Acute respiratory distress syndrome (ARDS) is a severe form of acute respiratory failure. The therapeutic management is currently based on the treatment of the cause of ARDS, and on mechanical ventilation with positive expiratory pressure (PEEP). Another strategy that could be used is Time Controlled Adaptive Ventilation (TCAV) method based on ventilation using the airway pressure release ventilation (APRV) mode.

Electrical impedance tomography (EIT) allows individual, non-invasive, real-time, bedside, radiation-free imaging of an anteroposterior section of the right and left lungs, with global and regional dynamic analyses.

The aim of the study is to evaluate EIT for PHigh titration of TCAV.

Acute respiratory distress syndrome (ARDS) is a severe form of acute respiratory failure with a mortality rate of up to 35% for the most severe forms. The therapeutic management is currently based on the treatment of the cause of ARDS, and on mechanical ventilation with positive expiratory pressure (PEEP). Another strategy that could be used is Time Controlled Adaptive Ventilation (TCAV) method based on ventilation using the airway pressure release ventilation (APRV) mode.

The TCAV method is based on a prolonged THigh set at a constant pressure, creating a continuous positive pressure phase associated with a brief release during a TLow allowing the elimination of carbon dioxide and the creation of an intrinsic PEEP. With long high pressure phase this method could result in better recruitment but could also expose the patient to overdistention. While the TLow setting is well defined, level of PHigh is not standardized.

Electrical impedance tomography (EIT) allows individual, non-invasive, real-time, bedside, radiation-free imaging of an anteroposterior section of the right and left lungs, with global and regional dynamic analyses. Results of recent studies have highlighted the benefits of EIT, especially for ARDS patients in titrating PEEP in volume-controlled ventilation.

To date, no published study has evaluated EIT for PHigh titration using the TCAV method in patients with severe ARDS.

Inclusion Criteria:

• Moderate to severe ARDS patients with more than 24 hours of mechanical ventilation
• Under sedation with a Richmond Rating Scale less than or equal to -2.

Exclusion Criteria:

• Patients with a pacemaker or automatic implantable defibrillator
• Pregnant women.
• Contraindications to chest belt placement (e.g., spinal or thoracic recent surgery)
• Undrained pneumothorax, broncho-pleural fistula
• Hemodynamic instability (i.e., use of vasopressors at > 2 ug.kg.min of norepinephrine)
• Patients on mechanical ventilation during more than 7 days

Patients with early moderate to severe ARDS under mechanical ventilation