AirwayLimitations of difficult airway prediction in patients intubated in the emergency department
Introduction
Failed laryngoscopy after rapid sequence intubation can have catastrophic consequences when coupled with the inability to ventilate the patient. In 1993, the American Society of Anesthesiologists created the American Society of Anesthesiologists Difficulty Airway Algorithm.1., 2. The first step of this algorithm involves assessment of the likelihood of difficult intubation using a laryngoscope. Three physiognomic features reported to be associated with difficult laryngoscopy include the size of the tongue relative to the pharynx (the'Mallampati score), limited neck mobility, and short thyromental distance.1., 2., 3., 4., 5., 6., 7., 8. These and other physiognomic screening tests of difficult laryngoscopy are now a routine aspect of preprocedural evaluation in elective anesthesia settings.
Mallampati scoring requires a cooperative patient sitting upright at 90 degrees, with the tongue fully protruded and the mouth opened as wide as possible.3., 4. Patient cooperation and maximal mouth opening effort are necessary to ensure validity and reproducibility.9 As described by Mallampati,3 the test is done without phonation, and several studies have demonstrated that phonation and patient cooperation significantly affect Mallampati scores.4., 9., 10., 11., 12., 13. Thyromental distance is measured with the patient upright, with full atlanto-occipital extension and the jaw protruded.4., 13., 14. Neck mobility testing for predicting a difficult airway, especially the evaluation of maximal atlanto-occipital extension, is contraindicated in patients with known or potential cervical spine pathology.
The prediction of the difficult airway has been credited within the anesthesia literature for a reduction in airway-related morbidity and mortality.2 Potential laryngoscopy difficulty in elective settings commonly leads to an alternative intubation strategy (such as awake fiberoptic intubation) that does not involve the ablation of spontaneous ventilation.1., 2., 15. Within the past 5 years, the prediction of the difficult airway has become a widely promoted concept within emergency medicine.16., 17., 18. Mallampati scoring and other screening tests of “the difficult airway” are now prominently featured in emergency medicine reference texts.16., 17., 18. The ability to obtain such physiognomic measures before intubation to predict difficult airways in emergency department (ED) intubations has never been evaluated.
Rapid sequence intubation is the most common means of intubation in EDs.19., 20., 21., 22., 23., 24. It has many advantages over awake laryngoscopy, nasal, or surgical approaches in terms of first-pass success, overall success, speed, and complications.19., 22., 23., 25. Reported laryngoscopy failure rates range from 0.4% to 1.1% of all ED airways.19., 20., 21., 22., 23., 25. Having screening tests that could be applied to ED patients to predict laryngoscopy failure would be desirable, thereby averting “cannot intubate–cannot ventilate” situations and potentially improving patient safety. However, screening tests that cannot be consistently and properly applied or have poor positive predictive value might lead to alternate intubation techniques that have their own set of risks, and emergency physicians may not be as facile with alternative techniques compared with rapid sequence intubation. Finally, if physiognomic tests of laryngoscopy difficulty have limited potential for improving patient safety, this limitation needs to be recognized, and educational efforts should be directed elsewhere.
The objective of this study is to evaluate whether 3 commonly reported screening tests of laryngoscopy difficulty could have been assessed in ED patients we intubated during a 37-month period. We also want to specifically determine whether such tests would have been feasible in our rapid sequence intubation–associated laryngoscopy failures.
Section snippets
Study design
We performed a retrospective medical record review of all ED-intubated patients during the study period using electronic medical records, critical care flow sheets, and data from a trauma registry.
Setting
The study was conducted at an academic, urban, Level I trauma center with an ED census of approximately 50,000 and approximately 1,800 major trauma patients per year. There is a 4-year emergency medicine training residency program associated with the ED, and there are 25 attending physicians. All
Results
A total of 944 intubations occurred during the study period. The 88 patients presenting in cardiac arrest and 6 additional patients who experienced cardiac arrest in the ED were not considered for this study because laryngoscopy was undertaken immediately, and rapid sequence intubation was not a consideration. Among the 850 intubated patients not in cardiac arrest, 838 underwent rapid sequence intubation (Table). Fifty-three percent (451/850; 95% CI 50% to 57%) could not follow simple commands.
Limitations
Our study is a retrospective medical record review using specific criteria to define the feasibility of performing Mallampati scoring, thyromental distance measurement, and neck mobility testing in patients intubated in the ED. We did not attempt to use these tests prospectively.
The results of our study are significantly influenced by the fact that 71% (597/838) of the patients we intubated with rapid sequence intubation were trauma patients, and 61% (362/597) of this group were cervical spine
Discussion
According to the inability to follow simple commands and the presence of cervical spine immobilization, we conclude that Mallampati scoring, thyromental distance measurement, and neck mobility testing could not have been properly applied to at least two thirds of our patients who were intubated using a rapid sequence intubation technique. Among the 3 patients for whom rapid sequence intubation failed, no patients could have undergone all 3 screening tests; no patients were following simple
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Author contributions: RML conceived the study, performed the chart review, and wrote the initial draft. EAO and WWE assisted in the study design, provided revisions, and statistical support. RML takes responsibility for the paper as a whole.
Presented as an abstract at the Society for Academic Emergency Medicine annual meeting, Boston, MA, May 2003.
The authors report this study did not receive any outside funding or support.
Reprints not available from the authors.