Association between BMI and outcomes in critically ill patients: An analysis of the MIMIC-III database

Background : Obesity is a significant public health challenge, yet the link between BMI and mortality in critical illness remains unclear. Methods : This study analyzed 19,311 patients from the MIMIC-III database, categorized into underweight, healthy, overweight, and obese groups. Using Cox models and restricted cubic splines, we explored the complex relationship between BMI and mortality. Finally, multiple sensitivity analyses were performed to test the robustness of the results. Results : The proportion of underweight patients (2.3%) was the lowest, while overweight (34.8%) and obese (34.5%) patients constituted a large proportion. Being underweight portended a greater risk, while being overweight or obese was associated with a lower risk of mortality, which is consistent with the sensitivity analysis. Moreover, we observed a typical L-shaped relationship between BMI and the risk of mortality with and without adjustment, with the lowest mortality occurring at approximately 32 kg/m². The overall pattern of the nonlinear association between BMI and mortality was similar for most subgroup analyses. Conclusions : Underweight was associated with a greater risk of mortality, while obesity and overweight were both associated with a lower risk of mortality in critically ill patients. BMI had a typical L-shaped association with the risk of mortality.