External high frequency oscillation in cats. Experience in the normal lung and after saline lung lavage.

In an effort to develop a method of assisted ventilation that would avoid endotracheal intubation, 11 anesthetized, paralyzed, nonintubated adult mongrel cats with normal lungs were externally oscillated by means of a thoracoabdominal chamber connected to a vacuum source and a high frequency oscillator. Chamber pressure was adjusted to the desired negative pressure using the vacuum source, and the animal was then oscillated above and below this pressure. The lowest PaCO2 and AaPO2 were observed at 3 Hz. Tidal volume (VT) fell (p less than 0.001) with increases in frequency, and lung volume (VL) rose with increased negative chamber pressure (p less than 0.001). In 11 additional tracheostomized cats, a stiff lung was created by repeated saline lung lavage. External high frequency oscillation (EHFO), using pressures comparable to those used for conventional mechanical ventilation (CMV), was associated with a significant increase in PaO2 (p less than 0.001), and a significant fall in AaPO2 (p less than 0.01) compared with that during CMV. Lung volume was significantly higher during EHFO (p less than 0.001) and, as in the normal lung, VT fell with increasing frequencies to 15 Hz (p less than 0.001). There were no significant frequency-dependent variations in gas exchange or VL. An increasingly negative mean chamber pressure was associated with a significant increase in PaO2 (p less than 0.05) and VL(p less than 0.005) and a significant decrease in PaCO2 (p less than 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)