What effect does applying PEEP have on the functional residual capacity (FRC) of the lungs?

Applying Positive End-Expiratory Pressure (PEEP) increases the functional residual capacity (FRC) of the lungs. FRC is defined as the volume of air remaining in the lungs after a normal expiration. When PEEP is utilized, it prevents the collapse of the alveoli at the end of expiration, effectively recruiting collapsed lung units and increasing the overall volume of air available. This recruitment of alveoli and the increased volume result in an elevated FRC.

The application of PEEP is particularly beneficial in patients with conditions such as acute respiratory distress syndrome (ARDS) or other forms of hypoxemia, as it promotes better oxygenation by improving lung compliance and increasing the surface area for gas exchange. This enhancement of FRC contributes to improved ventilation-perfusion matching and is an essential part of mechanical ventilation strategies.