Pao2 and intratracheal pressure in oscillatory ventilation in experimental respiratory failure.

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Abstract
To study the effect of high-frequency ventilation on pulmonary gas exchange in respiratory failure, PaO2 [arterial partial pressure] and other pulmonary gas exchange parameters were measured for ventilatory rates of 0.5, 1.2, 4.8 and 16 Hz in dogs, in which acute respiratory failure was created by i.v. infusion of oleic acid. Either the mean intratracheal pressure [mPit] or the end-tidal intratracheal pressure was controlled. A loud-speaker ventilator was modified so as to enable variation of the intratracheal pressure. Ventilation was measured using an ultrasonic instrument which counts the number of turbulent eddies. The tidal volume was set slightly higher than that determined for healthy animals, but the resulting PaCO2 values were consistently higher than normal when PaO2 values were low. With [mPit] kept constant at 5, 10 and 15 cm H2O, PaO2 values with an FIO2 [inspiratory O2 fraction] of 1 were between 41 and 46 at mPit of 5, 65 and 82 at 10 cm H2O, 278 and 423 at 15 cm H2O. No increase in PaO2 was observed with the increase in respiratory frequencies. If anything, a slight reduction in PaO2 at 8 and 16 Hz was observed, though not statistically significant. With the end-tidal intratracheal pressure constant, PaO2 varied but again correlated well with mPit.

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