Pressure support and flow-cycled, assisted mechanical ventilation in acute lung injury.

Pressure support is a ventilatory mode, available with many microprocessor ventilators, which is patient-triggered, pressure-limited, and flow-cycled. This study compared the respiratory and hemodynamic effects of PS used as a stand-alone mode of ventilation with those of conventional patient-triggered, flow-cycled, assisted mechanical ventilation. Instruments for hemodynamic and respiratory measurements were placed in ten spontaneously breathing, anesthetized sheep. In each animal, baseline measurements were made during PS and flow-cycled AMV. Acute lung injury was then instituted by instilling hydrochloric acid in the endotracheal tube, and after 60 minutes, measurements were repeated. No hemodynamic or respiratory variables differed, either before or after ALI, between PS and AMV. This study demonstrates that PS, when used as a stand-alone mode of ventilation, has similar hemodynamic and respiratory effects as flow-cycled AMV.