Model-driven closed-loop feedback infusion of atracurium and vecuronium during hypothermic cardiopulmonary bypass

Abstract

Objectives : This study was designed to investigate the performance of a computer-controlled infusion of atracurium and vecuronium during cardiac surgery requiring hypothermic cardiopulmonary bypass. Design : Prospective, randomized study. Setting : A single university hospital. Participants : Twenty patients scheduled for cardiac surgery. Interventions : After induction of anesthesia with fentanyl and diazepam, 10 patients were randomly allocated to receive a bolus of atracurium and 10 patients a bolus dose of vecuronium to facilitate endotracheal intubation. The initial bolus was followed by a computer-controlled closed-loop feedback infusion of atracurium or vecuronium until the patients were transferred to the postoperative intensive care unit. The desired level of neuromuscular blockade, as measured by EMG, was set to 90%. Anesthesia was maintained with a mixture of oxygen and air and either enflurance or halothane. Measurements and Main Results : The groups were similar with respect to patient characteristics. Except during hypothermic CPB, the controller kept the neuromuscular blockade near the set point in both groups. During hypothermic CPB the maximal oscillation of muscle relaxation was within 10% from the set point. When CPB was initiated, the mean rates of infusion of the muscle relaxants increased from the pre-CPB values, but the change of the infusion rate was not statistically significant for atracurium. During the remainder of CPB, the infusion requirements of both muscle relaxants were greatly reduced, but rewarming essentially returned the infusion requirements to pre-CPB values. Conclusions : The computer-controlled infusion can be used for the administration of atracurium and vecuronium during CPB.