Background: Subarachnoid block is the preferred method of anesthesia for caesarean section, but it is associated with hypotension and bradycardia, which may be deleterious to both parturient and baby. Animal studies suggest that in the presence of decreased blood volume, 5–HT may be an important factor inducing the Bezold Jarisch reflex via 5–HT3 receptors located in intracardiac vagal nerve endings. In this study, we evaluated the effect of ondansetron, as a 5–HT3 receptor antagonist, on the haemodynamic response and required dose of vessopressors  following subarachnoid block in parturients undergoing elective caesarean section.

Methods: Hundred  parturients scheduled for elective caesarean section were randomly allocated into two groups. Before induction of spinal anaesthesia Group A (n = 50) received normal saline ; Group B (n = 50) received ondansetron , 4mg. Blood pressure, heart rate and vasopressor requirements were assessed.

Results: No significant difference were observed in demographic profile of both the group. Decrease in HR was observed in both the group and the difference is found to be statistically significant at every 3 minutes interval except at 12 mins. Decrease in mean arterial pressure was lower in the group receiving ondansetron. Vasopressor requirement in group B patients were less compared to group A patients.