not periglottic pathology and one can ventilate the LMA, the LMA makes an conduit to the If ventilation is poor after LMA because the LMA is not well with the laryngeal or there is major periglottic tracheal intubation may be If ventilation is poor after LMA insertion because the patient has airway and tracheal intubation likely will be ASA difficult airway algorithm has been to and used by the anesthesia for approximately 5 and to be well as by published The algorithm awake intubation if difficulty with the airway is recognized, the patient serious difficulty is after the induction of general anesthesia, and an in and techniques to be employed based on the training, and experience of the The laryngeal mask airway has two major as a routine airway during general anesthesia and as a conduit for tracheal intubation. As the laryngeal mask airway into the ASA difficult airway algorithm in as a conduit for fiberoptic tracheal intubation in the awake and the patient who cannot be intubated ventilation may or may not be and as both a and an emergency airway in the With multiple uses and multiple places of the laryngeal mask airway is an important within the ASA difficult airway algorithm. importantly, the clinical of LMA use in "cannot ventilate, cannot intubate" has been and in patients whose lungs cannot be ventilated because of obstruction and whose trachea cannot be intubated to not periglottic the LMA should be immediately and considered as the first is a (pharyngeal and or If the tube in the esophagus it does the of the the lungs can be ventilated via the in the the two If the tube in the the lungs can be ventilated via the