What is auto-PEEP and what causes it?

• A. Intrinsic PEEP from incomplete expiratory emptying; caused by short expiratory time, high rate, airway obstruction.
• B. PEEP set by clinician to raise mean airway pressure.
• C. A measure of alveolar dead space.
• D. Positive end-expiratory pressure due to cuff leakage.

Answer: (A)

Auto-PEEP is the intrinsic PEEP that builds up in the lungs when expiration is not completed before the next inspiration begins. Because air remains trapped at the end of expiration, the airway pressure stays positive even before the next breath starts. The main idea is that incomplete expiratory emptying leads to dynamic hyperinflation and airway pressure from within the patient’s own ventilatory cycle, not from something the clinician sets.

This happens when the expiratory time is too short for the amount of air being exhaled, which can occur with a high respiratory rate or a short expiratory phase (I:E ratio too short) and when there is airway obstruction or resistance that slows exhalation. In diseases like COPD or bronchospasm, reduced expiratory flow makes auto-PEEP more likely. Auto-PEEP can increase the work of breathing, hamper ventilation, and may require adjustments to the ventilator settings or treatment of the underlying obstruction.

It’s not extrinsic PEEP set by the clinician to raise mean airway pressure, it’s not a measure of alveolar dead space, and it’s not due to cuff leakage.