Toward quality improvement of thoracic aortic surgery: estimating volume-outcome effect from nationwide survey

Background: Although understanding the association between surgical volume and outcome has been the focus of much research, no study has yet reported the volume-outcome effect for thoracic aortic surgery. Methods: From the clinical database, we identified and analyzed 2875 procedures that took place across 36 centers between 2003 and 2005. The effect of hospital procedural volume was assessed for each outcome measure using a hierarchical mixed-effects logistic regression model. Clinical risk factors, procedural year, clinical processes, range of replacement, hospital volume and surgeon volume were set as fixed effects and sites were used as random intercepts. Results: The logistic regression model revealed that hospital thoracic aortic surgery volume was linked to statistically significant decreases in both 30-day mortality (p = 0.127: OR 0.988-0.999) and operative mortality (p = 0.022: 0.989-0.999). In addition, subgroup analysis showed that increased hospital volume was associated with reduced mortality rates in patients under 65 years of age (p = 0.038: 0.982-0.999) and in high-risk surgical candidates (p = 0.019: 0.989-0.999). Thoracic aortic surgery volume of surgeons, hospital adult cardiovascular surgery volume and surgeons adult cardiovascular surgery volume did not significantly impact these outcomes. Conclusions: In this study higher annual hospital thoracic aortic surgery volume of hospitals is associated with reduced mortality rates for thoracic aortic surgery. In Japan it is not the hospital general adult cardiovascular surgery volume, but the hospital specific thoracic aortic surgery volume that might be preferable for quality indicator of thoracic aortic surgery.