Body Mass Index and Postsurgical Outcomes in Older Adults.

Importance: High body mass index (BMI) has been associated with increased postoperative complications including mortality in the general population, leading many perioperative clinicians to recommend preoperative lifestyle modifications aimed at achieving normal body weight. However, aging introduces physiological changes associated with frailty, such as altered body composition, fat redistribution, and stature reduction due to height loss, all of which may modify the association between BMI and surgical outcomes in older adults. Objective: To determine if a higher BMI in older adults who are undergoing major elective surgery is associated with rates of all-cause mortality. Design, Setting, and Participants: Cohort study of adults aged 65 years or older presenting for surgery from February 2019 to January 2022 at a preoperative clinic before planned major elective surgery at a large academic Center in Southern California. Exposure: Body mass index. Main Outcomes and Measures: Postoperative outcomes included all-cause 30-day and 1-year mortality, postoperative delirium, discharge disposition, and complications classified using the Clavien-Dindo system. Results: The study included 414 older adults undergoing major elective surgery with a mean (SD) age of 75.9 (7.2) years; 54.8% (95% CI, 50.2%-60.4%) of the cohort were female. The prevalence of frailty was 24.2% (95% CI, 20.3%-28.5%), and 37.0% (95% CI, 32.6%-41.8%) of the cohort was prefrail. The overall 30-day all-cause mortality rate was 11.0% (95% CI, 8.5%-14.5%). Patients categorized as overweight (BMI, 25.0-29.9; calculated as weight in kilograms divided by height in meters squared) had the lowest 30-day all-cause mortality rate, with a significant risk reduction compared with patients with a normal BMI (18.5-24.9) (1 of 128 patients [0.8%] vs 25 of 133 patients [18.8%]; odds ratio [OR], 0.03; 95% CI, 0.01-0.26; P = .001). This association remained significant in the multivariable logistic regression model after adjusting for potential confounders (OR, 0.14; 95% CI, 0.06-0.34; P < .001). Patients categorized as underweight (BMI <18.5) had the highest 30-day all-cause mortality rate (15 of 20 patients [75.0%]; 95% CI, 55.0%-90.0%). Conclusions and Relevance: In this observational cohort study of older adults undergoing major elective surgery, being overweight was associated with lower odds of 30-day all-cause mortality. These findings suggest that traditional weight loss recommendations based on achieving normal BMI may need to be reevaluated for this population.