Neostigmine requirements for reversal of neuromuscular blockade following an infusion of mivacurium.

PURPOSE To study the efficacy of neostigmine compared with placebo for the antagonism of neuromuscular blockade at the end of a mivacurium infusion, and to determine its optimal dose. METHODS One hundred adult patients undergoing an elective surgical procedure received a standardized anaesthetic with 20-30 micrograms.kg-1 alfentanil, a propofol infusion and nitrous oxide. Muscle relaxation was maintained at 90-95% T1 depression with 0.2 mg.kg-1 mivacurium followed by an infusion. Neuromuscular blockade was measured with an integrated evoked electromyogram in response to train-of-four (TOF) stimuli at the ulnar nerve every 20 sec. Patients were randomized into four groups. At the end of surgery, the mivacurium infusion was stopped and patients received, immediately, in a double-blind manner, neostigmine (10, 20, or 40 micrograms.kg-1) or placebo according to a random number table. The T1 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 postoperative nausea and vomiting (PONV) was recorded in the recovery room. RESULTS Data from 94 patients who completed the protocol were analysed. Compared with placebo, neostigmine 10 micrograms.kg-1 did not reduce the time to TOF > 0.70 (17.0 +/- 5.1 vs 14.6 +/- 4.2 min respectively). However the time was decreased with neostigmine 20 micrograms.kg-1 and 40 micrograms.kg-1 (P < 0.001), but with no difference between these last two groups (11.4 +/- 3.0 and 11.4 +/- 3.5 min respectively). Changes in systolic blood pressure and heart rate were not different between the four groups. Very few PONV events were observed in all groups (global incidence 7.4%). CONCLUSION Recovery of neuromuscular blockade following a mivacurium infusion is accelerated by neostigmine. A dose of neostigmine 20 micrograms.kg-1 appears optimal with no further reduction in recovery time obtained from a larger dose.