Risk-Adjusted Analysis of Outcomes Following Elective Open Abdominal Aortic Aneurysm Repair

Abstract

The purpose of this study was to describe a method to analyze outcomes following open abdominal aortic aneurysm (AAA) repair while considering the variability in patients' preoperative risk. Consecutive patients undergoing elective open infrarenal AAA repair during a 4-year period (2000-2003) were reviewed. Thirty-day or in-hospital mortality was the major outcome variable. Preoperative mortality risk was estimated for each patient using a validated scoring system that considers age, renal dysfunction, and coronary artery and cerebrovascular disease. A risk-adjusted cumulative sum method was used to compare observed versus predicted outcomes by assigning a risk-adjusted score, based on log-likelihood ratios, to each patient. These cumulative scores were sequentially plotted with preset control limits to allow for "signaling" when results were substantially different than expected (doubling or halving of odds ratios). Four hundred and sixty-three patients were studied with an overall early mortality rate of 4.5% (n = 21). Patients were allocated to three different preoperative risk groups (low, n = 89; medium, n = 160; high, n = 214) according to a medical comorbidity-based scoring system. Predicted (P) and observed (O) mortality rates for each group were as follows: low, 2.4% (P) and 2.2% (O); medium, 4.1% (P) and 4.4% (O); high, 9.3% (P) and 5.6% (O). The resulting risk-adjusted scores for each patient were plotted sequentially. This plot was flat for the first year and then adopted a negative slope crossing the lower control limit after 266 patients, indicating improved results compared to those expected. This coincided with the adoption of routine intraoperative cell saver use in our practice. This form of analysis allows for the prospective evaluation of results while considering patient-mix variabilities.