The effect of a perioperative ketamine infusion on the incidence of chronic postsurgical pain-a pilot study.

Chronic postsurgical pain (CPSP) is a common and debilitating complication of major surgery. We undertook a pilot study at three hospitals to assess the feasibility of a proposed large multicentre placebo-controlled randomised trial of intravenous perioperative ketamine to reduce the incidence of CPSP. Ketamine, 0.5 mg/kg pre-incision, 0.25 mg/kg/hour intraoperatively and 0.1 mg/kg/hour for 24 hours, or placebo, was administered to 80 patients, recruited over a 15-month period, undergoing abdominal or thoracic surgery under general anaesthesia. The primary endpoint was CPSP in the area of the surgery reported at six-month telephone follow-up using a structured questionnaire. Fourteen patients (17.5%) reported CPSP (relative risk [95% confidence interval] if received ketamine 1.18 [0.70 to 1.98], P =0.56). Four patients in the treatment group and three in the control group reported ongoing analgesic use to treat CPSP and two patients in each group reported their worst pain in the previous 24 hours at ≥3/10 at six months. There were no significant differences in adverse event rates, quality of recovery scores, or cumulative morphine equivalents consumption in the first 72 hours. Numeric Rating Scale pain scores (median [interquartile range, IQR]) for average pain in the previous 24 hours among those patients reporting CPSP were 17.5 [0 to 40] /100 with no difference between treatment groups. A large (n=4,000 to 5,000) adequately powered multicentre trial is feasible using this population and methodology.