Quantitation of the interaction between atracurium and succinylcholine using closed-loop feedback control of infusion of atracurium

The authors used closed-loop feedback control of infusion of atracurium to study the effect of prior administration of succinylcholine on neuromuscular blockade induced by atracurium in patients undergoing otolaryngologic surgery. Anesthesia was maintained with nitrous oxide in oxygen, flunitrazepam, and fentanyl. Of 14 patients given atracurium, seven were given prior administration of succinylcholine and seven were not. Interaction between the two drugs was quantified by determining the asymptotic steady-state rate of infusion necessary to produce a constant 90% neuromuscular blockade. This was accomplished by applying nonlinear curve-fitting to data on the cumulative dose requirement during anesthesia. The neuromuscular blocking effect of atracurium was found to be greater after prior administration of succinylcholine. The asymptotic steady-state rate of infusion (+/- SD) for atracurium was 0.27 +/- 0.06 mg.kg-1.h-1 for patients given succinylcholine and 0.38 +/- 0.10 mg.kg-1.h-1 for those not given succinylcholine. The clinical implication of this study is that the clinician should be aware of the fact that an induction dose of 1 mg/kg of succinylcholine does reduce atracurium requirement for 90% neuromuscular blockade by approximately 30%.