[Effects of continuous positive pressure ventilation and superimposed high frequency oscillation on pulmonary edema following endotracheal injection of hydrochloric acid in dogs].

Pulmonary gas exchange was investigated in dogs with pulmonary edema following endotracheal injection of hydrochloric acid during superimposed high frequency oscillation (HFO) and continuous positive pressure ventilation (CPPV) using six inert gas elimination method. When ventilatory condition was changed from IPPV to HFO during pulmonary edema, PaO2 decreased from 61 +/- 4 mmHg to 49 +/- 9 mmHg and Qs/Qt increased from 73 +/- 8% to 77 +/- 9%. However, no change appeared in the perfusion distribution. When ventilatory condition was changed from IPPV to CPPV during pulmonary edema, PaO2 increased from 61 +/- 9 mmHg to 113 +/- 45 mmHg. Qs/Qt showed a tendency to decrease from 62 +/- 7% to 51 +/- 9%, and perfusion shifted toward the low VA/Q region. During HFO, a PEEP-like effect was not generated and mean airway pressure did not increase. Therefore, Qs/Qt was not decreased and PaO2 was not improved. During CPPV, an increase in PaO2 was the result of a decrease in true shunt rather than an improvement in the ventilation-perfusion maldistribution.