The standard 15° left tilt during cesarean delivery has long been recommended, but its actual clinical benefit has been questioned in recent studies. We investigated whether starting metaraminol at a higher dose in the supine position could maintain neonatal umbilical arterial pH as effectively as the conventional left tilt approach. A total of 124 healthy women scheduled for elective cesarean delivery were randomly assigned to either a supine position (n = 62) or 15° left tilt (n = 62) following spinal anesthesia with 0.5% bupivacaine (9 mg). Metaraminol infusion began at 2.7 μg·kg⁻¹·min⁻¹ for the supine group and 2.0 μg·kg⁻¹·min⁻¹ for the tilt group. Infusion rates were adjusted using a standardized protocol to maintain maternal systolic blood pressure. The primary outcome was umbilical arterial pH, with secondary outcomes including base excess, maternal blood pressure, and incidence of hypotension or reactive hypertension.
Umbilical arterial pH and base excess in the supine group were comparable to the tilt group (pH: 7.325 [7.29–7.35] vs 7.33 [7.30–7.35], P = 0.76; base excess: −0.92 ± 2.77 mM vs −0.98 ± 2.59 mM, P = 0.9). Maternal systolic blood pressure and hypotension rates were similar between groups, whereas reactive hypertension was more frequent in the supine group (P < 0.001). For healthy parturients (BMI < 35 kg/m²), a higher starting dose of metaraminol in the supine position provides neonatal acid–base outcomes equivalent to the 15° left tilt, suggesting the tilt may not be necessary when blood pressure is actively managed.
