Impact of Hospital Volume on In-Hospital Cardiac Arrest Mortality: Trends Before and During the COVID-19 Pandemic.

Background Hospital volume is frequently associated with clinical outcomes in patients with critical illnesses. This study aims to evaluate the impact of hospital volume on in-hospital mortality among patients with in-hospital cardiac arrest (IHCA) during the pre-pandemic period (2017-2019) and the COVID-19 pandemic era (2020-2021), using data from the Nationwide Inpatient Sample (NIS) database. Methods We conducted a retrospective analysis of 304,030 IHCA admissions (2017-2019) and 287,695 admissions (2020-2021) using the NIS database. Hospitals were categorized by annual IHCA volume into three groups: low (≤33rd percentile), medium (33rd-67th percentile), and high (≥67th percentile). Survey-weighted logistic regression was used to assess the association between hospital volume and in-hospital mortality, adjusting for demographics, comorbidities, hospital characteristics, and the Elixhauser index. Propensity score matching was used for pairwise comparisons across volume groups. Results During the pre-pandemic period (2017-2019), high-volume hospitals were associated with significantly higher in-hospital mortality than medium-volume hospitals before propensity score matching (adjusted odds ratio (OR): 1.100; 95% CI: 1.035-1.169; p = 0.02). After matching, this association persisted, with high-volume centers showing a modest but statistically significant increase in mortality (OR: 1.075; 95% CI: 1.001-1.154; p = 0.046). In the pandemic period (2020-2021), high-volume hospitals remained associated with higher IHCA mortality, with significantly elevated odds of death compared to both low-volume (OR: 1.239; 95% CI: 1.101-1.394; p < 0.001) and medium-volume hospitals (OR: 1.115; 95% CI: 1.026-1.211; p = 0.01) after matching. When stratified by COVID-19 status, high-volume hospitals in the non-COVID-19 subgroup continued to show significantly higher mortality rates than medium-volume hospitals after adjustment and matching (OR: 1.097; 95% CI: 1.009-1.192; p = 0.003). However, among COVID-19-positive patients, no statistically significant associations were found between hospital volume and in-hospital mortality after matching (medium vs. low: OR 1.125; 95% CI: 0.856-1.480; p=0.398; high vs. low: OR 1.387; 95% CI: 0.942-2.042; p = 0.098; high vs. medium: OR 1.116; 95% CI: 0.883-1.411; p=0.357). Conclusion Hospital volume was associated with in-hospital mortality, varying by pandemic period and patient subgroup. Before the pandemic, high-volume hospitals had a modestly higher mortality rate, a pattern that persisted among non-COVID-19 patients during the pandemic. No significant association emerged for COVID-positive patients, suggesting that system-level strain, rather than viral effects, was the primary driver. These findings highlight the need for surge-adaptive protocols to maintain IHCA care quality during periods of operational stress.