The early and delayed analgesic effects of ketamine after total hip arthroplasty: a prospective, randomized, controlled, double-blind study.

Background: Ketamine has been shown to have a morphine-sparing effect soon after surgery. Nevertheless, whether this effect still exists after being combined with nonsteroidal antiinflammatory drugs and acetaminophen, and whether ketamine can decrease chronic pain after nononcologic surgery remain unclear. Thus, we designed a study to assess ketamine's effect on acute and chronic postoperative pain when combined with multimodal analgesia after total hip arthroplasty (THA).

Methods: Patients scheduled for primary nononcologic THA using standardized general anesthesia were randomized. They received IV ketamine before incision (0.5 mg/kg), and a 24-h infusion (2 microg x kg(-1) x min(-1)) or a similar blinded saline bolus and infusion. Postoperative analgesia included IV acetaminophen, ketoprofen, plus morphine/droperidol patient-controlled analgesia for 48 h. Data pertaining to pain scores, morphine consumption, and need for crutches were collected for 6 mo after THA. Our primary outcome was 24-h morphine consumption.

Results: One hundred fifty-four patients were included (placebo, 75; ketamine, 79). Patients and operative data were similar in both groups. Ketamine decreased morphine consumption at 24 h from 19 +/- 12 mg to 14 +/- 13 mg (P = 0.004). At Day 30, ketamine decreased the proportion of patients needing 2 crutches or a walking frame from 56% to 31% (P = 0.0035). From Day 30 to Day 180, ketamine decreased the proportion of patients with persistent pain at rest in the operated hip (P = 0.008). At Day 180, 21% of placebo group patients (15 of 70) experienced pain at rest in the operated hip versus 8% (6 of 72) in the ketamine group (P = 0.036, odds ratio 0.33, 95% confidence interval 0.12-0.91, risk reduction 67%).

Conclusions: Ketamine had a morphine-sparing effect after THA, even when morphine was combined with multimodal systemic analgesia. It also facilitated rehabilitation at 1 mo and decreased postoperative chronic pain up to 6 mo after surgery.