What is the primary purpose of PEEP in mechanical ventilation?

• A. To prevent alveolar collapse at end expiration and improve oxygenation
• B. To increase mean airway pressure
• C. To enable spontaneous breathing only
• D. To reduce tidal volume

Answer: (A)

PEEP keeps the airway pressure positive at the end of expiration, which prevents tiny airways and alveoli from collapsing. When alveoli stay open after exhalation, more surface area is available for gas exchange, ventilation-perfusion matching improves, and the amount of blood that bypasses ventilated units (shunt) decreases. The result is better oxygenation. While raising end-expiratory pressure also increases mean airway pressure, the primary goal of PEEP is to recruit and stabilize alveoli to improve oxygenation, not simply to force spontaneous breathing or to reduce tidal volume (those are governed by other ventilator settings). If PEEP is set too high, it can limit venous return and cause overdistension, so it’s titrated to balance recruitment with hemodynamics.