CPAP (Continuous Positive Airway Pressure) is used to assist a sick or injured patient by supplying generally enriched air at above atmospheric pressure to the patient.

CPAP maintains constant pressure during both inspiration and expiration of a spontaneously breathing patient. This keeps the smaller airways open and prevents the collapse of alveoli at the end of expiration, thereby minimising the work of breathing. CPAP also produces an increase in pressure inside the chest, including the surface surrounding the heart. This makes it easier for the left ventricle to eject blood and reduces cardiac work through a reduction in left ventricular preload. CPAP may be used in this way to assist patients with "weakened" hearts. Concentrated oxygen supplies also assist patient recovery in a delicate state.