Pre-emptive analgesic efficacy of tramadol compared with morphine after major abdominal surgery

Studies of pre-emptive analgesia in humans have shown conflicting results. This prospective, randomized, double-blind, controlled study was designed to test the hypothesis that a reduction in postoperative morphine consumption can be achieved by tramadol administered after induction of anaesthesia.

Ninety patients were allocated randomly to receive i.v. tramadol (1 mg kg(-1)) (Group T), morphine (0.1 mg kg(-1)) (Group M) or saline 2 ml (Group S) after induction of anaesthesia. At peritoneal closure, a standardized (0.1 mg kg(-1)) morphine loading dose was given to all patients for postoperative pain management. Patients were allowed to use a patient-controlled analgesia (PCA) device giving bolus doses of morphine 0.025 mg kg(-1). Discomfort, sedation, pain scores, cumulative morphine consumption, and side-effects were recorded at 1, 2, 6, 12 and 24 h after the start of PCA.

There were no significant differences between groups in mean pain, discomfort, and sedation scores at any study period. Cumulative morphine consumption was significantly lower in Group M at 12 and 24 h after starting the PCA than in Group S. In Group T, it was lower only after 24 h (28% less in Group M and 17% less in Group T; P<0.017). There were no significant differences in morphine consumption between Groups T and M.

Tramadol (1 mg kg(-1)), administered after induction of anaesthesia, offered equivalent postoperative pain relief, and similar recovery times and postoperative PCA morphine consumption compared with giving morphine 0.1 mg kg(-1). These results also suggest that presurgical exposure to systemic opioid analgesia may not result in clinically significant benefits .