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Anesthesiology:
doi: 10.1097/01.anes.0000268502.97033.fc
Correspondence

Predicting Difficult and Impossible Mask Ventilation

Reed, Allan P. M.D.

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To the Editor:—

The cannot intubate–cannot ventilate scenario is among the most feared situations confronting airway managers. Kheterpal et al.1 deserve congratulations for attempting to elucidate some of its intricacies.
To accomplish that, 61,252 adult patients undergoing anesthesia at their institution were enrolled in the study. Of this number, 22,660 cases underwent attempts at mask ventilation. Data were derived from all cases in which mask ventilation had been attempted. The Discussion explains and table 6 enumerates that 586 patients underwent elective awake intubation. Patients undergoing elective awake intubation do not receive attempts at mask ventilation and therefore were excluded from the most important aspects of data collection and calculations.
Awake intubation is performed for patients who are anticipated to have difficult or impossible mask ventilation and/or difficult or impossible laryngoscopy. These 586 patients were the most likely to have been difficult or impossible mask ventilations and/or difficult or impossible laryngoscopies. This is born out by the data. Comparing the awake fiberoptic intubation group with the standard induction group demonstrated a higher incidence of one or more risk factors in the awake group. There is no way of knowing the frequency of grade 3 or grade 4 mask ventilation, or the frequency of difficult or impossible intubation in these 586 patients. I expect the frequency to have been relatively high.
Having excluded the high-risk population from the data, only low-risk patients were analyzed. Consequently, their results and conclusions are not applicable to high-risk patients or even the general population of patients. Their conclusions are applicable to low-risk groups.
Furthermore, it is curious that beards, Mallampati-Samsoon class III and IV, and age older than 57 yr are identified as predictors of grade 3 mask ventilation (difficult mask ventilation) but are not named as predictors of grade 4 mask ventilation (impossible mask ventilation). Snoring is the only shared risk factor between grade 3 and 4 mask ventilation. Thyromental distance less than 6 cm was identified as a risk factor for grade 4 mask ventilation, but not grade 3. I would have anticipated more overlap between the two grades. It is noteworthy that Mallampati-Samsoon class III and IV is identified as a predictor of grade 3 mask ventilation but not as a predictor of grade 3 mask ventilation and difficult intubation.
Allan P. Reed, M.D.
Mount Sinai School of Medicine, New York, New York. allan.reed@msnyuhealth.org
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Reference

1. Kheterpal S, Han R, Tremper KK, Shanks A, Tait AR, O'Reilly M, Ludwig TA: Incidence and predictors of difficult and impossible mask ventilation. Anesthesiology 2006; 105:885–91

© 2007 American Society of Anesthesiologists, Inc.

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