A quarter of the patients admitted to the Shock Room or Resuscitation Room of an Emergency Department (ED) are admitted for severe hypoxemia resulting from acute respiratory distress. Like all life-threatening conditions, acute respiratory distress (ARD) requires a rapid identification and a prompt implementation of effective resuscitation measures. Oxygen treatment, first described in 1890, remains one of the most important discoveries in medicine. The purpose of oxygenation is to alleviate respiratory failure and to restore a satisfactory hematosis. The choice of the oxygen delivery device is based on the severity of the hypoxemia, the underlying physiological problems, the type of dyspnea and the patient's tolerance to the device. The most commonly used devices are nasal cannula, face mask and high-concentration face mask (conventional oxygen therapy). High Flow Nasal Oxygen (HFNO) is now widely used as a complement to conventional oxygen therapy in the EDs. HFNO ensures good clinical tolerance and better patient comfort (humidification and heating of inhaled gases...) than the other oxygen devices. The HFNO flow rate can go up to 60-70 L/min with an FIO2 (fraction of inspired oxygen inspired oxygen fraction) of 100% compared to a maximum output of 15 L/min with conventional oxygen-therapy. Given the lack of data and clinical trials concerning the systematic use of HFNO in EDs in cases of severe hypoxemia, a prospective study is essential. The purpose of this work is to evaluate the contribution of early administration of HFNO for patients with acute non-hypercapnic respiratory distress presenting in the ED, with the aim of obtaining rapid correction of hematosis. The objective of this work is to compare Conventional Oxygen Therapy (CO) delivered by nasal cannula or nasal-oral mask at flow rates up to a maximum of 15 liters, to HFNO with the hypothesis that HFNO would reduce the need for ventilation therapy escalation. The other hypotheses concern the interest of the HFNO in reducing the use of intensive care hospitalization and thus the costs of treating these patients.