Patients with respiratory failure often need oxygen and/or ventilatory support. Patients who need only oxygen support, usually received low flow oxygen (< 15 Liters / min), as well as in respiratory weaning. Now new devices can be used. They provide high flow oxygen with different benefits. This high flow devices provide exact fraction of inspired oxygen (FiO2), allows a positive end expiratory pressure and supplies a wash out flow. The hypothesis of this study is that the high flow oxygen enable more efficient oxygen administration than conventional oxygen. In addition, it would improve the effectiveness of the ventilation of the patient, through flushing the dead space.

The investigators hypothesized that when using high flow oxygen therapy, respiratory failure is relieved, as well as ventilation failure, so accessories are less stressed muscles, and this can be demonstrated by the electromyography (EMG) of sterno-mastoid..

Inclusion Criteria: patients with respiratory failure.

• Spontaneously breathing patient requiring administration at least 40% oxygen, or,
• Patient under mechanical ventilation, during respiratory weaning.

Exclusion Criteria:

• Facial trauma, active hemoptysis, pneumothorax, thoraco-abdominal surgery or upcoming intubation for spontaneously breathing patients.
• Neuromuscular disease, altered consciousness or agitation for patients under mechanical ventilation.