Threshold effects of baseline BMI on 30-day hospital mortality in critically Ill COPD patients: a multicenter retrospective study

Despite well-documented obesity paradoxes in critical illness, the precise relationship between body mass index (BMI) and mortality in critically ill chronic obstructive pulmonary disease (COPD) patients remains unclear. This study aimed to identify potential BMI thresholds associated with survival outcomes in this high-risk population. This retrospective multicenter cohort study analyzed 10,179 critically ill COPD patients from 208 U.S. hospitals in the eICU Collaborative Research Database (2014–2015). The exposure variable was BMI measured within 24 h of intensive care unit (ICU) admission. The primary outcome was in-hospital mortality. Covariates included demographics, laboratory parameters, disease severity scores, comorbidities, and treatments. Restricted cubic splines and two-piecewise linear regression models were used to identify non-linear BMI-mortality associations, with subgroup analyses stratified by 13 clinical variables. Among 10,179 patients (mean age 67.9 years; 50.0% male), overall ICU mortality was 5.6%. A BMI threshold of 20.8 kg/m2 (95%CI 20.5–21.2) was identified. Below this threshold, each 1 kg/m2 BMI increase was associated with 13% lower mortality risk (OR = 0.87, 95%CI 0.80–0.93, P 0.05). This retrospective analysis identified a BMI threshold of 20.8 kg/m2 associated with differential ICU mortality risk in critically ill COPD patients. These observational findings may inform BMI-stratified risk assessment in ICU COPD populations, though prospective validation is warranted.