IS INTRAMUSCULAR MIVACURIUM AN ALTERNATIVE TO INTRAMUSCULAR SUCCINYLCHOLINE

Background: Mivacurium's rapid onset and short duration of action in c hildren suggests that intramuscular administration might treat laryngo spasm and facilitate tracheal intubation without producing prolonged p aralysis. Accordingly, the authors measured the neuromuscular effects of intramuscular mivacurium in anesthetized infants and children. Meth ods: Twenty unpremedicated infants and children (3 months to 5 yr of a ge) were anesthetized with nitrous oxide and halothane and permitted t o breathe spontaneously. When anesthetic conditions were stable, mivac urium was injected into the quadriceps or deltoid muscle. Minute venti lation and adductor pollicis twitch tension were measured. The initial mivacurium dose was 250 mu g/kg and was increased (to a maximum of 80 0 mu g/kg, at which dose the trial was ended) or decreased according t o the response of the previous patient, the goal being to bracket the dose producing 80-90% twitch depression within 5 min of drug administr ation. Results: No patient achieved >80% twitch depression within 5 mi n of mivacurium administration, Peak twitch depression was 90 +/- 13% (mean +/- SD) for infants and 88 +/- 15% for children at 15.0 +/- 4.6 min and 18.4 +/- 6.4 min, respectively. Ventilatory depression (a 50% decrease in minute ventilation or a 10-mmHg increase in end-tidal carb on dioxide tension) occurred at 9.0 +/- 4.4 min in nine infants and 13 .6 +/- 7.5 min in 10 children; ventilatory depression did not develop in one infant given a dose of 350 mu g/kg. Time to peak twitch depress ion or ventilatory depression was not faster with larger doses. Conclu sions: Although ventilatory depression preceded twitch depression, bot h occurred later with intramuscular mivacurium than would be expected after intravenous mivacurium or intramuscular succinylcholine. The aut hors speculate that the onset of intramuscular mivacurium is too slow to treat laryngospasm or to facilitate routine tracheal intubation in infants or children, despite administration of large doses.