[2026-08-26] Timing of Ondansetron Administration for the Prevention of Spinal Hypotension in Nonobese Parturients Undergoing Elective Cesarean Section: A Prospective Cohort Study

Vollständiger Abstract

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Background: Ondansetron has been proposed as an adjunct to phenylephrine for prophylactic spinal hypotension (SH) during cesarean section (C-section). However, the optimal timing of administration is unclear. Objectives: To evaluate the timing of prophylactic ondansetron administration and other factors associated with SH in nonobese parturients undergoing elective C-section. Methods: This prospective cohort study enrolled 154 nonobese term parturients receiving elective C-section under spinal anesthesia (SA) with standardized prophylaxis, including phenylephrine, crystalloid coloading, and left uterine displacement. All patients received 4 mg of intravenous ondansetron at least 10 minutes before SA. The primary outcome was SH, defined as systolic blood pressure < 90% of baseline. Associations between ondansetron timing, perioperative variables, and SH were evaluated using multivariable logistic regression. Results: The incidence of SH was 62.3% (95% CI, 54.6%-70.1%). Extending the interval between ondansetron administration and SA beyond 10-20 minutes was not associated with a reduced risk of SH in either univariate or multivariable analyses. In contrast, a longer interval from SA to delivery independently predicted SH (adjusted odds ratio [OR], 1.61; 95% CI 1.27-2.05; P < .001). Neonatal outcomes were uniformly reassuring, with normal Apgar scores across all groups. Conclusions: Administering ondansetron approximately 10 minutes before SA appears sufficient for SH prophylaxis, with no additional benefit from prolonging the interval between ondansetron administration and SA. A shorter SA-to-delivery interval was associated with improved maternal hemodynamic stability. However, this association should not be interpreted as evidence of a causal relationship.