The purpose of this study is to evaluate the difference of the duration of weaning process from the ventilator between protocol-driven weaned patients and clinical judgment driven weaned patients.

All patients with prolonged weaning and who required tracheostomy are enrolled in the study. These patients are randomized as "Case or Control" by a computer program.

Patients can start the weaning process when the acute phase of the respiratory failure has been resolved and pressure support ventilation was setted.

For all this patients are calculated modified-BWAP(BWAP-M) and TOBIN indexes. The "Case" patients started the weaning protocol process only if BWAP-M value is more than 15 or BWAP-M 10-15 with Tobin index < 100.

If not, the BWAP-M and Tobin will be calculated every day. The Control patients will start weaning by clinical judgement even if the BWAP-M value is less than 10.

For all patients are calculated: the duration of weaning process, the ICU length of stay and the duration of the mechanical ventilation.

Inclusion Criteria:

1. all patients that are clinically identified as prolonged to wean (failed 3 spontaneous breathing trials or 7 days or more of mechanical ventilation after the initial unsuccessful trial) and tracheostomized in ICU
2. improvement or resolution of the underlying causes of acute respiratory failure ratio between pressure partial artery of oxygen and fraction inspired oxygen (PaO2/FiO2) >200 with fraction inspired oxygen (FiO2)< 0,45.
3. pressure supported ventilation at the time of enrollment.

Exclusion Criteria:

1. patients assessed as easy weaning and not tracheostomized;
2. patients already tracheostomized on admission to ICU.

difficult to wean patients