BACKGROUND: The antinociceptive action of intrathecal midazolam is well documented and the administration of midazolam by centroneuraxis route has been shown to produce segmental antinociception. This study was designed to evaluate the duration of sensory block and BIS sedation score of intrathecal midazolam-bupivacaine mixture in patients undergoing knee arthroscopy.

METHODS: In this double-blind prospective study, one hundred twenty seven patinets were randomly assigned to receive 4.5 ml of one of the following intrathecal solutions: 15 mg of 0.5% isobaric bupivacaine plus 1.5 ml of 0.9% saline (Group C; n = 34); 15 mg of 0.5% bupivacaine plus 0.5 ml of 0.1% midazolam and normal saline 1 ml mixture (Group 0.5; n = 28); 15 mg of 0.5% bupivacaine plus 1 ml of 0.1% midazolam and normal saline 0.5 ml mixture (Group 1; n = 27); 15 mg of 0.5% bupivacaine plus 1.5 ml of 0.1% midazolam (Group 1.5; n = 38). Time of sensory block until L5-S1 level regression occurred and sedation score using BIS, duration of effective analgesia connecting IV-PCA pump, blood pressure, heart rate, oxygen saturation and nausea/vomiting were recorded and observed.

RESULTS: A significantly longer sensory block duration was seen in group 0.5, 1, 1.5 patients compared with group C (P < 0.01). Correlation coefficent of midazolam dose and sensory block duration was 0.95. Duration of effective analgesia was also prolongated in midazolam-bupivacaine mixture groups (P < 0.01). Blood pressure, heart rate, oxygen saturation and nausea/ vomiting showed no differences among the groups. Sedation score was slightly decreased in only group 1.5, but not to the level of unconsciousness.

CONCLUSIONS: The results suggest that addition of midazolam 1.5 mg to 0.5% bupivacaine intrathecally provided prolongation of sensory block without any adverse effects.