Residual Neuromuscular Block and Adverse Respiratory Events

To the Editor: Murphy et al.1 recently presented convincing data that postoperative residual neuromuscular block (PONB) may have undesirable short-term clinical consequences. However, the authors' observations may also explain why so many clinicians seem to view the risk of PONB as minimal (failure to use even conventional peripheral nerve stimulators and/or failure to administer reversal agents at the end of anesthesia). There is ample evidence that PONB on arrival in the postanesthesia care unit is not a rare occurrence.2,3 If we define PONB as a train-of-four ratio less than an acceleromyographic value of 0.90 (an electromyographic or mechanomyographic value of 0.80) then the actual incidence of PONB on arrival to today's recovery rooms is probably not <20%.4 Thus, in Murphy's study at least 1431 subjects probably had some degree of PONB but did not suffer a noticeable adverse respiratory event. Put differently, Murphy's data suggest that PONB is associated with a frequency of short-term critical respiratory events of perhaps only 4% or 5%, and the incidence of actual long-term morbidity is likely to be much less than that. Hence, most patients seem to tolerate residual block of modest extent without untoward results. This is not to diminish the importance of Murphy's work. There is no reason to accept even infrequent adverse events if they can be prevented. However, when warning clinicians about the possible side effects of residual block it would seem prudent to maintain a sense of perspective and balance if one is to remain credible. Aaron F. Kopman, MD Department of Anesthesiology St. Vincent's Hospital Manhattan New York Medical College New York city, New York [email protected]