BACKGROUND: Intrathecal additives are often used to enhance spinal anesthesia. Midazolam has been reported to have a spinally mediated antinociceptive effect. The aim of this study was to evaluate the effect of midazolam in addition to hyperbaric bupivacaine in spinal anesthesia.

METHODS: Sixty ASA 1 or 2 adult patients scheduled for lower extremity surgery under spinal anesthesia were studied. Patients were allocated randomly to one of four groups to receive 2.8 ml of one of either of the following intrathecal solutions: hyperbaric bupivacaine 12 mg and normal saline 0.4 ml (group 1; n = 15), hyperbaric bupivacaine 12 mg, midazolam 0.5 mg and normal saline 0.3 ml (group 2; n = 15), hyperbaric bupivacaine 12 mg, midazolam 1 mg, and normal saline 0.2 ml (group 3; n = 15), or hyperbaric bupivacaine 12 mg and midazolam 2 mg (group 4; n = 15). The level, onset, and duration of spinal anesthesia as well as hemodynamic changes and side effects were assessed.

RESULTS: The duration of spinal anesthesia was increased in the midazolam addition groups. The duration of anesthesia was significantly increased in group 4 compared to the other 3 groups (P<0.05). The onset, blood pressure, heart rate, and levels of sedation were no different between the 4 groups. No neurological deficit or other significant adverse effects were recorded.

CONCLUSIONS: The addition of intrathecal midazolam to hyperbaric bupivacaine significantly improve the duration of spinal anesthesia without significant adverse effects. Therefore, the use of intrathecal midazolam in a dose not exceeding 2 mg can be used as an effective additive for spinal anesthesia.