Dose requirements of infusions of cisatracurium or rocuronium during hypothermic cardiopulmonary bypass

We investigated the influence of mild hypothermic cardiopulmonary bypass (C PB) on the dose requirements of cisatracurium or rocuronium used as a conti nuous infusion. We studied eight patients given cisatracurium and nine give n rocuronium. They were ASA class III and IV and scheduled for elective cor onary artery bypass grafting. Neuromuscular transmission was monitored elec tromyographically. After recovery of T1/T0 to 10%, a cisatracurium infusion or a rocuronium infusion was started at a rate of 1.5 or 10 mu g kg(-1) mi n(-1), respectively, and adjusted to maintain T1/T0 at 15%. Infusion rate a nd duration were recorded before, during and after CPB in each patient and the mean infusion rates were calculated. One-way ANOVA showed a statistical ly significant difference between the cisatracurium infusion rates before, during and after CPB: A T1/T0 of 15% could be achieved with a mean infusion rate of 1.1, 0.75 and 0.98 mu g kg(-1) min(-1) before, during and after CP B, respectively. There was no significant difference between the rocuronium infusion rates before, during and after CPB. The mean rocuronium infusion rate required to maintain T1/T0 at 15% throughout the procedure was 4.1 mu g kg(-1) min(-1). Cisatracurium infusion rates should be halved during CPB. Even after CPB, requirements are reduced. The same tendency occurs with ro curonium, but the changes in infusion rate were not statistically significa nt.