Combined continuous-flow, normal, and high-frequency ventilation

Ten anesthetized, paralyzed dogs were ventilated at 10 breath/min and 100 cycle/min with a valveless ventilator. When fresh respiratory gas was supplied at the carina or insufflated into the bronchi, there was a significant (p less than .05) reduction in PaCO2, which was maximal during high-frequency ventilation (HFV) with twice normal minute volume. There was no statistically significant advantage in using a more complicated system for bronchial insufflation compared with supplying the fresh gas through a single tube near the carina. The improvement in ventilation and oxygenation during HFV with gas at the carina was reduced markedly when normal lungs were injured by oleic acid. Thus, when peak airway pressure was minimized during HFV, there was a further improvement in gas exchange without an appreciable increase in airway pressure when the gas was supplied at the carina.