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Purpose: To determine the effects of midazolam, 30 ng·mL−1, on altered perception, mood, and cognition induced by ketamine. Methods: After ketamine was administered to achieve target concentrations of 50, 100, or 150 ng·mL−1 in 11 volunteers, perception, mood, and thought process were assessed by a visual analog scale. Mini-Mental State examination (MMSE) assessed cognition. Boluses of midazolam, 30, 14.5, and 12µg·kg−1, were injected every 30 min to maintain the plasma concentration at 30 ng·mL−1, which was reached 30 min after each injection. Results: Ketamine produced changes in perception about the body (P

Small-dose ketamine may enhance the analgesic effect of opiates. We studied the effect of IV coadministration of small-dose ketamine 50-100 [micro sign]g/kg with morphine 50 [micro sign]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 [micro sign]g/kg with placebo (Group 1, n = 35) or ketamine 50 [micro sign]g/kg IV (Group 2, n = 35), 75 [micro sign]g/kg IV (Group 3, n = 35), or 100 [micro sign]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 [micro sign]g/kg vs 145 +/- 9 [micro sign]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 [micro sign]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. (Anesth Analg 1999;89:98-103)