Critically ill patients feature a loss of fat-free mass (FFM) up to 440 g/day, which is associated with increased morbidity and prolonged recovery. In several clinical conditions, FFM or phase angle (PhA)derived from BIA have been associated with clinical outcome. However, solid data to support this association in ICU patients are lacking. Only one retrospective study of 51 ICU patients with acute respiratory failure correlated loss of active cell mass with mortality. In a pilot study performed in 55 ICU patients, the investigators observed that five kHz BIA PhA was significantly related to SOFA (r=0.38, P=0.03). The relation between PhA and mortality remains to be determined in ICU patients.

Classic ICU validated severity scores (e.g. Acute Physiology and Chronic Health Evaluation (APACHE), Sequential Organ Failure Assessment (SOFA), Simplified Acute Physiology Score (SAPS)) and recent nutritional scores have been developed to foresee the clinical outcome of ICU patients. Most of these scores are time consuming and suffer some degree of discriminative power (i.e. APACHE II and SAPS II are not validated in cardiovascular surgery patients).

PhA is reflecting intracellular status: altered intracellular water (ICW) to extracellular water (ECW) distribution is suggested by low PhA. PhA measurement does not require anamnestic parameters, body weight, and lab tests. It could easily, accurately and repeatedly measured at bedside. PhA has been correlated with the disease prognosis in HIV infection, hemodialysis, peritoneal dialysis, chronic renal failure and liver cirrhosis patients. These studies suggest that PhA may be useful in determining increased risk of morbidity in the ICU.

Computerized tomography (CT) images targeted on the 3rd lumbar vertebrae (L3) could accurately measure FFM13 and predict survival in cancer patients. Body composition evaluation by CT presents great practical significance due to its routine ICU use in the initial diagnosis or follow-up. The usefulness of measuring FFM with L3-targeted CT has never been evaluated in ICU patients.

Therefore, the investigators aim to conduct an international multicentre prospective observational study in ICU patients to assess the prognosis value of BIA PhA at admission, and to compare the performances of BIA and L3-targeted CT for FFM measurement.

Inclusion Criteria:

• equal or more than 18 years
• expected ICU length of stay of more than 48 hours
• no readmission within the 48 hours following ICU discharge
• no Implanted Cardiac Devices
• no pregnancy or lactation
• affiliated to health insurance regimen
• informed consent by patient or next of kin.

Exclusion Criteria:

• age below 18 years
• expected ICU length of stay <48 hours
• readmission within the 48 hours following ICU discharge
• Implanted Cardiac Devices
• pregnancy or lactation
• non affiliated to health insurance regimen
• no informed consent by patient or next of kin.

Patients hospitalized in medical and surgical intensive care units.