We evaluated the preemptive analgesic effect of a small dose of ketamine given before or immediately after surgery in a randomized, double-blinded study performed in 128 women undergoing total mastectomy. Group 1 patients received ketamine 0.15 mg/kg as a 5-mL i.v. injection 5 min before surgery and isotonic saline 5 mL i.v. at the time of skin closure. Group 2 received 5 mL i.v. of isotonic saline, then 0.15 mg/kg i.v. ketamine. A standard general anesthesia procedure including sufentanil was used. In the recovery room, patient-controlled analgesia i.v. morphine was used for postoperative analgesia. Postoperative pain was assessed by measuring morphine consumption and visual analog scale pain scores. No significant intergroup differences were seen in the pain scores. Patient-controlled analgesia morphine consumption was lower during the first 2 h after surgery in patients given ketamine at the time of skin closure. No patient complained of hallucinations or nightmares. The incidence of adverse effects was not different between the two groups. In conclusion, administering ketamine at the end of surgery is more effective in reducing morphine consumption than it is when given before surgery.
Implications: We administered the same small dose of ketamine before or after surgery. The preoperative administration of 0.15 mg/kg ketamine in patients undergoing total mastectomy did not elicit a preemptive analgesic effect. Ketamine given at closure reduced the patient-controlled analgesia morphine requirement in the first 2 h after surgery.