Reduction in spinal-induced hypotension with ondansetron in parturients undergoing caesarean section: a double-blind randomised, placebo-controlled study.

Background: Subarachnoid block is the preferred method of anaesthesia for caesarean section, but 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 following subarachnoid block in parturients undergoing elective caesarean section.

Methods: Fifty-two parturients scheduled for elective caesarean section were randomly allocated into two groups. Before induction of spinal anaesthesia Group O (n=26) received intravenous ondansetron 4 mg; Group S (n=26) received normal saline. Blood pressure, heart rate and vasopressor requirements were assessed.

Results: Decreases in mean arterial pressure were significantly lower in Group O than Group S from 14 min until 35 min. Patients in Group O required significantly less vasopressor (P=0.009) and had significantly lower incidences of nausea and vomiting (P=0.049).

Conclusion: Ondansetron 4 mg, given intravenously 5 min before subarachnoid block reduced hypotension and vasopressor use in parturients undergoing elective caesarean section.