NEOSTIGMINE REQUIREMENTS FOR REVERSAL OF NEUROMUSCULAR BLOCKADE FOLLOWING AN INFUSION OF MIVACURIUM

Purpose: To study the efficacy of neostigmine compared with placebo fo r the antagonism of neuromuscular blockade at the end of a mivacurium infusion, and to determine its optimal dose. Methods: One hundred adul t patients undergoing an elective surgical procedure received a standa rdized anaesthetic ic with 20-30 mu g.kg(-1) alfentanil, a propofol in fusion and nitrous oxide. Muscle relaxation was maintained al 90-95% T I depression with 0.2 mg.kg(-1) mivacurium followed by an infusion. Ne uromuscular blockade was measured with an integrated evoked electromyo gram in response to train-of-four (TOF) stimuli at the ulnar nerve eve ry 20 sec. Patients were randomized into four groups. At the end or su rgery the mivacurium infusion was stopped and patients received, immed iately in a double-blind manner; neostigmine (10, 20, or 40 mu g.kg(-1 )) or placebo according to a random number table. The TI and TOF ratio were recorded until adequate recovery of neuromuscular function (TOF ratio > 0.70), During the reversal period, non-invasive blood pressure and heart rate were recorded every minute, The incidence of postopera tive nausea and vomiting (PONV) was recorded In the recovery room, Res ults: Data from 94 patients who completed the protocol were analysed. Compared with placebo, neostigmine 10 mu g.kg(-1) did not reduce the t ime to TOF > 0.70 (17.0 +/- 5.1 vs 14.6 +/- 4.2 min respectively). How ever the time was decreased with neostigmine 20 mu g.kg(-1) and 40 mu g.kg(-1) (P < 0.001), but with no difference between these last two gr oups(11.4 +/- 3.0 and 11.4 +/- 3.5 min respectively). Changes in systo lic blood pressure and heart rate were not different between the four groups. Very few PONV events were observed in all groups (global incid ence 7.4%). Conclusion: Recovery of neuromuscular blockade following a mivacunum infusion is accelerated by neostigmine, A dose of neostigmi ne 20 mu g.kg(-1) appears optimal with no further reduction in recover y time obtained from a larger dose.