Recovery from Mivacurium Block with or without Anticholinesterase following Continuous Infusion in Obstetric Patients

Abstract

Neostigmine antagonism after suxamethonium followed by mivacurium chloride bolus and infusion was studied. Thirty ASA group I or II patients were given mivacurium 0.15 mg/kg followed by infusion during nitrous oxide-enflurane-pethidine anaesthesia. Train of four (TOF) stimuli were applied to the ulnar nerve at the wrist and TOF twitch height and ratio measured by TOF-GUARD nerve stimulator. Mivacurium infusion was titrated to give a 90% block of first twitch height. Patients were randomized into two groups. Group I patients recovered from the mivacurium block spontaneously while Group II patients were given neostigmine 0.05 mg/kg and atropine 0.02 mg/kg. Time to reach train of four ratio (TOFR) of 25%, 50% and 70% were measured. This study demonstrated a mean infusion rate of 5.1±1.8 μg/kg/min to maintain a 90% neuromuscular block. In the spontaneous recovery group, time to reach TOFR of 25%, 50% and 70% were 9.3±2.7 min, 13.5±3.0 min and 16.7±3.0 min respectively while the corresponding times in the neostigmine group were 5.2±1.7 min, 10.9±2.2 min and 16.1±7.4 min respectively. There were significant differences in the time taken to TOFR of 25% (P<0.0001) and 50% (P<0.05) but no difference in the time taken for TOFR to return to 70%. We concluded that mivacurium is suitable for use in caesarean section despite a decrease in plasma cholinesterase activity. Neostigmine antagonism is not required as a routine.