A randomized, double-blind trial comparing the effects of prophylactic norepinephrine versus phenylephrine infusion on umbilical artery hemodynamics during spinal anesthesia for elective cesarean delivery

Abstract Background Hypotension following neuraxial anesthesia is one of the most common complications during cesarean delivery. This study aimed to evaluate the effects of phenylephrine and norepinephrine on placental vascular resistance under neuraxial anesthesia for cesarean section using Doppler ultrasonography. Methods Seventy-six parturients scheduled for elective cesarean delivery under neuraxial anesthesia with ropivacaine were randomly assigned to receive either phenylephrine (50 µg/min) or norepinephrine (4 µg/min) via titration to maintain systolic blood pressure at baseline. Doppler ultrasonography was used to measure the systolic-to-diastolic velocity ratio (S/D), resistance index (RI), and pulsatility index (PI) of the umbilical artery at multiple time points within the first 10 min after neuraxial anesthesia. Umbilical arterial blood samples were collected at delivery for blood gas analysis. Results No significant differences were found between groups in umbilical artery blood gases or vascular resistance indices (S/D, PI, RI) at any time point. Within-group measurements remained stable. Additionally, adverse hemodynamic events and uterotonic agent use were comparable. Both vasopressors yielded similar neonatal and hemodynamic outcomes. Conclusion Both phenylephrine and norepinephrine demonstrated comparable effects on neonatal acid-base status, umbilical artery vascular resistance, and maternal hemodynamic stability. Trial registration Chinese Clinical Trial Registry, ChiCTR2100051326 (Registration date September 20, 2021).