In Reply:—

We appreciate the interesting comments made by Dr. Baum. Dr. Baum suggests that the experimental design may have produced the delays in tracheal extubation that were observed in the pancuronium group. In particular, the study requirement to maintain a moderate level of neuromuscular blockade in the operating room (1 to 2 twitches to train-of-four stimulation) may have resulted in a relative overdosage of the neuromuscular blocking agent (NMBA). We utilized neuromuscular monitoring to determine when additional doses of NMBAs were to be administered. In the pancuronium group, all subjects required maintenance dosing during cardiopulmonary bypass. However, no patients required additional pancuronium in the postbypass period. Although the study design allowed for the administration of NMBAs until the last 30 min of the surgical procedure, no patient in the pancuronium group received maintenance dosing during the last 90 min in the operating room. In contrast, approximately 30% of the subjects in the rocuronium group received additional NMBAs following separation from cardiopulmonary bypass. We believe that most cardiac anesthesiologists administer NMBAs during cardiopulmonary bypass. This belief is supported by the results of a national postal survey of cardiac anesthesiologists that assessed practice patterns in the use of NMBAs. 1 

We agree with Dr. Baum's statement that many cardiac surgical patients who receive pancuronium intraoperatively are routinely extubated within a few hours of the end of the surgical procedure. It is possible that some of these patients are extubated before full recovery of neuromuscular function has occurred. Previous studies have demonstrated that significant residual neuromuscular blockade may persist for up to 8 h in the intensive care unit when pancuronium is used. 2,3The high incidence of symptoms of moderate to severe muscle weakness following extubation in the pancuronium group in our study suggests that residual neuromuscular blockade may be present during the ventilatory weaning and extubation process. We believe that all cardiac surgical patients who receive a long-acting NMBA in the operating room should be carefully evaluated, using clinical criteria or neuromuscular monitoring, for residual neuromuscular blockade prior to extubation.

Murphy GS, Szokol JW, Marymont JH, Vender JS: The use of neuromuscular blocking agents in adult cardiac surgery: Results of a national postal survey (abstract). Anesth Analg 2002; 94: SCA68
McEwin L, Merrick PM, Bevan DR: Residual neuromuscular blockade after cardiac surgery: Pancuronium vs rocuronium. Can J Anaesth 1997; 44: 891–5
Van Oldenbeek C, Knowles P, Harper NJN: Residual neuromuscular block caused by pancuronium after cardiac surgery. Br J Anaesth 1999; 83: 338–9