Impact of the Standardized Intensive Care Unit Admission Ratio on Outcomes in Rapid Response System Activations: A Retrospective Multicenter Study in Japan

Background: Intensive care unit (ICU) admission rates after rapid response system (RRS) activation vary widely across institutions. This study examined institutional differences in ICU admission rates and their association with outcomes. Methods: A multicenter retrospective observational study was conducted using a Japanese in-hospital emergency registry, including patients with RRS activation between 2018 and 2022. The ICU admission rate (ICU admissions/RRS activations) and the standardized ICU admission ratio (SIAR; actual/predicted ICU admissions) for each of 35 participating institutions were calculated. The association between SIAR and outcomes was assessed using generalized estimating equation logistic regression with hospital-level clustering. The primary outcome was death within 30 days, and the secondary outcome was a composite of Cerebral Performance Category (CPC) of 3 or higher or death within 30 days. Outcomes were defined as events occurring during hospitalization, within a maximum of 30 days after RRS activation. Results: The study included 8,794 patients. The median ICU admission rate was 0.33 (interquartile range, 0.21 to 0.47), and the median SIAR was 0.98 (interquartile range, 0.75 to 1.17). In univariable analysis, SIAR showed a nonsignificant association with the incidence of death within 30 days (β = –0.05; 95% CI, –0.12 to 0.01; P = 0.108) and a significant negative association with the incidence of CPC of 3 or higher or death within 30 days (β = –0.15; 95% CI, –0.27 to –0.03; P = 0.015). In multivariable analysis, a 0.1-unit increase in SIAR was associated with an odds ratio of 0.98 (95% CI, 0.97 to 0.99; P = 0.104) for death within 30 days and 0.94 (95% CI, 0.92 to 0.96; P < 0.001) for CPC of 3 or higher or death within 30 days. Conclusions: Higher SIAR values were significantly associated with a lower incidence of CPC of 3 or higher or death within 30 days. Greater ICU utilization after RRS activation may improve outcomes, although underlying mechanisms require further study.