Fluid management in septic shock patients remain a great challenge. Insufficient fluid filling lead to hypovolemia, organ failure and increased death, whereas fluid overload was associated to an increased morbidity and mortality in several studies.

Several invasive and non invasive strategies have been developed during the past years to monitor the hemodynamic state of septic shock patients, but no method has been validated to objectively quantify fluid overload in septic shock patients.

The Body Composition Monitor (BCM) allow for measurement of total body water (TBW), extracellular water (ECW) and intracellular water (ICW) volumes using bioimpedancemetry. The BCW is daily used in patients who undergo renal dialysis to assess the effectiveness of fluid removal. The BCM has never been validated in septic shock patients.

The aim of the study is to investigate the accuracy of the BCM to measure the variation of the TBW during a fluid challenge of 500 ml of saline during the early phase of septic shock.

Patients suffering from septic shock admitted in our critical care unit for less than 24 hours will be eligible. TBW, ECW and ICW volumes will be measured using the BCM just before (T0), just at the end (T1) and 1 h after the end (T2) of a fluid challenge of 500 ml of saline. Fluid responsiveness will be assessed using trans thoracic echocardiography (TTE). TTE will be performed at T0, T1 and T2. Blood samples will be obtained at T0, T1 and T2 to dose biomarkers of endothelial dysfunction and of capillary leak. The effectiveness of fluid challenge on microcirculation will be investigated by measuring the tissue perfusion index of the urethral mucosa using the IKORUS UP device.

Patients will be followed until Day 28 after admission in the critical care unit.

Inclusion Criteria:

• Patient aged from 18 to 80 years old
• Admitted to ICU for septic shock for less than 24 h
• Fluid resuscitation decided by intensivist
• Patient affiliated to a social security system or recipient of a such system
• Patient/proxy not opposed to the study

Exclusion Criteria:

• Subject with amputation of 1 or more limbs
• Body mass index > 35 kg.m-2 ou < 18 kg.m-2
• Impossibility of setting up an arterial catheter for invasive blood pressure monitoring and / or a central venous catheter in the upper cava territory
• Patient with pacemaker and / or implantable cardioverter defibrillator
• Quality of cardio echo image insufficient to allow studied parameters measurement
• Moribund subject ( life expectancy expected less than 48 hours)
• Uncontrolled intracranial hypertension (intracranial pressure ≥ 20 mm Hg by ICP monitoring or by a pulsatility index ≥ 1.30 in the transcranial Doppler)
• Patient under ECMO/ECLS
• Legal incapacity or limited legal capacity
• Subject without health insurance
• Pregnant woman
• Subject being in the exclusion period of another study or provided for by the "National Volunteer File"

ICU patient requiring fluid resuscitation for septic shock