Residual postoperative paralysis. Pancuronium versus mivacurium, does it matter?

Based on a train-of-four (TOF) ratio greater than 0.70 as the standard of acceptable clinical recovery, undetected postoperative residual paralysis occurs frequently in postanesthesia care units. In most published studies, detailed information regarding anesthetic management is not provided. The authors reexamined the incidence of postoperative weakness after the administration of long- and short-acting neuromuscular blockers because few, if any, such comparative studies are available.

Ninety-one adult patients were studied. In group 1 (mivacurium, n = 35), anesthesia was induced with propofol/ fentanyl and maintained with nitrous oxide, desflurane, and opioid supplementation. The response of the adductor pollicis to ulnar nerve stimulation was estimated by palpating the thumb. Mivacurium (0.20 mg/kg) was administered for tracheal intubation, and an infusion was adjusted to maintain the TOF count at 1. When surgery was completed, the infusion was discontinued. When a second twitch could be detected, 7.0 micrograms/kg atropine and then 0.5 mg/kg edrophonium were administered. At 5 and 10 min, the mechanical TOF response was measured. Additional measurements were recorded if possible. Patients were tracheally extubated and discharged from the operating room when they could respond to verbal commands and no TOF fade was palpable. In group 2 (pancuronium-desflurane anesthesia, n = 29), the protocol was identical to that of group 1, except that 0.07 mg/kg pancuronium was administered for tracheal intubation. Additional increments (0.5 to 1 mg) were given as needed. Antagonism was accomplished with 0.05 mg/kg neostigmine and 0.01 mg/kg glycopyrrolate. In group 3 (pancuronium propofol-opioid, n = 27), the protocol was identical to that of group 2, except that anesthesia was maintained with nitrous oxide and a propofol-alfentanil infusion. In all groups, patients were assessed until a TOF ratio of 0.90 or more was achieved.

All of the patients in group 1 had TOF ratios greater than 0.80 on arrival in the postanesthesia care unit. Twenty of 35 patients had TOF ratios 0.90 or more while they were still in the operating room. Thirty-three of 35 patients had TOF ratios 0.90 or more within 30 min of reversal, and this value was reached in all patients by 45 min. Recovery parameters in groups 2 and 3 did not differ from each other. Hence data from these groups were pooled. Fifty-four of 56 patients who received pancuronium had TOF values of 0.70 or more, the remaining two patients had values of 0.6 to 0.7. In contrast to the mivacurium group, however, only four patients achieved a TOF ratio of 0.90 or greater while still in the operating room. Finally, eight of these patients did not achieve this degree of recovery within 90 min of reversal.

These results suggest that if nondepolarizing neuromuscular blockers are administered using tactile evaluation of the TOF count as a guide, critical episodes of postoperative weakness in the postanesthesia care unit should occur infrequently even with long-acting relaxants. Nevertheless, if full recovery is defined as return to a TOF ratio of 0.90 or more, then short-acting agents would appear to offer a wider margin of safety.