The influence of isoflurane on a continuous infusion of mivacurium

Sixty surgical patients were studied to evaluate the neuromuscular effects of mivacurium 0.15 mg.kg-1 (2 x ED95) for tracheal intubation. After intubation the patients were randomly allocated to receive alfentanil with either propofol (starting with 9 mg.kg-1 h-1, reducing to 6 mg.kg-1 h-1 after 20 min) or isoflurane (0.5% end-tidal). In addition, all the patients were given a continuous infusion of mivacurium 10 micrograms.kg-1 min-1 after tracheal intubation which was adjusted to maintain 90% depression of T1. Following mivacurium 0.15 mg.kg-1 T1 decreased below 25% in all but four patients. Mean (SD) percentage maximum block attained was 92.9% (12.5) after 309 (89)s. Tracheal intubation was completed 232 (155) s after administration of the relaxant and intubating conditions were graded as 'excellent' or 'good' in 56 patients. Although the mean (SD) mivacurium infusion rate for maintaining T1 at 10% was higher in the propofol group, 4.8 (2.1) compared with 4.4 (2.0) micrograms.kg-1 min-1 in the isoflurane group, this was not significantly different (p > 0.05). The mean (SD) recovery index was prolonged in the isoflurane patients, 757 (508)s, compared to those receiving propofol, 466 (219)s (p < 0.05).