The study aims to assess 1) the electrical activity of the diaphragm in mechanically ventilated patients during weaning from mechanical ventilation. 2) Whether the electrical activity of the diaphragm may predict the weaning outcome

Optimization of the time to liberate the patient from mechanical ventilation should be balanced between the risks associated with failed extubation and those related to prolonged mechanical ventilation. Weaning failure is associated with major complications. Even when weaning protocols and clinical predictors have been used to improve the weaning outcome, there is still a significant proportion of patients who fail to breath spontaneously with significant risks of pneumonia, prolonged mechanical ventilation and increased morbidity and mortality rate. Electrical activity of the diaphragm, a mirror of the respiratory drive and now available on an ICU ventilator may help to predict in a more accurate way the weaning outcome. The patients will be ventilated in NAVA with the titration method (1). As soon as patients passed successfully a daily screening EAdi will be measured during a spontaneous breathing trial.

Inclusion Criteria:

• All patients older than 18 years and mechanically ventilated for >= 48 h.
• In the resolving stage of the disease which brought to mechanical ventilation.
• Pao2/Fio2 ratio >150 on positive end-expiratory pressure (PEEP) <=8 cm H2O.
• Sedation discontinued for a minimum of 24 hrs
• Analgesia provided solely with morphine at a dosage of less or equal to 0.01 mg/kg/hr.
• Patient fully alert and cooperative.
• Intact respiratory drive evaluated with Glasgow Coma Scale >=10.

Exclusion Criteria:

• The attending physician refuses to allow enrolment
• The patient refuses informed consent
• Hemodynamic instability despite adequate filling (i.e. need for continuous infusion of epinephrine or vasopressin, or dopamine or dobutamine > 5 mcg/kg/min or norepinephrine > 0.1 mcg/kg/min to maintain systolic arterial blood pressure > 90 mmHg)
• No collaborative Patient
• Coagulation or platelets disorders
• neuromuscular disease
• phrenic nerve damage/diaphragm paralysis
• contraindication to exchange naso-gastric tube
• History of heart or lung transplantation
• Presence or suspicion of a central nervous system disorder