Fig. 6. Computer simulation of the blood propofol concentration in the presence and absence of a plasma alfentanil concentration of 80 ng/ml, with the infusion scheme used in this study (1 mg/kg intravenous propofol, administered in 1 min, followed by 3 mg · kg−1· h−1for 59 min), using the pharmacokinetic model with plasma alfentanil concentration incorporated as the only covariate (table 2).