To the Editor:
The new American Society of Anesthesiologists (ASA) Difficult Airway Guidelines shift a paradigm on mask ventilation: the definition of difficulty now emphasizes patient outcome. Previous literature focused on the complexity of this procedure for the clinician—as the word “difficulty” implies. The ASA update rightly redirects the focus onto objective results in the patient.
The outcome measure recommended is end-tidal carbon dioxide. The ASA definition of difficulty includes it, and the flowcharts specify mask ventilation adequate “as confirmed by end-tidal carbon dioxide.” This measure is both valid and accessible: capnography is objective, immediate, and highly visible to all, right there on our monitors.
The update does not define what end-tidal carbon dioxide reflects “adequate ventilation,” however. There is a simple scale7 that can be used to characterize and document ventilation based on end-tidal carbon dioxide: its grades C and D fit the ASA definition of difficulty (inadequate or absent end-tidal carbon dioxide).
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