Background: Spinal anaesthesia has many advantages for elective surgeries, but the undesired effect of hypotension is to be managed by different interventions. Induction of the Bezold Jarisch reflex in the setting of decreased blood volume, mediated through serotonin is hypothesised to be one of the factors contributing to hypotension. Recent studies suggested that ondansetron, a 5-hydroxytryptamine subtype 3 receptor antagonist, given prior to spinal anaesthesia may reduce the hemodynamic changes.

Aims: To evaluate the effects of two serotonin receptor antagonists, ondansetron and granisetron in the spinal anaesthesia induced hypotension, bradycardia, sensory and motor blockade using hyperbaric bupivacaine in patients undergoing elective surgeries.

Methods: A prospective observational study on 300 patients scheduled for elective surgery under spinal anaesthesia was donedividing them into 3 with 100 in each group, receiving intravenous ondansetron 4mg granisetron 1mg and saline 2mL respectively. Spinal anaesthesia was given using 3 ml 0.5% heavy bupivacaine. Mean arterial pressure, heart rate, vasopressor use, sensory and motor blockade, their regression were assessed. Chi-square test was used for analysing incidence of hypotension, ANOVA test for changes in mean arterial pressure, vasopressor use, motor and sensory blockade characteristics. p value<0.05 was considered statistically significant.

Results: The ondansetron group, compared to granisetron and control groups showed a lower incidence of fall in mean arterial pressure, and vasopressor use [p< 0.05] No significant changes in heart rate, onset and regression ofsensory and motor blockade were noted among three groups.

Conclusion: Intravenous ondansetron 4mg given before spinal anaesthesia in elective surgeries significantly decreased hypotension and vasopressor usage. There were no significant inter group differences in incidence of bradycardia, motor and sensory blockade.