Intraoperative low-dose ketamine infusion reduces acute postoperative pain following total knee replacement surgery: a prospective, randomized double-blind placebo-controlled trial.

OBJECTIVE To evaluate the effect of intraoperative low-dose ketamine with general anesthesia on postoperative pain after total knee replacement surgery. STUDY DESIGN A randomized, double-blind comparative study. PLACE AND DURATION OF STUDY Ankara Numune Training and Research Hospital, Turkey, from January and June 2011. METHODOLOGY Sixty adults undergoing total knee arthroplasty were enrolled in this study. The patients were randomly allocated into two groups of equal size to receive either racemic ketamine infusion (6 μg/kg/minute) or the same volume of saline. A visual analogue scale (VAS) was used to measure each patient's level of pain at 1, 3, 6, 12, and 24 hours after surgery. Time to first analgesic request, postoperative morphine consumption and the incidence of side effects were also recorded. RESULTS Low-dose ketamine infusion prolonged the time to first analgesic request. It also reduced postoperative cumulative morphine consumption at 1, 3, 6, 12, and 24 hours postsurgery (p < 0.001). Postoperative VAS scores were also significantly lower in the ketamine group than placebo, at all observation times. Incidences of side effects were similar in both study groups. CONCLUSION Intraoperative continuous low-dose ketamine infusion reduced pain and postoperative analgesic consumption without affecting the incidence of side effects.