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?

Purpose: 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.

Methods: 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.

Results: 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.

Conclusions: 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.