We thank Drs. Myatt and Patel for their interest in our data and comments. We agree that detailed, controlled data collection regarding the ease or difficulty of mask ventilation before and after administration of neuromuscular blockade would be of great interest. Unfortunately, as our original manuscript mentioned,1collecting these data using a large observational dataset is difficult. Aggregation of a 50,000-patient dataset has necessary limitations. Although observational data are exceptional for establishing the real-world effectiveness of different clinical management strategies, they are suboptimal for evaluating the optimal efficacy of a specific strategy under ideal circumstances.2 

It is not feasible to use a large observational dataset to define the impact of neuromuscular blockade on mask ventilation because of several issues: First, asking providers to document additional elements and attempt mask ventilation before neuromuscular blockade solely for research purposes may require institutional review board evaluation and patient consent. Second, the acuity of the induction period demands a parsimonious approach to documentation in general. Third, it would be difficult to control confounding clinical factors such as depth of anesthesia, dosage of neuromuscular blockade, experience of providers, mask ventilation technique, and timing of mask ventilation attempts.

Goodwin performed a prospective, controlled trial evaluating the impact of neuromuscular blockade in 30 patients with normal airways.3Contrary to our clinical experience and that espoused by Dr. Myatt, they found that neuromuscular blockade did not alter the efficacy of mask ventilation, measured by tidal volume. Because the studied population was limited to patients with normal airways, everyday clinicians are left to make decisions without data. Patients exhibiting risk factors for difficult mask ventilation such as obesity, limited jaw protrusion, bearded facial hair, advanced age, oropharyngeal disproportion, and a history of snoring4may be a population worthy of a controlled, prospective study. Such a study would prove to be time-consuming, expensive, difficult, and impractical, given the low incidence. Until then, our observational data describing the use of neuromuscular blockade in patients with impossible mask ventilation may have to suffice.

*University of Michigan Medical School, Ann Arbor, Michigan. sachinkh@med.umich.edu

Kheterpal S, Martin L, Shanks AM, Tremper KK: Prediction and outcomes of impossible mask ventilation: A review of 50,000 anesthetics. Anesthesiology 2009; 110:891–7
Haynes B: Can it work? Does it work? Is it worth it? The testing of healthcare interventions is evolving. BMJ 1999; 319:652–3
Goodwin MW, Pandit JJ, Hames K, Popat M, Yentis SM: The effect of neuromuscular blockade on the efficiency of mask ventilation of the lungs. Anaesthesia 2003; 58:60–3
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