Body Roundness Index and Mortality in ICU Patients

Body Roundness Index (BRI) is calculated using waist circumference and height, and reflects central adiposity more precisely than BMI. Despite growing evidence supporting BRI as a cardiovascular and metabolic risk predictor in general populations, its prognostic value in critically ill patients remains unexplored.

In this prospective multicenter cohort study, adult patients admitted to participating ICUs will be enrolled. Waist circumference will be measured using a standardized protocol (supine position, iliac crest landmark, end-expiration, inelastic tape, 0.1 cm precision) within 24 hours of ICU admission. BRI will be calculated using the formula: 364.2 - 365.5 × √(1 - ((WC/2π)² / (0.5×height)²)).

The primary outcome is ICU mortality. Secondary outcomes include 28-day mortality, hospital mortality, mechanical ventilation duration, ICU length of stay, and new acute kidney injury (KDIGO stage ≥2). The shape of the BRI-mortality relationship will be assessed using restricted cubic splines. BRI and BMI will be compared head-to-head for discriminative performance. Subgroup analyses will include sepsis patients to evaluate whether BRI resolves the obesity paradox observed with BMI.

Inclusion criteria

• Age ≥18 years
• ICU admission with expected stay ≥24 hours
• Waist circumference and height measurable within 24 hours of admission

Exclusion criteria

• Age <18 years
• ICU stay <24 hours
• Missing or unmeasurable anthropometric data (e.g., severe edema, abdominal wound, morbid obesity precluding measurement)
• Pregnancy
• Readmission (only first ICU admission included)