Mivacurium Infusion Requirements in Pediatric Surgical Patients During Nitrous Oxide-halothane and During Nitrous Oxide-narcotic Anesthesia

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 μg·m−2·min−1 during nitrous oxide-halothane anesthesia arid 375 ± 19 μg·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 μg·kg−1·min−1. This difference was not present when the infusion rate was calculated in terms of μg·m−2·min−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 ≥ 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.