The use of esophageal balloon catheter to estimate pleural pressure has gained renewed popularity in recent years. Indeed, measurement of transpulmonary pressure may allow a more pathophysiological-based approach to ventilator strategy in acute respiratory distress syndrome (ARDS) patients. Nevertheless, it is well known that esophageal balloon catheter derived parameters can be influenced by several patient-related or technical-related factors.

During a PEEP trial, the investigators will observe in-vivo the esophageal pressure and derived measurements obtained using different esophageal balloon calibration volumes.

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

ARDS patients undergoing volume control mechanical ventilation