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In this prospective study we tested the hypothesis that atropine administration, which is known to increase heart rate and cardiac output in infants, will result in a faster onset of neuromuscular block with atracurium. Thirty infants scheduled for elective surgery had anaesthesia induced with nitrous oxide and halothane. Fifteen patients were given atropine and 15 patients acted as controls. All the infants were given atracurium 0.5 mg.kg-1, and neuromuscular block was recorded with the Datex 221 neuromuscular transmission monitor. Although atropine caused an increase in heart rate compared to the control group (median 164 [range 151-182] vs 120 [98-160]min-1 P < 0.0001), there was not a statistically significant difference in the onset of neuromuscular block between the two groups. We conclude that onset of neuromuscular block after atracurium is determined mainly by noncirculatory factors and less by the circulation time to the muscle. The effect of atropine on the time course of neuromuscular block might be different with faster acting neuromuscular blockers.

This randomized blinded study tested the hypothesis that equipotent doses of vecuronium and mivacurium given in combination could achieve onset times to 90% neuromuscular block (B90) and intubation scores similar to succinylcholine. Thirty children were randomly assigned to one of three groups as follows. Group Sux received a single dose (1 mg.kg-1) of succinylcholine followed by normal saline. Group V1M1 received 0.08 mg.kg-1 of vecuronium followed by 0.1 mg.kg-1 of mivacurium. Group V2M2 received 0.16 mg.kg-1 of vecuronium followed by 0.2 mg.kg-1 of mivacurium. Anaesthesia consisted of propofol, fentanyl, and nitrous oxide. Neuromuscular response was monitored by adductor pollicis electromyography (Datex NMT). Sixty s after administration of the first injection, the laryngoscopy began, with the anaesthesiologist scoring the ease of intubation on a four category scale as excellent, good, poor, or inadequate. Time from injection to B90 was 39 (2.6)s after succinylcholine, which was not significantly different from 48 (3.5)s after vecuronium 0.16 mg.kg-1 and mivacurium 0.2 mg.kg-1 (V2M2). Mean time to B90 for group V1M1 was 64 (4.7)s, which was significantly different from that in group Sux. The intubation score was 'excellent' for all patients in groups Sux and V2M2 and for only seven of ten patients in group V1M1. Only combination of vecuronium (0.16 mg.kg-1) and mivacurium (0.2 mg.kg-1) provided rapid onset of neuromuscular blockade and excellent intubating conditions comparable to succinylcholine 1 mg.kg-1. This combination did result in prolonged recovery times.