Clinical pharmacodynamics of remifentanil under general anesthesia with propofol

Objective To investigate the clinical pharmacodynamic profiles of remifentanil under general anesthesia with propofol by heart rate(HR) and mean aterial pressure(MAP). Methods Twenty-four patients under general anesthesia with propofol were included in the study. According to the remifentanil constant infusion velocity during the general anesthesia,all patinets were equally randomized to Group Ⅰ 0.50 μg/(kg·min) ,Group Ⅱ 0.75 μg/(kg·min) and Group Ⅲ 1.00 μg/(kg·min) . Radial artery blood samples were drawn at 0,1,3,5,10,15 and 20 min during the remifentanil infusion and at 1,3,5,10,15,20,25 and 30 min after the remifentanil infusion for the determination of plasma remifentanil concentrations by high performance liquid chromatography with ultraviolet detector(HPLC-UV). The pharmacodynamics was analyzed with pharmacokinetics-pharmacodynamics(PK-PD) modeling. Results The effect intensity of HR and MAP was related to the remifentanil concentrations in effect compartment on the basis of the Sigmoid-Emax pharmacodynamics model. The pharmacodynamics parameters included Ke0 (0.439 ± 0.203)/min,γ 1.975 ± 1.067,EC50(4.883 ± 2.051) μg/L,Emax (36.4 ± 18.5) beat and Ke0 (0.463 ± 0.241)/min,γ 2.632 ± 1.889,EC50(4.372 ± 1.850)μg/L,Emax(0.359 ± 0.198)% using HR and MAP as measure of remifentanil drug effect,respectively. There was no significant difference between the pharmacodynamics parameters of three groups. The mean r2 of HR and MAP were 0.930 and 0.763,respectively (P 0.05). Conclusions There is no statistics difference of pharmacodynamics parameters between different infusion rates. HR can better quantitate the drug effect of remifentanil than MAP.