Abstract Body (Do not enter title and authors here): Introduction:
The Charlson Comorbidity Index (CCI) is a validated tool for estimating mortality risk based on comorbid conditions in the general medicine population. Whether CCI has predictive power for in-hospital mortality among patients admitted to the Cardiac Intensive Care Unit (CICU) or Medical Intensive Care Unit (MICU) after undergoing a rapid response (RRT) within 24 hours of admission has yet to be evaluated.

Hypothesis:
We aimed to assess whether CCI correlates with in-hospital mortality among patients admitted to CICU or MICU following a RRT within 24 hours of admission.

Methods:
We conducted a multicenter retrospective cohort study of 763 patients requiring RRT activation within 24 hours of admission. The patients were grouped by level of care required following RRT (MICU, CICU, or medicine floor). Demographic and clinical variables were analyzed using analysis of variance and chi-square test, as appropriate. CCI, which was calculated at the time of RRT, and mortality were plotted as a simple logistic regression.

Results:
Of the 763 patients, 183 (24.0) were admitted to MICU, 61 (8.0) to CICU, and 519 (68.0) remained on the general medicine floor. The average age was 68.6 years, with 52% being male and 48% being female. A total of 164 deaths were recorded, 69 (42%) occurring in the MICU, 13 (7.9%) occurring in the CICU, and 82 (50%) with patients on the medical floor. CCI was significantly associated with in-hospital mortality in the CICU with a moderate predictive relationship (p = 0.01, R-squared = 0.115) (Figure 1). CCI also correlated with inpatient mortality for patients who remained on floors (p<0.0001), with a notably weaker correlation of 0.056. In contrast, CCI did not correlate with mortality among patients admitted to MICU (p = 0.102).

Conclusion:
While the Charlson Comorbidity Index (CCI) demonstrated moderate predictive value for in-hospital mortality among CICU patients, it showed limited utility for those on the general medicine floor and no significant association in MICU patients. Our findings suggest that CCI may aid prognostication at the time of CICU admission, but it appears less effective in predicting outcomes for MICU and floor patients. Further studies are required to assess which risk calculator may correlate best with mortality across different inpatient care settings.