Effects of PEEP on respiratory mechanics in patients with COPD on mechanical ventilation.

We studied the effects of positive end-expiratory pressure (PEEP) applied by the ventilator on respiratory mechanics in ventilated patients with chronic obstructive pulmonary disease (COPD). Airway pressures, relaxed expiratory flow-volume curves and end-expiratory volumes (EEV) were measured. In all patients investigated without PEEP applied by the ventilator, an intrinsic PEEP level (PEEPi) and a concavity in the flow-volume curve was present. Ventilator-PEEP caused a significant decrease in PEEPi in all patients (p less than 0.01). In patients in whom ventilator-PEEP exceeded PEEPi, significant increases occurred in airway pressures and EEV (p less than 0.05) and moreover the shape of the flow-volume curve was changing. In patients in whom the level of ventilator-PEEP was below the PEEPi level, no significant changes in airway pressures, EEV or flow-volume curves were found. We conclude: 1) PEEP applied by the ventilator can reduce PEEPi in ventilated patients with COPD without significant changes in airway pressures, EEV or flow-volume curves. 2) Expiratory flow-volume curves can be used to estimate the effects of ventilator-PEEP on EEV.