Esophageal pressure measurement, obtained with the use of an esophageal balloon catheter, is fundamental to assess mechanical characteristics of the respiratory system during mechanical ventilation. The correct positioning of the catheter (usually at the medium third of the esophagus) is crucial for an accurate measurement of esophageal pressure. Usually the correct positioning of the catheter is verified with an occlusion test (If the patient is breathing spontaneously) or with thoraco-abdominal compressions (if the patient is sedated and paralyzed). Aim of this study is to compare the accuracy of these two methods at different PEEP and esophageal catheter positions.

Inclusion Criteria:

• Mechanical ventilation for clinical purposes

Exclusion Criteria:

• Hemodynamic instability
• Esophageal diseases
• Refusal of the patient

Patients admitted to ICU after surgery treated with mechanical ventilation