January 23, 2024

Emergency Department Observation Unit Utilization Trends From 2006 to 2019

Andrew Luo, MD
Christopher Baugh, MD, MBA, FACEP
David Meguerdichian, MD, FACEP
Dr. Andy Hung-Yi Lee, MD, MBA
Shih-Chuan Chou, MD

Emergency department observation units (EDOUs) help hospitals safely and efficiently manage patients. Since their inception in the early 20th century, EDOU use has been shown to decrease the length of stay and total cost of care, serving as an alternative to inpatient hospitalizations while increasing patient safety and satisfaction.1–3 In light of the ongoing overcrowding and boarding issues seen in EDs, EDOUs have helped streamline patient flow while also more efficiently allocating resources.4 Although the modalities by which hospital systems utilize EDOUs continue to evolve, there have not been any recent studies demonstrating the trends in EDOU usage at the national level in the United States (US). In this context, we aimed to use a nationally representative dataset to assess the changes in the utilization of EDOUs across US EDs over the past decade. Further, we also examined the changes in the demographics of EDOUs and patients’ clinical presentations between 2006 and 2019. 

Our study evaluated emergency department visit data from the National Hospital Ambulatory Medical Care Survey (NHAMCS) from 2006 to 2019. NHAMCS is an annual survey conducted by the Ambulatory and Hospital Care Statistics Branch of the National Center for Health Statistics (NCHS). The NHAMCS consists of multistage, probability samples of visits to hospital-based EDs in the US. Each encounter was assigned a weight and corresponding survey design variables to generate nationally representative estimates and standard errors. Detailed sampling and survey methodologies are available on the NCHS website. 

We compared the weighted proportions of ED visits leading to an initial EDOU disposition and the proportion of hospitalized ED visits (both inpatient and EDOU) with EDOU disposition between 2006-07 and 2018-19. We examined biannual trends of the weighted total national ED visits leading to hospitalization with generalized linear regression. We stratified our analysis by patient characteristics, including age, sex, insurance, and race/ethnicity, to examine demographics. Lastly, we compared the proportion of EDOU visits by presenting symptoms and disposition between 2006-07 and 2018-19. Annual trends in ED visit rates were examined using least squares regression with inverse variance weights. All analyses used survey procedures in Stata version 15.0/MP, incorporating complex survey designs and weights. Significance was defined at P <0.01 with 2-sided tests, as recommended by the NCHS. 

From our analysis, we found that NHAMCS sampled 71,339 visits in 2006-07 and 39,772 visits in 2018-19, representing an estimated 235,993,594 and 280,623,733 national visits, respectively. Between those periods, the proportion of ED visits with an EDOU disposition increased from 1.6% to 2.4% (p=0.007). EDOU visits also represented a significantly higher proportion of hospitalizations following ED visits, increasing from 10.1% to 14.9% (p=0.003). Weighted total EDOU visits grew from 3,716,799 to 6,644,577 (p=0.005), which represents an increase of 78% (Figure 1). The increase in EDOU dispositions grew the most among patients aged ≥75 years, non-Hispanic White and Black patients, and patients with private insurance and Medicare coverage compared to Medicaid. EDOU patients in both periods had similar presenting symptoms, but there was a notable increase in EDOU visits for neurological symptoms (5.4% to 10.0%; p=0.003). The proportion of patients admitted to inpatient services from the EDOU increased but was not statistically significant (21.4% vs. 30.7%, p=0.151).

We observed several notable findings in this nationally representative study of trends over the past decade. First, from 2006-07 to 2018-19, EDOU utilization grew more rapidly than overall ED visits. This growth is attributed mainly to the increase in elderly Medicare beneficiaries, which indicates that keeping elderly patients in EDOU in lieu of hospitalization may be an increasingly accepted practice across US hospitals. This is potentially driven by the added resources of PT and case management now found incorporated into most EDOUs. Second, we found a slower growth in Medicaid patients It is unclear if this is due to financial considerations or other factors at play. Additionally, the increase in EDOU visits for neurological symptoms may reflect an increase in EDOU patient complexity. Lastly, there was not a statistically significant increase in the proportion of patients admitted to inpatient services from the EDOU suggesting that most patients are being appropriately dispositioned to EDOU and do not need subsequent hospitalization. Further, this may also signal more complex patients who may have required admission are now managed and discharged after EDOU care, implying its potential value given time and cost savings compared to impatient admissions.

This initial study has several limitations. First, this study was retrospective, with the possibility of misclassification. NHAMCS is a cross-sectional survey and does not capture the nuances of individual patient encounters. However, because NHAMCS consistently collects data the same way annually, these trends likely reflect real trends in EDOU utilization. Second, the NHAMCS does not report cost and revenue metrics behind patients admitted to EDOU, so it is unclear how the increase in patients being monitored in EDOU affects hospitals’ financials. Third, we did not include data from 2020 and 2021, as COVID-19 significantly altered ED utilization and downstream EDOU usage. Future studies should examine how EDOU use has changed in the post-pandemic period and its implications on hospital systems. 

Observation Med Figure 1.png

Figure 1 - Demographic Change of EDOU Utilization (2006/2007 - 2018/2019)


Observation Med Figure 2.png

Figure 2 - Change in EDOU Chief Complaint by Organ System 



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