Lack of pre-emptive analgesic effect of (R)-ketamine in laparoscopic cholecystectomy

Aim: This study evaluated the pre-emptive analgesic effect of intravenous (i.v.) (R)-ketamine in laparoscopic cholecystectomy. (R)-ketamine was used due to the lower incidence of side-effects. Methods: Sixty patients who underwent surgery under general anesthesia were randomly allocated to 3 groups and studied in a double-blind manner. Two i.v. injections were administered: one after induction of anesthesia, approximately 3 min before surgery, and one after surgery. The placebo group (PLA, n=20) received saline in both injections. The preoperative group (PRE, n=20) received (R)-ketamine 1 mg/kg and then saline. The postoperative group (POST, n=20) received saline and their (R)-ketamine I mg/kg. Postoperatively, the patients used a patient-controlled analgesia (PCA) pump. Pain was evaluated with a visual analog scale (VAS) at 30 min and every hour for 4 h and with a verbal rating scale (VRS) at 24 h and after 7 days. Results: There were no occurence of side-effects from (R)-ketamine. VAS and VRS at 1, 2, 3, and 4 h postoperatively showed no statistical differences. In the POST group, extubation was delayed and pain score (VAS) at 30 min postoperatively was significantly lower (P<0.05) than the two other groups. There were no statistical differences in meperidine consumption during the first 4 h postoperatively and no differences in consumption of analgesics at 24 h and 7 days. Conclusion: In this study a 1 mg/kg dose of (R)-ketamine given at the end of surgery exerted a short-lasting hypnotic and analgesic effect. The same dose given preoperatively did not show postoperative analgesic effect or pre-emptive effect.