High-flow nasal cannula (HFNC) delivers a heated and humidified gas mixture at a flow greater than patient inspiratory flow demand. Several physiological studies have evaluated HFNC in neonates, infants, children, and adults. These found that HFNC improves gas exchange, applies positive pressure, flushes anatomical dead space, and decreases work of breathing. In adults, the FLORALI trial3 was the first to provide evidence of HFNC superiority over noninvasive ventilation (NIV) and standard oxygenation, which places the HFNC as the primary respiratory support for adults with hypoxemic acute respiratory failure.