Prophylactic Intravenous Ondansetron versus Phenylephrine Infusion for Preventing Spinal Anesthesia-Induced Hypotension during Planned Cesarean Section

International Journal of Obstetrics and Gynecology | Vol. 14, No. 9, September 2026 | pp. 1119–1130

DOI: 10.46882/2026/IJOG/000574

Original Research Article

Title: Prophylactic Intravenous Ondansetron versus Phenylephrine Infusion for Preventing Spinal Anesthesia-Induced Hypotension during Planned Cesarean Section

Names of Authors: Liam O'Connor¹, Yuki Saito²

Authors’ Affiliations:
¹ Department of Anaesthesia and Intensive Care, Coombe Women & Infants University Hospital, Dublin, Ireland
² Department of Anesthesiology, Osaka University Graduate School of Medicine, Osaka, Japan

Abstract:
Spinal anesthesia for scheduled cesarean delivery induces acute maternal hypotension due to sympathetic blockade. Prophylactic phenylephrine infusions represent the standard treatment protocol but can trigger maternal bradycardia. Prophylactic ondansetron blocks serotonin receptors, limiting the Bezold-Jarisch reflex. This prospective comparative clinical trial compared the hemodynamic stability achieved by a pre-procedural ondansetron bolus against a continuous phenylephrine infusion. Two hundred healthy parturients undergoing planned cesarean delivery under spinal block were assigned to two equal treatment arms: the ondansetron cohort (4 mg IV bolus 5 minutes before spinal block plus saline infusion; n = 100) or the phenylephrine cohort (IV saline bolus plus continuous phenylephrine infusion at 0.5 μg/kg/min; n = 100). The primary endpoint was the incidence of maternal hypotension (systolic blood pressure < 90 mmHg). The incidence of hypotension was 24.0% in the phenylephrine group and 28.0% in the ondansetron group, showing no significant variation (p = 0.52). However, maternal bradycardia (heart rate < 50 bpm) occurred significantly more often in the phenylephrine arm (14.0% vs. 1.0%, p < 0.001). Ondansetron also provided superior control against intraoperative nausea and vomiting symptoms (3.0% vs. 12.0%, p = 0.016). Neonatal cord blood gas metrics were excellent across both arms (p > 0.05). Prophylactic intravenous ondansetron bolus administration offers hemodynamic protection non-inferior to automated phenylephrine infusions while avoiding bradycardia risks and emetic complications.

Keywords: Spinal Anesthesia; Cesarean Section; Maternal Hypotension; Ondansetron; Phenylephrine Infusion; Bezold-Jarisch Reflex.

Manuscript Timeline: Received: July 24, 2026; Revised: September 12, 2026; Accepted: September 24, 2026; Published: September 29, 2026.

Citation: O'Connor L, Saito Y. Prophylactic Intravenous Ondansetron versus Phenylephrine Infusion for Preventing Spinal Anesthesia-Induced Hypotension during Planned Cesarean Section. International Journal of Obstetrics and Gynecology. 2026; 14(9): 1119–1130.

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