In intensive care units (ICUs), approximately 10% to 15%of patients ready to be separated from a ventilator experience extubation failure leading to reintubation. In patients considered at high risk, these rates can even exceed 20%. Because reintubation is associated with particularly high mortality a strategy of oxygenation aimed at avoiding reintubation deserves consideration. Although noninvasive ventilation may prevent postextubation respiratory failure in patients at high risk only 2 small-scale randomized clinical trials (RCTs) have shown decreased reintubation rates compared with standard oxygen. The most recent international clinical practice guidelines recommend the use of noninvasive ventilation to prevent post extubation respiratory failure in patients at high risk of extubation failure (7). However, up until now, no large-scale RCT has demonstrated a significant reduction of reintubation rates with noninvasive ventilation compared with standard oxygen. Thereby, most patients are treated with standard oxygen in clinical practice and only10% of them receive noninvasive ventilation after extubation in the ICU.

High-flow nasal cannula (HFNC) oxygen therapy is a new type of respiratory support system which can supply high flow mixed gases through special nasal prongs at a sufficient temperature and humidity for patient comfort. Many studies have confirmed that the comfort and tolerance of HFNC is significantly higher than that of NIV. As an alternative to NIV, HFNC has been shown to be as efficacious as NIV in preventing post-extubation respiratory failure or re-intubation in patients with hypoxemic respiratory failure.

High-velocity nasal insufflation, a form of high-flow nasal cannula, focuses on optimum efficiency of the dead-space purge to augment ventilation (removal of carbon dioxide from the dead space between breaths), in addition to providing other effects of high-flow nasal cannula. This is accomplished by use of small-bore nasal cannulae (typically 2.7-mm internal diameter for adult patients) to produce high velocity flow that is approximately 360% greater than that of the larger bore cannulae used in previous studies. According to flow analyses8 and clinical experience, high velocity nasal insufflation typically requires a flow of 25 to 35 L/min in adults to accomplish a complete purge of the extrathoracic anatomic reservoir between breaths.

All patients were submitted to, History, Clinical examination, ABG, Laboratory assessment: as needed, ICU scores: APACHE II score.

Weaning from mechanical ventilation procedure:

The procedure of weaning from mechanical ventilation will be considered as early as possible. Patients who received mechanical ventilation >24 h will receive daily screening of subjective and objective indices for assessment of readiness to wean. Weaning will be conducted according to the statement of the ERS, ATS, ESICM, SCCM and SRLF.

Subjects who fulfill criteria for weaning readiness will be extubated and randomized in a ratio of 1:1:1 to either HVNI or HFNC or Noninvasive ventilation.

Weaning procedure will be considered successful when the spontaneous breathing is sustained for 48 consecutive hours without respiratory distress, with pH>7.35 and PaO2>60 mm Hg in a patient breathing through a mask at FiO2≤0.5.

The weaning outcome is considered a failure when death occurred within 48 hours of extubation. Initiation of mechanical ventilation within 48 hours of liberation from MV will be also considered to be a failure.

Inclusion Criteria:

• Adults (≥18 years) intubated for >24 hours due to acute respiratory failure, identified as high-risk for extubation failure AND fulfilling standard readiness-to-wean criteria (e.g., resolution of cause of intubation, adequate gas exchange [P/F ≥150], hemodynamic stability, spontaneous breathing trial [SBT] success)

Exclusion Criteria:

• Patients with central nervous system disorders unrelated to hypercapnic encephalopathy or hypoxemia.
• Patients with post arrest encephalopathy.
• Patient with previous tracheotomy.
• Patients who received noninvasive ventilation without subsequent intubation.
• Patients with end organ failure.