Effect of Intravenous Ondansetron on Spinal Anaesthesia-Induced Hypotension During Caesarean Section

Background: Spinal anaesthesia has become the preferred method for elective caesarean sections due to its simplicity, speed, and reliability. However, a significant challenge with this technique is maternal hypotension, which can lead to nausea, vomiting, and decreased cardiac output, necessitating effective preventive measures. Ondansetron, a 5-HT3 receptor antagonist, is commonly used to prevent nausea and vomiting, and recent studies suggest its potential efficacy in reducing hypotension during spinal anaesthesia. Objective: To compare the frequency of hypotension during spinal anaesthesia for elective caesarean delivery between two groups: one receiving intravenous ondansetron and the other receiving normal saline as a placebo. Methods: This randomized controlled trial was conducted at the Department of Anaesthesia, Combined Military Hospital Sialkot, over six months (May 6, 2016, to November 6, 2016). A total of 60 pregnant women scheduled for elective caesarean delivery under spinal anaesthesia, aged 18-35 years, classified as ASA I or II, and carrying a singleton pregnancy at 37-42 weeks, were included. Exclusion criteria included contraindications to spinal anaesthesia, history of heart or lung disease, known hypersensitivity to the study medication, diabetes with blood sugar >180 mg/dl, hypertension with blood pressure >160/90 mmHg, morbid obesity, and fetal abnormalities. Participants were randomly assigned to Group A (intervention) receiving 4 mg ondansetron intravenously in 10 ml saline 5 minutes before spinal anaesthesia, or Group B (control) receiving 10 ml saline intravenously. Baseline vitals, including heart rate, mean arterial pressure, systolic and diastolic blood pressure, were recorded. Spinal anaesthesia was administered using a 25-gauge needle with 2.5 ml of hyperbaric 0.5% bupivacaine solution. Hypotension was managed with intravenous bolus of 100 mcg phenylephrine and 100 ml normal saline. Data were analyzed using SPSS version 25.0, with qualitative variables compared using chi-square tests and significance set at p ≤ 0.05. Results: The mean age of participants was 27.95±5.68 years, and the mean BMI was 24.12±3.30 kg/m². Baseline systolic blood pressure averaged 129.00±11.24 mmHg, diastolic blood pressure 71.67±6.99 mmHg, and mean arterial pressure 114.67±7.93 mmHg. In Group A, 8 out of 30 participants (26.7%) experienced hypotension compared to 17 out of 30 participants (56.7%) in Group B (p=0.036). Stratification by age revealed a significant difference in hypotension incidence in participants >26 years (p=0.028). No significant differences were observed when stratified by BMI 24 kg/m² (p=0.300). Conclusion: Administration of 4 mg intravenous ondansetron 5 minutes prior to spinal anaesthesia for elective caesarean delivery significantly reduces the frequency of hypotension compared to placebo, especially in patients older than 26 years. Ondansetron appears to be a practical and cost-effective prophylactic measure against spinal anaesthesia-induced hypotension, warranting further large-scale, multi-centre trials to validate these findings.