Background
The aim of this study was to examine the pharmacokinetic and pharmacodynamic profile of propofol during propofol remifentanil and propofol - alfentanil anaesthesia, when monitored by SFx.
Material and Method
Thirty-three ASA physical status I-II patients scheduled for laparoscopic cholecystectomy were prospectively randomized to 1 of 2 groups according to type of opioid used (remifentanil or alfentanil). The propofol infusion rate was adjusted to the spectral frequency index (SFx) value. Venous blood samples were collected from patients during and after anaesthesia. Propofol was assayed by means of the HPLC method with fluorescence detection. The remifentanil and alfentanil groups were compared in relation to pharmacokinetic and pharmacodynamic parameters of propofol and a t-test was used for statistical analysis.
Results
The propofol mean total body clearance rate and the volume of distribution were significantly higher in the propofol - remifentanil group. There were not any statistically significant differences between the groups in mean EC(50), E(0), E(max) and k(e0) values. However, large interindividual variability was observed in EC(50) and k(e0) mean values. The value of ET(50) was significantly higher in the remifentanil group.
Conclusions
Alfentanil decreases the elimination clearance and the volume of distribution at steady state of propofol to a greater extent than with remifentanil. Our results suggest that if propofol is administrated by manual control, the same infusion rate should be used in the presence of alfentanil and remifentanil. For target controlled infusion, the same target propofol concentration should be used when both remifentanil and alfentanil are coadministrated.

Keywords: Propofol - therapeutic use, Piperidines - pharmacology, Monitoring, Physiologic - methods, Demography, Anesthetics, Intravenous - pharmacology, Anesthesia, Intravenous - methods, Alfentanil - pharmacology