| Summary: | Background and objectives: Spinal anesthesia is an effective technique for many surgical procedures, but it is often associated with an increased risk of potentially deleterious hemodynamic disturbances. The benefits of prophylactic ondansetron for preventing spinal anesthesia-induced hypotension are still uncertain. Therefore, this study aimed to compare the effect of ondansetron and placebo before spinal block on the incidence of hypotension in patients having non-obstetric surgeries. Methods: Randomized, double-blind, parallel-group, superiority trial with a 1:1 allocation ratio. A total of 144 patients scheduled for non-obstetric surgeries with an indication for spinal anesthesia were randomized. Patients received intravenous ondansetron (8 mg) or placebo before standard spinal anesthesia. The primary outcome was the rate of hypotension in the first 30 minutes after spinal anesthesia. Results: Hypotension occurred in 20 of 72 patients (27.8%) in the ondansetron group and in 36 of 72 patients (50%) in the placebo group (Odds Ratio–OR = 0.38; 95% Confidence Interval–CI 0.19 to 0.77; p = 0.007). Fewer patients in the ondansetron group required ephedrine compared to the placebo group (13.9% vs. 27.8%; OR = 0.42; 95% CI 0.18 to 0.98; p = 0.04). Exploratory analyses revealed that ondansetron may be more effective than placebo in patients aged 60 years or older (OR = 0.12; 95% CI 0.03 to 0.48; p = 0.03). No difference in heart rate variations was observed. Conclusion: Our findings suggest that ondansetron can be a viable and effective strategy to reduce both the incidence of spinal anesthesia-induced hypotension and vasopressors usage in non-obstetric surgeries.
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