Patients intubated due to acute respiratory failure have a high risk of infectious complications, airway injuries and multiple organic failure, so performing a successful extubation from mechanical ventilation is key. Between 10 and 20% of patients develop extubation failure, which is related to an increased in-hospital death rate, infections, higher costs and longer hospital stays. High-flow nasal oxygen therapy delivers heated, humidified air at flows up to 60L/min, and an oxygen concentration close to 100%, providing a fresh air reservoir at the naseo-pharyngeal level, evening out the peak inspiratory flow rate of the patient, improving air conductance, promoting secretion management, increasing end-expiratory lung volume, and applying a positive end-expiratory pressure. Such effects result in decreased breathing work, dyspnea relief, improved use tolerance, increased oxygenation, and lower fraction of inspired oxygen in patients with hypoxemic respiratory failure. High-flow oxygen therapy has recently been described to decrease extubation failure in a group of patients classified with low failure risk, in comparison to Venturi mask, and it was not inferior to non-invasive mechanical ventilation in high risk patients. However, it is worth pointing out that a large percentage of the patients included in such studies did not develop acute respiratory failure primarily.

Given the beneficial effects described above, the investigators hypothesize that high-flow nasal oxygen therapy decreases the risk of extubation failure in a group of patients that required invasive mechanical ventilation due to primary acute hypoxemic respiratory failure.

Intubated patients recovering from primary acute hypoxemic respiratory failure who have passed a spontaneous breathing trial will be included in the study. Following extubation, patients will be randomized assigned to one of two study groups. Heart rate, breathing rate, median arterial pressure, FiO2, SpO2, and dyspnea and comfort levels will be measured at defined intervals after extubation (basal, 1 hour, 2 hours, 3 hours, 6 hours, 12 hours, 24 hours, and 48 hours). An arterial blood gas test will be performed 60 minutes and 24 hours after extubation. The number of patients fulfilling certain preset criteria regarding extubation failure will be determined.

Extubation failure shall be defined as the need for using invasive mechanical ventilation again within two days following extubation based on the criteria below:

• Breathing rate over 25 breaths per minute for more than two hours.
• Heart rate above 140 beats per minute or with a sustained increase or decrease greater than 20%.
• Clinical data showing fatigue of the respiratory muscles or an increase in breathing work.
• SaO2 <90%; PaO2 <80 mmHg with a FiO2 > 50%.
• Hypercapnia (PaCO2 >45 mmHg or >20% compared to the value before extubation) with a pH below 7.33.

Patients who do not fulfill the extubation failure criteria after the first 48 hours of admission may receive extra supplementary oxygen through any device (e.g., nasal cannula, face mask, reservoir mask, etc.). Every day, SpO2 will be measured and the moment when the patient reaches SpO2 >94% with no need for oxygen will be determined.

Inclusion Criteria:

Hypoxemic primary acute respiratory failure

Invasive mechanical ventilation for at least 48 hours

Successful Spontaneous Breathing Trial

Exclusion Criteria:

Immediate indication for invasive mechanical ventilation

Immediate indication for non-invasive mechanical ventilation

Self-extubation

One or more failed Spontaneous Breathing Trial

Chronic respiratory failure

Neuromuscular diseases

Tracheostomy.

Nasal cavity pathology

Facial surgery

Failure to authorize the informed consent