This prospective randomized double-blind placebo-controlled study will include 150 American Society of Anaesthesiologist physical status grade I (ASA I) pregnant women scheduled for elective caesarean delivery under spinal anaesthesia.
Patients will be randomly allocated into three groups (n = 50) to receive intravenous ondansetron 4mg in 10 mL normal saline (group O4), 6 mg in 10 mL normal saline(group O6), or placebo of 10 mL normal saline (group C), all 15-20 minutes before spinal anaesthesia.
Hemodynamic variables and other adverse effects will be assessed at 16 time points intraoperatively. Those variables include blood pressure, heart rate, oxygen saturation, nausea, vomiting, electrocardiographic changes, skin flushing, discomfort or pruritus, perioperative vasopressor requirements and patients' satisfaction.
Participants will be randomly allocated preoperatively as per randomizer.org software and will be blinded from other anaesthetists performing the spinal block and following patients intraoperatively.
