Reliability of hospital-level mortality in abdominal aortic aneurysm repair

Objective: The relationship between volume and surgical outcomes has been shown for a variety of surgical procedures. The effects in abdominal aortic aneurysm repair have continued to be debated. Reliability adjustment has been used as a method to remove statistical noise from hospital-level outcomes. However, its impact on aortic aneurysm repair is not well understood. Methods: We used prospectively collected data from the Vascular Quality Initiative to identify all patients who had undergone abdominal aortic aneurysm repair from 2003 to 2019. We first calculated the hospital-level risk-adjusted 30day mortality rates. We subsequently used hierarchical logistic regression modeling to adjust for measurement reliability using empirical Bayes techniques. The effect of volume on risk- and reliability-adjusted mortality rates was then assessed using linear regression. Results: Between 2003 and 2019, 67,073 abdominal aortic aneurysms were repaired, of which 11,601 (17.3%) were repaired with an open approach. The median annual volume was 7.4 (interquartile range, 3.0-13.3) for open repairs and 35.4 (interquartile range, 18.8-59.8) for endovascular repairs. Of the 223 hospitals that had performed open repairs during the study period, only 11 (4.9%) had performed $15 open repairs annually, and the risk-adjusted mortality rates varied from 0% to 75% across all centers. After reliability adjustment, the variability of the risk-adjusted mortality rates had decreased significantly to 1.3% to 8.2%. The endovascular repair risk-adjusted mortality rate variability had decreased from 0% to 14.3% to 0.3% to 2.8% after reliability adjustment. A decreasing trend in mortality was found with increasing an annual case volume for open repair with each additional annual case associated with a 0.012% decrease in mortality (P = .05); however, the relationship was not significant for endovascular repair (P = .793). Conclusions: We found that most hospitals do not perform a sufficient number of annual cases to generate a reliable center-specific mortality rate for open aneurysm repair. Center-specific mortality rates for low-volume centers should be viewed with caution, because a substantial proportion of the variation for these outcomes will be statistical noise rather than true center-level differences in the quality of care.

Automated summary

This study examines the relationship between surgical volume and mortality rates in abdominal aortic aneurysm repair using reliability adjustment and statistical methods. The findings suggest that most hospitals do not perform enough cases to generate reliable center-specific mortality rates for open aneurysm repair. The variability in mortality rates for low-volume centers is likely to be statistical noise rather than true differences in quality of care.