title: Emergency Department Crowding and Outcomes After Emergency Department Discharge.
abstract: OBJECTIVE
  We assess whether a panel of emergency department (ED) crowding measures, including 2 reported by the Centers for Medicare & Medicaid Services (CMS), is associated with inpatient admission and death within 7 days of ED discharge.
  
  
  METHODS
  We conducted a retrospective cohort study of ED discharges, using data from an integrated health system for 2008 to 2010. We assessed patient transit-level (n=3) and ED system-level (n=6) measures of crowding, using multivariable logistic regression models. The outcome measures were inpatient admission or death within 7 days of ED discharge. We defined a clinically important association by assessing the relative risk ratio and 95% confidence interval (CI) difference and also compared risks at the 99th percentile and median value of each measure.
  
  
  RESULTS
  The study cohort contained a total of 625,096 visits to 12 EDs. There were 16,957 (2.7%) admissions and 328 (0.05%) deaths within 7 days. Only 2 measures, both of which were patient transit measures, were associated with the outcome. Compared with a median evaluation time of 2.2 hours, the evaluation time of 10.8 hours (99th percentile) was associated with a relative risk of 3.9 (95% CI 3.7 to 4.1) of an admission. Compared with a median ED length of stay (a CMS measure) of 2.8 hours, the 99th percentile ED length of stay of 11.6 hours was associated with a relative risk of 3.5 (95% CI 3.3 to 3.7) of admission. No system measure of ED crowding was associated with outcomes.
  
  
  CONCLUSIONS
  Our findings suggest that ED length of stay is a proxy for unmeasured differences in case mix and challenge the validity of the CMS metric as a safety measure for discharged patients.
authors.affiliation: Department of Medicine, University of California, and the Department of Medicine, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, CA. Electronic address: gelareh@gabayan.com.
authors.forename: Gelareh Z
authors.initials: GZ
authors.lastname: Gabayan
authors.affiliation: Kasier Permanente Southern California, Department of Research and Evaluation, Pasadena, CA.
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Derose
authors.affiliation: Kasier Permanente Southern California, Department of Research and Evaluation, Pasadena, CA.
authors.forename: Vicki Y
authors.initials: VY
authors.lastname: Chiu
authors.affiliation: Kasier Permanente Southern California, Department of Research and Evaluation, Pasadena, CA.
authors.forename: Sau C
authors.initials: SC
authors.lastname: Yiu
authors.affiliation: Department of Medicine, University of California, and the Department of Medicine, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, CA.
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Sarkisian
authors.affiliation: Kasier Permanente Southern California, Department of Research and Evaluation, Pasadena, CA.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Jones
authors.affiliation: Department of Emergency Medicine, Oregon Health and Science University, Portland, OR.
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Sun
mesh_terms: D002140:California; D003441:Crowding; D004636:Emergency Service, Hospital / Q000458:organization & administration*; D005260:Female; D006801:Humans; D007902:Length of Stay / Q000706:statistics & numerical data*; D008297:Male; D010351:Patient Discharge; D012189:Retrospective Studies; D014850:Waiting Lists