Clinical communication
Difficult airway management in the emergency department

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Abstract

Most airway management in the emergency department is straightforward and readily accomplished by the emergency physician. The exact incidence of difficult intubations is difficult to discern from available evidence, but these are probably more frequent in the Emergency Department than in the operating room, given the urgent nature of the procedure and the lack of preparation of the patient population. A variety of adjuncts for airway management are available to assist in both intubation and ventilation. The utility of these adjuncts is detailed in this review, with emphasis on techniques most useful to the emergency physician.

Introduction

Emergency physicians are frequently required to provide timely, definitive airway management in acutely ill patients. As the specialty has emerged and then matured over the last two and a half decades, practitioners of Emergency Medicine have become increasingly proficient in this skill, and have modified their approaches to airway management significantly, relying less and less on assistance from other medical specialists (1). Residency training in Emergency Medicine, however, provides little training in the nonsurgical approach to the difficult airway (2). Emergency physicians are expected to emerge from residency with competence in the surgical management of the airway, but with improved intubation rates have come reduced opportunity for cricothyrotomy (3). Because patients presenting with difficult airways are uncommon but not rare, and because the very nature of emergency practice may predispose to difficulties with airway management, it behooves the emergency physician to become familiar with a range of airway-management techniques, including direct laryngoscopy with rapid sequence intubation (RSI), alternatives to laryngoscopy for intubation, rescue ventilation techniques, and surgical approaches to the airway. This review will concentrate upon recognition of the difficult airway, preparation for managing the difficult airway, and the various adjuncts available to facilitate intubation and ventilation in this setting.

The term “difficult airway” defies simple definition. It may be construed to mean difficult laryngoscopy, difficult mask ventilation, difficult endotracheal tube placement, or the failure to intubate or ventilate. Some of these ideas have been expressed quantitatively: difficult mask ventilation is defined by the American Society of Anesthesiology as the inability of a trained anesthetist to maintain the oxygen saturation above 90% by using face-mask ventilation (when the initial saturation was in the normal range) whereas difficult intubation is defined as an inability to place an endotracheal tube within 10 min or three attempts (4).

Difficult intubation usually corresponds to poor glottic visualization during direct laryngoscopy, or a high-grade laryngeal view with no ability to see the vocal cords or the glottic aperture (Figure 1) (5). Cormack and Lehane, in a paper that described the likelihood of difficult intubation in obstetrics, proposed a classification scheme for views of the laryngeal inlet obtained at laryngoscopy (5). This four-grade scheme has become the standard measurement of glottic views, and facilitates communication between researcher and practitioners as to the impact of the view obtained on the success of tracheal tube placement. Grade 1 corresponds to a view of all or most of the glottis; Grade 2 to a view in which only the posterior portion of the glottis is visible; Grade 3 to visualization of only the epiglottis; and grade 4 to inability to see the glottis or epiglottis at all (5). The authors maintain that Grade 3 and 4 views are rare and likely to be difficult to manage, whereas grades 1 and 2 are quite common and easily managed by the practicing anesthesiologist.

Difficulty with glottic exposure at direct laryngoscopy also can be quantitated by the “Percent of Glottic Opening (POGO)” score, which corresponds to the proportion of the opening that can be visualized (6). In addition, Adnet et al. have more recently proposed an intubation difficulty scale, which they then validated prospectively in 626 patients, and which corresponds well to the time required for intubation and a visual analog scale assessment of procedural difficulty by intubators (7).

Predicting which patients will present challenging or impossible ventilation, laryngoscopy, or intubation is troublesome and most assessments lack accuracy. False-positive and false-negative predictions are inevitable. However, some predictors have proven consistently useful, and combinations of predictors even more so. Perhaps the most utilized predictive scheme for airway assessment in anesthesiology is the Mallampati classification, which assigns three gradations of increasing difficulty in visualizing the posterior pharyngeal structures in order to predict difficult laryngeal exposure (8). The Samsoon and Young modification breaks this assessment into four classes, the highest grade divided into those whose soft palate can be seen and those whose cannot (Figure 2) (9). These predictive tools evaluate the size of the tongue, which must be displaced in order to view the glottis, relative to the oropharynx. In one study, 14 of 15 patients whose airway assessment fell into the Mallampati Class 3 were determined to have a poor laryngoscopic grade at direct laryngoscopy (10).

Many other airway assessment schemes have been proposed and evaluated, including evaluation of the jaw size, thyromental distance, and cervical range of motion 11, 12, 13, 14. Each of these has limited sensitivity and specificity, and most anesthesiologists combine an assessment of the Mallampati class, mouth opening, cervical range of motion, and thyromental distance to comprise a multifactorial approach to predicting difficulty in direct laryngoscopy. This approach successfully predicts difficulty in nearly all instances 15, 16. A simple “Rule of Three’s” also can be applied: If one can place three fingerbreadths between the teeth, between the mandibular genu and the hyoid bone, and between the thyroid cartilage and the sternal notch in neutral position, direct laryngoscopy probably will be successful (15). Recent evidence suggests that difficult bag-valve-mask (BVM) ventilation may be more frequent than previously thought (17). Langeron found that ∼5% of 1502 patients were difficult to ventilate by BVM under general anesthesia (SaO2 fell below 92% or unable to obtain evidence of effective ventilation) but this situation was anticipated in less than one fifth of these cases. Body mass index, advancing age, presence of a beard, lack of teeth, and a history of snoring all predicted difficult ventilation by BVM.

Unfortunately, these assessment tools have been derived from studies in which cooperative, composed patients are examined by anesthesiologists on preoperative rounds rather than by emergency physicians evaluating patients in extremis. The utility of these tools in the Emergency Department (ED) setting has not been demonstrated. Nevertheless, an appreciation of mouth opening, cervical mobility, thyromental distance, and tongue size can be rapidly gained and may help the emergency physician avoid a disastrous sequence of events when difficulty is likely.

Much had been done to document the occurrence of difficult airways in the perioperative setting. Grade 3 laryngoscopy, requiring multiple attempts at intubation, occurs in 1–4% among all types of patients, but was estimated to occur in only 1 of 2000 obstetric patients, who have relatively normal necks and cervical mobility 5, 11, 18, 19. Inability to intubate due to severe Grade 3 or Grade 4 laryngoscopic views is present in only 0.05–0.35% of operating room (OR) cases, but again appears to be more rare among those with normal cervical mobility 5, 9, 18, 20. Difficult mask ventilation occurs ∼5% of the time, as outlined above (17). Fortunately, inability to ventilate combined with inability to intubate is very rare in the OR, comprising less than 2 in 10,000 cases 13, 21. Mild difficulty with intubation requiring a change of blades or operators is fairly common, reportedly occurring in 1–18% of intubations in the OR 21, 22, 23.

