The pathophysiology of SARS-COV-2 related respiratory disease is still poorly understood, especially in its most severe form called acute respiratory distress syndrome (ARDS). In this case, very few studies have investigated changes in gas exchange during COVID-19 progression in spontaneously breathing patients. The investigators purpose in this study to explore the pathophysiology of gas exchange and time course changes in spontaneously breathing patients with acute respiratory failure due to COVID-19. Moreover, our aim is to identify early markers associated with worsening respiratory failure and requiring endotracheal intubation.

inclusion criteria :

• Patients with a COVID-19 confirmed infection.
• Admission in intensive care unit for an acute respiratory failure requiring oxygen flow above 6l/min by facial mask.
• Presence of an arterial catheter for blood sampling.

exclusion criteria :

• Patients on mechanical ventilation on admission to the ICU.
• Patients requiring immediate intubation on admission.
• Patients admitted to the ICU for more than 48 hours at the time of inclusion.
• Pulmonary embolism diagnosed before admission to the ICU.
• Minor patients
• Pregnant women
• Patients under curatorship or guardianship
• Persons deprived of liberty by a judicial or administrative decision