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

Marshima Chaosaowapa; Ratikorn Anusorntanawat

doi:10.33165/rmj.2027.e280315

Authors

Marshima Chaosaowapa Department of Anesthesia, Chaophrayayommarat Hospital, Faculty of Medicine, Kasetsart University, Suphan Buri, Thailand
Ratikorn Anusorntanawat Department of Anesthesia, Chaophrayayommarat Hospital, Faculty of Medicine, Kasetsart University, Suphan Buri, Thailand https://orcid.org/0000-0002-6844-595X

DOI:

https://doi.org/10.33165/rmj.2027.e280315

Keywords:

Cesarean section, Hypotension, Ondansetron, Prophylactic phenylephrine, Spinal anesthesia

Abstract

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.

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