To the Editor:
In their recent study on airway assessment, Langeron et al.1
described the results of their computer-scored examination as “paradigm changing.” Although I believe they are correct in producing a paradigm change in the airway examination, I believe that the change actually arises from their methods rather than their results, and that the change is more significant than they suspected.
A key piece of methodology in this study, as in every study on airway examinations since Mallampati’s 1985 article,2
was the definition of a “difficult intubation.” One definition chosen by Langeron et al.
was the use of either a gum bougie or a video laryngoscope following an unsuccessful attempt using a direct laryngoscope. Because this definition figured in about three quarters of the intubations counted as difficult, it had a considerable impact on their results and conclusions. However, the authors did not fully explore why the decision to use familiar and readily available instruments should define an intubation as difficult.
One reason may be that a direct look followed by use of an alternative instrument indicates an inadequate view of the larynx at direct laryngoscopy. This follows Mallampati’s precedent of using an inadequate direct laryngeal view as the indicator of a difficult intubation. That precedent was set in 1985, however, and well before the common use of either the indirect laryngoscope or the gum bougie. At that time, no commonly used instrument could improve an inadequate direct view at laryngoscopy. Today, though, the video laryngoscope and the gum bougie are both familiar and readily available to most practitioners, and the limitations of direct laryngoscopy have lost much of their significance. As a result, the adaptation of newer technology has effectively overridden Mallampati’s definition for difficult intubation.
This is the crux of an important contradiction between the goal and the method of this study. It uses instruments not available in 1985 to define a difficult intubation, but then those same instruments provide a path to successful intubation. This means the study results come from a methodology that tries to preserve the limits of 1985 laryngoscopy, when that same methodology actually demonstrates the increasing irrelevance of those limits.
At first, this seems to challenge the value of Langeron et al.’s study. However, that comes from seeing it as an extension of the Mallampati’s examination model. In a different light, the study results are seen to derive largely from the individual clinician’s judgment as to whether an intubation should be done using traditional or newer instruments. This is a significant change from results based on a graded laryngeal view that defines difficulty, although there is a significant overlap in the airways that each method takes note of. The change means that the airway examination no longer looks for an anatomical limit for just one type of instrument, but rather it seeks a way to distinguish which airways are better managed by one type of instrument or another.
This should be seen as the true paradigm shift of this study. By incorporating the observation that different types of instruments now contribute to successful intubations, the authors have moved the airway examination away from its original task of predicting failure. Instead, their examination differentiates airways according to their suitability for different types of instruments. By doing this, it reorients the examination to the improvement of overall laryngoscopy success rates. Furthermore, the results indicate that their airway examination may perform this task better than the older one predicted failure.
I believe it is fair to say that this study brings the predictive airway examination from the 20th century into the 21st, accounting for current technology in both the prediction and the performance of laryngoscopy. I also believe that newer technologies, such as computerized face recognition, will continue this evolution. They will continue to form the airway exam into a evaluation tool that guides us toward specfic patient-appropriate intubating instruments.
1. Langeron O, Cuvillon P, Ibanez-Esteve C, Lenfant F, Riou B, Le Manach Y. Prediction of difficult tracheal intubation: Time for a paradigm change. Anesthesiology. 2012;117:1223–33
2. Mallampati SR, Gatt SP, Gugino LD, Desai SP, Waraksa B, Freiberger D, Liu PL. A clinical sign to predict difficult tracheal intubation: A prospective study. Can Anaesth Soc J. 1985;32:429–34
© 2013 American Society of Anesthesiologists, Inc.