Peak airway pressure: why the fuss?

The preponderance of evidence indicates that high airway pressure is not by itself injurious to the lung. Rather, overdistention of the lung appears to be the fundamental mechanism underlying VALI. The physician must bear in mind the factors (ie, flow-resistive pressure losses, respiratory muscle activity, and abnormalities in rib cage or abdominal compliance) that may alter the relationship between PAP and lung volume. Under some circumstances, high PAP may, in fact, reflect lung overdistention, and maneuvers that minimize overdistention may also reduce PAP. Similarly, the goal of improving oxygenation may sometimes entail strategies (such as prolonging inspiratory time) that lower PAP. In these settings, however, the reduction in PAP should be regarded as a by-product of achieving another therapeutic goal and not an end point in and of itself. In other settings, such as the mechanically ventilated patient with severe airflow obstruction, measures that lower PAP by reducing inspiratory flow rate may worsen pulmonary hyperinflation, and thereby increase the risk of complications.