RR24. Improving the Power of the ASA Classification System to Risk Stratify Vascular Surgery Patients: The NSQIP-Defined Functional Status

Abstract

Recent publications 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. The National Surgical Quality Improvement Project (NSQIP) demonstrated that functional status is a strong predictor of mortality. Dividing ASA class III into two subgroups, based on NSQIP functional status, improves the predictive value of the ASA scheme. 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 were compared using the unpaired t-test. 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 postoperative complications was 0.16 in IIIA and 0.32 in IIIB (P < .001). Functionally dependent patients had a five-fold increase in mortality, and a significant increase in length of stay and postoperative complications. Subdividing ASA class III vascular surgery patients markedly improves the predictive value of the ASA classification system.