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National Surgical Quality Improvement Program (NSQIP) Risk Factors Can Be Used to Validate American Society of Anesthesiologists Physical Status Classification (ASA PS) Levels

Davenport, Daniel L. PhD*; Bowe, Edwin A. MD; Henderson, William G. PhD; Khuri, Shukri F. MD§; Mentzer, Robert M. Jr MD*

doi: 10.1097/
Original Articles

Objective: The purpose of this study was to determine the relationship between the American Society of Anesthesiologists’ Physical Status (ASA PS) classifications and the other National Surgical Quality Improvement Program (NSQIP) preoperative risk factors.

Background: The ASA PS has been shown to predict morbidity and mortality in surgical patients but is inconsistently applied and clinically imprecise. It is desirable to have a method for validating ASA PS classification levels.

Methods: The NSQIP preoperative risk factors, including ASA PS, were recorded from a random sample of 5878 surgical patients on 6 services between October 1, 2001 and September 30, 2003 at the University of Kentucky Medical Center. Mortality, morbidity, costs, and length of stay were obtained and compared across ASA PS levels. The ability of 1) ASA PS alone, 2) the other NSQIP risk factors, and, 3) all factors combined to predict outcomes was analyzed. A model using the other NSQIP risk factors was developed to predict ASA PS.

Results: ASA PS alone was a strong predictor of outcomes (P < 0.01). However, the other NSQIP risk factors were better predictors as a group. There was significant interdependence between the ASA PS and the other NSQIP risk factors. Predictions of ASA PS using the other factors showed strong agreement with the anesthesiologists’ assignments.

Conclusions: The NSQIP risk factors other than ASA PS can and should be used to validate ASA PS classifications.

The American Society of Anesthesiology's Physical Status Classification (ASA PS) is known to be a strong predictor of surgical outcomes. However, the ASA PS is limited because it lacks clinical precision and is inconsistently applied by different anesthesiologists. The National Surgical Quality Improvement Program tracks 60 preoperative risk factors, including the ASA PS. This study demonstrates that the other 59 risk factors are effective in predicting ASA PS and therefore can be used to validate ASA PS levels by hospital or anesthesiologist.

From the Departments of *Surgery and †Anesthesiology, University of Kentucky, Lexington, KY; ‡University of Colorado Health Outcomes Program, Denver, CO; and §National Surgical Quality Improvement Program, West Roxbury, MA.

Supported in part by a grant from the Agency for Healthcare Research and Quality through the American College of Surgeons under the direction of the National Surgical Quality Improvement Program.

Reprints: Daniel L. Davenport, PhD, Office of Decision Support, Department of Surgery, University of Kentucky, 800 Rose Street, Lexington, KY 40536-0298. E-mail:

© 2006 Lippincott Williams & Wilkins, Inc.