The Epidemiology of ICU Readmissions Across Ten Health Systems

ICU readmissions remain a critical concern, carrying increased morbidity, mortality, and cost. We examined the epidemiology of unplanned ICU readmissions across 19 hospitals in the Common Longitudinal ICU data Format (CLIF) Consortium from January 2020 to December 2021 and the MIMIC-IV database. The cohort included 185,241 adult ICU admissions, excluding postoperative or post-interventional procedure readmissions. Overall, 8.6% of ICU discharges were readmitted during the same hospitalization. Unplanned readmissions occurred in 1.9% of cases within 24 hours, 3.4% within 48 hours, and 4.5% within 72 hours of discharge. Readmitted patients experienced markedly higher in-hospital mortality (20.6% vs. 2.1%; p < 0.001). Compared with initial ICU stays, readmissions were associated with greater use of respiratory support (42.3% vs. 35.3%) and vasopressors (26.1% vs. 23.1%). Hospitals with stepdown units demonstrated comparable unplanned ICU readmission rates. These findings demonstrate that ICU readmissions remain common, are associated with poor outcomes, and require greater organ support. Improved characterization of high-risk subphenotypes is needed to inform safer discharge processes.