The ED50 and ED95 of ketamine for prevention of postoperative hyperalgesia after remifentanil-based anaesthesia in patients undergoing laparoscopic cholecystectomy

Various research programmes have shown that intraoperative infusion of remifentanil has been associated with postoperative hyperalgesia. Previous studies have demonstrated that low-dose ketamine can inhibit central sensitisation and prevent opioid-induced hyperalgesia (OIH). However, the optimal ketamine dose to prevent OIH has not been determined. In the present study we aimed to determine the ED50 and ED95 of ketamine for prevention of postoperative hyperalgesia after remifentanil-based anaesthesia in patients undergoing laparoscopic cholecystectomy. Fifty-four patients undergoing laparoscopic cholecystectomy were randomised into two groups: group C and group K. Group K was given ketamine before skin incision. An equal volume of normal saline was given to the patients in group C. Pain was assessed using visual analog scale (VAS) at 10 min after tracheal extubation. The ED50 and ED95 were determined by modified up-and-down method and the incidences of adverse effects were recorded. The incidences of adverse effects were similar in the two groups and the VAS score was significantly lower in group K than in group C. The ED50 and ED95 of ketamine for prevention of postoperative hyperalgesia were 0.24 mg/kg (95%CI, 0.20~0.30 mg/kg) and 0.33 mg/kg (95%CI, 0.28~0.62 mg/kg) respectively. The ED50 and ED95 of ketamine for prevention of postoperative hyperalgesia after remifentanil-based anaesthesia in patients undergoing laparoscopic cholecystectomy were 0.24 mg/kg and 0.33 mg/kg respectively.