Humidified high flow nasal cannula (HFNC) oxygen therapy utilizes an air oxygen blend allowing from 21% to 100% FiO2 delivery and generates up to 60 L/min flow rates. The gas is heated (35 to 40 degree Celsius) and humidified through an active heated humidifier and delivered via a single limb heated inspiratory circuit (to avoid heat loss and condensation) to the subject through a large diameter nasal cannula. Theoretically, HFNC offers significant advantages in oxygenation and ventilation over conventional methods (9). Constant high flow oxygen delivery provides steady inspired oxygen fraction (FiO2) and decreases oxygen dilution. It also washes out physiologic dead space and generates positive end expiration pressure (PEEP) that augments ventilation. In the current narrative review, Sotello et al. summarized factors explained the improvement in respiratory parameters by using HFNC. (1) Washout of the nasopharyngeal dead space; (2) Reduction in inspiratory resistance associated with gas flow through the nasopharynx; (3) Improvement in respiratory mechanical parameters associated with gas temperature and state of humidification; (4) Reduction in metabolic work associated with gas conditioning; (5) Provision of mild distending pressure.