Emergency department crowding: A national perspective

Study objectives: Our objective in this study is to profile diurnal variability in hourly emergency department (ED) census using the National Hospital Ambulatory Medical Care Survey (NHAMCS). Methods: A secondary analysis of ED visits in the NHAMCS survey for 2001 was performed. A sample of 34,546 ED visits was used to profile diurnal variability of hourly ED census. A hot-deck method was used to impute missing visit length and arrival time data. The hourly ED census was calculated from the time of arrival and visit length, using survey estimates that incorporated population weights. Results: The census varied 2.8-fold over the course of the day. The census was 1.8 times higher on days and 2.1 times higher on evenings than between midnight and 7:59 AM. Thirteen and a half percent of ED patients were admitted. Their visit length averaged 74% longer than the average for ED patients who were discharged. Admitted patients constituted 20% to 31% of the hourly census. The highest percentage was during the morning hours. Walkout rates increased from 0.87% in the lowest quartile of census to 1.66% in the highest quartile. Conclusion: Diurnal variability in ED crowding can be profiled nationally by calculating hourly ED census. ED crowding varies significantly over the course of the day, and admitted patients contribute disproportionately to crowding.