The relationship between hospital and intensive care unit length of stay*

OBJECTIVES: To assess variations in case-mix-adjusted hospital and intensive care unit length of stay and to examine the relationship between intensive care unit and hospital stay. DESIGN: Retrospective cohort study. SETTING: Sixty-nine intensive and cardiac care units in 23 U.S. hospitals during 2002 to 2008. PATIENTS: Intensive care unit admissions (202,300) who met inclusion criteria. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We obtained hospital and intensive care unit characteristics and patient demographic, clinical, diagnostic, and physiologic variables, mortality, and lengths of stay. We developed and validated a model to assess case-mix-adjusted hospital stay and modified and updated a previously validated model to assess adjusted intensive care unit stay. We used these models to compare observed and expected hospital and intensive care unit stay for each patient by calculating the observed minus expected length of stay. Mean observed intensive care unit stay was 4.33 days and mean predicted intensive care unit stay was 4.09 days (5.9-hr difference); mean observed hospital stay was 9.93 days and mean predicted hospital stay was 9.52 days (9.7-hr difference). Observed minus expected intensive care unit and hospital length of stay were significantly shorter (p < .01) at one intensive care unit and significantly longer (p < .01) at nine intensive care units. There was a correlation between hospital and intensive care unit observed minus expected length of stay across individuals (R2 = .40), which was much stronger across units (R2 = .76). CONCLUSIONS: Case-mix-adjusted benchmarks for hospital and intensive care unit stays reveal substantial differences in unit efficiency. Hospital and intensive care unit stays are strongly correlated at the patient and unit level, suggesting that there are causal factors common to both.