Title: Relationship of Body Mass Index and Postsurgical Outcomes in Older Adults: An Observational Cohort Study  

Author: Cecilia Canales, MD, MPH, MS, Myles Anderson, BS, David Elashoff, MD, PhD, Tristan Grogan, MS, Marcia Russell, MD, Robert Whittington, MD, Maxime Cannesson, MD, PhD, Catherine Sarkisian, MD, MSHS

Area of Concentration (Petal): Medical Education Leadership and Scholarship

Background: High body mass index (BMI) has been associated with increased postoperative complications including mortality in the general population, leading many perioperative providers to recommend lifestyle modifications aimed at achieving normal body weight. These interventions are intended to mitigate obesity-related health risks and improve postoperative outcomes. However, aging introduces physiological changes such as altered body composition, fat redistribution, stature reduction due to height loss, and is associated with frailty. These changes may modify the relationship between BMI and surgical outcomes in older adults. We hypothesized that higher BMI in older adults undergoing major elective surgery is protective against all-cause mortality.

Methods: We conducted an observational cohort study of older adults (65 years or older) presenting to a preoperative clinic prior to planned surgery. Frailty was assessed using the 5-item modified frailty index (mFI-5). At the time of the preoperative evaluation, we measured weight, unintended weight loss, and recommendations for weight loss. Postoperative outcomes included all-cause 30-day and 1-year mortality, postoperative delirium, discharge disposition, and complications classified using the Clavien-Dindo system. To evaluate the relationship between BMI categories and postoperative outcomes, multivariable logistic regression models were used, adjusting for age, sex, frailty, and comorbid conditions.

Results: The study included 414 older adults undergoing major elective surgery. The mean age was 75.9 ± 7.2, and 54.8% of the cohort were female. The prevalence of frailty was 24.2% and 37% of the cohort was pre-frail. The overall 30-day all-cause mortality rate was 11%. Patients categorized as overweight (BMI 25–29.9 kg/m²) had the lowest 30-day all-cause mortality rate, with a significant risk reduction compared to patients with a normal BMI (18.5–24.9 kg/m²) [1/128 (0.8%) vs. 25/133 (18.8%)]. This association remained significant in the multivariable logistic regression model after adjusting for potential confounders. Patients categorized as underweight (BMI <18.5 kg/m²) had the highest 30-day all-cause mortality rate [15/20 (75%)].

Conclusion: In this study, being overweight was associated with a protective effect against 30-day all-cause mortality in older adults undergoing major elective surgery. These findings suggest that traditional weight loss recommendations based on achieving normal BMI may need to be re-evaluated for this population; a higher BMI may confer a survival advantage in the perioperative setting.

Keywords: frailty, older adults, body mass index, postoperative outcomes