Ventilation by high-frequency oscillation in rabbits with oleic acid lung disease

Abstract

The feasibility and efficiency of ventilation by high-frequency oscillation (HFO) were examined in animals with diffuse hemorrhagic lung disease. Twenty-four hours after injection with 0.12 ml/kg oleic acid, 11 spontaneously breathing rabbits had a mean (+/- SD) arterial O2 partial pressure (PaO2) of 65 +/- 16 Torr and arterial CO2 partial pressure (PaCO2) of 38 +/- 7 Torr [inspired fractional O2 concentration (FIO2) of 0.21]. Following paralysis animals were ventilated using a high-frequency oscillator for periods of 20 min followed by three successive hyperinflations to prevent atelectasis. Maintaining a constant mean airway pressure (MAP) of 6 cmH2O and fresh gas flow (FGF) of 2 1/min (FIO2 = 0.21), all combinations of frequency (5, 10, 20, and 30 Hz) and stroke volume (Vs) 2.6, 5.0, and 8.9 ml) were tested. At each frequency, an increase in Vs tended to lower mean PaCO2. At each Vs, CO2 elimination appeared maximal at 20 Hz, an effect attributable to decreasing effective Vs with increasing frequency. With constant Vs, MAP, and frequency, increasing FGF from 1 to 2 or 61/min decreased mean PaCO2 (P less than 0.05). With constant Vs, frequency, and FGF, increases in MAP from 2 to 10 cmH2O increased mean PaO2 (P less than 0.05). HFO, coupled with periodic hyperinflation, supports satisfactory gas exchange in rabbits with oleic acid lung injury. The efficiency of gas exchange is improved by independent increases in Vs, FGF, MAP, or frequency.