The effect of the preemptive use of the NMDA receptor antagonist dextromethorphan on postoperative analgesic requirements

Both central sensitization after peripheral tissue injury and the developme nt of opiate tolerance involve activation of N-methyl-D-aspartate receptors . In this double-blinded, randomized study, we investigated the preemptive versus postincisional effects of dextromethorphan, an N-methyl-D-aspartate receptor antagonist, on postoperative pain management. Sixty ASA I and II p atients undergoing elective upper abdominal surgery were randomly allocated to three equally sized groups. The Preincisional group patients received d extromethorphan (120 mg) IM 30 min before skin incision and a placebo (isot onic saline) 30 min before the end of surgery. The Postincisional group rec eived the same dose of dextromethorphan30 min before the end of surgery and a placebo 30 min before skin incision, and the Control group received a pl acebo both 30 min before skin incision and 30 min before the end of surgery . A standard general anesthetic technique including fentanyl, propofol, iso flurane, and atracurium was used. Postoperative meperidine patient-controll ed analgesia (PCA) was used. There were no significant group differences in the median pain scores except in the visual analog scale at 6 h both at re st and on movement; these were significantly lower in the Preincisional gro up than the other two groups (P < 0.05). The mean time to initiation of PCA was significantly longer in the Preincisional than in the Postincisional a nd Control groups (mean [SD]: 10.7 [2.2 h], 5.4 [2.1 h], and 3.7 [1.6 h], r espectively; P < 0.001]. The 24-h PCA-meperidine consumption was significan tly less in the Preincisional than in the Postincisional and Control groups (mean [SD]: 140 [60 mg], 390 [80 mg], and 570 [70 mg], respectively; P < 0 .001]. The incidence of postoperative hypoxemia (Spo(2) < 90%) and nausea w as significantly less in the Preincisional group (P < 0.05). In conclusion, preincisional IM 120 mg dextromethorphan compared with the same postincisi onal dose significantly reduced postoperative meperidine consumption.