Prophylactic Phenylephrine Versus Norepinephrine Bolus for the Prevention of Post-Spinal Hypotension in Cesarean Section Under Spinal Anesthesia

Abstract

Background: Spinal anesthesia for cesarean delivery is frequently complicated by post-spinal hypotension, which can precipitate maternal symptoms and compromise uteroplacental perfusion; phenylephrine is commonly used for prophylaxis but may cause reflex bradycardia, while norepinephrine may better preserve chronotropy and hemodynamic stability. Objective: To compare prophylactic norepinephrine versus phenylephrine for prevention of post-spinal hypotension in parturients undergoing elective cesarean section under spinal anesthesia. Methods: In this randomized, double-blind, parallel-group study conducted at Services Hospital, Lahore, 280 ASA I–II term parturients (n=140/group) scheduled for elective cesarean delivery received standardized spinal anesthesia and fluid co-loading, followed by prophylactic vasopressor immediately post-intrathecal injection (phenylephrine 100 µg vs norepinephrine 8 µg). Blood pressure and heart rate were recorded at 1-minute intervals until delivery and 5-minute intervals thereafter. Hypotension was defined as SBP <100 mmHg or ≥20% reduction from baseline; rescue phenylephrine 25 µg boluses and atropine for HR <50 bpm were administered per protocol. Results: Hypotension occurred less frequently with norepinephrine than phenylephrine (22.9% vs 37.1%; RR 1.62; p=0.012) and bradycardia was markedly reduced (2.9% vs 15.7%; p<0.001). Norepinephrine improved the lowest intraoperative SBP (90 ± 9 vs 85 ± 10 mmHg; p=0.001), reduced hypotensive episodes (1.1 ± 0.4 vs 1.5 ± 0.7; p=0.002), lowered rescue vasopressor use (14.3% vs 27.1%; p=0.012), and decreased nausea/vomiting (10.0% vs 20.0%; p=0.031), with no difference in NICU admission (2.9% vs 4.3%; p=0.51). Norepinephrine remained protective in adjusted analysis (aOR 0.48; 95% CI 0.27–0.84; p=0.008). Conclusion: Prophylactic norepinephrine provides superior maternal hemodynamic stability compared with phenylephrine, with substantially less bradycardia and reduced rescue vasopressor requirements, without adverse neonatal effects.