Inclusion Criteria:  Patients hospitalized in the intensive care unit for COVID Age ≥ 18 years Patients or family/trusted person informed and not objecting to participating in the research  Exclusion Criteria:  Carbon monoxide poisoning Homozygous sickle cell disease Severe anemia (< 7 g/L) with associated hypoxemia Methemoglobinemia Sulfhemoglobinemia Sepsis, vasoconstrictive drugs Patients under guardianship / curators Patient under state medical aid