Dependence of the neuromuscular blocking effect of atracurium upon its disposition

We have assessed the profiles of plasma concentration of atracurium and its neuromuscular blocking effect on the first response of the train-of-four measured by electromyography after a short infusion of atracurium 0.25 mg kg-1, in 38 patients anaesthetized by one of three techniques. Measures of the temporal profile of neuromuscular block were found to correlate with pharmacokinetic variables. When anaesthetic technique was taken into account in a multivariate model, the time to onset of 10% deprssion of T1:T0 correlated positively with the central volume of distribution (P less than 0.05). The change in T1:T0 during the 1 min after 10% depression, and the logit of maximum depression were both correlated negatively with the central volume of distribution (P less than 0.05 and P less than 0.01, respectively). Both the times to 20% and 50% recovery of T1:T0 correlated strongly negatively with clearance (P less than 0.0001 for both measures). The findings support the conclusion that the effect of atracurium is dependent upon its disposition.