Mivacurium-induced Neuromuscular Blockade Following Single Bolus Doses and with Continuous Infusion during Either Balanced or Enflurane Anesthesia

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Abstract
Mivacurium chloride (BW B1090U) was administered to 72 patients during their elective surgery. The eight groups (nine subjects per cell) in the 2 .times. 2 .times. 2 study design differeed in three factors:the size of the mivarcurium bolus dose administered, whether or not this dose was followed by an infusion of mivacurium, and in the technique used for the maintenance of anesthesia. Four groups received a single bolus dose of mivacurium, 0.15 mg/kg, and the remaining four groups received mivacurium, 0.25 mg/kg, administered iv in 15 s. Precisely 2 min later, tracheal intubation was attempted. Conditions were judged to be good or excellent on most occasions, but intubation was not possible for two of the patients in the low-dose and one in the high-dose groups. Four groups, two at each bolus dose, received no additional mivacurium: there was a dose-dependent decrease in the rate of spontaneous recovery following the bolus dose. The other subdivision of groups was the use of either barbiturate-nitrous oxide-narcotic (balanced) anesthesia, or enflurane-nitrous oxide anesthesia; the anesthetic technique did not affect the pattern of spontaneous recovery from either bolus dose. Four groups, agains two at each bolus dose, subsequently received an infusion of mivacurium, adjusted to depress the twitch response by approximately 95%. Infusion rates averaged 6.0 .mu.g .cntdot. kg-1 .cntdot. min-1 in the groups receiving balanced anesthesia and 4.2 .mu.g .cntdot. kg-1 .cntdot. min-1 for those receiving enflurane anesthesia. Recovery following administration by infusion was slower than that observed following a bolus dose of mivacurium, 0.15 mg/kg but did not differ between the anesthetic groups. Plasma concentrations of mivacurium at the end of the infusion for patients receiving balanced and enflurane anesthesia averaged 227 ng/ml and 173 ng/ml, respectively.