Relationship Between the Level of Positive End-expiratory Pressure and Venous Congestion During Acute Respiratory Distress Syndrome.

All analyzes will be carried out with collection intention. All information required by the protocol is obtained from the clinical file of the Intensive care and Hyperbaric Medicine department of Angers University Hospital. This research is not involving humans on prospective data from care. This research does not require any specific investigation and does not involve no changes to support.

Clinical and biological data to be collected at inclusion (D1) :

* Demographic data: age, sex, weight (on the day of admission to intensive care and day of inclusion), medical history. * Cause of ARDS. * Ventilatory parameters: PEEP set by the clinician, total PEEP, Pplat, tidal volume, inspiratory and expiratory esophageal pressure if available as part of the treatment. * Hemodynamic parameters: systolic, diastolic, mean aretrial blood pressure ; central venous pressure (if available as part of routine care); heart rate; transpulmonary thermodilution monitor data (if available as part of the routine care) or Swan-ganz catheter (if available as part of the routine care), vasoactive treatments (type and dosage).

Assessments to be carried out as part of routine care on D1, between D3 and D5 and between D6 and D8 :

1. Measures relating to the mechanics of the respiratory system:

* Measurement of airway opening pressure (AOP). * Calculation of the R/I ratio (recruitability index) * The two PEEP levels, high and low, chosen by the clinician for performing the following measurements. 2. At the two PEEP levels, the investigator will retrospectively collect the following clinical, biological, and echographic measurements, which were prospectively recorded by the clinician.

* Cardiac ultrasound:

* Right ventricular function parameters (TAPSE, S' wave, Vmax IT, diameter VD). * Cardiac output. * LVEF (once only) * Evaluation of venous congestion by Doppler of the veins :

* Venous congestion is initially assessed by studying each flow individually. Doppler (suprahepatic veins, renal interlobar veins and portal vein) and graded in "absent", "moderate" or "severe" as follows :

* Suprahepatic veins: S wave \> D = absent (normal) ; S wave \< D = moderate ; Positive S wave = severe * Renal interlobar veins: Continuous flow = absent (normal) ; Biphasic flow = moderate ; Monophasic flow = severe * Portal vein: Pulsatility index \< 30% = absent (normal) ; Pulsatility index ≥ 30% and ≤ 50% = moderate ; Pulsatility index \> 50% = severe NB : calculation of the portal trunk pulsatility index (\[(Vmax - Vmin) / Vmax\], average of 3 measurements)

Then the VExUS score, integrating these three signals as well as the study of the diameter of the inferior vena cavan by ultrasound, is calculated as follows: * Grade 0 "absence of congestion": VCi \< 20mm; * Grade 1 "mild congestion": VCi ≥ 20 mm and suprahepatic venous Doppler, portal and renal normal or with signs of moderate congestion; * Grade 2 "moderate congestion": VCi ≥ 20 mm and presence one venous flow (suprahepatic, portal, or renal) showing evidence of severe congestion; * Grade 3 "severe congestion": VCi ≥ 20 mm and presence of several flows vein showing signs of severe congestion.

* Arterial and central venous gasometry (ScVO 2, PaCO2, PvCO2, lactate, PaO2, pH). * Collection of hemodynamic parameters: systolic blood pressure, mean, diastolic, heart rate, central venous pressure. * In patients with a pulmonary artery catheter: data collection following: systolic, diastolic and average PAP, cardiac index * Collection of ventilatory parameters: plateau pressure, total PEEP, and, if available, end-inspiratory and end-expiratory esophageal pressures. 3. Collection of renal function with:

* Serum creatinine and urea * Creatininuria on urine ionogram * 24-hour diuresis 4. Collection of weight and input-output balance 5. The echocardiographic data collected at inclusion and during follow-up will be processed a posteriori by two different observers.

End of monitoring data (D28):

During this visit, the following elements will be collected:

* Occurrence of acute renal failure (according to KDIGO criteria) on day 8. * Use or not of extra-renal purification * Survival at D28 (to characterize the population)

• In patients with a pulmonary artery catheter: evolution between venous congestion in abdominal venous flow and the VExUS score with right heart pressures (systolic, diastolic and mean pulmonary arterial pressure at D1, D3-D5 and D6-D8) [Time frame: From Baseline to day 8]
• Evaluate the evolution of venous congestion (VExUS score) according to the PEEP level over time (D1, D3-D5 and D6-D8) for each patient individually [Time frame: From baseline to Day 8]
• Evaluate the evolution of venous congestion in abdominal venous flows and the VExUS score according to PEEP level [Time frame: From baseline to Day 8]
• Incidence of acute renal failure at day 28 in patients with markers of significant venous congestion [Time frame: From baseline to day 28]
• Incidence of renal replacement therapy on day 28 in patients with markers of significant venous congestion [Time frame: From baseline to Day 28]
• Evolution of the level of venous congestion evaluated on the different abdominal Doppler venous flows (portal, suprahepatic and renal venous Doppler) and on the VExUS score between the different levels of PEEP (high and low) [Time frame: from day 3 to day 5]
• Evolution of the level of venous congestion evaluated on the different abdominal Doppler venous flows (portal, suprahepatic and renal venous Doppler) and on the VExUS score between the different levels of PEEP (high and low) [Time frame: From Day 6 to Day 8]
• Evolution between venous congestion in abdominal venous flow and the VExUS score and echocardiographic markers of right heart function (D1, D3-D5 and D6-D8) [Time frame: From baseline to day 8]