Management of the difficult airway in the ED has not been as well studied as that in the OR. Indeed, it is necessary to extrapolate from descriptive studies of airway management in the ED, in which significant portions of the population under study are excluded from the investigation for various reasons. Sakles et al., describe 610 patients undergoing intubation in an urban ED over 1 year, 84% of these were rapid sequence intubations (RSI) with a 99% success rate, and 1% required cricothyrotomy (25). Five percent of patients initially received an esophageal intubation; we can surmise, then, that ∼6% of these patients had a difficult airway. Overall, 5% required three or more attempts at direct laryngoscopy, and these could perhaps be added to the other 6% (if we presume no overlap between these and the patients having an esophageal tube), and thus some difficulty in intubation would range between 6% and 11%. However, some 16% of patients were deemed unfit for RSI, and the reasons for this are not apparent in all cases.

In the study of Tayal et al., the proportion of difficult airways among patients intubated is also somewhat obscure (26). Thirty percent of patients who were intubated were not included in the analysis because they did not meet the investigators’ requirement for eligibility for RSI. Again, 1% required cricothyrotomy. Thus, the actual incidence of difficult airways lies somewhere between the extremes of 1% and 30%. Even if we choose the lower figure, difficult airways in the ED population will not be considered rare, and they are probably much more commonly encountered in this setting than in the OR.

More recently, a multicenter study of ED airway management has been conducted (27). This investigation, a prospective, observational study of almost 6300 cases, comprises the most comprehensive data regarding emergency physician practices in management of the airway. In a query of the National Emergency Airway Registry data, Li reported esophageal intubation in ∼4% of cases, though only a small fraction of these were not immediately recognized (28). Rapid sequence intubation was the predominant method used to provide airways in this population, with over 98% success in over 4400 patients. Other methods included oral intubation with sedation only, oral intubation with no medications, and blind nasal intubation, all of which were significantly less successful techniques than RSI in securing the airway. Thus, RSI appears to be the most frequently used and most successful means of intubating the trachea in Emergency Medicine.

As noted above, the very nature of emergency practice may contribute to difficulties in airway management not encountered in more elective settings. The inability to ask the patient if he or she has encountered prior airway problems (including surgery or adverse anesthesia occurrences) due to confusion, extremis, or obtundation is common. Further, having the patient adopt a sitting position while examining the pharynx, thyromental distance, and cervical range of motion is frequently impossible due to the acute nature of the patient’s illness or the impracticality of adopting such positions. The presumption of a “full stomach” in all patients intubated emergently dictates the use of the RSI technique. The imposition of cricoid pressure and laryngoscopy at the earliest possible moment place increased demands upon the physician preparing to intubate the patient (29). The trauma patient places even more obstacles to intubation in the path of the emergency physician. Facial distortion, secretions, swelling, mandibular injury, and potential cervical spine injury all combine to make these patients among the most challenging airway-management problems (30). Cervical collars and in-line immobilization impact glottic exposure adversely, and up to 20% of these patients may have a Grade 3 or Grade 4 laryngoscopic view (31).

In summary, the difficult airway can be defined in different ways, and its exact incidence in the ED is not clearly delineated. Poor laryngoscopic grade is apparently more common in the ED population than in patients presenting for elective surgery, given the frequency of multiple attempts at intubation and esophageal intubation cited in the studies above. Nevertheless, failure to secure the airway by nonsurgical means is quite infrequent in the ED, on the order of 1% of cases.

In many cases, difficulty with glottic exposure may be predicted from even a cursory examination of the patient. In others, it is only apparent after a hypnotic and relaxant have been administered, during attempted direct laryngoscopy. This situation may quickly lead to multiple attempts to secure the airway, supraglottic swelling and bleeding, deterioration of ventilation, and hypoxemia with potential morbidity 32, 33, 34. Because of the potential for injury and mortality when airway disasters occur, the American Society of Anesthesiology (ASA) developed the ASA Difficult Airway Algorithm, which was introduced to the anesthesia community in 1993 (Figure 3) (4). Since its implementation in the United States, morbidity, mortality, and claims related to airway mismanagement in the OR have fallen significantly (35).

Unfortunately, the ASA algorithm has a number of characteristics that prevent direct application to the practice of Emergency Medicine, because of dissimilarities in airway management in the OR and the ED (Table 1). All airway management in the ED is urgent or emergent, often depriving the physician of the time necessary to evaluate the patient and plan this lifesaving intervention. Furthermore, each patient is presumed to have a full stomach in the ED, and therefore must undergo RSI, with its attendant time pressure and requirement for cricoid pressure, which may distort the view of the glottis. As noted above, the trauma patient presents unusual demands for airway management, including potential facial, cervical, and airway injury, and cervical immobilization during intubation. In the ED, intubation is conducted on the basis of patient need, whether for airway patency and protection or acute respiratory failure, whereas in the OR, patients are usually intubated to guarantee airway protection and ventilation during a reversible, pharmacologically maintained unconscious state. This leads to a strong emphasis in the ASA algorithm on preserving the option of reemergence from anesthesia to resume spontaneous ventilation if difficulty is encountered (4). This approach is often impossible in Emergency Medicine because the patients’ pathology dictates that a definitive airway be obtained by whatever means possible. Finally, the orientation toward the surgical airway is different among anesthesiologists and emergency physicians, as the latter generally have more training in provision of cricothyrotomy (36).

Can emergency physicians benefit from an algorithm similar to that of the ASA for management of the difficult airway? Perhaps. Walls, in his text on airway management in the ED, recommends the use of a “Universal Algorithm” for emergent provision of the airway, along with several more specific algorithms for consideration in specific circumstances (“difficult airway algorithm,” “crash airway algorithm,” “failed airway algorithm”) (37). Although these guidelines lack prospective validation, they represent a more appropriate application of principles and constraints to airway management in the ED setting.

