Effects of two methods of fentanyl bolus administration during remifentanil-based anesthesia on pain in the immediate postoperative period

Objective. To determine which method provides superior pain relief and recovery from anesthesia while minimizing adverse effects in the immediate postoperative period. Methods. We studied 70 patients undergoing gynecologic laparotomy. Anesthesia was induced with propofol and remifentanil. After tracheal intubation facilitated with vecuronium or rocuronium, anesthesia was maintained with sevoflurane and remifentanil. Patients were randomly assigned to receive 8 mu g/kg of fentanyl at the start of surgery (early-bolus group) or 6 mu g/kg of fentanyl at 60min before the anticipated end of surgery (late-bolus group). At the end of surgery, the times from discontinuation of sevoflurane until patient response to verbal commands and until extubation were recorded as indicators of recovery from anesthesia. Hemodynamic parameters, pain score, sedation grade, and incidence of side effects were evaluated at 0, 5, 10, 15, and 30 min after entering the post-anesthesia care unit (PACU). Results. A longer recovery time from anesthesia was required in the late-bolus group compared with the early-bolus group, whereas mean pain score was significantly lower in the late-bolus group compared with the early-bolus group. Furthermore, mean dose of fentanyl administered in the PACU was significantly higher in the early-bolus group compared with the late-bolus group. Sedation grade and incidence of adverse effects were similar between the groups. Conclusion. Administration of 6 mu g/kg fentanyl at 60min before the anticipated end of surgery during remifentanil-based anesthesia provided superior postoperative analgesia in the immediate postoperative period as compared with 8 mu g/kg fentanyl administered at the start of surgery.