News Release

High volume hospitals have lower death rates for many surgeries and HIV/AIDS, says UCSF study

Peer-Reviewed Publication

University of California - San Francisco

Hospitals that handle a large volume of patients for several common surgeries or for HIV/AIDS, have significantly lower death rates for those conditions than lower volume hospitals, according to a recent University of California, San Francisco study. The researchers say these findings may be used by Medicare and some employers to justify preferentially referring patients to high volume hospitals, a trend that merits further consideration.

Many previous studies have shown lower mortality rates when patients with certain conditions are admitted to high volume instead of low volume hospitals. But the new study, led by R. Adams Dudley, MD, MBA, assistant professor of medicine in UCSF's Institute for Health Policy Studies, is the first to combine these studies across all these conditions. It is also the first to estimate the annual number of hospital deaths in California that were potentially caused by admission to a low volume hospital.

The study appears in the March 1 issue of the Journal of the American Medical Association.

The researchers searched for the best study on several medical conditions, by judging how well the study adjusted for confounding factors, such as the fact that patients admitted to one hospital might be more sick than those admitted to another. They also favored studies that were conducted most recently, and those that included the greatest number of hospitals. They identified eleven conditions and procedures for which high volume hospitals clearly had lower death rates: ten procedures (such as coronary bypass surgery, coronary balloon angioplasty, and removal of pancreatic cancer) and treatment for HIV/AIDS.

To estimate the number of deaths in California attributable to the use of low volume hospitals, they applied the differences in death rates between high and low volume hospitals from the best studies to California hospitalization and death statistics. Dudley estimated that in 1997, 602 deaths in low volume California hospitals (26% of all deaths among patients in these studies) could have been avoided if low volume hospitals had the same death rates as high volume hospitals.

This is only an estimate, and not every low volume hospital has poor results, Dudley said, but the tendency for high volume hospitals to have lower death rates may convince some patients to reconsider where they go for complex treatments. "There are a lot of reasons to want to use your local hospital," he said, "but if you have one of these complicated problems and there is a hospital with more patients like you across town or in the next community, you may increase your chance of surviving by traveling a few miles."

The researchers also calculated how far low volume hospital patients would have had to travel to get to a high volume hospital. Surprisingly, 58% of low volume hospital patients would have needed to travel 10 or fewer additional miles, and 25% actually traveled to a low volume hospital that was farther away than the nearest high volume hospital.

This finding reflects a little recognized fact: in California and other places where most people live in cities, most low volume hospitals are in urban areas. For example, there are 42 hospitals in Los Angeles County that perform cardiac bypass surgery, and 16 of those did fewer than 200 bypass operations -- the minimum number recommended by the American College of Cardiology to maintain competency-in 1997.

One possible explanation for the reduced death rate at high volume hospitals is that practice makes perfect. "High volume hospitals may be better at these procedures because they do more," Dudley said. "However, the converse could also be true -- a hospital with better results may get more referrals, and so become a high volume hospital."

Whatever the reason for the difference between hospitals, studies such as Dudley's have convinced Medicare, the federal health program for senior citizens, to use volume as a criterion for approving hospitals to perform organ transplants or for designating hospitals as centers of excellence. Major employers in California are also considering the use of hospital volume as a referral criteria.

This raises important social questions, Dudley said. What if many patients are referred to high volume hospitals and away from low volume hospitals? Then hospitals that no longer perform coronary bypass, for example, might not have surgeons ready to do other kinds of heart procedures. "These issues need further public discussion and will require thoughtful approaches. Medicare and health plans may want to make sure their beneficiaries get the best possible care, but they do not want some communities to lose hospital services because patients are being referred away. This may require, for example, focusing referral efforts on cities in which several hospitals are providing the same service."

Co-authors are Kirsten Johansen, MD, UCSF assistant professor of medicine, Richard Brand, PhD, UCSF professor of biostatistics, and Deborah Rennie, a senior programmer at the Institute for Health Policy studies, and Arnold Milstein, MD, MPH, from the Pacific Business Group on Health and William M. Mercer, Inc.

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