Norepinephrine or Phenylephrine to Prevent Spinal Anesthesia-Induced Hypotension During Cesarean Section: A Double-Blinded, Randomized, Controlled Study of Fetal Cerebral Perfusion.

Purpose: Spinal anesthesia-induced hypotension can cause detrimental effects on both the mother and the fetus, and it remains a significant concern in obstetric anesthesia. The use of vasopressors is considered the most reliable and effective approach. Previous studies have shown that norepinephrine appears to be superior to phenylephrine in maintaining maternal heart rate and cardiac output. Therefore, we hypothesize that norepinephrine is more effective than phenylephrine in maintaining neonatal cerebral perfusion when used to prevent spinal anesthesia-induced hypotension.

Patients and methods: This study is a prospective, double-blinded, randomized trial. We enrolled 216 singleton parturients who were scheduled for elective cesarean delivery. The patients received a prophylactic intravenous infusion of either norepinephrine (0.08 μg/kg/min) or phenylephrine (0.5 μg/kg/min). Maternal cardiac output was not routinely monitored during the study period. Fetal ultrasound examinations were performed, with blood velocity measured in the middle cerebral artery and umbilical artery, and the cerebroplacental ratio calculated.

Results: Ninety subjects were ultimately analyzed in each group. The changes in blood velocity in the middle cerebral artery and umbilical artery, as well as the calculated cerebroplacental ratio at 3 and 6 minutes after spinal anesthesia, did not differ significantly between the two groups. The estimated difference of ΔCPR in two groups was - 0.01 (95% CI, -0.05-0.02, P = 0.491) at 3 minutes and was 0.02 (95% CI, -0.01-0.07, P = 0.204) at 6 minutes.

Conclusion: Prophylactic infusion of norepinephrine or phenylephrine at comparable doses has similar effects on fetal cerebral perfusion.