Difficult airway management in the emergency department.

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32 S. L. Orebaugh Figure 1. Grades of laryngeal exposure (reprinted with permission by Blackwell Science, Ltd. (9)). 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 highgrade 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). Prediction Predicting which patients will present challenging or impossible ventilation, laryngoscopy, or intubation is troublesome and most assessments lack accuracy. Falsepositive 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 Figure 2. Samsoon and Young modification of Mallampati classification, evaluating relative size of oropharyngeal structures in order to predict difficulty in laryngeal exposure during direct laryngoscopy. Higher class number suggests greater difficulty in glottic exposure (reprinted with permission by Blackwell Science, Ltd. (9)).
Difficult Airway Management 33 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 (11–14). 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 (SaO 2 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. Incidence 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 (21–23). 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.
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Difficult airway management in the emergency department.

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