Is there a minimum caseload that achieves acceptable operative mortality in abdominal aortic aneurysm operations?

BACKGROUND: Studies have shown correlation between operative workload and mortality for major operations. Is there a threshold for case volume that predicts an acceptable mortality for abdominal aortic aneurysm surgery?
METHODS: Hospital Episode Statistics (HES) Data for England between 1997-2002 was analysed using ICD-10 codes I71.x and OPCS-4 codes L16.x-L26.x. Mortality was identified by the method of discharge.
RESULTS: 31,078 operations on abdominal aortic aneurysms were studied in 223 NHS Trusts. 6,007 in-hospital deaths were identified in both elective and emergency cases (overall mortality rates 7.7% and 40%, respectively). Trusts with large elective workloads had reduced mortality for both elective and emergency operations. Using parabolic regression and logarithmic transformation, 14 elective operations per Trust per year was identified as a cut-off point above which the decrease in mortality rate with increasing case volume was relatively small. A similar effect was not seen with increasing emergency workload alone.
CONCLUSION: HES data analysis suggests increasing elective workload correlates with lower in-hospital mortality for elective and emergency operations on abdominal aortic aneurysm. Data suggests a range of hospital caseload that correlate with an acceptable elective and emergency mortality rate.