Assessment of Blood Viscosity in ARDS (Acute Respiratory Distress Syndrome)

Case Group Inclusion Criteria: * Age ≥ 18 ans * Moderate-to-severe ARDS according to the global definition: * with PaO₂/FiO₂ ≤ 200 mmHg (based on arterial blood gas analysis in patients receiving invasive or non-invasive mechanical ventilation or high-flow nasal oxygen therapy). * Participation agreement obtained (either from the patient themselves or from a relative) Exclusion Criteria: * ARDS that has been present for more than 72 hours * Terminally ill patient with death expected within 24 hours * Patient who has received a blood transfusion within the past month * Patient with a known hematologic malignancy (lymphoma; myeloma; acute or chronic leukemia) * Patient with a known hemoglobinopathy. * Hemorrhagic shock * Hemoglobin \< 70 g/dL Control group Inclusion Criteria: * Age ≥ 18 ans * Participation agreement obtained (either from the patient themselves or from a relative) Exclusion Criteria: * Presence of ARDS according to the global definition * P/F \< 300 mmHg * Presence of sepsis defined by an infection and a SOFA score delta ≥ 2. * Terminally ill patient with death expected within 24 hours * Patient who has received a blood transfusion within the past month * Patient with a known hematologic malignancy (lymphoma; myeloma; acute or chronic leukemia) * Patient with a known hemoglobinopathy. * Hemorrhagic shock * Hemoglobin \< 70 g/dL