Can ketamine potentiate the analgesic effect of epidural morphine, preincisional or postincisional administration?

A randomized controlled trial was conducted to determine the effect of adding epidural ketamine to epidural morphine comparing between giving ketamine at preincisional time and postincisional time on postoperative analgesia in patients undergoing gynecological operations. Eighty patients scheduled for gynecological operation under combined epidural-general anesthesia were randomly divided into 4 groups. Group 1 received epidural morphine 3 mg before skin incision. Group 2 received epidural morphine 3 mg after skin incision. Group 3 received epidural morphine 3 mg and ketamine 30 mg before skin incision. Group 4 received epidural morphine 3 mg and ketamine 30 mg after skin incision. Lidocaine 2 per cent with epinephrine 1:200,000 was used as the main anesthetic agent during the operation in all groups. Postoperative analgesics were pethidine 1 mg/kg intramuscularly or paracetamol 1,000 mg oral. The time to the first analgesic requirement and pain during 48 h were recorded. The amount of pethidine and paracetamol required and the time to the first dose of analgesic requirement were not significantly different among the groups. There were no differences in the incidences of pruritus, nausea, vomiting and nightmare. We concluded that adding ketamine to epidural morphine either by preincisional or postincisional administration did not potentiate the analgesic effect of epidural morphine.