Prophylactic Ondansetron for Preventing Spinal Anesthesia-Induced Hypotension in Elective Cesarean Section

Hypotension, Spinal Anesthesia, Cesarean Section

Ondansetron, Spinal anesthesia-induced hypotension, Bezold-Jarisch reflex, Shivering, Ephedrine, Obstetric anesthesia

Spinal anesthesia is the preferred technique for elective cesarean section, but it frequently causes maternal hypotension due to sympathetic blockade and the Bezold-Jarisch reflex, which can threaten both mother and baby. Ondansetron, a serotonin 5-HT3 receptor antagonist commonly used to prevent nausea and vomiting, may attenuate this reflex. The purpose of this prospective, randomized, controlled, single-blind study is to evaluate whether a single prophylactic intravenous dose of ondansetron (4 mg) given before spinal anesthesia reduces the incidence of hypotension in women undergoing elective cesarean section. Vasopressor (ephedrine) requirement, heart rate, postspinal shivering, intraoperative nausea and vomiting, and newborn Apgar scores are also compared between the ondansetron and control (saline) groups.

Design: Prospective, randomized, controlled, single-blind (participant), parallel-group, single-center trial conducted in the operating rooms of University of Health Sciences Gazi Yasargil Training and Research Hospital, Diyarbakir, Turkey. Participants: Term pregnant women aged 18-45 years, ASA physical status II, with a singleton pregnancy, scheduled for elective cesarean section under spinal anesthesia. Randomization: Eligible participants are allocated 1:1 by computer-generated simple randomization to the ondansetron group or the control group. The study solutions are identical in appearance, so participants are unaware of their group allocation. Interventions: Ten minutes before spinal anesthesia, the ondansetron group receives 4 mg ondansetron in 100 mL of 0.9% sodium chloride warmed to 37°C as an intravenous infusion; the control group receives 100 mL of 0.9% sodium chloride warmed to 37°C under the same conditions. Anesthesia protocol: Operating room temperature is maintained at 20±2°C. Spinal anesthesia is performed in the sitting position at the L4-L5 interspace with a 26G sharp-tip spinal needle using 0.5% hyperbaric bupivacaine, dosed according to the patient's height and weight. Simultaneously with spinal anesthesia, 20 mL/kg crystalloid (Ringer's lactate or 0.9% sodium chloride) is given as a rapid co-load infusion. Patients are positioned supine with approximately 15° left lateral tilt. After delivery, oxytocin is given as a 3 IU IV bolus followed by a 3 IU/hour infusion. The highest sensory block level is assessed by pin-prick. Hemodynamic management: Hypotension is defined as a mean arterial pressure (MAP) below 65 mmHg or a decrease of 20% or more from baseline at any measurement time. Hypotension is treated with 10 mg IV ephedrine, repeated as needed. Bradycardia (heart rate below 50 beats/min) with hypotension is treated with 0.5 mg IV atropine. Intraoperative nausea or vomiting is treated with 4 mg IV ondansetron as a rescue antiemetic regardless of group. Monitoring: Systolic, diastolic and mean arterial pressure, heart rate and SpO2 are recorded at baseline (before spinal anesthesia), at 3, 6, 9, 12, 15, 20, 25, 30 and 35 minutes after spinal anesthesia, and postoperatively. Nausea-vomiting episodes, postspinal shivering (Crossley and Mahajan five-point scale; grade 2 or higher considered clinically significant), total ephedrine and atropine use, sensory and motor block levels, and 1- and 5-minute Apgar scores are recorded. Withdrawal criteria: Need for intraoperative sedation, conversion to general anesthesia due to failed spinal anesthesia, serious drug reactions, other technical failures (including prolonged surgery), data loss, or participant withdrawal. Sample size: Power analysis (G\*Power; alpha 0.05, power 80%) indicated a minimum of 47 participants per group (94 in total); allowing for dropouts, 102 participants were planned. Statistical analysis: Group comparisons are performed using Welch's t-test, Mann-Whitney U test, Pearson chi-square or Fisher's exact test as appropriate; changes in MAP over time are analyzed with repeated-measures ANOVA. A p value \< 0.05 is considered statistically significant.

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Turkey (Türkiye)