• R F McLean, A J Baker, S E Walker, C D Mazer, B I Wong, and E M Harrington.
• Department of Anaesthesia, Sunnybrook Health Science Centre, University of Toronto, Ontario, Canada.
• Can J Anaesth. 1996 Jun 1; 43 (6): 580-4.

PurposeTo describe the serum concentrations of ketamine following a clinically relevant dosing schedule during cardiopulmonary bypass (CPB).MethodsDesignProspective case series.SettingTertiary care teaching hospital.PatientsSix patients undergoing coronary artery bypass grafting and over age 60 yr.InterventionFollowing induction of anaesthesia each patient received a bolus of ketamine 2 mg.kg-1 followed by an infusion of 50 micrograms.kg-1.min-1 which ran continuously until two hours after bypass.Main Outcome MeasuresKetamine 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.ResultsAt the time of aortic cannulation, ketamine concentrations were 3.11 +/- 0.81 micrograms.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).ConclusionThis 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 be use in order to assess the potential neuroprotective effects of ketamine in humans undergoing CPB.

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