Recovery of train-of-four after mivacurium

The present study was designed to determine the time-course of recovery of the train-of-four (TOF) ratio during spontaneous recovery from mivacurium-induced block. Fifteen patients, free of neuromuscular disease, undergoing general endotracheal anaesthesia with isoflurane were studied. After anaesthetic induction, patients received a bolus dose of mivacurium 0.15 mg.kg-1. The TOF was then recorded continuously every 12 sec with a mechanogram (adductor pollicis monitor). When the TOF ratio recovered spontaneously to 0.9, an additional 0.05 mg.kg-1 of mivacurium was given. The durations required for recovery from a TOF ratio of 0.3 to 0.7 (DUR0.3-0.7) and from a TOF ratio of 0.3 to 0.9 (DUR0.3-0.9) were determined. The DUR0.3-0.7 averaged 7.0 +/- 2.5 min (range 3.4-12.2 min). The DUR0.3-0.9 averaged 11.8 +/- 3.9 min (range 6.0-20.2 min). There was no evidence of prolongation of recovery times (cumulation) following repeated dosing. The present data indicate that, in patients with normal cholinesterase activity (clinical duration 7-25 min), waiting 20 min beyond the time when fade is no longer apparent by visual or tactile evaluation is sufficient to attain a TOF ratio greater than 0.7-0.9 during spontaneous recovery from mivacurium, and may enable anaesthetists to avoid antagonism of mivacurium-induced block.