Diverging Trends in Treated In-Hospital Cardiac Arrest in Intensive Care Units and General Wards Using Location-Specific Patient-Days

Background/Objectives: Hospital-level incidence estimates may obscure differences between intensive care units (ICUs) and general wards. We compared temporal trends in treated adult in-hospital cardiac arrest (IHCA) using location-specific patient-days. Methods: This retrospective study covered January 2016 to June 2026 at a South Korean teaching hospital. Monthly treated IHCA counts were modeled using negative binomial regression with patient-days as an offset, a setting × time interaction, and adjustment for the COVID-19 period and seasonality. Calendar-month score-based HAC analyses assessed robustness to serial correlation. January–March 2022 was excluded because arrest location was unavailable. Results: The incidence cohort comprised 1712 events: 1373 in ICUs and 339 in general wards. The combined rate was 1.06 per 1000 patient-days. The setting × time interaction was significant (monthly IRR 0.9843, model-based 95% CI 0.9768–0.9918), corresponding to a 17.3% annual decrease in the ICU-to-ward rate ratio. Calendar-month score-based HAC confidence intervals also excluded 1. ICU incidence declined (monthly IRR 0.9875, 95% CI 0.9825–0.9925), whereas the general-ward model showed no statistically significant temporal trend (IRR 1.0033, 95% CI 0.9975–1.0090; p = 0.263). Conclusions: Location-specific patient-day denominators identified different temporal trajectories in treated IHCA. These findings describe observed treated events and do not establish changes in underlying arrest risk or resuscitation performance.