Hospital Surgical Volumes and Mortality after Coronary Artery Bypass Grafting: Using International Comparisons to Determine a Safe Threshold.

OBJECTIVE To estimate a safe minimum hospital volume for hospitals performing coronary artery bypass graft (CABG) surgery. DATA SOURCE Hospital data on all publicly funded CABG in five European countries, 2007-2009 (106,149 patients). DESIGN Hierarchical logistic regression models to estimate the relationship between hospital volume and mortality, allowing for case mix. Segmented regression analysis to estimate a threshold. FINDINGS The 30-day in-hospital mortality rate was 3.0 percent overall, 5.2 percent (95 percent CI: 4.0-6.4) in low-volume hospitals, and 2.1 percent (95 percent CI: 1.8-2.3) in high-volume hospitals. There is a significant curvilinear relationship between volume and mortality, flatter above 415 cases per hospital per year. CONCLUSIONS There is a clear relationship between hospital CABG volume and mortality in Europe, implying a "safe" threshold volume of 415 cases per year.