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LETTER TO THE EDITOR

Residual Neuromuscular Block and Adverse Respiratory Events

Department of Anesthesiology; St. Vincent's Hospital Manhattan; New York Medical College; New York city, New York; akopman{at}nyc.rr.com

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.

REFERENCES

1. Murphy GS, Szokol JW, Marymount JH, Greenberg SB, Avram MJ, Vender JS. Residual neuromuscular blockade and critical respiratory events in the postanesthesia care unit. Anesth Analg 2008;107:130–7[Abstract/Free Full Text]
2. Kim KS, Lew SH, Cho HY, Cheong MA. Residual paralysis induced by either vecuronium or rocuronium after reversal with pyridostigmine. Anesth Analg 2002;95:1656–60[Abstract/Free Full Text]
3. Debaene B, Plaud B, Dilly MP, Donati F. Residual paralysis in the PACU after a single intubating dose of nondepolarizing muscle relaxant with an intermediate duration of action. Anesthesiology 2003;98:1042–8[Web of Science][Medline]
4. Hayes AH, Mirakhur RK, Breslin DS, Reid JE, McCourt KC. Postoperative residual block after intermediate-acting neuromuscular blocking drugs. Anaesthesia 2001;56:312–18[Web of Science][Medline]

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