This study investigates whether Body Roundness Index (BRI), an anthropometric measure derived from waist circumference and height, can predict mortality in adult intensive care unit (ICU) patients. BRI captures central adiposity and body fat distribution more accurately than Body Mass Index (BMI). In this prospective multicenter cohort study, BRI will be measured at ICU admission and its association with ICU mortality, 28-day mortality, hospital mortality, mechanical ventilation duration, ICU length of stay, and acute kidney injury will be evaluated. The predictive performance of BRI will also be compared with BMI.

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)

Adult patients admitted to the intensive care units of participating tertiary care centers in Turkey. Enrollment will be conducted prospectively across multiple centers following ethics committee approval at each site.

De-identified individual participant data underlying published results will be made available upon reasonable request.

Beginning 6 months after primary results publication, available for 2 years.

Researchers who provide a methodologically sound proposal. Requests should be directed to the corresponding author. Data will be shared after signing a data access agreement.