Heart attack death rates linked to ambulance diversion

June 12, 2011

Heart attack patients die at a higher rate when their nearest emergency room is so overtaxed that the ambulance transporting them is dispatched to another hospital, according to a new study led by scientists at the University of California, San Francisco.

The findings will be published online June 12, 2011 by JAMA, the Journal of the American Medical Association. The research also will be presented on June 13, 2011 at the AcademyHealth's annual research meeting in Seattle, WA.

"This is one of the first studies to tie patient-level outcomes to daily ambulance diversion logs across multiple cities and counties," says senior author Renee Y. Hsia, MD, assistant professor of emergency medicine at UCSF. She also works as an emergency physician attending at San Francisco General Hospital.

"Everyone knows that ER crowding is a problem. What people need to know is whether crowding affects them and their health. Those of us who work in the ER know that when it's crowded, it affects our ability to provide optimal care. In the study, we finally show that when ambulances are diverted, the outcomes of patients with acute myocardial infarction are worse. In fact, for every 100 patients who are unfortunate enough to have a heart attack when ambulances are being diverted for long periods of time, our study shows that there are three potentially avoidable deaths."

Ambulance diversion is triggered when a hospital's ER is too busy to accept new patients. The ER is temporarily closed, and the ambulance takes the patient to the next available ER, sometimes miles away. For patients undergoing a heart attack, the lost time can be critical.

Ambulance diversion is a particularly common practice in urban settings. The National Center for Health Statistics has estimated that hospitals divert more than half a million ambulances annually in the United States, especially in winter, averaging about one ambulance every minute.

The study examined the outcomes of 13,860 Medicare patients admitted between 2000 and 2005, as well as daily ambulance logs from four densely populated counties in California - Los Angeles, San Francisco, San Mateo and Santa Clara. The counties represent 63 percent of the state's population. The data encompassed 508 different zip codes and 149 emergency departments.

When the closest ER was on diversion status for at least 12 hours, long-term mortality rates of patients rose during a 30-day, 90-day, 9-month and 1-year period. For example, the 30-day mortality rate of heart attack patients unaffected by diversion on their day of admission was 15 percent compared to an 18 percent mortality rate for patients admitted to the hospital on days with more than 12 hours of diversion. One-year mortality for patients not affected by diversion was 29 percent compared to 32 percent for diverted patients, even when controlling for age, co-morbidities, catheterization capabilities, hospital size, and other factors.

The authors say the study points to the need for hospitals to reapportion resources to reduce ER crowding and prolonged ambulance diversion.

"While demand on emergency care is increasing...supply of emergency care is decreasing," the authors note. "If these issues are not addressed on a larger scale, ED conditions will deteriorate, leaving significant implications for all."
The study was supported by funding from the Robert Wood Johnson Foundation, the National Institutes of Health/National Center for Research Resources, and the Clinical & Translational Science Institute at UCSF. The sponsors had no role in the design and conduct of the study, in the gathering and analysis of data or the writing of the report.

UCSF is a leading university dedicated to promoting health worldwide through advanced biomedical research, graduate-level education in the life sciences and health professions, and excellence in patient care.Follow UCSF on Twitter @ucsf/@ucsfscience

University of California - San Francisco

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