HEALTH POLICY AND CLINICAL PRACTICE/ORIGINAL RESEARCH Disequilibrium Between Admitted and Discharged Hospitalized Patients Affects Emergency Department Length of Stay Marian J. Vermeulen, MHSc Joel G. Ray, MD, MSc, FRCPC Chaim Bell, MD, PhD, FRCPC Barry Cayen, MD, MSc, MPH Therese A. Stukel, PhD Michael J. Schull, MD, MSc, FRCPC From the Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada (Vermeulen, Stukel, Schull); the Department of Health Policy, Management and Evaluation (Vermeulen, Ray, Bell, Stukel, Schull), Department of Medicine (Ray, Bell, Schull), and Scholarship in Surgery Program (Cayen), University of Toronto, Toronto, Ontario, Canada; the Department of Emergency Services (Schull) and Clinical Epidemiology Unit (Stukel, Schull), Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; and St. Michael’s Hospital, Toronto, Canada (Ray, Bell). Study objective: Most patients are admitted to the hospital through the emergency department (ED), and ED waiting times partly reflect the availability of inpatient beds. We test whether the balance between daily hospital admissions and discharges affects next-day ED length of stay. Methods: We conducted a cross-sectional study of hospitals in metropolitan Toronto, served by a single emergency medical services provider in a publicly funded system. During a 3-year period, we evaluated the daily ratio of admissions to discharges at each hospital and the next-day median ED length of stay in the same hospital by using linear regression. Results: Across hospitals, the daily mean (SD) 50th percentile ED length of stay averaged 218 (51) minutes. As the inpatient admission-discharge ratio increased or decreased, next-day ED length of stay changed accordingly. Compared with ratios of 1.0, those less than 0.6 were associated with an 11-minute (95% confidence interval [CI] 5 to 16 minutes) shorter next-day median ED length of stay; at admission-discharge ratios of 1.3 to 1.4, ED length of stay was significantly prolonged by 5 minutes (95% CI 3 to 6 minutes). Admission-discharge ratios on weekends and among medical inpatients had a stronger influence on next-day ED length of stay; effects were also greater among higher-acuity and admitted ED patients. Conclusion: Disequilibrium between the number of admitted and discharged inpatients significantly affects next-day ED length of stay. Better matching of daily hospital discharges and admissions could reduce ED waiting times and may be more amenable to intervention than reducing admissions alone. The admission-discharge ratio may also provide a simple way of tracking and enhancing hospital system performance. [Ann Emerg Med. 2009;54:794-804.] Provide feedback on this article at the journal’s Web site, www.annemergmed.com. 0196-0644/$-see front matter Copyright © 2009 by the American College of Emergency Physicians. doi:10.1016/j.annemergmed.2009.04.017 INTRODUCTION More than 119 million emergency department (ED) visits occurred in the United States in 2006, a 32% increase during the last decade. 1 Recently, ED crowding and timeliness of care have become major concerns. 2 Lengthy ED waiting times are associated with an increased likelihood that a patient will leave without being seen 3 and of ambulance diversion. 4 Prolonging ED length of stay may compromise quality of care, 5 including delayed fibrinolysis for myocardial infarction 6 and stroke 7 and poorer outcomes in trauma patients. 8 Conversely, reducing ED length of stay leads to greater patient satisfaction 9 and potential cost savings. 10,11 Between 50% and 75% of all patients are admitted to hospital though the ED. 12 Overall, about 1 in 8 ED visits results in hospital admission, and the rate is higher in higher- volume urban centers. 1 ED function is intimately related to inpatient services and access to beds 13-16 : when resources are limited, availability of inpatient beds for patients admitted from the ED is diminished. 17,18 Elective surgery can compete for the same inpatient resources and thus also affect bed availability. A relative excess of inpatient admissions compared with discharges on a given day may produce a state of “disequilibrium,” reducing the availability of beds for urgent admissions from the ED. 15 Hospital occupancy only indirectly reveals this real-time 794 Annals of Emergency Medicine Volume , .  : December 