What is the primary purpose of PEEP in mechanical ventilation?

• A. To keep alveoli open at end-expiration
• B. To increase flow rate
• C. To shorten inspiratory time
• D. To increase airway resistance

Answer: (A)

Keep alveoli open at end-expiration. PEEP applies positive pressure at the end of the breath to prevent alveolar collapsing when air flow pauses between breaths. By keeping these units recruited, functional residual capacity increases, ventilation-perfusion matching improves, and oxygenation is enhanced because more alveoli participate in gas exchange. This works by raising the mean airway pressure, helping maintain open airways throughout the cycle, especially in lungs prone to collapse such as those with atelectasis or ARDS. Be aware that higher PEEP can raise intrathoracic pressure and may reduce venous return, so it’s balanced to optimize oxygenation without compromising circulation. The other options relate to flow, timing, or resistance and do not describe the main purpose of PEEP.