Pressure support (PS) is a commonly used mode of ventilation which is triggered based upon the patient's own inspiratory efforts. For the most part, pressure support is well tolerated by patients. However, because the trigger for pressure support is an inspiratory effort by the patient, and because the resulting support is constant, the ventilator response can be "out of sync" with the patient's needs. The problem of patient-ventilator asynchrony has been documented to be large in approximately one quarter of patients who require mechanical ventilation. Asynchrony is associated with increased or abnormal work of breathing (WOB) and prolonged duration of mechanical ventilation. Diagnosing asynchrony at the bedside can be challenging. Electrical activation of the diaphragm (Eadi) recording can provide clinicians with a more accurate picture of patient-ventilator synchrony and may thus result in decreased asynchrony and decreased or normalized work of breathing for the patient. The purpose of this physiologic study is to evaluate the role of protocolized pressure support ventilation (based upon Eadi) in comparison to standard pressure support ventilation.

Pressure support will be readjusted according to Eadi recording in different steps.

The optimized pressure support will be compared to the initial pressure support.

Inclusion Criteria:

Patients who are ventilated using a partial ventilator support mode (i.e. pressure support) and meet one of the following criteria:

• Known chronic pulmonary obstructive disease
• Suspected Intrinsic PEEP on the expiratory airway pressure and flow tracings
• Resistive pressure (i.e. eak pressure-Plateau pressure) higher than 20 centimeters of water (cmH2O) at a flow of 60 L/min or higher than 15 at a flow of 45 L/min in volume controlled ventilation (preferably after a tracheal aspiration maneuver)
• Known chronic restrictive pulmonary disease with respiratory failure
• Restrictive pulmonary disease characterized by a measured compliance of less than 30 ml/cmH2O
• Obesity with BMI ≥ 30 kg/m2
• Existence of frequent asynchronies noticed on the ventilator waveforms
• Expected duration of ventilation of more than 24 hours

Exclusion Criteria:

• Contraindication to Naso/orogastric tube (NGT/OGT) placement (known esophageal problem such as hiatal hernia or esophageal varicosities, active upper gastro-intestinal bleeding, any other contraindication to the insertion of a NGT/OGT)
• Poor short term prognosis (defined by the clinician in charge as a high risk of death during the next 7 days) or ongoing palliative treatment.
• Patients with "Do not resuscitate" order already established and in palliative care
• Patients younger than 18 years old