Aside from the emergency surgical airway achieved by open or percutaneous cricothyrotomy, which has been effectively used by emergency physicians for difficult airway management for more than two decades, there is a broad array of adjuncts to assist with ventilation or intubation (34). When the patient can be ventilated by BVM, but not intubated, these adjuncts may be employed to facilitate placement of an endotracheal tube. Some of these techniques are minor modifications of direct laryngoscopy. There are noninvasive and invasive techniques, blind techniques, and those involving direct visualization. Some are effective for unforgiving anatomy, but less so for glottic or supraglottic pathology. A discussion of the various adjuncts, procedures, and devices follows, with particular emphasis on those most appropriate for the emergency practitioner. It is of paramount importance, however, that when ventilation by BVM fails after inability to intubate the trachea, one makes immediate preparations for provision of a surgical airway or transtracheal jet ventilation, because hypoxemia will rapidly occur 34, 37, 38.

A large variety of retraction blades for laryngoscopy are available. Although many variations of the curved and straight blade exist, the Miller and MacIntosh blades, introduced about 50 years ago, remain pre-eminent 39, 40. Conventionally, the straight blade is inserted beneath the epiglottis and used to directly expose the glottis, whereas the curved blade fits into the vallecula, pulling on the hypoepiglottic ligament as it is lifted, to flip the epiglottis out of the way, allowing the operator to see the exposed glottis. Certain situations, such as a very “deep” glottis, or protuberant “buck” teeth, seem to favor use of the straight blade (41). Some variants of the Miller blade, such as the Phillips blade, have a higher vertical profile, answering one of the deficiencies of this type of blade: excellent visualization but inadequate space for endotracheal tube insertion (42). Other varieties of laryngoscope blade that may prove useful in unusual situations include angled blades, blades with no vertical flange, and blades with mirrors (Table 2) 39, 40, 42, 43, 44, 45, 46, 47, 48. Most of these are rarely used in clinical practice.

Of recent interest is a blade that can incorporate a prism for refraction, to improve the operator’s view of the larynx, and that also may be used without the prism for conventional laryngoscopy (45). Deemed the Belscope, it is a straight blade with a 45° angulation at its midpoint, and is available in three sizes. This blade has been studied extensively by its originator, for whom it is named, and applied successfully to normal anatomy and difficult airways (49). The McCoy laryngoscope blade is an articulating blade that allows one to lift the distal tip of the blade to improve the view of the glottis if the epiglottis impedes visibility (47). This blade has been compared in several studies to the standard MacIntosh blade, and can improve the laryngoscopic grade significantly, but does not do so consistently 50, 51. A double-angled laryngoscope blade has been developed that combines features of both the straight and curved laryngoscope blade (46). Its utility remains unproven. Lastly, the “Improved View MacIntosh” blade allows an enhanced view of the larynx, due to a concavity in the flat portion of the blade (48).

Aids to direct laryngoscopy include prisms, mirrors, and bougies, or Eschmann stylets. Initial use of the optical prism dates to the early 20th century, but little development of the technique occurred until the late 1960s, when Huffman described a prism made from Plexiglas for attachment to the vertical flange of the standard MacIntosh blade, which provides 20° of refraction (52). This helped the laryngoscopist gain a view of the glottis when a grade 3 or grade 4 view was present, facilitating intubation. These prisms are available today at low cost and are easy to use, although fogging can be troublesome unless the device is warmed before use, and the prism reduces the room for manipulation of the endotrachael tube (ETT).

Mirrors have been used to facilitate ETT placement when the glottis is difficult to visualize. These include blades with an integral mirror that provide an inverted view of the glottis, such as the Siker blade (43). The Neustein blade involves a mirrored attachment to the MacIntosh balde that includes a guide channel for a stylet, over which the ETT is passed after the blade is removed (53). Both of these devices result in an inverted image as viewed by the laryngoscopist, with some degree of initial unfamiliarity making their use cumbersome. Neither is frequently used in clinical practice.

At times, it is beneficial to insert a guiding catheter, or bougie, into the glottis, then slide an ETT over it. The device thus provides a means to intubate blindly during direct laryngoscopy, when the glottis is not well visualized 54, 55, 56. The malleable Eschmann stylet, with its stiff, angulated end, lends itself to this task because it is small enough to be maneuverable in the pharynx, where it is used to “probe” for the glottic opening, and its end is firm enough to rattle against the tracheal rings as it is placed in the trachea, providing the intubator a sense of correct placement (Figure 4). It is frequently used for difficult airway management in the ED in the U.K. (57).

Little comparative data exist to support the use of the Eschmann stylet in preference to other means of managing the airway in the ED, but numerous case reports and case series attest to its value in difficult intubation in the OR, and more recently in emergency practice 54, 55, 56. Interest in this low-cost, simple device appears to be increasing among emergency physicians. Moscati reported the efficacy of this device in three cases in the ED in which the glottic inlet could not be visualized and intubation by direct laryngoscopy had repeatedly failed (58).

The recently introduced Frova intubating stylet (Cook Critical Care, Bloomington, IN, USA) similarly allows blind intubation and passage of an ETT over the device, but is hollow and has an adaptor allowing jet ventilation or oxygen insufflation during the intubation. Other devices also can be used as stylets, including airway-exchange catheters, which permit attachment to an anesthetic circuit, resuscitation bag, or jet ventilation system. Use of a laryngotracheal anesthesia kit, with its plastic stylet, likewise has been described for this purpose (59).

Blind nasotracheal intubation (BNTI) remains a viable option for intubation in the ED, in routine intubation and difficult airway management. In the National Emergency Airway Registry study, this method was utilized in about 5% of all intubations, with a success rate of 85.7% within three attempts. In Dronen’s comparison of BNTI to direct laryngoscopy for intubation, the rate of successful intubation was significantly lower at 68%, in comparison to direct laryngoscopy with the use of succinylcholine for muscle relaxation, with which there were no failures (60). In addition, complication rates, mostly nasal bleeding and emesis, were much higher with BNTI. When paramedics utilized BNTI in 219 intubations, the rate of appropriate ETT placement improved from 58% to 72% when a directional tip control tube was utilized (61).

