Mivacurium chloride: a study to evaluate its use during propofol–nitrous oxide anaesthesia

We assessed the neuromuscular and cardiovascular effects of mivacurium chloride, a neuromuscular blocking agent, in 33 patients during propofol‐nitrous oxide anaesthesia. Neuromuscular function was assessed with supramaximal stimuli of the ulnar nerve, using surface electrodes at the wrist, with repeat trains of four. Mivacurium given as a bolus of 0.15 mg.kg−1 (ED95× 2) was found to be haemodynamically stable. Intubating conditions assessed at 2 and 2.5 min were either good or excellent. All patients developed a block of 100% in a mean (SD) time of 105 (34) s. There were mean (SD) intervals of 12 (2.4) min before the reappearance of the first twitch of the train of four (T1) following the bolus dose, and 15.8 (3.1) min for the Tl to reach 25% of its control value (TC). Seventeen patients received an infusion of mivacurium to maintain neuromuscular blockade (T1: TC 10–20%) with a mean (SD) infusion rate of 6.9 (2.2) μ.kg−1 min−1. Recovery from neuromuscular blockade was assessed with spontaneous offset or augmented with edrophonium following either the initial bolus or an infusion. Following a bolus it took a mean (SD) of 26.2 (3.7) min for the fourth twitch of the train of four (T4): T1 ratio to reach 0.7. In patients receiving an infusion with spontaneous offset it took a mean (SD) time of 12.0 (2.2) min to reach the T4: T1 ratio of 0. 7 from a Tl: TC value of 8.8. Edrophonium significantly decreased the recovery time in both groups. It took a mean (SD) time of 5.4 (2.2) min to reach a T4:Tl of 0.7froma T1:TC of 17.1% in the group receiving an infusion and 4.0 (0.7) min for the T4.T1 to reach 0.7 from a T1:TC value of 14.3% in the patients receiving a bolus only. We conclude that mivacurium is a suitable agent for neuromusccular relaxation and may have advantages over existing agents.