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

Acute respiratory distress syndrome (ARDS) is characterized by damage to the alveolar-capillary membrane, resulting in hypoxemia, decreased pulmonary compliance, and hemodynamic changes. Critical conditions (hypoxia; septic shock associated with ARDS) can alter blood viscosity. These changes in viscosity can affect blood flow and hemodynamics. There is only one clinical study that has measured one of the determinants of blood viscosity in ARDS (deformability), even though other parameters are involved in viscosity (elongation, deformability, hematocrit, etc.), and it is possible to measure blood viscosity comprehensively. To date, therefore, no study has evaluated the various parameters of blood viscosity in ARDS. The aim of this study is to investigate hyperviscosity in patients with ARDS and to assess whether this hyperviscosity correlates with respiratory or hemodynamic changes. The investigators will therefore compare blood viscosity and its determinants in patients admitted to the intensive care unit for ARDS and in patients admitted for other reasons (excluding ARDS or sepsis/septic shock). The investigators will also conduct a longitudinal assessment of changes in hemodynamic, respiratory, and viscosity parameters during ARDS

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