A growing number of studies have reported inverse relationships between hospital volume and surgical mortality, with lower mortality seen in higher-volume institutions. There have been numerous efforts to concentrate selected operations at high-volume hospitals. The Leapfrog Group, a consortium of large corporations and public agencies that purchase healthcare for their employees, has been among the most prominent advocates of volume-based referrals. Private payers and professional organizations have also established minimum-volume standards as part of Centers of Excellence accreditation programs for a variety of operations. “Despite these efforts, little is known if they have altered referral patterns for high-risk surgery,” says Jonathan F. Finks, MD.

Throughout the country, more and more surgical patients are being treated at high-volume hospitals, but the net effects on operative mortality can be difficult to predict. Dr. Finks says, “for example, hospital volume of a few high-risk cancer procedures, such as pancreatectomy, appears to be a strong predictor of operative risk. At the same time, relationships between surgical volume and outcome are much weaker for most operations.”

“Some strategies that appear to be of particular benefit include use of operating-room checklists, outcomes measurement and feedback programs, and national and regional collaborative quality-improvement initiatives.”

In a study published in the June 2, 2011 New England Journal of Medicine, Dr. Finks and colleagues at the University of Michigan used data from national Medicare claims to evaluate trends in the use of high-volume hospitals for major cancer resections and cardiovascular surgery. The investigators identified patients (aged 65 to 99) who underwent one of the following cancer and cardiovascular operations from 1999 through 2008: 1) esophagectomy, 2) pancreatectomy, 3) lung resection, 4) cystectomy, 5) repair of abdominal aortic aneurysm (AAA), 6) CABG, 7) carotid endarterectomy, and 8 ) aorticvalve replacement. Six of these procedures have been targeted for volume-based referral by the Leapfrog Group, while the two other procedures— lung resection and cystectomy—have been cited as potential candidates for regionalization. “Ultimately,” Dr. Finks says, “we wanted to find out if there were trends over the last decade toward concentration of these high-risk procedures in high-volume hospitals. We also evaluated trends in operative mortality and the extent to which changes in mortality were related to concentration of care within high-volume centers.”

Declining Mortality Rates

According to study data, surgery death rates dropped nationwide for the eight different high-risk surgeries performed on 3.2 million Medicare patients in the 10-year analysis. Median hospital volumes increased substantially for the four cancer procedures and AAA repair and slightly for aortic-valve replacement. Conversely, hospital volumes declined sharply during the study period for CABG and carotid endarterectomy. The reasons for increased hospital volumes varied according to procedure. For esophagectomy, increases in hospital volume were attributable to increasing market concentration (there was the same number of procedures nationwide, but fewer hospitals performing them). Increasing volumes for aortic-valve replacement were explained almost entirely by volume creep (an increase in the overall number of procedures nationwide). For the remaining four procedures, increasing hospital volume occurred as a result of both volume creep and market concentration.

“Mortality rates fell for all operations studied, which was a pleasant surprise,” says Dr. Finks. Mortality for all cancer operations declined between 11% and 19% during the study period (Figure 1). For cardiovascular procedures, mortality fell between 8% and 36% (Figure 2). Hospital volume helped explain a large portion of the decline in mortality for cancer surgeries. It explained 67% of the decline in deaths for pancreatectomy, 37% of the drop in cystectomy deaths, and 32% of the reduction in esophagectomy mortalities. Market concentration explained the majority of this effect for each of these procedures. “An interesting finding was that many low-volume hospitals appeared to stop doing high-risk cancer surgeries in the past decade,” says Dr. Finks. The number of Medicare patients needing surgery to treat pancreatic cancer, for example, increased by 50%, but the number of hospitals performing these surgeries decreased by 25%.

The study also demonstrated that a smaller proportion of declines in mortality could be attributed to increasing hospital volume for lung resection (16%), AAA repair (11%), and aortic-valve replacement (9%). Hospital volume had no role in declining mortality associated with CABG and carotid endarterectomy.

Striving for Patient Safety

Dr. Finks says that although high-risk surgeries appear to have become safer in the last decade, increased safety efforts are still needed. “Some strategies that appear to be of particular benefit include use of operating-room checklists, outcomes measurement and feedback programs, and national and regional collaborative quality-improvement initiatives,” he says. “Some procedures (eg, pancreatectomy and esophagectomy) have been linked to strong direct volume–outcome relationships, and referral to high-volume centers should continue to be encouraged for these surgeries. However, other strategies are likely to be more effective than volume-based referrals for most high-risk operations. It’s important for all constituents involved in the surgical care of patients to prioritize programs that have the potential to reduce mortality in all contexts in order to continue our progression toward safer surgery.”