['The effects of fentanyl with ketamine for postoperative pain are unknown. We investigated the adjuvant effects of ketamine for fentanyl patient-controlled analgesia.', 'Cervical and lumbar spine surgery patients were divided into three groups: ketamine 1 mg/kg followed by 42 and 83 microg x kg(-1) x h(-1) in ketamine-1 and ketamine-2 group, respectively, and a control group. Postoperative patient-controlled analgesia fentanyl was administered with a background infusion.', 'Pain scores and analgesia requirement in the ketamine-2 group were significantly lower than those of the control group after cervical surgery. Ketamine partially improved the analgesic effects of fentanyl after lumbar surgery.'] Does continuous low-dose ketamine improve the analgesic effects of fentanyl patient-controlled analgesia after cervical spine surgery?