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We studied 45 patients (ASA I-II) during propofol-alfentanil-N2O-O2 anaesthesia to determine if recovery from neuromuscular block induced by mivacurium is influenced differently by prior injection of atracurium or vecuronium. Neuromuscular function was monitored by adductor pollicis EMG. Patients were randomized to receive two doses of either mivacurium (150 and 70 micrograms kg-1), atracurium (350 and 75 micrograms kg-1) or vecuronium (70 and 15 micrograms kg-1) followed by a final dose of mivacurium 70 micrograms kg-1. The second and third doses of the muscle relaxants were administered at 25-30% recovery of the E1 (first EMG response in the train-of-four series). Following the final dose of mivacurium, the EMG response recovered to 25 and 95% in 10.4 +/- 3.9 and 19.7 +/- 5.7 min (mean +/- SD), respectively, if mivacurium was the only muscle relaxant. Respective times were 100% longer if mivacurium had been preceded by atracurium (23.8 +/- 3.3 and 39.8 +/- 6.9) or vecuronium (22.6 +/- 3.5 and 44.1 +/- 7.9 min) (P = 0.0001). The 25-75% recovery times in the three groups were 4.9 +/- 1.0, 8.7 +/- 2.4 and 10.5 +/ 2.5 min, respectively (P = 0.0001). Our results indicate that there is no benefit in giving mivacurium at the end of surgery after peroperative use of atracurium or vecuronium.

Spontaneous recovery of neuromuscular function after a bolus dose of 0.40 mg/kg atracurium was assessed in 60 newborn to adolescent patients during balanced anesthesia. Each patient was allowed to recover spontaneously until complete recovery of the single twitch (T1) response and the train-of-four ratio measured from the hypothenar muscle evoked compound EMG. The recovery times of T1 from the onset of relaxation to 10% recovery and to 100% recovery were significantly longer in patients under 10 kg of body weight than in the heavier patients (25 and 56 min vs 19 and 45 min, respectively, P less than 0.01). The rate of recovery, calculated as the recovery index (time between 25% recovery and 75% recovery of T1) was significantly longer in patients under 2 months of age than in older infants or children and adolescents. Atracurium remains, nevertheless, a relaxant of intermediate duration of action even in small infants.