Temporal trends in ambulance diversion in a mid-sized metropolitan area

To evaluate the amount of ambulance diversion in an emergency medical services (EMS) system and to investigate potential predictive factors.

Ambulance diversion status of hospitals in the four-county metropolitan Portland, Oregon, area has been recorded for approximately 15 years. These data are used by EMS transporting agencies to determine appropriate hospital destination for their patients. The authors calculated the total yearly hospital ambulance diversion time for "Total Ambulance Divert (TAD)" and "Critical Care Divert (CCD)" for the time period between January 1, 1996, and December 31, 1999. Yearly EMS 9-1-1-generated patient transport volume, hospital emergency department (ED) census volume, total population, amount of health maintenance organization (HMO) penetration, and number of licensed and available hospital beds were calculated for each yearly interval. Kendall's tau-b correlation was used to determine significant secular trends. Potential predictive factors for the amount of ambulance diversion were tested using Pearson's correlation.

Total TAD increased 122.5% (p = 0.04), total CCD increased 64.4% (p = 0.50), total EMS transport volume increased 16.1% (p = 0.04), total ED census increased 9.4% (p = 0.04), total licensed beds decreased 5.7% (p = 0.17), total available beds decreased 15.8% (p = 0.17), HMO penetration increased 4.7% (p = 0.04), and total population increased 9.7% (p = 0.04) over the four-year study period. CCD and TAD were not significantly related to each other (p = 0.50). The only significant factor associated with the increase in TAD was number of available beds (p = 0.03). There were no significant factors associated with CCD.

TAD increased significantly over time and was associated only with the decrease in available hospital beds.