A 25-year retrospective analysis of the American Society of Anesthesiologists physical status classification: did we “up-code” young obese patients when obesity was not yet considered a disease?

Christopher Guerry, John F. Butterworth

The influence of obesity on anesthetic risk remains controversial, and obesity has only recently been specifically identified as a criterion by which a patient can be given a higher American Society of Anesthesiologists-physical status (ASA-PS) score. Nevertheless, we hypothesized that clinicians had assigned obese patients a greater ASA-PS score before obesity became an "official" criterion in 2015. Basic demographic and physical details were collected on patients receiving anesthetics in the Virginia Commonwealth University Health System between 1986 and 2010. The risk ratio (RR) of "up-coding" ASA-PS classification assignments was calculated for patients of varying body mass index (BMI). We specifically focused on the subset of patients aged 20-29 yr in whom the medical sequelae of obesity would not yet likely be manifest. Among a total of 194,698 patients, the percentage who were obese increased from 20% to 39% between 1986 and 2010. Obese patients of all ages were more likely than non-obese patients to be classified as ASA-PS II-IV rather than ASA-PS I. The RR and ratio of RR analyses indicated a consistent pattern of up-coding patients with greater BMI (contingency table Chi-square: P < 0.001). Most notably, relative to patients with a normal BMI, young obese patients aged 20-29 yr had an increased likelihood of up-coding in ASA-PS compared with obese patients in the older cohorts. These findings suggest a consistent and temporally stable practice of up-coding obese patients despite this lack of explicit guidance. The ASA House of Delegates' recent decision to specifically mention obesity reinforces long-existing practices regarding ASA-PS coding and will likely not degrade the validity of data sets collected before the change.