The role of magnesium in preventing postoperative hyperalgesia

Objectives: Intraoperative remifentanil administration results in acute opioid tolerance that is manifested by increased postoperative pain, opioid requirement and specifically periincisional hyperalgesia. The aim of this study was to investigate the effect of magnesium in preventing remifentanil-induced hyperalgesia. Methods: This study was performed on 60 (ASA I-II) patients planned for abdominal hysterectomy. Sixty patients were randomized into two equal groups. Before anesthesia, saline solution was given to the patients in group I (control group), 50 mg/kg i.v. magnesium in group II (magnesium group). Anesthesia was induced with 1 mu g/kg remifentanil combined with 4-5 mg/kg thiopental and 0.5 mg/kg atracurium, maintained with 0.5 MAC sevoflurane and 0.4 mu g/kg/min remifentanil in both groups. Sevoflurane concentration was titrated according to autonomic responses. Thirty minutes before the anticipated end of surgery, a 0.15 mg/kg bolus dose of morphine was intravenously. At the end of surgery, patients received tramadol i.v via a PCA device. Pain score, tramadol demand and delivery were assessed at 2, 4, 6, 12, 24 h after surgery. Total tramadol consumption were recorded for 24-48 h after surgery. Periincisional hyperalgesia was assessed by measuring pain threshold to pressure by using an algometer and electronic von Frey filaments before operation and at 28-48 h postoperatively. Results: The pain scores and cumulative tramadol consumption were significantly lower in the magnesium group compared with the control group (p< 0.05). Pressure and mechanical pain threshold were significantly less at 24-48 h postoperatively in control group than magnesium group. Conclusion: Magnesium administered preemptively reduced remifentanil-induced hyperalgesia.