Continuous positive airway pressure (CPAP) is the use of continuous positive pressure to maintain a continuous level of positive airway pressure. It is functionally similar to positive end-expiratory pressure, except that PEEP is an applied pressure against exhalation and CPAP is a pressure applied by a constant flow. The ventilator does not cycle during CPAP, no additional pressure above the level of CPAP is provided, and patients must initiate all of their breaths.