The median effective concentration (EC50) of propofol with different doses of fentanyl during colonoscopy in elderly patients

Background: Propofol and fentanyl are the most widely administered anesthesia maintaining drugs during colonoscopy. In this study, we determined the median effective concentration (EC50) of propofol required for colonoscopy in elderly patients, and the purpose of this study was to describe the pharmacodynamic interaction between fentanyl and propofol when used in combination for colonoscopy in elderly patients. Methods: Ninety elderly patients scheduled for colonoscopy were allocated into three groups in a randomized, double-blinded manner as below, F0.5 group (0.5 mu g.kg(-1) fentanyl), F1.0 group (1.0 mu g. kg(-1) fentanyl) and saline control group. Anaesthesia was achieved by target-controlled infusion of propofol (Marsh model, with an initial plasma concentration of 2.0 mu g. ml(-1)) and fentanyl. Colonoscopy was started 3 min after the injection of fentanyl. The EC50 of propofol for colonoscopy with different doses of fentanyl was measured by using an up-and-down sequential method with an adjacent concentration gradient at 0.5 mu g. ml(-1) to inhibit purposeful movements. Anaesthesia associated adverse events and recovery characters were also recorded. Results: The EC50 of propofol for colonoscopy in elderly patients were 2.75 mu g. ml(-1) (95 % CI, 2.50-3.02 mu g. ml(-1)) in F0.5 group, 2.05 mu g. ml(-1) (95 % CI, 1.98-2.13 mu g. ml(-1)) in F1.0 group and 3.08 mu g. ml(-1) (95 % CI, 2.78-3.42 mu g. ml(-1)) in control group respectively (P < 0.05). Patients in the F1.0 group had a significantly longer awake time and length of hospital stay than those in control group (P < 0.05). Conclusion: Increasing doses of fentanyl up to 1.0 mu g. kg(-1) reduces the propofol EC50 required for elderly patients undergoing colonoscopy, and there was no significant difference in anaesthesia associated adverse events but prolonged awake and discharge time.