high-flow nasal oxygen
Ordinary nasal oxygen trickles in at a few litres a minute, so a gasping patient draws in lots of unenriched room air around it and the actual oxygen they receive is diluted and unpredictable. High-flow nasal oxygen instead pushes warmed, moistened, oxygen-rich gas through wide nasal prongs at a rate that can match or exceed a person's own peak inspiratory flow — up to around sixty litres a minute — so each breath is filled with gas of a reliable, set oxygen concentration.
Beyond simply delivering more oxygen, the high flow does several useful things. It flushes carbon-dioxide-laden gas out of the nose and throat so the next breath starts fresher, it generates a small amount of positive pressure that helps keep air sacs open, and — because the gas is warmed and humidified — it is far more comfortable and less drying than cold high-flow oxygen would be, which lets patients tolerate it for long periods.
High-flow nasal oxygen sits between an ordinary mask and full ventilation, and it is especially useful in type 1 (hypoxemic) respiratory failure, including pneumonia and COVID-19. An honest caveat: it supports oxygenation but does little for severe carbon dioxide retention, and a patient who keeps deteriorating still needs escalation to non-invasive ventilation or intubation; relying on it too long can dangerously delay that step.
A patient with COVID-19 pneumonia whose saturation keeps dropping on a face mask is switched to high-flow nasal oxygen at fifty litres a minute, which raises his oxygen and lets him eat and talk while being supported.
High flow delivers a reliable oxygen concentration while remaining comfortable enough for prolonged use.
Two settings are adjusted independently: the flow rate (which provides the wash-out and pressure effects) and the oxygen fraction (which sets how rich the gas is).