\*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 mechanically ventilated patients under spontaneous mode 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 mechanically ventilated patients under spontaneous mode.
* 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, Fio2 level od pressure support and of PEEP, in addition to the tidal volume and RR.
