Although the intrathecal (IT) administration of midazolam has been reported to have analgesic effect in humans, it is not clear whether IT midazolam can prolong the duration of sensory block to T10 dermatome that is required block level for lower extremity surgery. The effect of 1 or 2 mg of IT midazolam added to bupivacaine on the duration of spinal anesthesia to T10 were examined in orthopedic patients.

Sixty six adult patients were randomly allocated to receive 11 mg of intrathecal 0.5% hyperbaric bupivacaine alone (Group B, n = 22) or with 1 mg (Group BM-1, n = 22) or 2 mg (Group BM-2, n = 22) of midazolam. Both the patients and the observers were blinded to the drug solutions and patient groups. The onset and duration of sensory block to T10, BIS, OAA/S scale, hemodynamic variables, and side effects during the operation and recovery were compared among the groups.

The onset of sensory and motor block were not different among the groups. However, the duration of sensory block to T10 in the Group BM-2 was prolonged more 52.2, 42.2 minutes than the Group B and the Group BM-1, respectively. The BIS scale of the Group BM-2 tended to be lower than the Group B and the Group BM-1 but there were no statistical significance. The OAA/S scale were significantly higher in the Group BM-2 than the Group B and the Group BM-1 during operation. There were no differences in hemodynamic variables and side effects among the groups.

Intrathecal addition of midazolam 2 mg to bupivacaine prolonged the duration of spinal block to T10 in orthopedic patients.