Intravenous Ondansetron to Attenuate the Hypotensive, Bradycardic Response to Spinal Anesthesia in Healthy Parturients

The investigators hypothesize that given prophylactically, intravenous ondansetron will attenuate the drop in blood pressure and heart rate frequently seen after spinal anesthesia. Eighty-six American Society of Anesthesiologists (ASA) physical status I or II in preoperative patient assessment, parturients age of 18 to 45 years scheduled to undergo elective caesarean section will be enrolled. Patients will be randomized to 2 groups: the ondansetron group, receiving 8 mg intravenous ondansetron diluted in 10 mL of saline; or the placebo group, who were administered 10 mL of saline given 5 minutes prior to performing the spinal anesthetic. Investigational Pharmacy will randomize and dispense study drug. Baseline measurements of vital signs will be taken. Otherwise standard management will then be used: * Patients must be NPO for 8 hours * Pulse oximetry, EKG monitoring, noninvasive blood pressure at a minimum of every 3 minutes, more frequently if decided by the provider. * Standard lumbar puncture in a sitting position the L3-L4 or L4-L5 * Whitacre pencil-point, 25 gauge * Injectate: 2 mL of 0.75% hyperbaric bupivacaine, 100 mcg preservative free morphine, 20 mcg fentanyl * Immediately after completing the subarachnoid injection, patients will be laid supine with left lateral uterine displacement The sensory level of anesthesia will be assessed in the standard fashion every five minutes using ice. The motor component will tested using the Bromage scale for spinal anesthesia (0, no paralysis; 1, inability to lift the thigh \[only knee/feet\]; 2, inability to flex the knee \[only feet\]; 3, inability to move any joint in the legs).