It has been showed that over assist and patient ventilator asynchrony often occur in mechanical ventilated patients, especially in patients who failed weaning, which are associated with a prolonged duration of mechanical ventilation.Neurally adjusted ventilatory assist (NAVA) improves patient-ventilator synchrony, prevents excessive assist induced diaphragm inactivation. So the aim of this study was to detect that whether NAVA compared with PSV has the ability to reduce the duration of weaning in difficult to wean patients.

Intubated patients who were deemed ready for weaning by the clinical team but failed the first spontaneous breathing trials (SBT) or weaning were screened for eligibility. After enrollment, nasogastric tube eligible patient was replaced with a modified EAdi catheter. Then the patients were switched to a Servo-i ventilator. According to a random digits table, eligible patients were allocated randomly to ventilation with NAVA or pressure support ventilation (PSV). In PSV group, ventilator settings were determined by the physicians who in charge of the patients, and EAdi signals were not available for ventilator settings. In NAVA group, a daily NAVA level titration was performed to select the NAVA level which got approximate 50% unload, if the patients can't tolerate PSV or NAVA, PCV should be used to insure the ventilation safety. If the patients were under PCV mode, screening should be done by the researchers every 3 hours to make sure whether they will tolerate PSV or NAVA. In both group, daily measurement of diaphragmatic function was performed (only preformed in the first 10 patients of each group), followed by a 30 minutes SBT with PSV 5-7 cmH2O. Patients who were able to tolerate the SBT were extubated. Patients who completed the SBT and remained extubated > 48 h were considered successfully extubated. Patients who failed SBT, or required noninvasive ventilation (NIV), or were re-intubated, or deceased within 48h post-extubation were considered extubation failure. Local sedation protocol including daily wakeup was performed during the research period. All continuous sedative infusions were discontinued at least 1 hour before the measurement of diaphragmatic function and SBT. Main end point was the duration of weaning, and second end point was extubation rate, diaphragmatic function and patient ventilator asynchrony.

Inclusion Criteria:

Intubated patients who were deemed ready for weaning by the clinical team but failed the first spontaneous breathing trials (SBT) or weaning

Exclusion Criteria:

1. age <18 or >80 years,
2. tracheostomy
3. treatment abandonment
4. history of esophageal varices
5. gastro-esophageal surgery in the previous 12 months or gastro-esophageal bleeding in the previous 30 days
6. coagulation disorders (INR ratio>1.5 and APTT>44 s)
7. history of acute central or peripheral nervous system disorder or severe neuromuscular disease
8. history of leukemia, severe chronic liver or chronic cardiac disease
9. solid organ transplantation
10. malignant tumor.