Components of institution-free days as a composite outcome after critical illness: A retrospective cohort study

Objective To describe the components of institution-free days (IFD) after intensive care unit (ICU) admission and assess the distribution of IFD at 365 d across various admission categories. Design Multicentre, retrospective cohort study. Setting Adult patients (aged ≥18 y) admitted to 12 ICUs in Queensland from 2017 to 2020. Main outcome measures IFD is the primary composite outcome defined as the number of days alive and free of healthcare institution exposure. IFD is calculated by subtracting total number of days with healthcare institution exposure from 365. Distribution of IFD and its components were evaluated across four prespecified subgroups-diagnostic category, comorbidity groups, age quartiles, and remoteness of area of residence. Results 44 541 ICU admissions were analysed, of which 19 706 (44.2%), 17 488 (39.2%), and 7347 (16.5%) were medical, elective, and nonelective surgical admissions, respectively. The median IFD was higher for elective surgical patients as compared to nonelective surgical and medical admissions (348 d [interquartile range (IQR): 330–355] vs. 330 [IQR: 267–349] d vs. 325 [IQR: 185–349]). Hospital readmission days were the major contributor to IFD, with 60.4% of all survivors experiencing at least one hospital readmission day within 365 d. The mean hospital readmission days were highest for nonelective surgical admissions as compared to elective and medical admissions (18.5 [standard deviation (SD):18.4] vs. 13.9 [SD: 15.9] vs. 16.1 [SD: 19.2] days). Conclusion Hospital readmission days were the predominant contributor to institution-days and principal driver of lower IFD for ICU survivors. Medical ICU admissions had the least IFD, followed by nonelective surgical and elective surgical patients.