Comparative Efficacy of Intermittent Bolus Doses of Phenylephrine and Norepinephrine in Preventing Maternal Bradycardia during Cesarean Section under Spinal Anesthesia: A Randomized Controlled Trial

Background and Aims: Maternal hypotension is a common concern during cesarean sections (CS) with spinal anesthesia and can have adverse consequences for both the mother and fetus. This study aimed to investigate the prophylactic effectiveness of intermittent boluses of phenylephrine and norepinephrine in preventing maternal bradycardia during maintenance of systolic blood pressure (SBP) within 90–100% of baseline. Material and Methods: Two hundred American Society of Anesthesiologists physical status -II parturients scheduled for CS with subarachnoid block (SAB) were randomly assigned to Group A (phenylephrine, 50 µg) or Group B (norepinephrine, 4 µg). The primary goal was to assess the incidence of maternal bradycardia (≤50 bpm) whilst SBP maintenance at 90-100% of baseline. The secondary objectives encompassed total boluses administered, episodes of hypertension (≥120% of baseline), Intraoperative nausea and vomiting (IONV), and neonatal APGAR scores. The time from intrathecal injection to fetal delivery (induction–delivery interval) was also evaluated. Results: Both norepinephrine and phenylephrine groups effectively prevented spinal-induced hypotension, with similar outcomes However, Group A (phenylephrine) experienced a significantly higher incidence of bradycardia (18%) compared to Group B (norepinephrine) with only 5% (P=0.016). Episodes of hypertension, IONV, and neonatal APGAR scores were comparable between the two groups. Conclusion: Intermittent boluses of norepinephrine and phenylephrine demonstrated equivalent efficacy in preventing spinal-induced hypotension during CS. However, norepinephrine exhibited an advantage over phenylephrine by significantly reducing the incidence of bradycardia. These findings support the consideration of norepinephrine as an effective alternative vasopressor for maintaining maternal hemodynamics during CS under SAB.