Improving the Power of the ASA Classification System to Risk Stratify Vascular Surgery Patients: The NSQIP-Defined Functional Status
Alexander Kraev M.D., James W. Turner M.D., Lisa Galati-Burke P.A., Gregg S. Landis M.D.
Background: Recently published reports have shown that the American Society of Anesthesiology (ASA) classification system has limited applicability in vascular surgery patients. The majority of patients undergoing vascular procedures are designated ASA III, limiting discrimination in preoperative risk assessment. The 2007 National Surgical Quality Improvement Project (NSQIP), containing over 170,000 surgical cases, demonstrated that functional status is an important predictor of mortality. We propose that dividing ASA class III into two subgroups, based on NSQIP-defined functional status, improves the predictive value of the ASA scheme.
Methods: The 2007 NSQIP database was queried for ASA class III patients undergoing vascular surgery procedures. Patients were divided into groups IIIA and IIIB based on independent or dependent (partial or complete) functional status, respectively. Difference in 30-day survival between subgroups was evaluated using Kaplan-Meier and logistic regression analyses. Differences in postoperative morbidity and length-of-stay (LOS) were compared using the unpaired t-test.
Results: ASA Class III patients having undergone vascular surgery procedures numbered 11555. Of those 9913 (85.7%) patients were independent (IIIA), and 1642 (14.3%) were dependent (IIIB). Mean 30-day mortality was 1.3% in subgroup IIIA, and 6.5% in IIIB (logrank p < .001, χ² - 137.8), Figure 1. Mean lengths of stay between subgroups IIIA and IIIB were 5.4 and 13.2 days (P < .001). The risk of NSQIP-defined postoperative complications was 0.16 in IIIA and 0.32 in IIIB (P < .001).
Conclusion: A five-fold difference in mortality was observed between patients that were functionally independent and dependent. A significant increase in length-of-stay and incidence of postoperative complications was also observed in subgroup IIIB. Subdividing ASA class III vascular surgery patients markedly improves the value of the ASA classification system. Given the “high-risk” nature of patients with peripheral vascular disease, the addition of functional status determination to the preoperative assessment will facilitate improved outcomes.