The Association Between Body Mass Index and 28-day Mortality in Patients With Sepsis: A Retrospective Cohort Study

Background Sepsis is a severe clinical syndrome with high morbidity and mortality in intensive care units (ICUs). Body Mass Index (BMI) shows a rising trend of obese patients being admitted to ICUs. The relationship between BMI and the clinical outcome of sepsis remains highly debated.Methods The data used in this study were sourced from the Intensive Care Information Center IV (MIMIC-IV) database. Baseline information extracted within 24 hours of ICU admission was categorized according to World Health Organization (WHO)'s BMI classifications. A multivariate Cox regression model and curve fitting assessed the independent correlation between BMI and the primary outcome.Results A total of 7836 patients were included in the study and categorized into five groups based on BMI. The overall 28-day mortality rate was 21.94% (1719/7836). Class I obesity (17.14%) and class II/III obesity (13.49%) individuals tended to be younger and male. Compared to patients with normal BMI (32.55%), those with low BMI (5.79%) had a 47% increased risk of 28-day mortality (HR 1.47, 95% CI 1.16-1.85, P = 0.0013), while class II/III obesity patients had a 17% lower 28-day mortality rate (HR 0.83, 95% CI 0.71-0.97, P = 0.0218). Curve fitting revealed a nonlinear relationship between BMI and 28-day mortality. The Kaplan-Meier survival analysis highlighted variations in survival rates across the five groups (P = 0.0123), with underweight patients exhibiting poorer survival outcomes.Conclusion In sepsis patients, a low BMI is related to higher 28-day mortality compared to those with a normal BMI. Conversely, patients with a BMI >= 35 kg/m2 have significantly reduced mortality risks.