Esophageal balloon calibration (EBC) has been proposed during controlled mechanical ventilation in intubated patients in order to optimize esophageal pressure (Pes) signal. Actually, at our knowledge, no data exist about EBC during assisted ventilatory modes such as Pressure Support Ventilation (PSV). The primary endpoint of the present investigation is to assess the feasibility of EBC during PSV and PSV plus Sigh.

Assisted ventilatory modes, nowadays, have been proved to reduce complications related to controlled mechanical ventilation. With these modes, ventilatory cycling is under the patient's control to an extent depending on the type of ventilatory modality.

Sigh improves oxygenation and lung mechanics during pressure control ventilation and pressure support ventilation (PSV) in patients with acute respiratory distress syndrome.

In order to better quantify the effects of both PSV and PSV plus Sigh on respiratory mechanics, the esophageal pressure monitoring could be helpful. However, esophageal pressure (Pes) assessment requires esophageal ballon calibration (EBC) as demonstrated in intubated patients under controlled mechanical ventilation.

At our knowledge, no data exist about EBC during assisted ventilatory modes. The primary aim of the present study is to evaluate the effects of PSV and PSV plus Sigh ventilation on esophageal balloon best volume in patients admitted to the intensive care unit for acute respiratory failure.

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Inclusion Criteria:

• patients older than 18 years;
• undergoing mechanical ventilation for more than 24 hours (in volume-controlled mode) and with readiness to run assisted ventilation;

Exclusion Criteria:

• severe COPD with air trapping clinical suspicion;
• hemodynamic instability requiring inotropic or vasopressor support;
• any contraindications to esophageal catheter positioning