Positive End-expiratory Pressure and Esophageal Catheter Optimal Calibration Volume in ARDS Patients

Inclusion Criteria: * Diagnosis of ARDS with a PEEP of at least 8 cmH2O * Fraction of inspired oxygen not higher than 80% * Intubated and ventilated in Volume Control Ventilation mode set by the attending physician according to clinical criteria * Need of continuous sedation through intravenous anesthetics and full neuromuscular blockade Exclusion Criteria: * Been pregnant or breastfeeding * Hemodynamic instability * Presence of tracheobronchial fistula * Known pneumothorax * Leak in airway circuitry * Presence of any kind of inhalator therapy (e.g. Heliox, nitric oxide, anesthetic conserving device) * Recent history of nasal trauma or lesion of nasal cavity * Recent history of esophageal, gastrointestinal, ENT, thoracic or cardiac surgery (less than 2 months) * Known or suspected esophageal varices * Congenital, acquired or drug-induced hemostatic disorder * Thrombocytopenia (less than 50000/mm3) * Recent history of Traumatic Brain Injury or thoraco-abdominal trauma (less than 1 months) * Rib or sternal fractures