Stylets have evolved in function, cost, and complexity. In the late 1950s, Yamamura described transillumination for use in nasotracheal intubation (62). Use of the lighted stylet, or lightwand, has been well described since then, as a blind technique in the face of difficult intubation, as well as for routine airway management 63, 64, 65. Early commercial lightwands suffered from poor illumination and misdirection of the light, so that a darkened room was necessary to see the halo produced in the glottic area during insertion into the airway. The lamp switch was often placed in an awkward position. Further, an overly rigid stylet could cause retraction of the ETT out of the glottis when the lightwand was withdrawn (63). Newer models have improved upon visibility of the light as well as the ergonomics of the device (66). The Trachlite (Laerdahl, Long Beach, CA, USA), a two-piece lighted stylet, allows the ETT to be placed without dislodging it when the device is withdrawn, due to a retractable wire stylet. A locking device for the proximal portion of the ETT and an adjustable length stylet also represent significant improvements of the Trachlite over earlier lighted stylets (66).

In the OR, lighted stylet intubation has proven reliable and highly successful. Ainsworth described intubation in 200 patients under general anesthesia within 60 sec, whereas Weiss reported a series of 250 patients with 99% success in intubation using the lighted stylet 65, 67. In 950 surgical patients, use of the Trachlite illuminating stylet was compared to direct laryngoscopy for efficacy in tracheal intubation (66). Direct laryngoscopy was found to require more time, produce more complications, and result in a higher failure rate (3% vs. 1%). In 186 documented or suspected difficult airways, Hung utilized the lighted sylet for intubation at the induction of anesthesia with success in 99% of these patients (68). In a series of 28 trauma patients with suspected cervical spine injury, the lightwand was employed for intubation with 100% success as reported by Weiss (69). In prehospital care, Vollmer reported the use of the lighted stylet by Emergency Medicine residents in 24 patients with 88% success in less than 45 sec (70).

In Emergency Medicine, lighted stylets have also proven useful for airway managment in facial trauma, and appear to facilitate intubation while preserving immobility of the cervical spine 70, 71. The device has been adapted for nasotracheal intubation as well as orotracheal use (70). Complications are infrequent with use of the lighted stylet (63).

Stylets have been modified to include optical viewing fibers as well as lighting. Such stylets may be used for routine or difficult tracheal intubation 73, 74, 75. These devices allow direct visualization of structures at the tip of the endotracheal tube as it is inserted, simplifying intubation when a poor laryngoscopic grade is encountered, and facilitating confirmation of tube placement. Some of the available instruments display the image on a video screen at the bedside, while others require the operator to look through an objective lens as the device is inserted into the airway 73, 74. These instruments are best used in conjunction with a laryngoscope or the hand of an assistant to elevate the mandible and soft tissues out of the way for optimum visualization. Limitations include potential fogging and interference with the view by secretions, the need to become familiar with viewing characteristics, and the cost of the devices, which is considerable.

The intubating fiberoptic stylet has not been subjected to controlled, comparative studies in the management of the difficult airway. However, in small series, it has proven useful for airway management in the OR. In 32 patients undergoing general anesthesia for surgery, 94% of cases were intubated successfully on the first attempt and the remainder on the second attempt using this device (74). Gravenstein compared the fiberoptic stylet with direct laryngoscopy and with bronchoscopic intubation in 75 patients under general anesthesia, evaluating the time required for intubation, the quality of the view of the glottis, and the frequency of complications (75). The authors reported a shorter time for intubation using the fiberoptic stylet than for the bronchoscope, and a lower rate of postoperative sore throat than direct laryngoscopy, but also noted that the least favorable laryngoscopic view occurred with the fiberoptic stylet. When compared to conventional intubation with direct laryngoscopy utilizing an Eschman stylet in simulated grade 3 laryngoscopy in a mannequin model, Biro described 100% success using the fiberoptic intubating stylet in tracheal tube placement by 45 anesthetists in 225 intubations, whereas there was a 40% rate of tube misplacement (20% esophageal, 20% endobronchial) utilizing direct laryngoscopy under these circumstances (76).

Occasionally, the emergency physician will attempt RSI, only to find that intubation is impossible due to abnormal anatomy, pathology, or poor visibility. Much less frequently, ventilation by mask will fail in the same patient, despite attempts to optimize it (17). When both of these conditions are met, desaturation and hypercarbia will occur within minutes, or possibly seconds, depending on the degree of preoxygenation, the patient’s body mass, current oxygen utilization, and associated cardiopulmonary pathology (34). Cricothyrotomy or transtracheal jet ventilation should be quickly carried out, but an adjunct to ventilation may be utilized to temporize while preparations for the more invasive procedure are made. Aids to ventilation are placed in either the supraglottic or infraglottic airway, depending upon the clinical situation.

The laryngeal mask airway (LMA) (LMA of North America) has been in widespread use by anesthesiologists in Europe since the 1980s, when it was developed by Brain (77). It was introduced in the U.S. in the early 1990s, and is utilized worldwide for the conduct of anesthesia. The device is composed of a semirigid tube attached to an inflatable “mask” that is placed into the hypopharynx, and advanced over the larynx. When inflated, this mask provides a seal around the glottic aperture (78). The LMA is available as a reusable device as well as a disposable one, in sizes ranging from those for neonates to those for large adults.

LMA insertion requires skill, practice, and familiarity with the conformation of the device (77). However, it may be inserted without muscle relaxants, and lends itself to emergency ventilation, because it provides a greater degree of airway patency than does a face mask. The LMA has been utilized as an emergency ventilation adjunct in a variety of circumstances 78, 79, 80. It also can be used effectively as a “bridge” to fiberoptic intubation, because an ETT of size 6.0 or smaller may be passed through the LMA and over the fiberscope, while the lumen of the device effectively guides the bronchoscopist to the laryngeal opening 79, 80, 81. Limitations include a seal that is unreliable at high peak inspiratory airway pressures: about one-third of the tidal volume is lost during positive pressure ventilation with the LMA when the peak inspiratory pressure reaches 30 cm of H2O, and the effectiveness of ventilation deteriorates further as peak airway pressures increase (82). Failure to protect the patient against aspiration of gastric contents is another concern. Mucosal trauma may occur on insertion of the LMA, and placement is occasionally difficult, particularly for the unfamiliar operator 77, 78, 79, 80. A new version of the LMA, which soon will be introduced in the U.S., will have a port for gastric emptying (83).

