• Michael J Schull, Kate Lazier, Marian Vermeulen, Shawn Mawhinney, and Laurie J Morrison.
• Clinical Epidemiology Unit and the Department of Emergency Services, Sunnybrook and Women's College Health Sciences Centre, Toronto, Ontario, Canada.
• Ann Emerg Med. 2003 Apr 1;41(4):467-76.

Study ObjectiveWe determine the relationship between physician, nursing, and patient factors on emergency department use of ambulance diversion.MethodsData were collected at 1 ED in Toronto, Ontario, Canada, on the duration of ambulance diversion during consecutive 8-hour intervals from January to December 1999 (intervals=1,095). By using time series methods, the association between ambulance diversion and nurse hours, physician on duty, and boarded patients was determined. Covariates included patient volume, assessment time, and boarding time.ResultsA total of 37,999 patients were treated in the ED over the study period (2% major trauma, 16% ambulance arrivals, and 22% admitted). Nurse hours per interval averaged 60. A mean of 3.2 admitted patients were boarded in the ED each interval. For admitted patients, the time from registration to admission order and from admission order to ED departure averaged 5.2 and 3.5 hours, respectively. There was no ambulance diversion during 170 (15.5%) intervals, whereas 17 (1.5%) intervals were continuously on diversion. In time series analyses, ambulance diversion increased with the number of admitted patients boarded in the ED (6.2 minutes per patient; 95% confidence interval [CI] 2.6 to 9.8 minutes), the number admitted per interval (4.6 minutes per patient; 95% CI 0.1 to 9.1 minutes), assessment time (9.9 minutes per hour; 95% CI 3.3 to 16.5 minutes), and boarding time (11.3 minutes per hour; 95% CI 5.6 to 17.0 minutes). Thirteen of 15 emergency physicians were not associated with ambulance diversion, 1 was associated with reduced use (-36.3 minutes; 95% CI -65.2 to -7.5 minutes), and 1 was associated with increased use (47.6 minutes; 95% CI 4.5 to 90.6 minutes). ED nurse hours were not associated with diversion. Ambulance-delivered patient volume was associated with diversion (5.2 minutes per patient; 95% CI 2.7 to 7.8 minutes), but walk-in patients and patients with major trauma were not.ConclusionAdmitted patients in the ED are important determinants of ambulance diversion, whereas nurse hours and most emergency physicians are not. Reducing the volume of walk-in patients is unlikely to lessen the use of diversion.

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