*Objectives:

Primary : to assess the diagnostic performance of the decrease in pulse pressure variation (PPV) during a passive leg raising test (PLR) to predict preload responsiveness in spontaneously breathing patients hospitalized in intensive care.

Secondary

• Evaluate the diagnostic performance of the increase in pulse pressure (PP) during a PLR test to predict preload responsiveness in this same population.
• Compare before/after PLR measurements other hemodynamic data (blood pressure, cardiac output, heart rate).
• Experimental scheme: it is a diagnostic and monocentric study.
• Population / patients:

Inclusion criteria:

• Patient over 18 years old.
• Hospitalized in intensive care.
• For which the clinician in charge of the patient will need to predict the response to fluids and decide on a possible infusion of fluids, because of:
• Acute circulatory failure with mean arterial pressure < 65mmHg or < 30mmHg of its baseline value for hypertensive patients.
• And/or other signs of hemodynamic instability (tachycardia, mottling, oliguria, hyperlactatemia).
• In spontaneous ventilation and without ventilatory assistance.
• Previously equipped with an arterial catheter.
• Affiliated to a social security scheme.

Non-inclusion criteria:

• Patient with arrythmia (PPV is not applicable).
• Patient with intra-abdominal hypertension (PLR test is not valid).
• Patient with a contraindication/impossibility to the PLR maneuver (lower limb amputation, respiratory intolerance).
• Patient with poor echogenicity noted previously.
• Patient protected by law.
• Investigation Plan:

Patients meeting the inclusion criteria and not presenting any non-inclusion criteria may be included. The patient will be informed, or his/her relatives if he/she is unable to express their will, of the objectives and the progress of the study. If the patient, or his/her relatives, does not object to participate to the study, the course of the study will be as follows:

1. The following measurements will be performed before and after the PLR test in spontaneously breathing patients (SB) to evaluate the preload dependency:
   • Hemodynamic data: systolic (SAP), diastolic (DAP), mean (MAP), pulse pressure (PP), heart rate (HR), value of the Pulse Pressure Variation (PPV), cardiac index (CI) if cardiac output monitoring is already present.
   • Echographic data including: time-velocity integral of sub-aortic flow VTI Sub AO); aortic outflow chamber diameter (Diam outflow tract); data from the transmitral pulsed Doppler as well as the data from the tissue Doppler at the mitral annulus (E wave velocity; A wave; E' wave); left ventricular end-diastolic surface.
2. Collection of demographic parameters (age, sex, comorbidities), acute pathology and severity scores (SAPSII, APACHE II, SOFA) in the patient file.
3. Collection of oxygenation parameters: mode (conventional oxygen therapy or High Flow), Fio2 or liter O2/min, Flow if applicable.