Objective: To determine the propofol effect site target concentration at which 50% of patients did not respond to stimulation for colonoscopy (EC50colonoscopy) using a target controlled infusion (Schnider model) and to investigate whether fentanyl reduces these required concentrations.

Material and Method: Subsequent to an approval from the institute medical ethics committee, 40 unpremedicated patients, ASA physical status 1-2, aged 18-70 years, BMI less than 30 kg/m2 and scheduled for elective colonoscopy were randomly assigned to a saline-propofol group (control group) or a 1 mcg/kg fentanyl-propofol group (fentanyl group). Propofol was initiated using a target controlled infusion. Initial effect site target concentration (EC) administered to the first patient in each group were 2.5 mcg/ml. For each subsequent patient, EC was determined by the response of the previous patient by the Dixon’s up-and-down method (with 0.5 mcg/ml as a step size). Individual patient response to colonoscopy was described as ‘no movement’ or ‘movement’. EC50colonoscopy values were obtained by calculating the mean of 20 patients in each group.

Results: The patient demographic data were not significantly different between the two groups. Total propofol dose in the control group was also significantly higher than that in the fentanyl group. The values for EC50colonoscopy were 3.25 + 0.47 mcg/ml in the control group and 2.65 + 0.40 mcg/ml in the fentanyl group (p = 0.00).

Conclusion: The propofol EC50  for colonoscopy was decreased by supplemental 1 mcg/kg fentanyl with no significant difference in hemodynamic values between the two groups.

Keywords: Anesthesia, Target controlled infusion, Effect site target concentration, Propofol, Colonoscopy