Severe obesity is not a ‘mild disease’

Thanks to Smith and colleagues for their paper on functional and disease burdens in obesity. ¹ This work is important.

It showed that functional impairment was the norm, not the exception. Only one in 10 patients could walk within 10% of the predicted distance—even after that distance prediction had been revised down for body mass index (BMI). The authors also noted that the cohort carried a high burden of comorbid disease, including serious problems like sleep apnoea, diabetes and renal impairment.

A number of patients in the study were classified as American Society of Anesthesiologists’ Physical Status II (ASA PS Class II), however. The definition of ASA PS Class II is ‘mild disease without substantive functional limitation’. ² Although a BMI of 30 to 40 is listed as an example of this in the ASA PS guidelines, the combination of severe obesity, multi-system disease and functional impairment is manifestly inconsistent with that definition.

Why did clinicians implicitly label severe obesity as ‘mild disease’? And why is there this inconsistency between the ASA Physical Status definition and its obesity example? Have we become desensitised because obesity is so commonplace? Is ‘50 the new 40’ for us to recognise it as serious? If so, this study should help to correct that skewed perspective.

It is time to revise this example in the ASA Physical Status definition and ‘upsize’ its classification of severe obesity. Most patients whose BMI is over 35 meet the criteria for ASA PS Class III.