Could antivomiting agent ondansetron prevent low blood pressure during spinal anesthesia for caesarean section?

Spinal anaesthesia will be performed for elective caesarean section. The procedure will be performed in sitting position. Atraumatic spinal Whitacre needle, 27-gauge, 9 mm of length will be employed. The level of puncture by spinal needle will be between third and fourth or fourth and fifth lumbar vertebra. Upon confirmation of cerebrospinal fluid flow, the mixture of hyperbaric 0,5% bupivacaine, 25 mcg of fentanyl and 150 mcg of morphine will be administered intrathecally. Depending on pateint's height, eight (in case that height is less than 165 cm) or ten miligrams of 0.5% hyperbaric bupivacaine will be given. Participants will be randomly assigned in one of three groups, namely control group and in two interventional groups. Participant in arm 2 will receive 4 mg (2 ml) of ondansetron intravenously diluted with 8 ml of saline in 10 ml syringe, while study participants in arm 3 will be given 8 mg (4ml) of ondansetron intravenously, diluted with 6 ml of saline in 10 ml syringe. Both interventional groups (arm 2 and arm3) will receive ondansetron 5 minutes before commencement of spinal anaesthesia procedure. The study drug will be previously prepared by anaesthesia resident, while attending anaesthesiologist will be unaware of syringe content. All participants in all three arms will receive 10 mg of metoclopramide intravenously after completion of intrathecal drug administration. All drugs administered in operating theatre during anesthesia will be recorded by anaesthesia resident.