Health policy/original research
Effect of Emergency Department Crowding on Outcomes of Admitted Patients

Presented as an abstract at the American College of Emergency Physicians Research Forum, October 2011, San Francisco, CA; and at the Academy Health Annual Research Meeting, June 2012, Orlando, FL.
https://doi.org/10.1016/j.annemergmed.2012.10.026Get rights and content

Study objective

Emergency department (ED) crowding is a prevalent health delivery problem and may adversely affect the outcomes of patients requiring admission. We assess the association of ED crowding with subsequent outcomes in a general population of hospitalized patients.

Methods

We performed a retrospective cohort analysis of patients admitted in 2007 through the EDs of nonfederal, acute care hospitals in California. The primary outcome was inpatient mortality. Secondary outcomes included hospital length of stay and costs. ED crowding was established by the proxy measure of ambulance diversion hours on the day of admission. To control for hospital-level confounders of ambulance diversion, we defined periods of high ED crowding as those days within the top quartile of diversion hours for a specific facility. Hierarchic regression models controlled for demographics, time variables, patient comorbidities, primary diagnosis, and hospital fixed effects. We used bootstrap sampling to estimate excess outcomes attributable to ED crowding.

Results

We studied 995,379 ED visits resulting in admission to 187 hospitals. Patients who were admitted on days with high ED crowding experienced 5% greater odds of inpatient death (95% confidence interval [CI] 2% to 8%), 0.8% longer hospital length of stay (95% CI 0.5% to 1%), and 1% increased costs per admission (95% CI 0.7% to 2%). Excess outcomes attributable to periods of high ED crowding included 300 inpatient deaths (95% CI 200 to 500 inpatient deaths), 6,200 hospital days (95% CI 2,800 to 8,900 hospital days), and $17 million (95% CI $11 to $23 million) in costs.

Conclusion

Periods of high ED crowding were associated with increased inpatient mortality and modest increases in length of stay and costs for admitted patients.

Introduction

Emergency department (ED) crowding has become an international health delivery problem.1, 2, 3 Increasing frequency of ambulance diversion and left-without-being-seen visits have led the Institute of Medicine to describe US EDs as nearing “the breaking point,”1 and multiple other countries have experienced a surge of ED crowding during the past decade. National policy responses have varied from none to system-wide performance targets.2

Establishing a definitive relationship between ED crowding and subsequent mortality may motivate policymakers to address ED crowding as a top public health priority. Limitations of previous studies assessing the effect of ED crowding on admitted patients include small hospital samples (n=1 to 6),4, 5, 6, 7, 8 lack of case-mix adjustment for comorbidities and primary illness diagnosis,3, 4, 5, 6, 8 lack of adjustment for potential hospital-level confounders, and restriction to specific subgroups such as patients with acute myocardial infarction,9 trauma,10 pneumonia,11 or critical illness.12

To address these limitations, we studied the effect of ED crowding on patient outcomes in a regional cohort of adult patients admitted through an ED. ED crowding was represented by a hospital-normalized measure of ambulance diversion hours on the day of admission. We hypothesized that high ED crowding would be associated with increased inpatient mortality rates, length of stay, and hospital costs in a general population of hospitalized patients.

Section snippets

Study Design and Participants

We performed a retrospective cohort study of adult admissions through the EDs of nonfederal California hospitals for 2007. Hospital-level exclusion criteria were the absence of basic or comprehensive emergency services, facilities that closed their hospital or ED in 2007, and facilities that primarily served children (because ED crowding may have differential effects in pediatric compared with adult populations13). We excluded hospitals that were prohibited from diverting ambulances by local

Results

The Figure illustrates the construction of the study cohort. Excluded hospitals were more likely to be located in single-hospital, low-population-density counties and served patients who were more likely to be young, white, and poor than those treated at included hospitals (Table E1, available online at http://www.annemergmed.com). Our study cohort included 995,379 admissions occurring through the ED at 187 hospitals. Admission and hospital level characteristics are presented in Table 1 and

Limitations

Our study is subject to potential limitations. First, ambulance diversion hours may be an imperfect measure of ED crowding. For example, this measure may be poorly sensitive to ED crowding at facilities that rarely request ambulance diversion. Furthermore, daily diversion hours may not reflect ED crowding experienced by an individual patient, and variation in ED crowding may be greater within than across days.22 Unfortunately, the time of ED evaluation is unavailable through the Office of

Discussion

Patients admitted through the ED during periods of high ED crowding died more often than similar patients admitted to the same hospital when the ED was less crowded. There were also modest increases in inpatient length of stay and hospital costs. These findings persisted after extensive case-mix adjustment for patient demographics, comorbidities, and primary discharge diagnosis. Our fixed-effect model controls for confounding by facility characteristics, and our hospital-normalized definition

References (37)

  • O. Miro et al.

    Decreased health care quality associated with emergency department overcrowding

    Eur J Emerg Med

    (1999)
  • D.B. Richardson

    Increase in patient mortality at 10 days associated with emergency department overcrowding

    Med J Aust

    (2006)
  • A.J. Singer et al.

    The association between length of emergency department boarding and mortality

    Acad Emerg Med

    (2011)
  • P.C. Sprivulis et al.

    The association between hospital overcrowding and mortality among patients admitted via Western Australian emergency departments

    Med J Aust

    (2006)
  • Y.C. Shen et al.

    Association between ambulance diversion and survival among patients with acute myocardial infarction

    JAMA

    (2011)
  • C.E. Begley et al.

    Emergency department diversion and trauma mortality: evidence from houston, Texas

    J Trauma

    (2004)
  • D.B. Chalfin et al.

    Impact of delayed transfer of critically ill patients from the emergency department to the intensive care unit

    Crit Care Med

    (2007)
  • R.P. Shenoi et al.

    Ambulance diversion as a proxy for emergency department crowding: the effect on pediatric mortality in a metropolitan area

    Acad Emerg Med

    (2009)
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    Supervising editor: Brendan G. Carr, MD, MS

    Author contributions: BCS, REW, DZ, and SMA designed the study. BCS obtained funding for this study. BCS and RYH were responsible for data collection. BCS supervised the overall data collection process, had full access to all the data in the study, and takes responsibility for the integrity of the data and the accuracy of the data analysis. WH and HM were responsible for data management and cleaning. REW and L-JL performed the data analysis. BCS and RYH drafted the article. All authors contributed substantially to article revisions and approved the final article for submission. BCS takes responsibility for the paper as a whole.

    Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article as per ICMJE conflict of interest guidelines (see www.icmje.org). This study was supported by an Emergency Medicine Foundation Health Policy grant and US federal grant R03 HS18098. Dr. Sun was supported by NIH/NIA grants K12 AG001004 and the UCLA Older Americans Independence Center, P30-AG028748. Dr. Hsia was supported by the NIH/NCRR/OD UCSF-CTSI grant KL2 RR024130 and the Robert Wood Johnson Foundation Physician Faculty Scholars. The contents do not represent the official views of the Emergency Medicine Foundation, the Agency for Healthcare Research and Quality, the National Institutes of Health, or the Robert Wood Johnson Foundation. The funding sponsors had no role in design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the article.

    Please see page 606 for the Editor's Capsule Summary of this article.

    Publication date: Available online December 6, 2012.

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