Reliability of the ASA Physical Status Classification System in Predicting Surgical Morbidity: a Retrospective Analysis

Abstract

The American Society of Anesthesiologists (ASA) Physical Status Classification System has been used to assess pre-anesthesia comorbid conditions for over 60 years. However, the ASA Physical Status Classification System has been criticized for its subjective nature. In this study, we aimed to assess the correlation between the ASA physical status assignment and more objective measures of overall illness. This is a single medical center, retrospective cohort study of adult patients who underwent surgery between November 2, 2017 and April 22, 2020. A multivariable ordinal logistic regression model was developed to examine the relationship between the ASA physical status and Elixhauser comorbidity groups. A secondary analysis was then conducted to evaluate the capability of the model to predict 30-day postoperative mortality. A total of 56,820 cases meeting inclusion criteria were analyzed. Twenty-seven Elixhauser comorbidities were independently associated with ASA physical status. Older patient (adjusted odds ratio, 1.39 [per 10 years of age]; 95% CI 1.37 to 1.41), male patient (adjusted odds ratio, 1.24; 95% CI 1.20 to 1.29), higher body weight (adjusted odds ratio, 1.08 [per 10 kg]; 95% CI 1.07 to 1.09), and ASA emergency status (adjusted odds ratio, 2.11; 95% CI 2.00 to 2.23) were also independently associated with higher ASA physical status assignments. Furthermore, the model derived from the primary analysis was a better predictor of 30-day mortality than the models including either single ASA physical status or comorbidity indices in isolation (p < 0.001). We found significant correlation between ASA physical status and 27 of the 31 Elixhauser comorbidities, as well other demographic characteristics. This demonstrates the reliability of ASA scoring and its potential ability to predict postoperative outcomes. Additionally, compared to ASA physical status and individual comorbidity indices, the derived model offered better predictive power in terms of short-term postoperative mortality.

Keywords: ASA physical status; Comorbidity indices; Elixhauser comorbidities; Postoperative mortality.

Fig. 1

Visualization of the sensitivity analysis results that derived from multivariable ordinal logistic regression model. The odds ratio estimates and their corresponding 95% Wald confidence intervals demonstrate the odds of the next higher ASA physical status associated with the change in the corresponding covariates. For continuous variables, the odds ratios correspond to a unit increase in the risk factors

Fig. 2

Visualization of the Receiver Operating Characteristic (ROC) curves comparison in terms of the predictive capability of models for postoperative 30-day mortality. Model 1 consists of the covariates that derived from primary analysis, model 2 consists of the covariates that derived from sensitivity analysis, and model 3 consists of the ASA physical status