Minimum effective dose of intrathecal hyperbaric bupivacaine for cesarean section with and without prophylactic norepinephrine infusion: Randomized triple-blinded trial

Background and Aims: Vasopressor usage can affect the rostral spread of intrathecal drug and, hence, its requirement during cesarean delivery. Although a decreased spread is evidenced with phenylephrine, there is no data for norepinephrine usage. The present study aimed to evaluate the minimum effective dose of intrathecal hyperbaric bupivacaine for cesarean section with and without prophylactic norepinephrine infusion. Material and Methods: Patients scheduled for elective cesarean section under combined spinal-epidural block were randomized to receive intravenous infusion of norepinephrine (0.05 mu g/kg/min) or normal saline (placebo), initiated immediately after intrathecal injection. Postspinal hypotension in either group (systolic arterial pressure <= 0.8 baseline) was treated with norepinephrine 4 mu g rescue. Dose of intrathecal hyperbaric bupivacaine (0.5%) was decided for individual patients using up-and-down sequential allocation method. Primary outcome measure was the minimum effective dose of intrathecal hyperbaric bupivacaine (0.5%) defined as ED50, while secondary observations included spinal block characteristics and neonatal outcomes. Results: Demographic parameters were statistically similar between both groups (P > 0.05). ED50 of intrathecal hyperbaric bupivacaine was 7.8 mg (95% confidence interval [CI]: 6.7-8.8) and 7.4 mg (95% CI: 6.1-8.7) for normal saline and norepinephrine group respectively (P = 0.810). Block characteristics were similar between both groups as was neonatal APGAR score, but umbilical artery base excess was greater for norepinephrine versus normal saline group (-4.4 +/- 3.6 vs. -6.5 +/- 2.4, P = 0.038). Conclusion: Use of prophylactic norepinephrine (0.05 mu g/kg/min) during cesarean delivery does not require adjustment of intrathecal hyperbaric bupivacaine.