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## Continuous Positive Airway Pressure (CPAP) Continuous positive airway pressure (CPAP) is the application of positive baseline pressure (pressure elevated above ambient pressure) during continuous spontaneous ventilation. The positive baseline pressure increases the patient's functional residual...

## Continuous Positive Airway Pressure (CPAP) Continuous positive airway pressure (CPAP) is the application of positive baseline pressure (pressure elevated above ambient pressure) during continuous spontaneous ventilation. The positive baseline pressure increases the patient's functional residual capacity (FRC), recruiting previously unventilated or underventilated alveoli, which improves oxygenation. Before initiation of CPAP, it is important to determine that the patient is capable of sustaining eucapnic ventilation, as documented by an appropriate partial pressure of carbon dioxide ($P_{a}CO_{2}$) and pH from an arterial blood gas. The patient interface for CPAP may include a mask, an artificial airway (endotracheal or tracheostomy tube), and, in the neonate, nasal prongs. The key to the patient interface is that it must seal to allow the pressure to build above ambient pressure. Leaks can result in pressure loss and a fall in FRC, oxygen saturation ($SpO_{2}$), and partial pressure of oxygen ($P_{a}O_{2}$). ## Bilevel Positive Airway Pressure (BiPAP) Bilevel positive airway pressure (BiPAP) is the application of positive airway pressure during inspiration and exhalation (baseline pressure) during spontaneous ventilation. The inspiratory positive airway pressure (IPAP) and the expiratory positive airway pressure (EPAP) are set independently of one another. The IPAP must always be set higher than the EPAP. The IPAP level improves ventilation ($P_{a}CO_{2}$) and oxygenation in conditions due to hypoventilation. The EPAP level functions much like CPAP, recruiting underventilated alveoli during exhalation, which increases FRC and oxygenation. The difference between the two pressures (IPAP-EPAP) is sometimes termed the drive pressure of pressure support. Increasing the drive pressure improves ventilation ($P_{a}CO_{2}$) and measures how much assistance (pressure) the patient requires to maintain adequate ventilation ($P_{a}CO_{2}$ and pH).