Comparison of Proportional Assist Ventilation And Neurally Adjusted Ventilator Assist

Inclusion Criteria: * Intubated patients. * Mechanical ventilation for a respiratory reason. * Expected duration of Mechanical ventilation \> 48 hrs. * Spontaneous breathing. * Sedations stopped for more than 24 hours. Exclusion Criteria: * \- Main contra indications to NAVA: gastro-oesophageal surgery in the previous 12 months, oesophageal obstruction, gastro-esophageal bleeding in the previous 30 days, history of esophageal varices, facial trauma or surgery, neuromuscular diseases, individuals with known or suspected phrenic nerve dysfunction. * Main contra indications to PAV: airway leak, body weight \<25 kg, neuromuscular diseases. * Hemodynamic instability defined as the current administration of vasopressors or inotropic drugs. * Severe hypoxemia defined as PaO2/FiO2 ratio \<200. * Decision to withhold life-sustaining treatment. * Pregnant women. * Minors \< 18 years.