Prevention of nausea and vomiting comparing ondansetron and dexamethasone versus placebo in cesarean section under regional anesthesia

INTERVENTION: 300 patients are randomized to one of three groups in a 1:1:1 ratio. Ondansetron group: Participant receive 4 mg of ondansetron in 5 mL normal saline Dexamethasone group: Participant receive 4 mg of dexamethasone in 5 mL normal saline Placebo group: Participant receive 5 mL normal saline In all groups, study drugs are administered at the time of lumbar puncture for the administration of the anesthetic‐analgesic mixture (9 mg of bupivacaine + 25 micrograms fentanyl 100 micrograms of morphine) by the anesthesiologist responsible for the case. Patients are evaluated intraoperatively, and then 2, 6 and 24 hours after intrathecal morphine. They are questioned about nausea and vomiting, need for rescue antiemetics, itching and pain using a numeric scale to indicate the severity of these symptoms (nausea, itching and pain). If patients have vomiting or severe nausea (numerical rating scale >7) postoperatively, they receive 4 mg of dexamethasone and 4 mg of ondansetron as antiemetic rescue therapy. CONDITION: 1. Postoperative nausea and vomiting 2. Pruritus ; Signs and Symptoms PRIMARY OUTCOME: 1. Incidence of nausea and vomiting is measured using a numerical rating scale (NRS) at 2, 6 and 24 hours after intrathecal morphine; 2. Relative risk of nausea and vomiting by dividing the percentage cases of nausea and vomiting in the control group by the percentage cases in each of the intervention groups; 3. Number needed to treat for nausea and vomiting is measured by the inverse of the Absolute Risk reduction (ARR) (% of cases of nausea on placebo group ‐ % of cases of nausea on ondansetron or dexamethasone group) intraoperatively, at 2, 6 and 24 hours after intrathecal morphine SECONDARY OUTCOME: 1. Incidence of pruritus is measured using a numerical rating scale (NRS) intraoperatively, at 2, 6 and 24 hours after intrathecal morphine; 2. Relative risk of pruritus by dividing the percentage cases of pruritus in the control group by the percentage cases in each of the intervention groups INCLUSION CRITERIA: 1. Pregnant patients scheduled for elective caesarean 2. Age between 18 ‐ 40 years old 3. Spinal (Subarachnoid) anesthesia with intrathecal morphine 4. ASA Physical status 1‐2