Coronary Artery Bypass Surgery: The Relationship between Inhospital Mortality Rate and Surgical Volume after Controlling for Clinical Risk Factors

This study uses a new database containing clinical risk factors for cardiac surgery to investigate the relationship between surgical volume (hospital and surgeon) and inhospital mortality rate for all patients receiving coronary artery bypass surgery in New York State in 1989. Also, hospitals with significantly higher and lower mortality rates than expected on the basis of patient preoperative risk factors are identified. The results demonstrate that both annual surgeon volume and annual hospital volume are significantly (inversely) related to mortality rate. The 36% of all coronary bypass operations performed in hospitals with annual bypass volumes of 700 or more by surgeons with annual bypass volumes of 180 or more had a risk-adjusted mortality rate of 2.67% in comparison to a risk-adjusted mortality rate of 4.29% for other bypass operations. Furthermore, low surgical volumes were a major contributor to the outlier status of four of the five hospitals with significantly higher mortality rates than expected.