Efficacy of prophylactic intravenous ondansetron on the prevention of hypotension during cesarean delivery: a dose-dependent study.

OBJECTIVE This study was to determine the optimal dosage of ondansetron for preventing maternal hypotension during cesarean delivery. METHODS One hundred and fifty parturient women scheduled for elective cesarean section were randomly assigned to five groups (n=30). Five minutes prior to spinal anesthesia, women were injected with 5 ml of physiological saline (S), 2 mg (O2), 4 mg (O4), 6 mg (O6), or 8 mg (O8) of ondansetron in saline, respectively. Maternal blood pressure and heart rate were measured at 2-min intervals for 30 min. The serum parameters in umbilical cord blood were analyzed after delivery. RESULTS Compared with group S, the incidence of maternal hypotension was significantly lower in groups O4 and O6 (P < 0.05). The umbilical venous pH was significantly higher in group O4 (P < 0.05); while the partial pressure of carbon dioxide (Pco2) was significantly lower in groups O4, O6, and O8 (P < 0.05); and the bicarbonate (Hco3 (-)) and base excess in extracellular fluid (BEecf) were significantly lower in groups O6 and O8 (P < 0.05). Moreover, minimal changes of systolic blood pressure, diastolic blood pressure, and mean arterial blood pressure were observed in group O4 (P < 0.05). CONCLUSION The optimal dose of ondansetron preloading was 4 mg during cesarean delivery.