What physiologic effect does raising the PEEP have on a patient receiving NIV?

Raising the Positive End-Expiratory Pressure (PEEP) in a patient receiving Noninvasive Ventilation (NIV) primarily leads to an increase in Functional Residual Capacity (FRC). FRC is the volume of air remaining in the lungs after a normal expiration, and elevating PEEP helps to maintain a greater volume of air in the lungs at the end of expiration. This can enhance gas exchange by recruiting collapsed or under-inflated alveoli, improving ventilation-perfusion matching, and thereby increasing overall oxygenation.

While increased FRC generally aids in reducing the work of breathing and can be beneficial for lung compliance, the direct physiologic effect of raising PEEP is more accurately reflected in its ability to increase FRC. This adjustment provides a larger reservoir of air in the lungs, which can be crucial for patients with conditions that involve atelectasis or decreased lung volumes.

In the context of the other options, while decreasing work of breathing can be a consequence of improved mechanics associated with higher FRC, it is not the primary direct effect of increased PEEP on lung physiology. Similarly, changes to lung compliance may occur but are not guaranteed, as compliance can vary based on the underlying condition of the patient's lungs. Higher