Effect of ondansetron in attenuation of post-spinal hypotension in caesarean section: A comparison of two different doses with placebo

Abstract

Context: Spinal anaesthesia (SA) is the preferred anaesthesia for Caesarean section. Hypotension and bradycardia are the most common side effects caused by sympathetic blockade with a parasympathetic overdrive, aortocaval compression, and the Bezold Jarisch reflex (BJR) which is mediated by serotonin (5 HT3) receptors. Ondansetron is a 5HT3 antagonist commonly used as an anti-emetic. The present study evaluated the effects of two different doses of ondansetron on the haemodynamic changes associated with SA for Caesarean section and the advantage of higher dose over the other. Aims: To study the effect of ondansetron in two different doses on the haemodynamic changes associated with spinal blocks. To compare the need of vasopressors if required and the incidence of nausea and vomiting with the two different doses of ondansetron in comparison with placebo in these patients. Settings and Design: Prospective, comparative, randomized, double-blinded placebo controlled study. Materials and Methods: After hospital ethics clearance 180 parturients undergoing Caesarean section were randomly divided into 3 groups before administration of SA. Group C received 10 ml of normal saline. Group F received 4 mg ondansetron with 8 ml normal saline. Group E received 8 mg ondansetron with 6 ml normal saline. All the patients were monitored for haemodynamics, vasopressor requirement and side effects and the results were compared. Three groups were compared using one-way analysis of variance with Tukey's multiple comparison post hoc test; the results were considered significant when P < 0.05. Adverse events were analysed with Chi-square test and was significant at P < 0.01. Results: The change in the heart rate (HR) was not significant statistically. The fall of systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) was statistically significant at all time intervals intraoperatively after administration of SA (P value <0.001) when compared to pre-operative values. The fall of SBP when compared between groups was significant after administration of SA, 111.92 ± 17.36 mmHg for Group C, group F was 122.16 ± 18.68 mm Hg and group E was119.29 ± 16.88 mmHg (P value = 0.04). The incidence of hypotension in patients was lesser in the group that received ondansetron, Group C (6, 14), Group F (3, 4) and Group E (1, 6) after administration of SA and at 5 minutes after administration of SA (P value = 0.03) but comparable between the ondansetron groups. Conclusions: Intravenous ondansetron reduced the incidence of hypotension, nausea and vomiting after administration of SA but there was no added advantage of 8 mg ondansetron over 4 mg.