Continuous positive airway pressure (CPAP) is the use of continuous positive pressure to maintain a continuous level of positive airway pressure in a spontaneously breathing patient. It is functionally similar to positive end-expiratory pressure (PEEP), 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 above the level of CPAP (Figure 9). The breath types are all spontaneous with a sinusoidal flow waveform.