Criteria hit for rating hospitals

Hospitals that perform the highest number of a particular procedure -- such as cardiac surgery or treating premature babies -- may not necessarily be the best at that procedure, according to two new studies published yesterday.

For health insurers and employers who increasingly try to direct consumers to hospitals that provide the best medical care, the studies call into question the assumption that patient volume is a reliable measure of quality, and suggest that the healthcare system must come up with a better way for consumers to chose high-quality hospitals and doctors.

Over the years, some studies have supported the connection between high patient volume and lower death and complication rates. And a prominent national consortium of businesses, called the Leapfrog Group, publishes on its website the numbers of patients individual hospitals treat for six high-risk procedures, including coronary artery bypass surgery.

But researchers who studied death rates for coronary artery bypass surgery patients and for very low-birth-weight infants said hospitals with the highest numbers of these patients are not necessarily the best at caring for them.

In fact, they found volume explained very little of the difference between hospitals' success rates. Researchers reported their findings in the Journal of the American Medical Association.

Hospitals at which more than 450 bypass operations were performed annually, for example, had a mortality rate of 2.5 percent, while those where surgeons did fewer than 150 operations a year had a 3.2 percent mortality rate -- a small difference.

But for younger patients who did not have risk factors such as obesity that would make surgery more dangerous, patient volume made no difference in mortality rates.

Researchers studied 267,089 bypass operations at 439 hospitals during 2000 and 2001, using a database kept by the Society of Thoracic Surgeons.

"Everybody, from the public to major payers like Medicare, would like simple, easy ways to tell which hospitals are better and where they should go," said Dr. Eric Peterson of Duke University Medical Center and lead author on the cardiac surgery study. "Patient volume seems like the answer. But sending your employees to one place over another based on volume probably isn't a good idea. Many small centers have equal or better results than large centers."

Another group of researchers studied 94,110 very low-birth-weight infants born in 332 Vermont Oxford Network hospitals between 1995 and 2000. The network is a voluntary group of US hospitals with neonatal intensive care units. The study showed higher mortality for the babies in hospitals that admitted 50 or fewer low-birth-weight infants annually. But at busier NICUs, volume made little difference in how well babies fared. A hospital's past mortality rate was a far better predictor of patient outcomes. The mortality rate for hospitals with fewer than 50 admissions was 15 percent; for all other hospitals, it was 13 percent.

"There was very little variation, so if insurers want to design a way to refer members to particular hospitals, volume is not a good way to do it," said Jeannette Rogowski, a Rand Corp. researcher and lead author. "We need better quality measures and that's going to take more research."

While previous studies have shown higher patient volume leads to lower mortality, Peterson and Rogowski said those studies used databases that were older and contained fewer details about patients, such as their ages and general health.

Mortality rates, researchers said, are a good quality measure. But because hospitals with sicker patients will have more die, mortality rates must be adjusted statistically to account for the mix of patients. This is one reason it is difficult for consumers to gather meaningful hospital mortality rates on their own.

The Leapfrog Group, based in Washington, D.C., is working with the Vermont Oxford Network to obtain risk-adjusted mortality rates for specific procedures at individual hospitals. "We welcome these studies, and we're not surprised by them," said Leapfrog spokeswoman Claire Turner. "From the beginning we expressed a preference for outcome data, but that has not been publically available. We've used volume in the absence of anything else."

Indeed, researchers credited the Leapfrog Group with keeping the pressure on hospitals to become more accountable to consumers. Dr. David Shahian, a cardiac surgeon at Lahey Clinic in Burlington who wrote an editorial that accompanied the bypass surgery study, said patient volume statistics remain a good indicator of quality for complex, rare procedures such as removal of the esophagus or pancreas. But for more common procedures such as bypass surgery, he said, proven standards of care such as whether doctors prescribe beta blockers to surgery patients may be a better measure of quality.

Liz Kowalczyk can be reached at kowalczyk@globe.com.