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 dextromethorphan 30 min before the end of surgery an d a placebo 30 min before skin incision, and the Control group received a p lacebo both 30 min before skin incision and 30 min before the end of surger y. A standard general anesthetic technique including fentanyl, propofol, is oflurane, and atracurium was used. Postoperative meperidine patient-control led analgesia (PCA) was used. There were no significant group differences i n the median pain scores except in the visual analog scale at 6h both at re st ment; these were significantly lower in the Preincisional group than the other two groups (P < 0.05). The mean time to initiation of PCA was signif icantly longer in the Preincisional than in the Postincisional and Control groups (mean [SD]: 10.7 [2.2 h], 5.4 [2.1 h], and 3.7 [1.6 h], respectively ; P < 0.001). The 24-h PCA-meperidine consumption was significantly 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 was signific antly less in the Preincisional group (P < 0.05). In conclusion, pre incisi onal IM 120 mg dextromethorphan compared with the same postincisional dose significantly reduced postoperative meperidine consumption.