A major cause of admission to intensive care is acute circulatory failure resulting from organ hypoperfusion due to factors such as hypotension and myocardial dysfunction. The standard treatment, including volume expansion and vasopressor/inotropic agents, often leads to water and sodium overload, increasing the risk of morbidity and mortality in the ICU. The combination of this overload and myocardial dysfunction lead to venous congestion, particularly affecting the lungs, kidneys and gastrointestinal system. Effective fluid management is therefore crucial to maintain a balance between adequate tissue perfusion and prevention of fluid overload. Fluid tolerance, defined as a patient's ability to tolerate additional volumes of solutes without adverse effects, is assessed retrospectively by clinical signs (capillary refill time, oedema, hepatojugular reflux, etc.) and ultrasound scores (VExUS score, LUS score, etc.). However, these indicators do not fully reflect the complexity of venous congestion in patients with various conditions.

Assessing fluid tolerance remains a challenge in clinical practice. It requires a personalised approach and the use of dynamic tests such as passive leg raising to predict response to vascular filling. Despite their common use, there are no studies evaluating the ability of changes in congestion markers during passive leg raising to predict fluid tolerance.

In conclusion, the main hypothesis is that changes in ultrasound congestion parameters (VExUS score, LUS score and others) during passive leg raising could predict a patient's subsequent tolerance to volume expander.

Inclusion Criteria:

• Adult patient
• Patient who has provided non-opposition (or health proxy or a close relative if unable to receive the information)
• Patient admitted to intensive care and requiring volume expander

Exclusion Criteria:

• Person subject to a legal protection measure (curatorship, guardianship)
• Person subject to a legal protection measure
• Pregnant, parturient or breast-feeding women
• Poor echogenicity assessed by the operator
• Chronic AC/FA
• Mechanical cardiac assistance

Eligible patients will be identified by the investigator on admission to the intensive care unit.