The effect of nefopam on morphine overconsumption induced by large-dose remifentanil during propofol anesthesia for major abdominal surgery.

Opioids may activate pain facilitatory systems opposing analgesia. We investigated whether large-dose remifentanil given during IV anesthesia caused postoperative morphine overconsumption and whether nefopam (a centrally acting analgesic) could reduce this. Sixty patients scheduled for abdominal surgery were included in this prospective, randomized study. The first 30 patients received either small-dose (Group S: 3 ng/mL) or large-dose (Group L: 8 ng/mL) remifentanil administrated by a target-controlled infusion during propofol anesthesia. Before skin closure, patients received morphine 0.15 mg/kg. Another 30 patients also received nefopam 20 mg intraoperatively. Postoperative pain was controlled by titration of morphine, followed by patient-controlled morphine analgesia (PCA). Morphine was requested earlier in Group L than in Group S (10 [1-63] min versus 37 [5-90] min, median [range]; P < 0.002). The dose of morphine by titration was larger in Group L than in Group S (0.28 [0.04-0.38] mg/kg versus 0.16 [0.03-0.41] mg/kg; P < 0.05). PCA morphine consumption and pain scores were similar. There were no differences between the nefopam groups in the time to first morphine request or in the dose of morphine by titration. Postoperative morphine overconsumption occurred after large-dose remifentanil and propofol anesthesia during the early postoperative period. Pretreatment with nefopam could be useful to prevent pain sensitization induced by opioids.