Association between body mass index and mortality in intensive care unit patients with sepsis: A retrospective cohort study

The link between body mass index (BMI) and outcomes in intensive care unit (ICU) patients with sepsis is inconsistently supported by the available data. This study aimed to examine the association between BMI and mortality among ICU patients with sepsis. On the basis of their BMI values upon admission to the ICU, sepsis patients from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database were categorized as low weight, normal weight, overweight, or obesity group. The primary outcome measure was in-hospital mortality and the secondary outcome was 90-day mortality. Multivariable logistic regression was used to examine the association between BMI categories and in-hospital mortality. Kaplan-Meier methods with log-rank testing were used to compare 90-day survival across groups, and Cox proportional hazards models were applied to estimate the association between BMI and 90-day mortality. Subgroup analyses were also performed. In an external cohort, inverse probability of treatment weighting (IPTW) was applied as a supplementary analysis, and propensity score matching (PSM) was performed as a sensitivity analysis to assess the robustness of the observed associations. A total of 13,864 patients with sepsis were included (low weight: 339; normal weight: 3,582; overweight: 4,564; obesity: 5,379). Overall in-hospital mortality was 15.4%. In multivariable logistic regression analyses, compared with the normal weight group, the adjusted odds ratios (ORs) for in-hospital mortality were 1.68 (95% confidence interval [CI]: 1.29-2.20) in the low weight group, 0.77 (95% CI: 0.67-0.88) in the overweight group, and 0.74 (95% CI: 0.65-0.85) in the obesity group. The overall 90-day mortality was 22.9%. In multivariable Cox proportional hazards models, compared with the normal weight group, the adjusted hazard ratios (HRs) for 90-day mortality were 1.62 (95% CI: 1.34-1.94) in the low weight group, 0.78 (95% CI: 0.71-0.85) in the overweight group, and 0.74 (95% CI: 0.68-0.81) in the obesity group. Subgroup analyses by age and sex showed consistent associations. In the external cohort, a BMI ≥ 32 kg/m² was also associated with lower in-hospital and 90-day mortality after adjustment. In conclusion, BMI was associated with mortality among ICU patients with sepsis. In this retrospective cohort, higher BMI was associated with lower in-hospital and 90-day mortality compared with low or normal BMI after adjustment. These findings are observational and should not be interpreted as evidence of a protective effect or causality.