Remifentanil is a useful opioid, but it induces postoperative hyperalgesia and acute tolerance associated N-methyl-D-aspartate (NMDA) receptor. This study was aimed to investigate whether small dose ketamine, NMDA receptor antagonist, prevent remifentanil induced postoperative hyperalgesia or acute tolerance after combined anesthesia with propofol and remifentanil using target controlled infusion (TCI) in patients undergoing mastectomy.

Fourty ASA physical status 1 or 2 women, undergoing mastectomy were randomly assigned to two groups to receive intraoperative infusion of ketamine at 3 µg/kg/min rate after injection of ketamine 0.3 mg/kg as a loading dose (Group K) or saline infusion after saline loading at the same rate and dose (Group C). All the patients were anesthetized with propofol and remifentanil to maintain bispectral index (BIS) 40-60, mean arterial pressure within 20% of basal values. Remifentanil was infused with target controlled infusion (TCI) to the effect site (concentration: 2.0 ng/ml). Postoperative paine scores (visual analog scale: VAS), morphine requirements, and sedation scores were recorded for 48 hours postoperatively.

The VAS scores and morphine requirements of the Group K were significantly lower than those of the Group C at the postanesthetic care unit and at the ward for 24 hours postoperatively. The extubation time was delayed in Group K compared with Group C.

Intraoperative infusion of small dose ketamine reduced postoperative pain and morphine requirements after combined anesthesia with propofol and remifentanil in patients undergoing mastectomy.