The LMA has proven useful both as an alternative to BVM in cardiopulmonary arrest and as a rescue device in difficult airway management. Among intensive care unit nurses, Martin found that the LMA proved easier to use, and provided a better tidal volume with less likelihood of airway obstruction than BVM ventilation with or without an oral airway (84). When untrained volunteers were assessed for the ability to ventilate patients under general anesthesia, Alexander described marked improvement in success of ventilation and oxygenation when the LMA was used, compared to BVM ventilation (85). He reported a 43% rate of failure to ventilate effectively with the latter device, whereas the LMA was successful in all but 13% of cases. Likewise, Smith found that anesthetists were better able to maintain oxygen saturation and a patent airway in 64 patients under general anesthesia randomly assigned to ventilation using the LMA as opposed to a face mask (86).

In an evaluation of LMA utility in prehospital care, Pennant described placement of LMA by paramedics in 100% of cases in less than 40 sec, whereas endotracheal tube placement required more than twice that long and resulted in 31% misplacement (87). Davies described placement of an ETT or LMA in a mannequin by paramedics with little training: 94% of LMA insertions were successful, compared to only 51% of ETT insertions (88).

Little comparative clinical data exist to support use of the LMA in the ED. It has been well established during difficult airway management and rescue ventilation in the OR 79, 80, 81. Experienced practitioners can usually insert the LMA within 20 s, with a success rate of ventilation of 98% (89). Parnet described the use of the device as the adjunct of first choice by academic anesthesiologists facing difficult-intubation or difficult-ventilation situations in 17 cases over 2 years, with a 94% success rate, whereas other modalities were significantly less successful (90). Only one case report has been published to date describing failure of the LMA in a cannot-intubate/cannot-ventilate situation (91). Thus, the considerable experience with the LMA in unexpected difficult airway management in the OR may substantiate an attempt at its use when considering a surgical airway for the failed airway in the ED because it can be inserted so quickly and with high expectation of success (92). Its use may allow the conduct of an orderly, composed surgical airway, as opposed to a very hastened procedure in a desaturating patient.

In a meta-analysis of the literature, Brimacombe found that the incidence of reported aspiration of gastric contents during use of the LMA is exceedingly low, on the order of 2/10,000 cases, a rate similar to that encountered with general anesthesia with the use of a cuffed endotracheal tube (93). A new model of the LMA, recently introduced, incorporates a dorsal cuff, a drainage tube for insertion of a gastric tube, a double cuff configuration, and an introducer device. The Proseal LMA (Laryngeal Mask Company, Henley-on-Thames, UK) has been evaluated in a randomized, crossover study in anesthetized patients, in which it was compared to the LMA (94). The authors reported 100% success with both devices, but noted that the LMA was judged easier to insert, and could be placed more quickly, with higher success on the first attempt. A gastric tube was placed successfully through the Proseal LMA in all cases.

The intubating laryngeal mask airway (ILMA) (Fastrach, LMA of North America, Long Beach, CA, USA) is a derivation of the LMA that facilitates endotracheal intubation after placement of a laryngeal mask and which has some features distinct from the conventional one. The laryngeal mask is attached to a rigid stainless-steel airway tube, which has a larger internal diameter than the standard adult LMAs, and which has a handle to ease placement. This tube admits a flexible, reinforced endotracheal tube specially manufactured for this laryngeal mask. The mask and tracheal tubes come in three sizes for adults.

The ILMA has received significant study in anesthesiology, but little in the ED. Nonetheless, the device has promise for managing the difficult airway in either setting. The enormous popularity of the LMA in Europe and other areas around the world has led to ready acceptance of the ILMA. In Australia, Agro described its use in 110 patients slated for general anesthesia, with 95% success in establishing ventilation through the laryngeal mask (95). However, the authors encountered resistance to ETT insertion, requiring some form of adjustment of the apparatus, in 60% of patients, with an intubation time averaging 79 s. In a multicenter study from the U.K., Baskett assessed the efficacy of the ILMA in intubation of 500 patients undergoing general anesthesia, again with 95% success in ventilation through the mask portion of the device (96). The authors had ∼80% success on the first intubation attempts, with 4% of patients requiring three attempts and a failure rate of 4%. In another report from Britain, Brain used the ILMA to attempt intubation of 150 patients undergoing general anesthesia, with success in ventilating all of the patients with the laryngeal mask (97). In half of patients, resistance to ETT placement was encountered, requiring one of several adjusting maneuvers before intubation was successful. The study included 13 patients with “potential or known” airway difficulty, all of whom were intubated successfully. A slate of four different adjusting maneuvers is described, based upon the level at which resistance to ETT advancement is encountered (97). In 38 patients with known difficult airways, based on historical failure of laryngoscopy or physical examination features predicting difficulty, Joo assessed the utility of the ILMA compared to awake intubation with the fiberoptic bronchoscope (FOB) (98). All awake FOB attempts were successful, but only half of patients could be intubated blindly with the ILMA. The other half required the use of a bronchoscope, and 10% required involvement of a second operator to place the ETT.

Less data exist that evaluate the ILMA for airway management in the ED. Asai, simulating trauma resuscitation with manual in-line immobilization of the cervical spine in anesthetized patients, evaluated the ILMA for intubation in 40 cases (99). The ILMA was used in conjunction with FOB to ensure correct placement, and this tandem was compared to direct laryngoscopy with use of an Eschmann stylet. The authors reported 85% success of intubation with the ILMA under these circumstances, but less than half of the patients in the laryngoscopy group were successfully intubated with these restrictions. Rosenblatt reported three cases of successful intubation with the ILMA in patients in whom direct laryngoscopy had failed in the ED (100). The authors commented of the ILMA that “proficiency in its use requires practice under controlled conditions,” and suggested that “the emergency physician seek out elective practice” before assuming it can be used successfully under emergent circumstances.

Some authors have attempted to study the utility of the ILMA in the hands of unskilled or inexperienced operators, as might occur among paramedics or nurses during resuscitation attempts. When use of the ILMA was evaluated among untrained airway operators, and compared with their ability to perform direct laryngoscopy and intubation in a random cross-over trial involving anesthetized patients, Avidan found that the participants performed poorly with each device, with a 35–40% overall success in intubation (101). In a cadaver study, medical students were assessed in their ability to ventilate with the ILMA or the LMA (102). The authors found that the students could more effectively ventilate with the ILMA than the LMA (92% vs. 76%, respectively). However, they could intubate successfully with the ILMA in only 67% of cases. Thus, the ILMA may be preferred to the LMA for emergency ventilation in the ED, given its higher success rate and its potential for converting ventilation to intubation of the trachea. However, intubation through the device requires practice and familiarity, and is not met with a high degree of success in the neophyte. Furthermore, the device is much more expensive than the disposable LMA.

