Crystalloid Co-loading versus Ondansetron Effect on Hemodynamic Stability of Cesarean Section Patients Anesthetized by Subarachnoid Block in Karbala, Iraq

Background: Subarachnoid block-induced hypotension and bradycardia remain a frequent andclinically significant complications during cesarean section. Strategies such as fluid co-loading and ondansetron have been employed to mitigate these effects, but their comparative effectiveness remains under investigation.Objective: To compare the effectiveness of 8 mg IV ondansetron versus 500 mL crystalloid co‐loading in reducing subarachnoid block-induced hypotension and bradycardia.Methods: A prospective randomized comparative study carried out in the Gynecology andObstetrics Hospital, Imam Al-Hassan Al-Mujtaba Teaching Hospital, Gynecology and ObstetricsDepartment, Karbala, Iraq from October 2024 to March 2025. A total of 180 women wereassessed for eligibility, and only 172 were included and allocated into three groups: the co-loading group (57 women) received 500 mL saline solution 0.9% IV starting rapidly with intrathecal injection of local anesthesia; the ondansetron group (58 women) received 8 mg of ondansetron IV and both intervention groups (co-loading and ondansetron) received preloading ~10-mL/kg saline solution 0.9% IV; and the control group (57 women) received only preloading ~10-mL/kg saline solution 0.9% IV.Results: Ondansetron reduced the overall hypotension from 73.7% (control) to 55.2% (P = 0.038) and vasopressor dose from 18.7±12.9 mg to 8.5±9.8 mg (P < 0.001). Co-loading did not significantly reduce the overall hypotension (64.9%, P = 0.31). Bradycardia incidence was low and similar across groups (P = 0.233). Ondansetron also reduced nausea/vomiting (P = 0.007) and shivering (P = 0.019).Conclusion: Ondansetron demonstrated superior effectiveness in reducing subarachnoid block-induced hypotension, vasopressor use, intraoperative nausea/vomiting, and shivering, compared to crystalloid co-loading.