The goal of this pilot interventional no-profit study is to evaluate airway pressure, esophageal pressure and variations in lung volume distribution with EIT in mechanically ventilated patients admitted to our UTI with respiratory failure after the application of an abdominal weight and resulting increase of intra-abdominal pressure.

Inclusion Criteria:

• Invasive mechanical ventilation in acute respiratory failure (PaO2/FiO2 <300 mmHg)
• Need of PEEP trial
• Need of urinary catheter (used to measure IAP)

Exclusion Criteria:

• Contraindication to EIT use
• Pacemaker or other metal device in thoracic region
• Contraindication to abdominal weight placement
• Surgical or traumatic incision on the abdomen
• Severe abdominal hypertension
• Esophageal diseases that counterindicate naso-gastric tube placement
• Severe hemodynamic instability (norepinephrine > 0.1 mcg/kg/min; dobutamine or dopamine > 5 mcg/kg/min; epinephrine every dosage)
• Severe obesity (BMI > 35 kg/m2)
• Need of > 7 kg weight to reach 5 mmHg IAP increase