Effects of intrathecal midazolam on postoperative analgesia when added to a bupivacaine-clonidine mixture

Background: Previous clinical and experimental studies have shown that a midazolam-clonidine mixture has a synergistic antinociceptive effect. This study evaluated the postoperative analgesic effect of adding midazolam to an intrathecal bupivacaine-clonidine mixture. Methods: One hundred ten patients scheduled to undergo elective lower-extremity surgery were enrolled in this double-blind, randomized trial. Spinal anesthesia was administered by using 1 of 2 mixtures. Group B-C received 12.5 mg isobaric 0.5% bupivacaine, 30 mu g clonidine, and 0.4 mL 0.9% saline. Group B-C-M received the B-C mixture plus 2 mg of midazolam in a 0.4-mL solution. Motor and sensory block levels were assessed before, during, and after the procedure until regression of the block to S2. Sedation levels were determined before anesthesia, during surgery, and at the end of the procedure. Postoperative analgesia was assessed every 15 minutes by using a visual analog scale. Duration of sensory and motor blocks was determined based on a modified Bromage scale, and time of the first pain relief request was noted. Results: Duration of sensory block, time of first postoperative analgesic request, and amount of postoperative morphine administered were comparable between groups. However, the motor blockade lasted significantly longer in the B-C-M group compared with the B-C group (287 +/- 73 minutes vs 257 +/- 72 minutes, respectively; P < .05). Conclusion: Addition of midazolam to an intrathecal B-C mixture does not potentiate postoperative analgesia but prolongs the motor blockade.