What is the role of PEEP in mechanical ventilation for patients?

The role of positive end-expiratory pressure (PEEP) in mechanical ventilation is primarily to increase functional residual capacity (FRC). By maintaining some pressure in the airways at the end of expiration, PEEP helps to prevent the complete collapse of alveoli, promoting better oxygenation and ventilation efficiency. Increasing the FRC allows for more gas exchange surface area in the lungs, enhancing the ability to oxygenate the blood and remove carbon dioxide effectively.

In clinical practice, increasing FRC with PEEP can improve the recruitment of collapsed or poorly ventilated lung units, leading to improved overall lung compliance and a reduction in shunting, where blood is not adequately oxygenated. This can be particularly beneficial in patients with conditions like acute respiratory distress syndrome (ARDS) or other forms of lung injury.

The other options do not capture the primary function of PEEP effectively. While PEEP may have effects on cardiac output and oxygen demand under certain circumstances, its key purpose is to improve lung mechanics and gas exchange by increasing functional residual capacity.