Postoperative analgesia with i.v. patient-controlled morphine: effect of adding ketamine.

We have studied the effect of adding ketamine to i.v. morphine patient-controlled analgesia (PCA) for the treatment of pain after laparotomy. Thirty patients were allocated randomly to receive PCA with saline or ketamine in a double-blind, randomized study. Analgesia was started in the recovery room when visual analogue scale (VAS) scores were > 4. A bolus dose of morphine 3 mg was given to all the patients followed by i.v. PCA. Simultaneously, an infusion of ketamine 2.5 micrograms kg-1 min-1 or saline was started. Pain scores, morphine consumption and side effects were noted for up to 48 h after the start of PCA. VAS scores decreased significantly with time (P = 0.0001) and were similar (P = 0.3083) in both groups. Cumulative morphine consumption at 48 h was significantly lower in the ketamine group (28 mg) than in the control group (54 mg) (P = 0.0003). Nausea was less frequent in the ketamine group (P = 0.03).