Auto-PEEP and dynamic hyperinflation in COPD patients during controlled mechanical ventilation and high frequency jet ventilation.

We investigated the levels of auto-PEEP and dynamic hyperinflation during high frequency jet ventilation (HFJV) and controlled mechanical ventilation (CMV) in six patients with chronic obstructive pulmonary disease within the first 36 h of acute exacerbation. The comparative evaluation was performed at similar conditions of gas exchange in HFJV and CMV: PaO2 77.6 +/- 11 mmHg vs 80.8 +/- 12 mmHg; PaCO2 46.8 +/- 2.5 mmHg vs 47 +/- 2.8 mmHg; pH 7.38 vs 7.38. In this situation, the values of auto-PEEP and dynamic hyperinflation, expressed as delta over the apneic functional residual capacity (FRC) did not differ: (auto-PEEPHFJV 8.9 +/- 3.8 cmH2O; auto-PEEPCMV 8.8 +/- 4.7 cmH2O; delta FRCHFJV 0.56 +/- 0.19 l; delta FRCCMV 0.54 +/- 0.2 l). This result suggests that, with a suitable machine setting and similar gas exchanges, HFJV produces the same level of auto-PEEP and dynamic hyperinflation as CMV in patients with chronic obstructive pulmonary disease.