Adjusting outcome measurements for case-mix in a vascular surgical register--is it possible and desirable?

Abstract

We analysed the variation in the outcome of infrainguinal bypass surgery between departments in a register for clinical audit to see if variation in case-mix influenced the results. The study was a retrospective analysis of 764 infrainguinal bypass operations performed from 1988 to 1990 at six Swedish surgical departments. Results were assessed at 30 days and at 1 year postoperatively. There was a significant variation (p < 0.01) in mortality and amputation rates both at 30 days and at 1 year and in patency rate at 30 days. There were also differences in case-mix. Differences were found in indication, location of distal anastomosis and graft type. Regression analysis found that mortality was influenced by age, diabetes and heart disease and patency rate by location of the distal anastomosis and graft type. When 'hospital' was added as a variable in the regression analysis it was also found to be a significant indicator. Location of the distal anastomosis was the main factor in adjusting patency for case-mix.