Background: Interhospital transfers are shown to be associated with increased length of stay (LOS), mortality, and discharge to facility.[1,2] Delirium has been associated with similar outcomes. Our prior data showed that interhospital transfers had 1.91 times the risk of delirium when compared to ED admissions. We hypothesized that an interaction between admission source, namely interhospital transfer, and the presence of delirium results in increased length of stay (LOS), risk of discharge to a facility and mortality.
Methods: Retrospective cohort study of all adults admitted to a medical, surgical, neurologic and OBGYN services at academic medical center. Unit of analysis was admission source (IHT vs ED) as the independent variable. The primary outcomes were LOS, discharge to a facility and mortality. Delirium was defined using twice daily brief confusion assessment method (bCAM). Staged multivariable regression models controlling for confounders were used to evaluate the association between admission source and the outcomes of discharge to a facility, LOS and mortality adjusting for delirium as an effect modifier.
Results: 25,886 hospital admissions were included in this study, and 2,382 (10.9%) developed delirium during hospitalization. Admissions from the ED without delirium were treated as the reference group. The odds of discharge to a facility were 4.481 times higher in admission through IHT with delirium when compared to ED admissions without delirium. Admission through IHT with delirium had 1.967-fold (95% CI 1.877-2.061) longer LOS when compared to admission through the ED without delirium. Finally, admissions through IHT with delirium had 3.602 (95% CI 2.364-5.488) the odds of mortality when compared to admissions through the ED without delirium. Table 1 summarizes this data and shows that the interaction between admission source and delirium is less than multiplicative and closer to additive.
Conclusions: The interaction between admission source and delirium suggests that admission source has a different impact on LOS, discharge to a facility and mortality based on whether delirium is present or not. Presence of delirium in IHT admissions has a nearly additive effect on the odds of discharge to a facility, mortality and increased LOS.