Two Prophylactic Bolus Doses of Phenylephrine Coadministered With Oxytocin to Prevent Hypotension During Elective Cesarean Section: A Single-Center Randomized Controlled Trial

BackgroundIntravenous oxytocin at delivery lowers systemic vascular resistance and worsens subarachnoid blockinduced hypotension.Prophylactic phenylephrine coadministered with the oxytocin bolus is a rational strategy, but the optimal dose has not been settled. ObjectiveTo determine whether, compared with a 75 µg bolus, a 100 µg bolus of phenylephrine coadministered with oxytocin at cord clamping reduces the incidence of maternal hypotension in parturients undergoing elective lower segment (low transverse) cesarean section under spinal anesthesia at a tertiary teaching hospital in Puducherry, India, from September 2024 to December 2025. MethodsIn a prospective, single-center, double-blinded, randomized trial, 80 parturients with American Society of Anesthesiologists physical status (ASA-PS) II scheduled for elective cesarean section under spinal anesthesia were randomly allocated in a 1:1 ratio to phenylephrine 75 µg (group A) or 100 µg (group B), coadministered with oxytocin 3 IU at cord clamping.The primary outcome was the incidence of hypotension, defined as a systolic blood pressure (SBP) below 90 mm Hg or a fall of 20% or more from the baseline SBP, within six hours after the subarachnoid block. ResultsHypotension occurred in 10 of 40 women (25.0%) in group A and three of 40 women (7.5%) in group B (risk difference = 17.5 percentage points, odds ratio = 4.04, exact 95% confidence interval (CI) = 0.93 to 24.90, Fisher exact p = 0.066), so the pre-specified primary comparison did not reach statistical significance.Hypotensive episodes and rescue phenylephrine were fewer in group B (mean rescue dose = 17.5 µg versus 5.0 µg, Mann-Whitney U p = 0.035).Serial hemodynamics were similar at all 12 time points.No bradycardia or reactive hypertension occurred. ConclusionCompared with a 75 µg bolus, a 100 µg prophylactic phenylephrine bolus coadministered with oxytocin at cord clamping was associated with a lower incidence of maternal hypotension, but the difference was not statistically significant on the pre-specified Fisher's exact test.Compared with 75 µg, the 100 µg dose required less rescue phenylephrine, and no bradycardia or reactive hypertension occurred with either dose.An adequately powered trial is needed before a preferred dose can be recommended.