PLASMA-CONCENTRATION AND PROTEIN-BINDING OF ALFENTANIL DURING HIGH-DOSE INFUSION FOR CARDIAC-SURGERY

We have studied plasma protein binding of alfentanil in 10 patients gi ven a mean total dose of 949 mu g kg(-1) as the principal anaesthetic agent for coronary artery bypass grafting. The mean unbound fraction o f plasma alfentanil increased from 0.09 to 0.16 after administration o f heparin and to 0.26 after beginning cardiopulmonary bypass (CPB). Af ter CPB until the end of surgery, the unbound fraction decreased to 0. 12. These changes in the unbound fraction were associated with signifi cant changes in plasma total and unbound concentrations of alfentanil also. Within the first I min of CPB, total alfentanil concentration ha d decreased by more than the unbound concentration and the decrease ob served in the latter disappeared rapidly. From induction of anaesthesi a until awakening of the patient, plasma protein binding of alfentanil was related significantly (P = 0.0166) to the serum concentration of orosomucoid (alpha(1)-acid glycoprotein).