Acute respiratory distress syndrome remains a serious condition, with a mortality rate of between 30 and 50%. The use of mechanical ventilation with small tidal volumes, and by limiting the plateau pressure in the respiratory tract below 30 cm H2O has been shown to reduce mortality by approximately 10%, probably by reducing pulmonary hyperinflation and pulmonary lesions induced by mechanical ventilation. It is therefore now established that the respirator settings influence patient prognosis. However, around 30% of patients with ARDS ventilated with these settings supposedly protective continue to present signs of pulmonary hyperinflation on tomodensitometry, suggesting an additional reduction in the tidal volume could be required in certain patients. Electrical impedance tomography (EIT) is a new imaging technique that gathers functional pulmonary information at bedside.

This technique also allows a regional analysis, allowing the complexity of the spatial distribution of ARDS pulmonary lesions to be understood. The hypothesis is that EIT is a reliable method to detect at-risk situations of lesions induced by mechanical ventilation among patients with ARDS.

Inclusion Criteria:

• Aged ≥18 years
• Hospitalised in the medical resuscitation department of the Croix Rousse hospital, Lyon, Fr
• With ARDS according to the 1994 American-European Consensus Conference
• Duration of ARDS less than 96 hours
• With invasive mechanical ventilation
• With sedative and analgesic treatment for adaptation of the respirator with or without neuromuscular blocking agents
• Consent obtained from patient family
• Indication for thoracic scanner as judged by the physician in charge of the patient

Exclusion Criteria:

• Excessively serious respiration precluding the modifications to ventilation planned in the protocol

  • severe hypoxemia defined as sever by arterial blood pressure/fraction of inspired oxygen (PaO2/ FiO2) below 100 mm Hg in dorsal decubitus position
  • uncontrolled respiratory acidosis, defined by a pH below 7.25, despite an increase of respiratory frequency up to 35/min and a tidal volume up to 8 mL/kg of predicted weight
  • respiratory system plateau pressure higher than 30 cm H2O, with a tidal volume below or equal to 6 mL/kg of predicted weight.

• Contraindication for transport to the radiology department

  • uncontrolled hemodynamic instability defined by a mean arterial blood pressure below 65 mm Hg, despite use of antihypotensive agents
  • patient requiring continuous dialysis without possibility for disconnection for reason of uncontrolled metabolic acidosis (pH<7.20).

• Without reliable monitoring during transport of the patient to the radiology department

  • absence of invasive arterial pressure measurement
  • unreliable measurement of arterial saturation in oxygen (SpO2) defined by a perfusion index below 0.5.

• Intracranial hypertension

• Impossible to apply EIT electrodes on the thorax of the patient (burns, dressings, …)

• Undrained pneumothorax or bronchopleural fistula

• Scanner unavailable for the study (broken down, overloaded program, …)

• Contraindication esophageal balloon catheter

  • Known or suspected esophageal disease (tumor, esophageal varices, esophagitis, diverticulum, ...)
  • Latex allergy

• Patient previously included in the study

• Vulnerable persons (as defined in laws L1121-5 to L1121-7, L1121-8 and L1122-1-2