An experimental study of different ventilatory modes in piglets in severe respiratory distress induced by surfactant depletion.

In 19 anesthetized piglets 3 ventilatory modes were studied after inducing pulmonary insufficiency by bronchoalveolar lavage by the method of Lachmann. The lavage model was considered suitable for reproduction of severe respiratory distress. This model was reproducible and stable with respect to alveolar collapse, decrease in static chest-lung compliance and increase in extravascular lung water. The ventilatory modes studied were volume-controlled intermittent positive-pressure ventilation (IPPV), pressure-controlled inverse ratio ventilation (IRV), and pressure-controlled high-frequency positive-pressure ventilation (HFPPV). The 3 ventilatory modes were used in random sequence for at least 30 min to produce a ventilatory steady state. Ventilation with no PEEP, permitting alveolar collapse, was interposed between each experimental mode. The ability to open collapsed alveoli, i.e. alveolar recruitment, was different. The recruitment rate for IPPV was 74%, but for IRV and HFPPV it was 95%, respectively. Although IRV provided the best PaO2, this was at the expense of high airway pressures with circulatory interference and reduced oxygen transport. In contrast to this, HFPPV provided lower airway pressures, less circulatory interference and improved oxygen transport. In the clinical setting there might be negative effects on vital organs and functions unless the ventilatory modes are continuously and cautiously adapted to the individual requirements in different phases of severe respiratory distress. Therefore, one ventilatory strategy could be to "open the airways" with IRV, but then switch to HFPPV in an attempt to maintain the airways open with lesser risk of barotrauma and with improved oxygen transport.