title: Emergency department crowding predicts admission length-of-stay but not mortality in a large health system.
abstract: BACKGROUND
  Emergency department (ED) crowding has been identified as a major threat to public health.
  
  
  OBJECTIVE
  We assessed patient transit times and ED system crowding measures based on their associations with outcomes.
  
  
  METHODS
  Retrospective cohort study.
  
  
  METHODS
  We accessed electronic health record data on 136,740 adults with a visit to any of 13 health system EDs from January 2008 to December 2010.
  
  
  METHODS
  Patient transit times (waiting, evaluation and treatment, boarding) and ED system crowding [nonindex patient length-of-stay (LOS) and boarding, bed occupancy] were determined. Outcomes included individual inpatient mortality and admission LOS. Covariates included demographic characteristics, past comorbidities, severity of illness, arrival time, and admission diagnoses.
  
  
  RESULTS
  No patient transit time or ED system crowding measure predicted increased mortality after control for patient characteristics. Index patient boarding time and lower bed occupancy were associated with admission LOS (based on nonoverlapping 95% CI vs. the median value). As boarding time increased from none to 14 hours, admission LOS increased an additional 6 hours. As mean occupancy decreased below the median (80% occupancy), admission LOS decreased as much as 9 hours.
  
  
  CONCLUSIONS
  Measures indicating crowded ED conditions were not predictive of mortality after case-mix adjustment. The first half-day of boarding added to admission LOS rather than substituted for it. Our findings support the use of boarding time as a measure of ED crowding based on robust prediction of admission LOS. Interpretation of measures based on other patient ED transit times may be limited to the timeliness of care.
authors.affiliation: *Department of Research and Evaluation, Kaiser Permanente Southern California, Pasadena †Department of Medicine, University of California ‡Department of Medicine, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, CA §Department of Emergency Medicine, Oregon Health and Science University, Portland, OR.
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Derose
authors.forename: Gelareh Z
authors.initials: GZ
authors.lastname: Gabayan
authors.forename: Vicki Y
authors.initials: VY
authors.lastname: Chiu
authors.forename: Sau C
authors.initials: SC
authors.lastname: Yiu
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Sun
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D057286:Electronic Health Records; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D007902:Length of Stay / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013997:Time Factors; D014850:Waiting Lists; D055815:Young Adult