[Operating principles, physiological effects and practical issues of high-flow nasal oxygen therapy].

First-line symptomatic treatment of acute respiratory failure (ARF) usually requires standard oxygen therapy, of which the limits have nonetheless led to the development of heated and humidified high-flow nasal oxygen therapy (HFNO). HFNO enables the delivery, through simple nasal cannula, of up to 100% of well-heated and humidified fraction of inspired oxygen (FiO2), at a maximum flow rate of 50 to 70 L/min of gas according to the devices chosen (specific or ventilator). The technical characteristics and operating principles of HFNO (coverage of the patient's spontaneous inspiratory flow, improved conditioning of the inspired gases, comfortable nasal cannula) yield a number of interdependent physiological effects that improve not only oxygenation conditions but also ventilatory mechanics. While it could be indicated in many clinical situations, including first-line hypoxemic ARF, the simplicity of HFNO implementation and the respiratory comfort it procures should in no way minimize the clinical monitoring of patients for whom endotracheal intubation may be required, and should not be unduly delayed.