Propofol produces anesthesia with rapid recovery but also causes pain on injection. This study was designed to evaluate the effects of two different concentrations of remifentanil for minimizing the pain caused by propofol and to compare the hemodynamic changes during propofol-remifentanil infusion.

In a randomized, double-blind study of 80 patients, we compared the severity of the injection pain of propofol between two groups of patients. The initial effect-site target concentration of remifentanil was set at 4 ng/ml (the R4 group, n = 40) or 8 ng/ml (the R8 group, n = 40). After the effect-site concentration of remifentanil was achieved, the infusion of propofol was started with the concentration of 4 µg/ml. The remifentanil-related complications were evaluated and the severity of the pain caused by propofol was compared by using a four-point scale during the propofol infusion. The heart rate and arterial blood pressure were measured at pre-induction, just before intubation and at 1 minute after intubation.

The severity of injection pain of propofol was significantly lower in the R8 group than in the R4. There was no significant difference in the incidence of remifentanil-related complications between the two groups. Compared with the pre-induction values, the heart rate and arterial blood pressure were significantly lower at pre-intubation and at 1 minute after intubation in the R4 and R8 groups.

Pretreatment with an effect-site concentration of 8 ng/ml remifentanil may be useful for minimizing the propofol injection pain compared with 4 ng/ml remifentanil.