Neuromuscular and clinical effects of a new non depolarizing muscle relaxant [mivacurium chloride] during nitrous oxide fentanyl and nitrous oxide-isoflurane anesthesia

ABSTRACT

The neuromuscular and clinical effects of mivacurium chloride were studied during nitrous oxide-oxygen-fentanyl [BAL group n = 54] or nitrous oxide-oxygen-isoflurane [ISO group n = 54] anesthesia in adult surgical patients who received mivacurium either as a single bolus dose, repeated bolus doses, or an infusion. Neuromuscular response was evaluated by recording the force of contraction of the adductor of the thumb during train of four stimulations at 0.1 Hz. Mivacurium produced a dose-dependent neuromuscular block in each group. The dose response curve for the ISO group was significantly shifted to the left of that for the BAL group. The estimated ED 50 and ED 95 were 0.42 mg/kg and 0.074 mg/kg for the BAL group and 0.029 mg/kg and 0.05 mg/kg for the ISO group. Infusion rates averaged 7.5 ug/kg/min. in the BAL group and 5.4 ug/kg/min. in the ISO group. Plasma concentration of mivacurium at the end of infusion averaged 206 ng/ml for the BAL group and 171 ng/ml for the ISO group. The recovery indices [T 25 - T 75] for initial bolus dose, repeated bolus doses, and mivacurium infusion were not significantly different in each anesthetic group. There were no significantly hemodynamic changes in groups given mivacurium doses up to and including 2 x ED 95 by bolus i.v. administration