The esophageal-tracheal combitube (ETC) (Sheridan Catheter Corporation, Argyle, NY, USA) is another airway rescue device that facilitates ventilation by bringing the source of oxygen closer to the glottis than does the standard face mask. This dual lumen tube is generally inserted blindly into the pharynx, and is then advanced into either the esophagus (95–99% of cases) or the trachea (103). Ventilation through the color-coded, numbered tubes is then employed to determine the position of the tube. The ETC enjoys more popularity in the emergency setting than the LMA in the U.S. 104, 105.

The ETC has been used effectively in routine and emergent airway management in anesthesia, in prehospital airway management, in cardiopulmonary resuscitation, and in the ED management of difficult airways 103, 105, 106, 107. The ETC has been shown to be a reliable device for prolonged mechanical ventilation in ICU patients (108). During cardiac arrest, this device has proven efficacious to provide adequate ventilation with shorter intubation times than standard direct laryngoscopy (109). Critical care nurses were able to ventilate with the ETC during resuscitations as effectively as physicians intubating these patients (107). Among prehospital providers not trained to intubate the trachea, a modified, randomized, cross-over study design was used to compare the ease of insertion and adequacy of ventilation among the ETC, LMA, and pharyngeal tracheal lumen airway (105). Successful insertion and ventilation occurred more frequently with the ETC than with the other two devices, and was preferred by this group of providers.

Indications for use of the ETC include predicted difficult airway and inability to visualize the glottis during direct laryngoscopy 103, 104, 106. This adjunct may be inserted with the use of a laryngoscope as well as blindly. Advantages of the ETC include the potential for reduced risk of aspiration when compared to a face mask or the LMA, preservation of cervical spine immobilization, and the ability to insert the device when a laryngoscope is not available 103, 104, 105, 106. The relatively large size of the ETC and its inherent stiffness predispose to esophageal dilatation, and lacerations of the piriform sinus and esophagus have been reported 110, 111.

At times, the ETC and LMA are rendered ineffectual by supraglottic or glottic pathology, such as swelling, abscess, tumor or foreign body, or by unfavorable anatomy that precludes their placement, such as limited mouth opening. Under such circumstances, an approach to emergent ventilation that utilizes an infraglottic, percutaneous route is an alternative. Transtracheal “jet” ventilation (TTJV) requires the placement of a large-bore i.v. or other catheter through the cricothyroid membrane, or even directly into the trachea 12, 113. This is connected, preferably by a tight-fitting luer-lock connection, to a high-pressure oxygen source, which is used to oxygenate and ventilate the patient 114, 115. The catheter also may be attached to a resuscitation bag via the connector of a size 3 ETT or to wall oxygen from a regulator at its highest flow, utilizing a hole cut in the tubing to control flow of oxygen by periodic occlusion with the thumb or finger 116, 117. These arrangements do not provide ventilation as effectively as does a high pressure (50 PSI) oxygen source, which may be delivered either by an oxygen tank with a “step down” regulator or directly by the hospital’s wall oxygen system 112, 118. A variety of components can be assembled piecemeal to create such a system, but commercially available systems are more reliable and are reasonably priced 112, 119.

When oxygen at high pressure (20–50 PSI) and high flow (0.5–1.0 L/sec) is delivered by TTJV, air may be entrained at the catheter tip, augmenting the tidal volume and increasing the risk of barotrauma. Given the low rates and high pressures involved, adequate tidal volume for an adult usually can be delivered in 0.5–1 sec. Utilizing a lung model with a set compliance of 50 mL/cm H20, a 1-sec inspiratory time and a 50 PSI oxygen source, tidal volumes generated vary from about 600 mL with an 18-gauge i.v. catheter to over 1200 mL with a 14-gauge catheter (112).

TTJV was demonstrated to be successful in providing adequate ventilation in cardiac arrest patients as early as 1972, when Jacobs described its use in 40 cases (116). While utilizing a high-pressure oxygen source, the author was able to maintain an average pO2 of 300 mm Hg, and a pCO2 of 22 mm Hg with peak airway pressures of 15–25 cm H2O. Smith in 1975 described the use of TTJV in 80 patients who underwent airway surgery under anesthesia (120). Fifty-two of these cases involved elective use of the technique, while 28 of the patients were managed while in respiratory distress. Provided that adequate pressures are utilized to provide necessary flow rates, numerous investigators have demonstrated that normocarbia can be maintained while ventilating patients with this technique 115, 116. Most of the patients described in these investigations were under general anesthesia, in contrast to patients in acute respiratory failure who are frequently encountered in the ED. TTJV also has been useful in high-grade upper airway obstruction, as in the case of a patient with a large carcinoma at the base of the tongue who sustained a respiratory arrest (120). TTJV has been used effectively as a ventilation strategy in cannot-intubate and cannot-ventilate (“failed airway”) situations 112, 118, 119. The technique has also proven useful in pediatric airway emergencies (122).

When TTJV is utilized, ample time must be allowed for the passive recoil of the lungs to force exhalation of the insufflated gas (2–3 sec), or “stacking” of breaths, and barotrauma may result. Pneumothorax, pneumomediastinum, and subcutaneous (s.c.) air have all occurred as a result of TTJV 120, 123. Contraindicatons to TTJV include distorted anatomy that would make placement of the catheter difficult or impossible, bleeding diathesis, and complete airway obstruction (112). Adverse effects include barotrauma, as described above, bleeding at the site of insertion, and loss of position of the catheter if it is not held firmly during ventilation 115, 118, 119.

Retrograde intubation (RI) was first reported in 1960 (124). This invasive technique allows for blind placement of an endotracheal tube over a guidewire or catheter that is inserted percutaneously at the level of the cricothyroid membrane or cricotracheal ligament and directed “retrograde” through the pharynx to the mouth or nose. The procedure was originally described with use of a red-rubber catheter introduced through a tracheostomy, and has evolved to include the use of a guidewire placed percutaneously through the lumen or Murphy Eye of an endotracheal tube (Figure 5) 125, 126. Because an ETT has the potential to move laterally about the wire, and impact on the aryepiglottic fold or arytenoid cartilages, the technique frequently incorporates a guide catheter placed over the wire before the ETT is inserted (127). Available commercial kits frequently include this catheter as well.

