Emergency Department Crowding in Relation to In-hospital Adverse Medical Events: A Large Prospective Observational Cohort Study

Background: Emergency department (ED) crowding has been linked with adverse medical events. However, this association was inadequately controlled for potential confounding variables.

Objectives: To investigate whether ED crowding is independently associated with risk of in-hospital death and morbidity, and longer total hospital stay.

Methods: Prospective observational cohort study of all patients (≥ 18 years) presenting to the ED of an academic teaching hospital in Leuven, Belgium from June 21, 2010 to July 20, 2012. Multivariate logistic regression and proportional hazard analysis was used to control for risk factors. ED occupancy was determined for 108,229 included patients and labeled "ED crowding" when occupancy was within the highest quartile of occupancy. Outcomes within 10 days of ED admission included in-hospital death, hospital-acquired morbidities, and total hospital stay.

Results: During ED crowding, a median of 58 (interquartile range 55-63) patients were present for 40 licensed treatment bays. After controlling for all baseline risk factors and as compared with the lowest quartile of ED occupancy (30 [26-32] patients), ED crowding was not independently associated with mortality (odds ratio [OR] 0.94, 95% confidence interval [CI] 0.74-1.19; p = 0.6), but tended to be associated with higher incidence of hospital-acquired pneumonia (OR 1.24, 95% CI 0.96-1.62; p = 0.09).

Conclusions: Failing to control for baseline risk factors may have led to false-positive associations between ED crowding and mortality in previous studies. After controlling for risk factors, we showed that ED crowding was associated with longer hospital stays but not with increased mortality.