Small-dose ketamine enhances morphine-induced analgesia after outpatient surgery

Small-dose ketamine may enhance the analgesic effect of opiates. We studied the effect of IV coadministration of small-dose ketamine 50-100 mu g/kg with morphine 50 mu g/kg on postoperative morphine requirements and pain in 140 patients undergoing outpatient surgery, Midazolam 1-2 mg was administered in the holding area. Anesthesia was induced with propofol 2-2.5 mg/kg and was maintained with desflurane in a nitrous oxide/oxygen mixture. Patients received morphine 50 mu g/kg with placebo (Group 1, n = 35) or ketamine 50 mu g/kg IV (Group 2, n = 35), 75 mu g/kg IV (Group 3, n = 35), or 100 mu g/kg IV (Group 4, n = 35) 15 min before the end of the operation. Pain and drowsiness were assessed using visual analog scales on arrival in the recovery room, then every 15 min until the time of discharge to phase 2 recovery (phase 1 recovery), Morphine consumption in Groups 3 and 4 was approximately 40% less than that in the control group (91 +/- 9 and 89 +/- 8 mu g/kg vs 125 +/- 9 mu g/kg; P < 0.05 for both). Pain scores in Groups 3 and 4 were approximately 35% less than those in the control group at all time periods (P < 0.0001 for all). There was no significant group difference in drowsiness scores. Small-dose ketamine 75-100 mu g/kg IV, enhanced morphine-induced analgesia after outpatient surgery. Simultaneous use of small doses of ketamine with morphine enhances the pain relief produced by morphine. Implications: Simultaneous use of small doses of ketamine with morphine enhances the pain relief produced by morphine.