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.