Body mass index and post-operative outcomes in older adults after major surgery

Up to 40% of major elective surgery are performed in older adults. Various frailty assessments have been developed to risk stratify older adults undergoing surgery. However, these are often complex and time-consuming to administer. There is need for a convenient and pragmatic screening tool. We hypothesize that body mass index (BMI) can be used to identify older adults at risk of poorer outcomes following major elective surgery. We queried an institutional Perioperative Anaesthesia Subject Area Registry to identify older adults (aged ≥ 65) who underwent major elective surgery between January 2020 and December 2021. A BMI of less than 18.5 kg/m2 was defined as underweight, 18.5–22.9 kg/m2 normal-weight, 23.0–27.4 kg/m2 overweight and ≥ 27.5 kg/m2 as obese. We built multivariable regression models to test associations between BMI and outcomes including overall length of stay(LOS), LOS in intensive care(ICU) and 30-day mortality. Six thousand five hundred forty-eight older adults underwent major elective surgery. Mean BMI was 25.8 kg/m2, mean hospital LOS was 9 days, ICU LOS 8.6 h, and 30-day mortality 0.1%. 244(4%) had low and 1057(16%) had very high BMI. Being underweight was associated with longer overall LOS (IRR 1.31, 95% CI 1.19–1.44). There was no difference in 30-day mortality between BMI groups. Extremes of BMI was associated with an overall longer overall LOS in hospital in older adults undergoing major elective surgery. BMI can serve as a supplementary tool to identify at-risk older adults for targeted interventions.