Changes in total and unbound concentrations of sufentanil during target controlled infusion for cardiac surgery with cardiopulmonary bypass.

BACKGROUND: Target controlled infusion (TCI) with sufentanil is usually performed using the Gepts model, which was derived from patients undergoing general surgery. It is, however, known that pharmacokinetics of sufentanil can be changed during cardiopulmonary bypass (CPB). We tested whether TCI during coronary artery bypass surgery with CPB produces constant total, unbound sufentanil concentration-time course or both.

METHODS: After IRB approval, written informed consent was obtained from 38 male patients (48-74 yr) undergoing coronary artery bypass surgery. Anaesthesia was managed with propofol and TCI of sufentanil, using the Gepts model, targeting plasma concentrations of 0.4 (n=18) or 0.8 ng ml(-1) (n=20). Arterial blood samples were taken before, during, and after CPB. Total and unbound sufentanil concentrations were measured by HPLC with tandem mass spectrometry. The accuracy of the TCI model was assessed by the prediction error, and a pharmacokinetic model was determined by population analysis.

RESULTS: The median prediction error of the TCI with the Gepts model before, during, and after CPB was 59.6, 3.9, and -10.4%, respectively. The unbound sufentanil concentrations increased significantly during CPB. Pharmacokinetic modelling showed an increase in elimination and intercompartmental clearance after initiation of CPB.

CONCLUSIONS: Neither total nor unbound sufentanil concentrations remained constant when performing a TCI with the Gepts model in coronary artery bypass surgery with CPB. A pharmacokinetic model derived from patients undergoing cardiac surgery with CPB might improve the performance of TCI in this population.