The Effect of Adding Functional Classification to ASA Status for Predicting 30-Day Mortality

BACKGROUND: The functional capacity to perform the activities of daily living is identified as an independent predictor of perioperative mortality but is not formally incorporated in the American Society of Anesthesiologists (ASA) classification. Our primary objective was to assess whether functional capacity is an independent predictor of 30-day and long-term mortality in a general population and, if so, to define how it may formally be incorporated into the routine preoperative ASA classification assessment. METHODS: This retrospective, observational cohort study was conducted using 1998 to 2009 data extracted from the Veterans Affairs Surgical Quality Improvement Program of Western New York, a perioperative prospectively maintained database. Mortality follow-up was performed for all records in 2013. This population-based sample included all patients undergoing any noncardiac surgery (n = 12,324). Each patient's ASA class (assigned preoperatively) was appended with subclasses A or B, with A representing patients who were functionally independent and B representing partially or fully dependent patients. The primary outcome was all-cause mortality during the follow-up period. Secondary outcomes included 30-day postoperative complications and mortality. Multivariate logistic regression was used to identify independent risk factors for mortality. RESULTS: The likelihood for mortality was significantly lower for A patients than B patients within each ASA class. The odds ratios for mortality for group A patients significantly favored survival over group B within each ASA class (0.14, 0.29, and 0.50, for ASA class II, III, and IV, respectively, each P < 0.0001). The odds ratio for mortality of IIB over IIIA patients was 1.92 (95% confidence interval CI, 1.19-3.11; P = 0.01); 1.29 (95% CI, 1.04-1.60; P = 0.03) for IIIB over IVA patients; and 2.03 (95% CI, 0.99-4.12, P=0.11) for IVB over ASA V patients, despite each higher class carrying a greater disease burden, by definition. The area under the curve the receiver operator characteristic curve was 0.811 ± 0.010 for traditional ASA classification in predicting death within 30 days, which improved 4.7% to 0.848 ± 0.008 using the modified ASA classification, P < 0.00001. CONCLUSIONS: Functional capacity was an independent predictor of mortality within each ASA class, indicating that it should be considered for incorporation into the routine preoperative evaluation. Functional dependence may be an indication for increasing a patient's ASA class by 1 class-point to better reflect his or her perioperative risk, but prospective validation of these findings is recommended, as this is a preliminary study.