National Surgical Quality Improvement Program (NSQIP) risk factors can be used to validate American Society of Anesthesiologists Physical Status Classification (ASA PS) levels

Abstract

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.

Figures

FIGURE 1. The NSQIP risk factors other than ASA PS were used to predict ASA PS using an ordinal regression model. The agreement between the predictions and the anesthesiologist assignments is shown as the distribution of the difference between them for 5878 patients. The difference terms are normally distributed around agreement (0). Predictions disagreed by more than one level in only 0.8% of the patients.