Urban hospital 'clusters' do shift high-risk procedures to key facilities, but more could be done.

Since the 1990s, rapid consolidation in the hospital sector has resulted in the vast majority of hospitals joining systems that already had a considerable presence within their markets. We refer to these important local and regional systems as "clusters." To determine whether hospital clusters have taken measurable steps aimed at improving the quality of care-specifically, by concentrating low-volume, high-complexity services within selected "lead" facilities-this study examined within-cluster concentrations of high-risk cases for seven surgical procedures. We found that lead hospitals on average performed fairly high percentages of the procedures per cluster, ranging from 59 percent for esophagectomy to 87 percent for aortic valve replacement. The numbers indicate that hospitals might need to work with rival facilities outside their cluster to concentrate cases for the lowest-volume procedures, such as esophagectomies, whereas coordination among cluster members might be sufficient for higher-volume procedures. The results imply that policy makers should focus on clusters' potential for restructuring care and further coordinating services across hospitals in local areas.