Auto-positive end-expiratory pressure and dynamic hyperinflation

Deviation of end-expiratory lung volume from the elastic equilibrium volume of the respiratory system is recognized as a cardinal feature in mechanically ventilated patients with severe chronic obstructive pulmonary disease (COPD) and acute asthma. The presence of dynamic hyperinflation implies that alveolar pressure remains positive throughout expiration. At the end of the expiration, this positive difference between alveolar and external airway pressures is termed auto-positive end-expiratory pressure (PEEP) or intrinsic-PEEP. The aims of this article are (1) to review the physiologic mechanisms of auto-PEEP and the use of PEEP in counterbalancing auto-PEEP and (2) to examine the clinical criteria for application of PEEP in patients with COPD.