Intraoperative high dose fentanyl induces postoperative fentanyl tolerance

Purpose: In a randomized, double-blind clinical trial. we compared the postoperative analgesic effect and dose consumption of fentanyl after intraoperative high dose and low dose fentanyl administration. Methods: Sixty ASA class I to II female patients undergoing total abdominal hysterectomy (TAH), were randomly allocated to receive either 1 mu g.kg(-1) (low dose group, n = 30) or 15 mu g.kg(-1) (high dose group, n 30) fentanyl during induction of anesthesia. Anesthesia depth was maintained with inhalation of halothane in the low dose group, or combined with 100 mu g.hr(-1) fentanyl iv in the high dose group. Postoperative pain was treated with an intravenous patient-controlled analgesia system and was assessed with a visual analog pain score at rest. Results: Patients in the high dose group had higher pain intensity at four and eight hours postoperatively, more fentanyl consumption and a greater incidence of emesis in the postoperative period of 16 hr than those in the low dose group (P < 0.05), Heart rate, blood pressure, and respiratory rate were similar between the two groups. Conclusion: Our results suggest that acute fentanyl tolerance develops after administration of high dose fentanyl during surgery and, consequently, results in a higher postoperative pain intensity and greater fentanyl consumption.