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

Background: 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. We calculated 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. 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) ≥ 3 or death within 30 days” . Outcomes were defined as events occurring during hospitalization, within a maximum of 30 days following RRS activation. Results: The study included 8,794 patients. The median ICU admission rate was 0.33 (IQR, 0.21–0.47), and the median SIAR was 0.98 (IQR, 0.75–1.17). In univariable analysis, SIAR showed a non-significant association with the incidence of “death within 30 days” (β = –0.05, 95% CI [–0.12, 0.01]; P = 0.108) and a significant negative association with the incidence of “CPC ≥ 3 or death within 30 days” (β = –0.15, 95% CI [–0.27, –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, 0.97–0.99; P = 0.104) for “death within 30 days”, and 0.94 (95% CI, 0.92–0.96; P < 0.001) for “CPC ≥ 3 or death within 30 days”. Conclusions: Higher SIAR values were significantly associated with a lower incidence of “CPC ≥ 3 or death within 30 days”. Greater ICU utilization after RRS activation may improve outcomes, though underlying mechanisms require further study.