Regardless of gender, at least 18 years of age and diagnosed with severe Hypoxia (PaO2/FiO2 < 300 mm Hg), dyspnea with severe rest at stake accessory muscles of respiration, respiratory rate (RR) ≥ 25 CPM, PaCO2 ≤ 45 mmHg, patient with an arterial catheter and without hemodynamic instability, Glasgow Coma Scale ≥ 12/15, written consent. Participants were also required to have a sufficient level of education to understand study procedures and be able to communicate with site personnel.