Intubation is a common procedure in the intensive care unit. Hypoxemia is the most frequent complication of this procedure. Monitoring the end-tidal of oxygen is recommended in operating room (OR). End-tidal of oxygen (EtO2) \>90% is an indication of a correct preoxygenation. This monitoring is not used in routine in intensive care unit (ICU). There is no recommendation on the monitoring of end-tidal of oxygen in intensive care unit. In practice, clinicians use pulsed oxygen saturation (SpO2) to determine whether the patient is sufficiently preoxygenated. However, this parameter is not a good indicator of a correct preoxygenation. In the OR, patients are compliant during the preoxygenation period and the measure of EtO2 with the face mask monitor is considered reliable because i) mask leakage is minimal and ii) the patient can breathe slowly and regularly. Theses conditions are not available in critical ill patients requiring emergency intubation. EtO2 measured on the facemask may not reflect true EtO2. This concern about the reliability of EtO2 measurement via the facemask justifies that we conduct a study to compare EtO2 measured on a facemask (facemask EtO2) to EtO2 measured in pharynx (via e nasopharyngeal catheter). The aim of this study is to determine whether the measurement of EtO2 on facemask is reliable in patients in ICU.