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, the investigators evaluated the effect of ondansetron, as a 5-HT3 receptor antagonist, on the haemodynamic response following subarachnoid block in parturients undergoing elective caesarean section.

Inclusion Criteria:

• Undergoing an elective lower segment caesarean section.

Exclusion Criteria:

• Patients with contraindications to subarachnoid block (patient refusal, unstable haemodynamics, coagulation abnormality),
• History of hypersensitivity to ondansetron or local anaesthetic agents,
• Hypertensive disorders of pregnancy,
• Cardiovascular insufficiency,
• Receiving selective serotonin reuptake inhibitors or migraine medications.