In a patient with poor lung compliance, how might the pop-off valve behave during manual ventilation?

• A. It should be closed completely
• B. It should be set to maximum open
• C. It may vent more easily to limit peak pressures
• D. It should be removed

Answer: (C)

Pressure-relief is the key idea here. When lung compliance is poor, the lungs are stiff, so delivering the same volume requires higher airway pressures. The pop-off valve serves to prevent dangerous peak pressures by venting excess gas to the atmosphere. In this situation, it will tend to vent more readily to limit peak airway pressures and protect the lungs from barotrauma. Closing it completely or removing it would raise the risk of injurious pressure build-up, while simply setting it to a maximum open state doesn’t change the fundamental safety role—it’s the relief it provides that matters.