Continuous infusion of mivacurium in children

Mivacurium is a new short-acting competitive neuromuscular blocking agent. Infusion requirements for the maintenance of a stable 90-99% muscle twitch depression were determined in 28 children anaesthetized with nitrous oxide and 1% halothane (inspired) in oxygen or nitrous oxide in oxygen and opioid. Neuromuscular block was assessed by monitoring the force of contraction of the adductor of the thumb during train-of-four (TOF) stimulation at 0.1 Hz. Infusion rate and twitch depression were analysed from 15 to 75 min and from 75 to 135 min after the start of the infusion. In the first period of evaluation, the mean infusion requirement was 10.4 (SEM 0.92) micrograms kg-1 min-1 during the halothane anaesthesia and 13 (1.4) micrograms kg-1 min-1 during the opiod anaesthesia (P less than 0.05). This difference was present also during the second 60-min period. There was no significant correlation between infusion rates required to maintain greater than 90% depression of the first twitch (T1) of the TOF and plasma cholinesterase concentrations. Regardless of the anaesthetic regimen, children recovered rapidly after discontinuing the infusion. The recovery index (25-75% recovery of T1) for all patients was 5.4 (0.57) min with no significant differences between the groups.