Hypotension is seen in as many as 50% of the parturients undergoing lower segment caesarean section (LSCS) under spinal anaesthesia. Hypotension due to spinal anaesthesia is mainly caused by sympathetic blockade . In obstetric patients spinal anaesthesia induced hypotension is further aggravated due to aortocaval compression by gravid uterus. Many techniques such as lower legs compression, uterine displacement, using vasopressor and administering fluids has shown a decrease in incidence of hypotension.

In this study, we plan to study and compare the effect of 8mg intravenous (IV) ondansetron and placebo given prophylactically 5 minutes (min.) before spinal anaesthesia on incidence of hypotension in patients undergoing elective caesarean section.

For this study a total of 174 patients (n=174)  undergoing elective caesarean section who satisfy the inclusion criteria will be randomly divided into two groups of 87 each (n=87) (A and B),Group A will receive 8mg of IV ondansetron and group B will receive placebo 5min. before spinal anaesthesia .

 When patient arrives in the operating room (OR), IV cannula will be inserted and haemodynamic variables will be measured. After this patient will receive 4mg of IV ondansetron (Group A) and 8mg of IV ondansetron  5min. before spinal anaesthesia. After this spinal anaesthesia will be administered. Patient will be put in supine position immediately. Surgery will be allowed to proceed after the block reaches T6 sensory level (complete sensory block). Quantitative values of ephedrine use (mg) and IV crystalloids (L) will be recorded.

Haemodynamic parameters including systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial blood pressure (MAP), pulse rate (PR), oxygen saturation (SPO₂), and respiratory rate (RR) will be recorded preoperatively and intraoperatively. The data will be collected in a prescribed proforma and statistically analysed.