High-flow nasal cannula (HFNC) is a rather novel system to provide oxygen therapy, which provides flows up to 60 liters/minute (LPM) of heated and humidified gas through nasal prongs. HFNC is increasingly being used in patients with acute respiratory failure. In healthy volunteers and in patients with acute respiratory failure it has been shown to induce several effects beyond those expected for a standard oxygen therapy, such as increased carbon dioxide (CO2) clearance and positive airway pressure.

One of the potential indications for HFNC is to facilitate weaning from mechanical ventilation and extubation. As weaning failure is one of the most complex challenges in mechanically ventilated patients, the use of HFNC after extubation, in order to prevent reintubation, has been evaluated in some clinical trials, with promising results. However, the role of HFNC postextubation is still controversial, and information regarding its effects on the pathophysiologic mechanisms of weaning failure is lacking.

The goal of this proposal is to compare the acute physiologic effects of postextubation HFNC versus standard oxygen therapy, in critically ill patients, on relevant mechanisms related to weaning failure: work of breathing, lung function, systemic hemodynamics.

This will be a randomized crossover study which 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 HFNC and one hour of standard oxygen therapy, 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:

• Mechanical ventilation (MV) through an orotracheal tube for at least 48 hours
• PaO2 /FiO2 ratio ≤ 300 mmHg
• Potential for weaning as determined in routine daily screening (precipitating cause leading to MV in resolution, adequate oxygenation (PaO2/FiO2 ≥150 mmHg with FiO2 ≤0.4 and PEEP ≤8 cm H2O), arterial pH >7.25, hemodynamic stability (no vasopressors or Noradrenaline ≤0.1 mcg/kg/min), temperature <38°C, presence of inspiratory effort and appropriate spontaneous cough, and the patient is not receiving sedatives and is awake and able to follow simple commands)
• Decision to perform a spontaneous breathing trial by the attending physician

Exclusion Criteria:

• Patients ventilated for decompensated chronic obstructive pulmonary disease
• Contraindications to HFNC, which include abnormalities or surgery of the face, nose, or airway that preclude an appropriate-fitting nasal cannula.
• Contraindications for esophageal balloon catheter insertion (eg. severe coagulopathy, esophageal varices, and history of esophageal or gastric surgery)
• Contraindication for use of electric impedance tomography (eg. Pacemaker)
• Presence of tracheostomy
• Refusal to participate by the attending physician
• Do not resuscitate order

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