Managed care and open-heart surgery facilities in California

More than 25 percent of hospitals in California that offer open-heart surgery performed fewer than the number recommended by minimum volume guidelines in 1991. This DataWatch examines the characteristics of these hospitals and the patients they treat. The analysis suggests that the market share of these providers has remained constant over recent years, despite substantial growth in managed care. Simple explanations-for example, that these hospitals are serving isolated geographic markets or are hospitals in transition-do not explain the phenomenon. Medicare beneficiaries represent approximately half of the patient volume at these facilities. Health maintenance organizations (HMOs) are more likely to send their enrollees to high-volume facilities.