Assessment of the interaction between atracurium and suxamethonium at 50% neuromuscular block using closed-loop feedback control of infusion of atracurium

Abstract

We have studied the effect of prior administration of suxamethonium on the infusion requirements of atracurium at 50% neuromuscular block in patients undergoing elective general surgery. Anaesthesia was maintained with nitrous oxide in oxygen, propofol and fentanyl. Of 20 patients given atracurium, only 10 were given prior administration of suxamethonium 1 mg kg-1. At the beginning of the infusion, atracurium 0.3 mg kg-1 was given by bolus administration. Interaction between the two drugs was assessed by determining the steady state rate of infusion necessary to produce a constant 50% neuromuscular block. This was accomplished by applying non-linear curve fitting to data on the cumulative dose requirements during anaesthesia. The neuromuscular blocking effect was found to be similar with or without prior administration of suxamethonium. The mean steady-state rate of infusion for atracurium was 0.19 (SD 0.03) mg kg-1 h-1 for patients given suxamethonium and 0.18 (0.09) mg kg-1 h-1 for those who were not given suxamethonium. Thus prior administration of suxamethonium did not affect the infusion requirements of atracurium at 50% neuromuscular block, unlike the situation at constant 90% neuromuscular block. © 1994 British Journal of Anaesthesia.