Weaning is one of the most complex challenges in mechanically ventilated patients. Increased work of breathing after extubation would play a central role in weaning failure. Currently, non-invasive ventilation (NIV) is recommended to prevent weaning failure in high-risk patients. On the other hand, high-flow nasal cannula (HFNC), which is a novel system capable of administering gas mixtures (air and oxygen) with a flow of up to 60 liters/min, has been used to prevent weaning failure in this kind of patients. The use of NIV and HFNC after extubation has been evaluated in some clinical studies. However, the evidence is controversial, and the information regarding the physiological effects that each therapy induces in recently extubated patients at high risk of weaning failure is lacking.

The goal of this proposal is to compare the acute physiological effects of postextubation NIV versus HFNC in critically ill patients at high risk of weaning failure on relevant mechanisms related to weaning failure: Work of breathing, lung function, ventilation distribution, systemic hemodynamics.

This will be a randomized crossover study that will include critically ill mechanically ventilated patients, who fulfill criteria indicating they may be ready for weaning from mechanical ventilation, and in whom a spontaneous breathing trial (SBT) is planned to determine if they should be extubated. After checking eligibility and obtaining informed consent, patients will be monitored with an esophageal catheter (esophageal/gastric pressures to determine work of breathing, and electric activity of diaphragm to determine neuromechanical coupling), and a noninvasive ventilation monitor (electric impedance tomography to assess global and regional ventilation). Work of breathing, lung function, and systemic hemodynamics will be assessed during the SBT. Inclusion in the study will be confirmed only if they pass the SBT and are extubated. During the first 2 hours after extubation, patients will undergo one hour of NIV and one hour of HFNC, with the crossover sequence being randomized previously at the time of inclusion and with assessments repeated at the end of each treatment period.

Inclusion Criteria:

1. Mechanical ventilation (MV) through an orotracheal tube for at least 48 hours

2. PaO2 /FiO2 ratio ≤ 300 mmHg (during the MV period)

3. Potential for weaning

   • Precipitating cause leading to MV in resolution
   • PaO2 /FiO2 ratio ≥ 150 mmHg
   • PEEP ≤ 8 cmH2O
   • pH > 7,25
   • SpO2 ≥ 90% with FiO2 ≤ 0.4; BPM ≤35
   • Hemodynamic stability (noradrenaline ≤ 0.1mcg / kg / min and SBP 90-160; HR <140)
   • Temperature <38 ° C
   • Presence of inspiratory effort and appropriate spontaneous cough
   • Decision to perform a spontaneous breathing trial by the attending physician

4. High risk of weaning failure defined by a history of: (i) Previous failed extubation, (ii) Chronic heart or respiratory failure, or (iii) MV ≥ 7 days.

Exclusion Criteria:

1. Contraindications to NIV or HFNC, which include abnormalities, trauma or surgery of the face or nose.
2. Contraindications for esophageal balloon catheter insertion (eg. severe coagulopathy, esophageal varices, and history of esophageal or gastric surgery)
3. Contraindication for use of electric impedance tomography (eg. Pacemaker)
4. Tracheostomy
5. Refusal to participate by the attending physician
6. Do not resuscitate order

Analysis of work of breathing and of data derived from Electric impedance tomography will be performed blind to arm assignment