Mivacurium infusion requirements following vecuronium: different response between adults and children

The mivacurium infusion requirements following vecuronium were evaluated in 15 adults and 15 children in an open prospective clinical study. This study was undertaken to elucidate whether potentiation of effect occurred when a mivacurium infusion was administered after vecuronium was used for the facilitation of tracheal intubation. The adult patients were anaesthetized with N2O:02, propofol and fentanyl, the children with halothane (1%) N2O:O2. Vecuronium 100 micrograms.kg-1 was administered during stimulation of the ulnar nerve with train-of-four stimuli at 0.1 Hz. The force of contraction of adductor pollicis was recorded. Upon recovery of the twitch response from vecuronium, a mivacurium infusion was started at 4 micrograms.kg-1.min-1, thereafter adjustments were made to maintain the first twitch of the train-of-four (T1) at 1-10% of control. The mean (+/- SE) initial infusion requirements in children of mivacurium was 4.3 (0.4) micrograms.kg-1.min-1 which increased linearly (P < 0.001) over the next 90 min to 10 micrograms.kg-1.min-1. In adults the infusion requirement was lower than in children and remained at approximately 3 micrograms.kg-1.min-1 over the next 75 min. At the end of the surgical procedure, the children recovered faster than the adults with no child requiring reversal. Because of prolonged recovery ( > 20 min), seven adults required reversal with 15-70 micrograms.kg-1 neostigmine. Mivacurium infusion requirements following vecuronium are higher in children than adults. Potentiation of the effects of mivacurium were seen when vecuronium preceded mivacurium. This potentiation of effect lasted longer in adults than in children.