VENTILATION TECHNIQUES TO MINIMIZE CIRCULATORY DEPRESSION IN RABBITS WITH SURFACTANT DEFICIENT LUNGS

Changes in aortic blood flow were measured in rabbits with both normal and surfactant depleted lungs in order to elucidate the effect of dif ferent modes of ventilation on the circulation while optimizing arteri al oxygenation (P-aO2). Conventional mechanical ventilation (CMV), rev ersed inspiratory to expiratory ratio of CMV(IRV), high frequency posi tive pressure ventilation (HFV), and high frequency oscillation (HFO) were used. Normocapnia was maintained throughout during different mode s of ventilation. In normal lungs the aortic blood flow during IRV was significantly lower with similar levels of P-aO2 compared with CMV, H FV, and HFO. In lavaged lungs, without positive end-expiratory pressur e (PEEP), the aortic blood flow during CMV was significantly higher th an with other modes of ventilation. When 10 cm H2O of PEEP was applied , the P-aO2 increased maximally to normal values at all modes of venti lation, but the aortic blood flow was significantly reduced (P < 0.05) during CMV and IRV compared to HFV and HFO. The aortic blood flows at 5 cm H2O of PEEP were very similar during CMV, HFV, and HFO but signi ficantly reduced during IRV. This study showed that at an optimal arte rial oxygenation with higher PEEP levels, maintenance of aortic blood flow was maximal during HFV and HFO. (C) 1994 Wiley-Liss, Inc.