Gas exchange during high frequency flow-interruption in rabbits before and after bronchoalveolar lavage

The performance of a high frequency flow-interrupter (HFFI) type neonatal ventilator was evaluated on nine adult rabbits (control) and on five adult rabbits after bronchoalveolar lavage (BAL). Tidal volumes and airway pressures were measured during conventional ventilation and during HFFI at rates of 4, 6, 8, 10, and 12 cycles/s. Tidal volumes were adjusted to maintain PaCO2 between 35 and 42 mm Hg in control rabbits and 35-55 mm Hg in BAL rabbits; a positive end-expiratory pressure of 4 cm H2O was applied to BAL rabbits to reduce atelectasis and improve gas exchange. The normalized tidal volume required to maintain PaCO2 within the specified range during HFFI varied between 2.02 ml/kg (0.30 SD) and 2.55 (0.41) in control rabbits and between 2.65 (0.57) and 2.97 (0.51) in BAL rabbits. In neither group did the normalized tidal volume vary systematically with the rate of ventilation (p less than 0.05). Mean airway pressures were lower during HFFI than during conventional ventilation in control rabbits but comparable in the BAL group. Peak inflation pressures were greater during HFFI than conventional ventilation in control rabbits but similar in the BAL group. End-expiratory lung volume was not affected by ventilation rate during HFFI in control rabbits. We conclude 1) that HFFI can maintain gas exchange in rabbits suffering from acute respiratory distress with airway pressures that are comparable to those measured during conventional ventilation and 2) the capacity of HFFI to ventilate the lungs with significantly lower airway pressures than conventional ventilation depends, in part, on the condition of the lungs.