Effects of Prophylactic Infusion of Equivalent Doses of Norepinephrine and Phenylephrine in Preventing Spinal Anesthesia-Induced Hypotension During Cesarean Delivery on Fetal and Maternal Outcomes: A Dual-Center, Non-Inferiority Controlled Trial

Background: Numerous studies have compared the effects of norepinephrine and phenylephrine on maternal and neonatal outcomes during cesarean delivery. However, the infusion rates are often based on clinical experience, resulting in non-equivalent doses. We aimed to compare the effects of norepinephrine and phenylephrine at equivalent doses on fetal and maternal outcomes, and assess their efficacy at the 90% effective dose (ED90). Methods: A total of 100 parturients scheduled for cesarean delivery were randomly allocated to receive either 0.10 mu g/kg/min norepinephrine (Group NE) or 0.60 mu g/kg/min phenylephrine (Group PE) to prevent spinal anesthesia-induced hypotension. The primary endpoint was neonatal umbilical arterial (UA) pH and the incidence of maternal hypotension, while secondary endpoints included hemodynamic changes within the first 15 minutes, maternal adverse events, and additional neonatal measures. Results: Of the 95 subjects who completed the study, the UA pH in Group NE (7.296 +/- 0.041) was found to be non-inferior to Group PE (7.292 +/- 0.040), with a mean difference of 0.003 [95% confidence interval (CI): -0.016 to 0.022; P = 0.009]. The incidences of hypotension (NE: 8.3% vs PE: 10.6%, P = 0.701), hypertension, nausea, and vomiting were comparable between groups. However, bradycardia incidence was significantly reduced in Group NE compared to Group PE (2.1% vs 12.8%, P = 0.046). The two groups showed no significant difference in systolic blood pressure (SBP) at most time points within the first 15 minutes, except at 7 minutes. Group NE also had a higher heart rate (HR) than Group PE in most measurements. Both groups showed similar neonatal outcomes. Conclusion: Prophylactic infusion of 0.10 mu g/kg/min norepinephrine was non-inferior to 0.60 mu g/kg/min phenylephrine in terms of neonatal UA pH. These findings further support the safety of norepinephrine in obstetric anesthesia, although additional research is warranted to assess its long-term maternal and neonatal outcomes.