Shown on the upper graphic is time versus flow for an individual mechanically ventilated patient. Expiratory flow should normally reach zero before the onset of inspiration. However, when auto-PEEP is present, expiratory flow does not reach zero before inspiration. The arrow indicates that inspiration for each breath begins before expiratory flow has reached zero.
Auto-PEEP: Auto positive end-expiratory pressure; lpm: liters per minute.