Effect of pre-emptive ketamine on sensory changes and postoperative pain after thoracotomy: comparison of epidural and intramuscular routes

Background. In this study we have evaluated the efficacy of ketamine via i.m. and epidural routes for the control of post-thoracotomy pain. Methods. The study was randomized, double blinded and placebo controlled. With the approval of the Faculty Ethics Committee, 60 patients undergoing elective thoracotomy were randomized into three equal groups. Group IM had i.m. ketamine 1 mg kg(-1) in 2 ml plus epidural normal saline; Group EPI had epidural ketamine 1 mg kg(-1) in 10 ml plus i.m. normal saline; Group C had epidural normal saline 10 ml plus i.m. normal saline 10 ml. Anaesthesia was standardized. Postoperative analgesia was maintained with epidural patient-controlled analgesia using bupivacaine and morphine. Visual analogue scale values and analgesic consumption were evaluated at 2, 4, 6, 8, 10, 12, 24 and 48 h after surgery. The areas of allodynia, pin-prick hyperalgesia and pressure hyperalgesia were measured at 48 h, and days 15 and 30 in all groups. Results. Intraoperative fentanyl requirement was significantly lower in Group EPI than Group C. The morphine and bupivacaine requirements were significantly lower in Group EPI than the other two groups in the postoperative period. There was reduced pin-prick hyperalgesia and touch allodynia in the EPI group. There were no side-effects attributable to ketamine. Conclusion. The results of the present study demonstrate that pre-emptive epidural ketamine is effective in reducing intra- and postoperative analgesic requirements, hyperalgesia and touch allodynia.