Positive airway pressure (PAP) is a method of respiratory ventilation used primarily in the treatment of sleep apnea, for which it was first developed.
A Continuous Positive Airway Pressure (CPAP) machine is used mainly by patients for the treatment of sleep apnea at home, by delivering a stream of compressed air via a hose to a nasal pillow, nose mask, or full-face mask, splinting the airway (keeping it open under air pressure).

CPAP ventilation is also commonly used for critically ill patients in hospital with respiratory failure. In these patients, CPAP can prevent the need for endotracheal intubation, or allow earlier extubation. However, CPAP candidates are often reluctant to use this therapy, since the nose mask and hose to the machine look uncomfortable and clumsy, and the airflow required for some patients can be vigorous. Some patients adjust to the treatment within a few weeks, others struggle for longer periods, and some discontinue treatment entirely.

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Adapted from Gibson M. Wiki Doc. Positive airway pressure. Internet. Available at: http://www.wikidoc.org/index.php/CPAP Accessed on June 18, 2018.