Fluid administration is the first-line treatment in hypovolemic states in critically ill patients. Prediction of fluid responsiveness is possible with echocardiography by assessing the variation of the sub-aortic velocity-time integral (AoVTI) during a passive leg raising test (PLR) or Mini-fluid challenge. However, VTI-Ao measurement is not feasible in all patients due to poor echogenicity. Validation of new fluid-responsiveness indices may facilitate the evaluation in this patient population. Among the available indices, variation of the sub-pulmonary VTI is a potential criterion.

Inclusion Criteria:

• Patient with measurable sub-pulmonary VTI in at least one of the two windows: parasternal short-axis or subcostal.
• Patient with measurable sub-aortic VTI in apical 4-chamber view before and after PLR maneuver.
• Patient with suspected hypovolemia or whose hemodynamic status justifies vasopressor infusion.

Exclusion Criteria:

• Severe left ventricular dysfunction defined by left ventricular ejection fraction (LVEF) < 30%.
• Severe right ventricular dysfunction defined by TAPSE < 12 mm.
• Cardiac arrhythmia or atrial fibrillation.
• Abdominal compartment syndrome.
• Amputation of one or both lower limbs.
• Intracranial hypertension.
• Pregnant women (ruled out by systematic pregnancy test at ICU admission).
• Minors.

In patients with suspected hypovolemia, a cardiac ultrasound is performed as part of routine care. A patient is eligible if it is possible to measure both sub-aortic VTI (gold standard) and sub-pulmonary VTI in one of the two echocardiographic windows described in the literature (parasternal short-axis or subcostal).