The effects of magnesium sulfate infiltration on perioperative opioid consumption and opioid-induced hyperalgesia in patients undergoing robot-assisted laparoscopic prostatectomy with remifentanil-based anesthesia

BACKGROUND: Opioids not only exert an antinociceptive effect, but also modulate central N-methyl-D-aspartate (NMDA) receptors, resulting in hyperalgesia and acute opioid tolerance. This study was aimed to investigate the effect of the NMDA receptor antagonist, magnesium in preventing remifentanil-induced hyperalgesia. METHODS: For this study, 75 patients scheduled for robot-assisted laparoscopic prostatectomy were randomly allocated into three groups of patients whose incision sites were infiltrated: Group M, with 25% magnesium sulfate 80 mg/kg; Group S, with the same volume of saline under remifentanil-based anesthesia, and Group D, with the same volume of saline under desflurane based anesthesia. All three groups were infiltrated into incision sites after pneumoperitoneum. Intraoperative evaluation included mean remifentanil dose, and postoperative evaluation included pain severity at time intervals of 30 min, 6, 12, 24 and 36 hours, time to first postoperative analgesic requirement, and analgesic dosage required during 24 hours. RESULTS: Mean remifentanil doses during the intraoperative periods in group M were significantly lower than those in group S (P < 0.001). The time to first postoperative analgesic requirement in postoperative period in groups M and D was significantly longer than that in group S (P < 0.001). Visual analog scale scores for pain in groups M and D were significantly lower than those in group S for 12 hours after operation. CONCLUSIONS: A relatively high dose and continuous infusion of remifentanil were associated with opioid induced hyperalgesia. Wound infiltration with magnesium sulfate decreased opioid consumption and reduces opioid induced hyperalgesia.