High-flow oxygen therapy is applied with a special binasal high-flow nasal cannula (HFNC), and a heated inspiratory breathing circuit. It is used for the application of heated and humidified blended air and oxygen at high flow rates, typically set between 30 l/min and 50 l/min. This high flow can provide more constant inspiratory oxygen concentrations than conventional oxygen therapy and can also generate some positive end expiratory pressure. HFNC systems are also used to wash out expired CO2 from the inspiratory dead space in the airways with oxygen enriched gas. High-flow oxygen therapy can effectively be used to treat patients with mild to moderate levels of hypoxemic respiratory failure. As a preventive measure against post-extubation respiratory failure, high-flow cannulas have shown to be effective and consistently be better tolerated then NIV therapy.