Hospital volume may not be best criteria for selecting hospital for coronary bypass surgery


For coronary artery bypass graft surgery (CABG), hospital procedural volume is only modestly associated with outcomes and therefore may not be an adequate quality indicator, according to a study in the January 14 issue of The Journal of the American Medical Association (JAMA).

There have been recent calls for using hospital procedural volume as a quality indictor for CABG surgery, but further research into analysis and policy implication is needed before hospital procedural volume is accepted as a standard quality measure, according to background information in the article.

Eric D. Peterson, M.D., M.P.H., of the Duke Clinical Research Institute, Durham, N.C., and colleagues examined the association between hospital CABG procedural volume and outcome using clinical data available from the Society of Thoracic Surgeons (STS) National Cardiac Database. The analysis included 267,089 CABG procedures performed at 439 U.S. hospitals between January 1, 2000, and December 31, 2001.

The researchers found that the median (interquartile range) annual hospital volume for isolated CABG procedures was 253 (165-417), with 82 percent of centers performing fewer than 500 procedures per year. The overall operative mortality was 2.66 percent. After adjusting for patient risk and clustering effects, rates of operative mortality decreased with increasing hospital CABG volume (0.07 percent for every 100 additional CABG procedures). "While the association between volume and outcome was statistically significant overall, this association was not observed in patients younger than 65 years or in those at low operative risk and was confounded by surgeon volume. The ability of hospital volume to discriminate those centers with significantly better or worse mortality was limited due to the wide variability in risk-adjusted mortality among hospitals with similar volume. Closure of up to 100 of the lowest-volume centers (i.e., those performing 150 or less CABG procedures/year) was estimated to avert fewer than 50 of 7,110 (less than 1 percent of total) CABG-related deaths," the researchers write.

"Our study [expanded on] prior analyses using contemporary analytic techniques to properly account for clinical factors, differences in site variability, and clustering within sites. We found that, compared with high-volume hospitals, low-volume hospitals tended to operate on patients with higher risk and under more emergent conditions," the author write. "Our study further demonstrates the limitations of using hospital volume as an indicator of the quality of CABG surgery. Hospital volume had generally poor predictive accuracy as a means of identifying hospitals with significantly better or worse CABG mortality rates. Similarly, using volume as a sole referral criterion for selecting a provider would unfairly defer cases from nearly half of very-low-volume centers with outcomes equal or better than overall STS mortality results."

"In this national study we found that hospital procedural volume was only modestly associated with risk-adjusted CABG mortality rates; however, there were many low-volume hospitals with low mortality rates and some high-volume centers with rates higher than expected. This study suggests that hospital CABG surgery volume is best considered as a surrogate for quality in a setting where other more direct process and outcome assessments are not available. Instead it seems more reasonable to support the continued growth of national clinical databases, which are capable not only of tracking risk-adjusted surgical care patterns and outcomes, but also of improving them," the authors conclude. (JAMA. 2004;291:195-201. Available post-embargo at

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Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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