Effect of body mass index on postoperative recovery to independent living: a retrospective cohort study*

Abstract

Introduction: Living with obesity is a risk factor for diabetes, cardiovascular disease and cancer. The ‘obesity paradox’ suggests patients who are overweight or living with mild obesity experience better outcomes after surgery and critical illness compared with patients living with normal weight. However, little is known about the generalisability and possible mechanisms of the obesity paradox. This study investigated the relationship between BMI and loss of independent living after surgery. Methods: We analysed adult patients who lived independently before non-cardiac, non-bariatric, non-ambulatory surgery. We used a multivariable restricted cubic spline model, with a BMI of 22.0 kg.m^-2 set as our reference point. The primary outcome was loss of independent living (adverse discharge), defined as in-hospital mortality or discharge to a skilled nursing facility. Results: Among 73,813 patients, 9495 (12.9%) were unable to live independently after surgery. Adjusted analyses showed a U-shaped relationship between BMI and adverse discharge, with calculated risk ratios and confidence intervals for each distinct BMI in the cohort compared with our reference weight of 22.0 kg.m^-2. Patients who were underweight had significantly elevated risks (adjusted risk ratio (aRR) 1.46 (95%CI 1.34–1.59) for patients with BMI 15.0 kg.m^-2). Similarly, patients living with severe obesity had a higher risk of adverse discharge destination (aRR 1.07 (95%CI 1.01–1.13) and 1.36 (95%CI 1.24–1.48) for patients with BMIs of 40.0 kg.m^-2 and 50.0 kg.m^-2, respectively). In contrast, patients who were overweight or living with obesity class 1 had reduced risks of adverse discharge (aRR 0.90 (95%CI 0.88–0.92) and 0.89 (95%CI 0.84–0.94) for BMIs of 25.0 kg.m^-2 and 30.0 kg.m^-2, respectively). Discussion: This study shows a U-shaped relationship between BMI and the risk of postoperative loss of independent living. Patients with mild obesity experienced a lower risk of losing the ability to live independently after surgery.