On a ventilator expiratory flow-time trace, how is auto-PEEP detected?

On a ventilator expiratory flow-time trace, how is auto-PEEP detected?

• A. Expiratory flow returns to zero before the next breath
• B. Expiratory flow does not return to zero before the next breath
• C. Inspiratory flow remains above baseline
• D. No change in expiratory flow pattern

Answer: (B)

Auto-PEEP is intrinsic air trapping from incomplete expiration, so the airway still has positive pressure when the next breath is ready to start. On the expiratory flow-time trace, this shows up as the expiratory flow not returning to zero before the next breath begins. In other words, there’s residual flow at the end of expiration, indicating air is still leaving the lungs slowly while the ventilator is preparing for the next inspiration, which elevates end-expiratory pressure. If expiratory flow did return to zero before the next breath, expiration would be complete and there’d be no auto-PEEP. The other patterns don’t reflect this incomplete expiration, hence they’re not correct.

Auto-PEEP is intrinsic air trapping from incomplete expiration, so the airway still has positive pressure when the next breath is ready to start. On the expiratory flow-time trace, this shows up as the expiratory flow not returning to zero before the next breath begins. In other words, there’s residual flow at the end of expiration, indicating air is still leaving the lungs slowly while the ventilator is preparing for the next inspiration, which elevates end-expiratory pressure. If expiratory flow did return to zero before the next breath, expiration would be complete and there’d be no auto-PEEP. The other patterns don’t reflect this incomplete expiration, hence they’re not correct.