Effect of maintenance bolus on the recovery profile of a short-acting nondepolarizing muscle relaxant

Abstract

Study objective: To evaluate the effect of different maintenance boluses of a short-acting nondepolarizing neuromuscular blocking drug on its spontaneous recovery profile during anesthesia.

Design: Prospective, randomized, double-blind, dose-ranging study.

Setting: University-based medical center.

Patients: 69 ASA physical status I and II consenting adult outpatients undergoing general anesthesia with an anticipated duration of at least 2 hours.

Interventions: Patients were randomized to one of three study groups. Following induction of anesthesia with propofol and fentanyl, rapacuronium 1.5 mg x kg(-1) intravenously (i.v.), was administered to facilitate tracheal intubation. Anesthesia was maintained with desflurane 4% end-tidal in combination with nitrous oxide 67% in oxygen. When the first twitch (T(1)) in the train-of-four (TOF) returned to 25% of its baseline value, a maintenance dose of rapacuronium 0.25 mg x kg(-1) i.v. (Group 1), 0.5 mg. kg(-1) i.v. (Group 2), or 0.75 mg. kg(-1) i.v. (Group 3) was administered. The time course of neuromuscular block was monitored at the wrist using standard electromyography.

Measurements and main results: The times for recovery of the T(1) to 25% of the baseline value following different maintenance doses of rapacuronium were only 6.3 +/- 2.2, 7.5 +/- 2.3, and 9.6 +/- 2.5 minutes, in Groups 1, 2 and 3, respectively. However, the times for the TOF ratio to return to 0.7 were 44 +/- 15, 53 +/- 20, and 66 +/- 30 minutes in Groups 1, 2, and 3, respectively. Although recovery times were significantly longer after rapacuronium 0.75 mg x kg(-1) i.v. (Group 3), there were no significant differences in any of the recovery variables between Groups 1 and 2.

Conclusions: Spontaneous recovery of the T(1) to 25% of the baseline value occurred 6 to 10 minutes after a maintenance bolus dose of rapacuronium 0.25 to 0.75 mg x kg(-1) i.v. However, recovery to a TOF>0.7 required 44 to 66 minutes during desflurane anesthesia.