Background Hypotension and bradycardia are common complications of spinal anesthesia. Intraoperative hypotension and bradycardia may lead to complications that require additional treatment and increase cost. The literature identifies intervention strategies to attenuate spinalinduced hypotension (SIH) and bradycardia.1 Prophylactic administration of ondansetron, a serotonin 5-hydroxytryptamine receptor antagonist, prior to spinal anesthesia is associated with reduced SIH and bradycardia.1,2,3,4,6 The objective of this scholarly project was to report the practice of ondansetron prophylaxis for SIH and bradycardia and the rate of rescue interventions in patients who received ondansetron prior to spinal anesthesia.

Methods Retrospective, multi-center observational evidence-based practice project conducted at Providence Sacred Heart Medical Center (PSHMC) and Providence Holy Family Hospital (PHFH) • Approved by the PSHMC Clinical Innovation and Research Council, and deemed exempt by Providence Health Care Institutional Review Board • Data was retrospectively extracted, de-identified, encrypted, and stored in a HIPAA-compliant REDCap database • Eligibility inclusion criteria: obstetric and orthopedic surgery undergoing spinal anesthesia from January 2018 to December 2019, age 18-90 years old, ondansetron administered prior to spinal anesthesia, spinal anesthesia with bupivacaine 0.5% and bupivacaine 0.75% • Exclusion criteria: general anesthesia with ETT/LMA, spinal anesthesia medications other than bupivacaine, other surgical services • Univariate and bivariate analyses to report baseline group comparability and prophylactic ondansetron relationships • Multivariable analysis to report independent risk factors • Multivariate analysis to report descriptive time series

Discussion This retrospective EBP project demonstrated a gap in practice with the administration of prophylactic ondansetron to attenuate SIH and bradycardia across service lines and facilities. Rates of prophylactic ondansetron administration prior to spinal anesthesia were 42-73% among obstetric surgery. Rates of prophylactic ondansetron were 2-12% among orthopedic surgery. This project is retrospective and observational in nature, which cannot account for confounding factors that may affect the results. Limitations of this project include the inability to differentiate the use of ondansetron for prophylactic SIH or post-operative nausea and vomiting. Other SIH and bradycardia prevention strategies may have also been performed but not described in this project (such as fluid pre-loading or co-loading, prophylactic low dose phenylephrine infusion, or prophylactic vasopressor prior to spinal anesthesia). This project suggests EBP improvements for the utilization of ondansetron to attenuate SIH and bradycardia.