bupivacaine sparing effect of intrathecal midazolam in sub-arachnoid block for cesarean section

Background: Hypotension during subarachnoid block for caesarean section (CS) is the most common and potentially dangerous complication. Bupivacaine has been implicated for this effect in a dose dependent manner. Hypotension can be prevented by using lower doses of bupivacaine with intrathecal midazolam as an adjuvant drug, though the optimum dose-ratio of bupivacaine with midazolam remains unaddressed. Materials and Methods: A prospective, randomized, double-blind study was conducted enrolling 120 consecutive ASA grade I obstetric patients undergoing elective CS in a tertiary care hospital. A baseline supine position noninvasive blood pressure (BP) was recorded. All patients were preloaded with 500 ml of lactated Ringers′ solution. Varying doses of 0.5% hyperbaric bupivacaine were used (7.5mg in group II, 6mg in group III and 5mg in group IV), in combination with 2mg midazolam in each group. Appropriately matched controls were given 11mg bupivacaine alone (Group I). Intra-operatively, BP was measured at every 2 minutes till 30 minutes and every 10 minutes thereafter. Hypotensive episodes [Systolic BP (SBP) < 100 mmHg] were recorded in each group. Quality of surgical anesthesia was graded as "excellent", "good" and "poor" as per the validated scoring system. The outcomes in different groups were compared by one-way ANOVA . intra group comparisons were done with t test Results: All the four groups had 30 patients each. The incidence of hypotension was significantly lower in the groups using low-dose bupivacaine and midazolam, with a lesser fall in SBP than group I. Onset of sensory and motor blocks, and quality of surgical anesthesia were unaffected in group II while significant deterioration was noticed in groups III and IV. Conclusion: We found that 7.5 mg bupivacaine with 2 mg midazolam is the optimum dose ratio combination to be used in subarachnoid block for caesarean section.