Mivacurium infusion requirements in pediatric surgical patients during nitrous oxide-halothane and during nitrous...

We were interested in determining the infusion rate of mivacurium required to maintain approximately 95% neuromuscular blockade during nitrous oxide-halothane (0.8% end-tidal) or nitrous oxide-narcotic anesthesia. Neuromuscular blockade was monitored by recording the electromyographic activity (Datex NMT) of the adductor pollicis muscle resulting from supramaximal stimulation of the ulnar nerve at 2 Hz for 2 s at 10-s intervals. Mivacurium steady-state infusion requirements averaged 315 +/- 26 micrograms.m-2.min-1 during nitrous oxide-halothane anesthesia and 375 +/- 19 micrograms.m-2.min-1 (mean +/- SEM) during nitrous oxide-narcotic anesthesia. Higher levels of pseudocholinesterase activity were generally associated with a higher mivacurium infusion requirement. During both anesthetics, younger age was associated with a higher infusion requirement when the infusion requirement was calculated in terms of micrograms.kg-1.min-1. This difference was not present when the infusion rate was calculated in terms of micrograms.m-2.m-1. There was no evidence of cumulation during prolonged mivacurium infusion. There was no difference in the rates of spontaneous or reversal-mediated recovery between anesthetic groups. After the termination of the infusion, spontaneous recovery to T4/T1 greater than or equal to 0.75 occurred in 9.8 +/- 0.4 min, with a recovery index, T25-75, of 4.0 +/- 0.2 min (mean +/- SEM). In summary, pseudocholinesterase activity is the major factor influencing mivacurium infusion rate in children during nitrous oxide-narcotic or nitrous oxide-halothane (0.8% end-tidal) anesthesia.