Constant positive airway pressure. A review

Constant positive airway pressure (CPAP) represents a major advance in the treatment of hypoxaemia. By increasing the functional residual capacity (FRC), airway closure and airway resistance are minimized. Ventilation and perfusion are more evenly matched so that gas exchange is made more efficient. In addition, the lung remains on a favourable portion of the compliance curve so that the work of breathing is reduced. The increased oxygenation is achieved at the lowest possible inspired oxygen concentration (FiO2) to minimize oxygen toxocity. A unified approach to the terms used, as well as their abbreviations, is presented.