Atracurium, vecuronium, and pancuronium do not alter the minimum alveolar concentration of halothane in humans

Abstract

The authors studied 64 unpremedicated, healthy surgical patients, aged 42 ± 14 yr, to determine the effects of atracurium, vecuronium, and pancuronium on the minimum alveolar concentration (MAC) of halothane. Anesthesia was induced using halothane/nitrous oxide/oxygen via a mask without the administration of other drugs. Nitrous oxide was discontinued, the trachea was intubated without prior administration of neuromuscular blocking drugs, and anesthesia was maintained with halothane in oxygen. Participating patients were assigned to one of five groups: 1) no neuromuscular blocking drug (control group, n = 9); 2) atracurium 0.5 mg/kg (n = 10); 3) atracurium 1.0 mg/kg (n = 15); 4) vecuronium 0.1 mg/kg (n = 20); or, 5) pancuronium 0.1 mg/kg (n = 10). Tourniquets, inflated to 300 mm Hg immediately before iv administration of neuromuscular blocking drug and 15-30 min prior to skin incision, were used to isolate extremities from circulating neuromuscular blocking drug in all patients. A positive response to stimulation was defined as movement of at least one extremity occurring distal to the tourniquet within 1 min following skin incision. The first patients in the control and atracurium groups were studied at an end-tidal halothane concentration of 0.95%. The first patient in the pancuronium group was studied at a halothane concentration of 0.75%, and the first patient in the vecuronium group at 0.70%. Subsequent patients were studied at end-tidal halothane concentrations 0.10% above or below that of the preceding patient, depending on the presence or absence of movement with skin incision. Control MAC for halothane was 0.74% ± 0.09% (mean ± SEM). Atracurium, 0.5 and 1.0 mg/kg, did not significantly change the MAC of halothane (0.74% ± 0.08% and 0.77% ± 0.05%, respectively). The MAC of halothane was also unchanged from control in the patients given vecuronium and pancuronium (0.78% ± 0.04% and 0.74% ± 0.12%, respectively). Thus, clinical doses of atracurium, vecuronium, and pancuronium do not change the MAC of halothane in humans.