More than 30% of the patients receiving spinal anesthesia develop hypotension. Hypotension developed during cesarean section (C/S) under spinal anesthesia may jeopardize uteroplacental circulation leading to fetal compromise and even fetal death.

The effect of prophylactic ondansetron on blood pressure after spinal anesthesia has not been compared in a clinical trial with that of a vasoconstrictor. The investigators will compare ephedrine and ondansetron for the prevention of maternal hypotension after spinal anesthesia for elective cesarean delivery.

Some vasopressive drugs including ephedrine and phenylephrine have been widely used to prevent maternal hypotension. Although ephedrine has mixed a-adrenoceptor activity , it maintains arterial pressure mainly by increases in cardiac output and heart rate as a result of its predominant activity on β1-adrenoceptors. It has been demonstrated that ondansetron preloading with crystalloid infusion reduces maternal hypotension in parturient women undergoing cesarean delivery.

Ondansetron has been widely used in the clinic to prevent nausea and vomiting caused by cancer chemotherapy, radiation therapy, and surgery. Ondansetron has been proven as a well-tolerated drug, but the most common side effects of ondansetron include headache, constipation, diarrhea, asthenia, and somnolence.

Inclusion Criteria:

• age >18, <40 years;
• American Society of Anesthesiologists physical status I or II;
• term pregnancy
• singleton pregnancy;
• elective cesarean delivery under spinal anesthesia

Exclusion Criteria:

• Patients with a history of diabetes mellitus other than gestational diabetes,
• hypertension,
• body mass index >40 kg/m2,
• complicated pregnancy, allergy to study drugs,
• long QT syndrome,
• Contraindication to spinal anesthesia
• Patients who required general anesthesia were withdrawn from the study.

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request

This is a double-blind study at the level of patients, careproviders, and outcome assessors. Anesthesiologists, surgeons, and operating personnel did not know which study treatment was used. Syringes were identical in terms of volume, color, viscosity, and odor.