Effects of extrinsic positive end-expiratory pressure on mechanically ventilated patients with chronic obstructive pulmonary disease and dynamic hyperinflation.

OBJECTIVE

To examine the circulatory and respiratory effects of extrinsic positive end-expiratory pressure (PEEPe) in patients with chronic obstructive pulmonary disease (COPD) and dynamic hyperinflation during controlled mechanical ventilation.

DESIGN

Different levels of PEEPe were applied randomly in mechanically ventilated patients with COPD and dynamic hyperinflation.

SETTING

Respiratory Intensive Care Unit of a University Hospital.

PATIENTS

9 patients with acute respiratory failure and dynamic hyperinflation due to acute exacerbation of COPD.

INTERVENTIONS

PEEPe 35%, 58% and 86% of intrinsic PEEP (PEEPi) were applied.

MEASUREMENTS AND RESULTS

Using flow-directed pulmonary artery catheters hemodynamic measurements were obtained, while simultaneously lung volumes, airflows and airway pressures were recorded. In order to estimate alveolar pressures (Palv), rapid airway occlusions during passive expiration were also performed. At no level of PEEPe were significant changes in cardiac output, gas exchange variables, dead space, airways inflation resistances and respiratory system static end-inspiratory compliance observed. At high level of PEEPe central venous, mean pulmonary arterial and pulmonary capillary wedge pressures were increased significantly. All but one patient were flow-limited during passive expiration. PEEPe 86% of PEEPi caused a significant increase in end-expiratory lung volume and total PEEP. Iso-volume pressure-flow curves showed volume-dependence expiratory flow limitation in 2 patients, while in 8 patients volume-dependence of critical driving pressure (Palv-mouth pressure) that decreased flows was also observed.

CONCLUSIONS

The effects of PEEPe on iso-volume flow and hence on lung mechanics and hemodynamics, depend on many factors, such as airways resistances, lung volumes and airway characteristics, making the patient response to PEEPe unpredictable.