The technique of retrograde intubation has been used effectively in the traumatized patient as the presence of blood or secretions in the pharynx does not detract from successful intubation via this route 125, 128. Retrograde intubation also has been useful in difficult airway management in both anesthesiology and Emergency Medicine 125, 129, 130. However, this technique has not been widely applied in Emergency Medicine. Data regarding its application are limited to case reports and case series. RI has been described anecdotally in a number of difficult airway situations, including management of patients with large oral cancers, spinal cord injury, oral infections, pharyngeal edema, laryngeal carcinomas, and airway anomalies (126). Barriot described its use by emergency physicians in the field, where it was employed successfully in 13 patients with severe maxillofacial trauma who could not be intubated by direct laryngoscopy in the prehospital setting, and in another six patients in whom the technique was used electively (128). In the hands of those who use the technique frequently, RI appears to have a high success rate. Of 383 applications described in the literature by 1996, the technique was effective in 98.5% of cases (126).

However, preparation and administration of retrograde intubation usually requires over 2 min to complete, and sometimes considerably longer 126, 128. This means of managing the difficult airway may therefore be useful when a patient presents with an obvious or suspected difficult airway, yet has relatively well-preserved oxygenation and ventilation (as in head or facial trauma). RI also could be employed when RSI fails, but mask ventilation is still possible, allowing time to complete the procedure.

RI is a reasonably safe procedure. Adverse effects include bleeding and, rarely, hematoma formation 99, 100, 101. Subcutaneous emphysema or pneumomediastinum may occur but these complications are usually transient and self-limited 97, 102, 103. Bleeding diathesis is a relative contraindication to the technique, as are distorted neck anatomy and laryngeal injury 93, 104, 105.

Variations on the technique of RI include the use of an epidural catheter instead of a guide wire, and its use in combination with fiberoptic bronchoscopy 136, 138, 139. The guide wire may be placed through the suction channel of the fiberscope, leading the endoscopist directly to the laryngeal opening despite secretions or unfavorable anatomy. The wire is then removed and the intubation carried out with direct visualization through the fiberscope.

Introduced in the 1960s, FOBs are available in a variety of sizes, depending upon their use, and are usually 55 or 60 cm in length (140). Instruments used solely for intubation tend to be smaller in diameter (1.8–4.0 mm) than those used for diagnosis and therapy of pulmonary disease, which feature a larger working channel to admit biopsy forceps and other instruments. The fiberscope consists of a universal cord, which carries light in fiberoptic bundles from the light source; a handle containing an eyepiece, control lever for bending the distal tip of the scope, suction button and access port to the working channel; and an insertion cord that contains light bundles and the image transmission bundle, along with the tip control wires to allow bending of the tip forward or backward (141).

Awake intubation with a fiberscope requires ample time and preparation of the patient. Even in emergent circumstances, bronchoscopy requires 5–6 min to perform, and, ideally, with such preparatory measures as patient sedation, topical and regional anesthesia of the airway, and administration of an anticholinergic preparation to dry secretions, 15–20 min is required 130, 140.

While controlled studies or comparisons of efficacy are few, case reports and series abound in the anesthesia literature of the utility of FOB in management of the difficult airway 142, 143, 144, 145, 146, 147, 148. The effectiveness of FOB for intubation of the patient with a cervical spine injury is well established 143, 146, 148. The intubating bronchoscope plays a very important role in awake intubation of the patient with a suspected or known difficult airway (130). Under these circumstances, the success rate of the procedure is almost 99%. The simultaneous use of direct laryngoscopy with FOB may improve the success rate of the technique by displacing soft tissues that can impede the fiberscopic view of the glottis (149).

The nasotracheal approach to the airway with FOB is often simpler than the oral approach because the instrument is aimed directly at the glottis as it emerges from the nasopharynx into the hypopharynx (140). Intubation over the bronchoscope can be successfully performed through an LMA and around the ETC 130, 150. There are many advantages to the technique, including applicability to all age groups, excellent airway visualization, ability to insufflate oxygen during the procedure, high success rate, and immediate confirmation of ETT placement (146).

There are significant limitations to bronchoscopic intubation. In the presence of uncontrolled secretions, mucus, or bleeding in the airway, visibility is difficult or impossible. Suction through these instruments is relatively ineffective, but by attaching an oxygen source to the suction channel of the instrument, oxygen insufflation may be used to blow offending matter away from the lens to improve visibility. Furthermore, the natural compression of soft tissues of the oropharynx and hypopharynx in the supine, anesthetized patient can make the approach to the airway difficult due to physical obstruction and poor visibility. This is a greater problem in oral intubation than nasal intubation. Effective means to address this concern include use of a specialized oral airway such as the Ovassapian airway or Williams airway, a jaw thrust by an assistant, or direct laryngoscopy provided by an assistant 130, 140, 141. Finally, advancement of the endotracheal tube over the FOB is difficult in up to 25% of cases, as the bevel of the tube may catch on the arytenoid cartilages or aryepiglottic folds. Withdrawing the endotracheal tube, and rotating it 90° in either direction usually solves this problem, but about 10% of the time one cannot advance the tube, requiring a change to a smaller tube or a different approach to the airway (140). Barriers to facility include an initial training period, a relatively slow learning curve, and failure to retain skills when the procedure is infrequently utilized (140).

In the ED, little systematic study has accrued on the utility and efficacy of FOB in airway management. Delaney reported a series of 57 intubations carried out by two emergency physicians trained on a mannequin in the use of a 50-cm fiberoptic scope (151). The cases were selected for the skill level of the physicians (more than half were overdose patients). The authors reported a 13% failure rate, and 22% of the patients had significant bleeding with the nasotracheal approach. In another study of fiberoptic intubation in the ED, the authors reported that only 75% of 39 patients were successfully intubated by use of the fiberscope, whereas 95% of a comparable group of patients were managed successfully with direct laryngoscopy (152). Levitan, in a study of ED practices at U.S. teaching hospitals, found that the FOB was seldom employed as a means of management of the difficult airway (2).

