non-invasive ventilation
When breathing muscles are tiring, it helps to have something push air in for you on each breath. Non-invasive ventilation does exactly that, but without putting a tube into the windpipe: a tightly fitting mask over the nose or face connects to a machine that delivers pressurised air, giving the patient's own breaths a powered boost. The word non-invasive simply means the airway is left intact.
The machine usually delivers two pressures: a higher pressure during inspiration that helps inflate the lungs and ease the work of breathing, and a lower pressure during expiration that holds the air sacs open between breaths. By augmenting each breath, it increases the volume of air moved, which is why it is so effective at clearing built-up carbon dioxide. Its classic, well-proven roles are acute type 2 respiratory failure from a COPD exacerbation and the breathlessness of cardiogenic pulmonary edema.
Non-invasive ventilation can spare a patient the risks of intubation and sedation, and it can be started, paused, and stopped easily. But it has real limits: the patient must be awake enough to protect their own airway and cooperate with the mask, and it cannot help someone who is unconscious, vomiting, or in cardiac arrest. An honest caveat: it is a time-limited trial, not a guarantee — a patient who does not improve within an hour or two usually needs to move on to intubation rather than persist.
A patient with a COPD flare and a high carbon dioxide is fitted with a non-invasive ventilation mask; over the next hour his pH improves, his drowsiness lifts, and intubation is avoided.
Mask-delivered pressure can support failing breathing muscles without a breathing tube.
Two-pressure non-invasive ventilation is often called BiPAP; the related CPAP delivers a single constant pressure and is the mainstay of sleep apnea and some pulmonary edema.