Bolus ketamine does not decrease hyperalgesia after remifentanil infusion

Abstract Background and aim: Several animal and human studies have proposed that acute tolerance to opioids might be manipulated by NMDA receptor antagonists. This study was designed to test the opioid-induced hyperalgesia produced by remifentanil, and to evaluate the effect of ketamine under these conditions. Methods: Forty-seven ASA 1-2 patients undergoing lumbar disc operation were randomly assigned into 3 anaesthetic regimens. The patients were not premedicated. After standard anaesthesia induction with propofol and vecuronium, group R and group K patients received a remifentanil infusion of 0.1 μg kg−1 min−1. Group K also received 0.5 mg kg−1 ketamine bolus before remifentanil infusion. Group S was the control group and equal volume of saline instead of remifentanil was infused throughout the operation. Groups R and S also received a bolus of the same volume of saline instead of ketamine by an anaesthesiologist blinded to the study. After the surgery under desflurane anaesthesia, patient-controlled a...