Several rigid fiberoptic laryngoscopes are available. The oldest, and most familiar, is the Bullard laryngoscope (Circon, ACMI, Stamford, CT, USA). The operator inserts the scope into the hypopharynx, and under indirect vision through the eyepiece, advances the blade into position cephalad to the glottis. The endotracheal tube can then be pushed forward off the stylet, into the glottis during visualization. The Bullard laryngoscope is indicated for airway management when the glottis is difficult to visualize due to unfavorable anatomy, and when preservation of cervical spine immobilization is essential. It also may be used for routine laryngoscopy and intubation. Other rigid fiberoptic scopes include the Upsherscope (the Upsher Laryngoscope Corporation, Foster City, CA, USA) and the WuScope (Actis Corporation, Dublin, CA, USA).

None of these devices has undergone rigorous trials in the ED to compare them with conventional means of managing the airway. Watts described a comparison of the time required for intubation and the degree of cervical extension utilizing the Bullard scope and direct laryngoscopy, both with and without in-line cervical immobilization, in patients under general anesthesia (154). The degree of spine extension and the time to intubation were similar, except when cervical immobilization was imposed, at which time the average duration required for intubation with the Bullard laryngoscope was significantly prolonged, from 25–40 sec. However, Schulman reported in a randomized trial in 50 patients under anesthesia that, in comparing the Bullard scope to a flexible fiberscope during in-line cervical immobilization, intubation was significantly easier to accomplish, and required less time with the rigid apparatus (155).

The Upsherscope, a relatively new rigid scope incorporating a C-shaped steel blade with enclosed fiberoptic bundles and an intubation channel, proved to have no advantage over direct laryngoscopy in enabling intubation in a group of 300 patients randomly assigned to airway management in the OR by either technique (156). In fact, the authors reported a 15% failure rate with the Upsherscope, compared to only 3% with direct laryngoscopy. Yet another rigid fiberoptic scope, the WuScope, was compared to direct laryngoscopy in 87 patients randomized to either form of airway management during in-line cervical immobilization to simulate potential cervical injury during anesthesia for elective surgery (157). The authors found similar rates of intubation success, but longer times to intubation and lower glottic visualization scores using the WuScope.

The time-honored means of obtaining a rapid definitive airway when both intubation and ventilation fail is the insertion of a tracheal tube through an incision in the neck. Although discouraged in the early part of the 20th century because of complications occurring after the procedure, chiefly subglottic stenosis, cricothyrotomy was reestablished as a safe technique for airway management after the paper by Brantigan appeared, documenting a much lower complication rate than expected (158). The technique involves a vertical incision in the midline over the palpable laryngeal cartilages, followed by a transverse incision in the cricothyroid membrane, or a single transverse incision through the skin, s.c. tissue, and cricothyroid membrane if the interval is palpable 158, 159. Recent studies have focused on the “rapid four-step technique” for cricothyrotomy (160). Holmes described its use in cadavers by inexperienced personnel, and compared this method to the standard technique (161). The authors reported equal success with each method (88% vs. 94%, respectively), with identical complication rates of 38%, but more rapid tracheal tube insertion with the rapid four-step technique, which required an average of only 43 sec compared to an average of 134 sec for the conventional method. In another cadaver model, Davis described a significantly higher incidence of complications with the rapid four-step technique, primarily cricoid cartilage fracture (162).

Cricothyrotomy also may be accomplished with a wire-guided technique, similar to the Seldinger technique for cannulating blood vessels. After puncture of the cricothyroid membrane with a thin-walled needle and aspiration of air to confirm position, a wire is advanced through the needle, which is then removed. After a small incision in the skin and insertion of a dilator, the airway is inserted over the dilator and wire. In a randomized, cross-over trial performed on cadavers, Chan et al. compared the standard technique of cricothyrotomy to the Melker wire-guided method (164). The authors found that 14 of 15 physicians participating preferred the wire-guided technique, while overall success was similar for both methods. Eisenberger reported that inexperienced clinicians attempting to perform cricothyrotomy on cadavers had a low success rate of only 60–70%, with either the standard or wire-guided technique (165).

Whatever method is chosen to perform cricothyrotomy by the emergency physician, this procedure remains the most reliable and time-honored definitive airway procedure in a “failed airway” scenario (37). The morbidity and mortality of this technique, when carried out for long-term airway management, appears to be similar to that of tracheostomy 158, 166.

In the prehospital realm, surgical airways generally have been employed for massively injured patients with significant facial trauma. Spaite described attempted cricothyrotomy in 16 patients with an 88% success rate, and a complication rate of 31% (167). Boyle, in a retrospective study of cricothyrotomy by flight nurses in a teaching hospital helicopter program, described 69 attempts of this procedure among 2108 patients transported. The procedure was accomplished successfully in 98.5% of cases with only one failure, and a low complication rate of 8.7% (168).

Perhaps the best means of coping with the problem of difficult intubation or failed airway is to prevent their occurrence altogether. This requires that the initial attempt at direct laryngoscopy is optimized, in order to avoid repeated attempts at intubation that may cause bleeding and swelling in the pharynx and supraglottic area, and then a vicious cycle in which each attempt leads to a greater likelihood of failed intubation and ventilation with potentially disastrous consequences (41). Optimizing laryngoscopy requires appropriate positioning of the patient to align the pharyngeal, oral, and laryngeal axes for visualization of the glottis; effective muscle relaxation with an appropriate dose of succinylcholine or a nondepolarizing agent; the use of a laryngoscope blade type and size which best fits the situation; and the use of optimal external laryngeal pressure by the laryngoscopist 41, 169. In this maneuver, laryngeal pressure is exerted by the right hand during laryngoscopy, to maneuver the larynx into a position in which the glottis can be best seen. An assistant then maintains this directed pressure while the laryngoscopist accepts and places the ETT with the right hand. The maneuver, which initially seems awkward, is rapidly learned, and has been shown to substantially improve the laryngoscopic view in most patients (Figure 6) (170). Alternately, the assistant may apply pressure “backwards, upwards and rightwards” (BURP maneuver) (169). When all of these factors are taken into account, the first attempt at laryngoscopy is likely to be the best attempt, without loss of precious seconds to correct suboptimal aspects of the procedure after a poor view of the glottis becomes evident.

Section snippets

Conclusions

Emergency physicians manage the airway with great efficacy for the vast majority of cases that present to the ED requiring such intervention. However, a small subset of patients will cause difficulty in laryngoscopy, intubation, and BVM ventilation, because of either unfavorable anatomy or facial, airway or cervical pathology. This is more likely in the ED than elsewhere in the hospital because of the emergent nature of most airway management and the inability to assess the patient ahead of

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