Ketamine concentrations during cardiopulmonary bypass

Abstract

Purpose: To describe the serum concentrations of ketamine following a clinically relevant dosing schedule during cardiopulmonary bypass (CPB). Methods: Design: Prospective case series. Setting: Tertiary care teaching hospital. Patients: Six patients undergoing coronary artery bypass grafting and over age 60 yr. Intervention: Following induction of anaesthesia each patient received a bolus of ketamine 2 mg · kg-1 followed by an infusion of 50 μg · kg-1 · min-1 which ran continuously until two hours after bypass. Main Outcome Measures: Ketamine serum concentrations were measured at five minutes after bolus, immediately following aortic cannulation, 10 and 20 min on CPB, termination of CPB, termination of the drug infusion and three and six hours after infusion termination. Results: At the time of aortic cannulation, ketamine concentrations were 3.11 ± 0.81 μg · ml-1, these levels decreased by one third with the initiation of CPB. By the end of CPB the concentrations had returned to levels roughly equivalent to those observed at the time of aortic cannulation. Following cessation of the infusion, ketamine concentration declined in a log-linear fashion with a half-life averaging 2.12 hr. (range 1.38-3.09 hr). Conclusions: This dosage regimen maintained general anaesthetic concentrations of ketamine throughout the operative period. These levels should result in brain tissue concentrations in excess of those previously shown to be neuroprotective in animals. Thus we conclude that this infusion regimen would be reasonable to use in order to assess the potential neuroprotective effects of ketamine in humans undergoing CPB.