Which disease is most prone to auto-PEEP?

• A. Asthma
• B. Pneumonia
• C. Emphysema
• D. Pulmonary fibrosis

Answer: (C)

Intrinsic PEEP comes from air trapping when expiration isn’t complete before the next breath starts. This happens when the expiratory time constant is long due to high airway resistance and/or reduced elastic recoil. Emphysema fits this best because destruction of elastic tissue in the lungs lowers elastic recoil and creates dynamic airway collapse, making expiration slower and more incomplete. The result is residual air in the lungs at the end of expiration, which raises baseline airway pressure during ventilation.

Pneumonia stiffens the lungs and reduces compliance, which doesn’t typically promote marked air trapping. Pulmonary fibrosis is a restrictive disease with low compliance and small volumes, also not the classic setup for auto-PEEP. Asthma can cause airway obstruction and some air trapping, but the loss of elastic recoil and the chronic hyperinflation seen in emphysema make auto-PEEP more likely in emphysema.