Emergency department crowding associated with increased 30‐day mortality: a cohort study in Stockholm Region, Sweden, 2012 to 2016

Abstract

Objectives: Emergency department (ED) crowding is a major problem across the world. Studies investigating the association between crowding and mortality are many, but the quality is inconsistent and there are very few large, high-quality multicenter studies that are properly designed to deal with confounding due to case mix. The aim of this study is to investigate the association between ED crowding and 30-day mortality. Methods: We conducted an observational cohort study at all 7 EDs in Stockholm Region, Sweden 2012-2016. The crowding exposure was defined as the mean hourly ED census during the shift that the exposed patient arrived, divided with the expected ED census for this shift. The expected ED census was estimated using a separate linear model for each hospital with year and shift as predictors. The exposure was categorized in 3 groups: reference (lowest 75% of observations), moderate (75%-95% of observations), and high (highest 5% of observations). Hazard ratios (HR) for all-cause mortality within 30 days were estimated with a Cox proportional hazards model. The model was adjusted for age, sex, triage priority, arrival hour, weekend, arrival mode, chief complaint, number of prior hospital admissions, and comorbidities. Results: 884,228 patients who visited the ED 2,252,656 times were included in the analysis. The estimated HR (95% confidence interval) for death within 30-days was 1.00 (0.97-1.03) in crowding category 75%-95% and 1.08 (1.03-1.14) in the 95%-100% category. Conclusions: In a large cohort study including 7 EDs in Stockholm Region, Sweden we identified a significant association between high levels of ED crowding and increased 30-day mortality.

Emergency department crowding and mortality in 14 Swedish emergency departments, a cohort study leveraging the Swedish Emergency Registry (SVAR)

“…The estimated risk for admitted patients in the Stockholm county was 6% higher in the moderate crowding category and 11% higher in the high category compared to the reference. In our prior study [ 10 ], in the Stockholm county in 2012–2016 (which included two more EDs), the estimated HR was 1.08 (1.03–1.14) in the high crowding category which is consistent with the present results. Compared to our prior study, a new finding is the suggested mortality association already in the moderate crowding category.…”

“…However, it assumes that the estimated hazard ratios are the same across EDs. This may have reduced the accuracy of the model since the EDs here are more heterogenous compared to our prior study [ 10 ] with a similar methodology. The definition of the proxy-measure for crowding is new and has only been tested in one prior study [ 10 ] and by the same research group.…”

“…For example, a large ED at 4 PM during a weekday will have a much higher expected ED census than a small ED in the middle of the night during a weekend. The exposure was categorized in three categories: Reference (0-75% of observations), moderate (75%-95% of observations), and high (highest 5% of observations) [10]. A visual explanation of the definition can be found in Figs 1 and 2.…”

“…Crowding is for example associated with mistakes [ 2 ], delayed interventions [ 3 – 5 ] and adverse events [ 4 , 6 , 7 ] together with stress [ 8 ], burnout and dissatisfaction among staff [ 9 ]. Crowding has also been shown to be associated with increased mortality [ 10 – 13 ]. However large multicenter studies of high quality are still scarce.…”

“…However large multicenter studies of high quality are still scarce. In our prior study [ 10 ], including almost all ED patient visits in the Stockholm County during 2012–2016, a new proxy-measure of ED crowding was introduced and defined as the mean ED census divided by the expected ED census during a shift at the particular ED. The measure was associated with increased 30-day mortality, but this has so far not been confirmed in other studies and settings.…”