Parameters Derived from the Pulmonary Pressure–Volume Curve, but Not the Pressure–Time Curve, Indicate Recruitment in Experimental Lung Injury

Abstract

In acute lung injury, ventilation avoiding tidal hyperinflation and tidal recruitment has been proposed to prevent ventilator-associated lung injury. Information about dynamic recruitment may be obtained from the characteristics of pressure-volume (PV) curves or the profile of pressure-time (Paw-t) curves. Six anesthetized pigs with lung lavage-induced acute lung injury were ventilated with lung-protective settings. We measured the effects of a standard recruitment maneuver on hysteresis area and ratio obtained from the PV curve and on the stress index obtained from the Paw-t curve and correlated this with aerated and nonaerated lung volumes as measured by multislice computed tomography. Hysteresis area and ratio correlated with aerated lung volume (r = 0.886). The recruitment maneuver resulted in an increase in aerated (+12%) and a decrease (-18%) in nonaerated lung. Hysteresis area correlated with alveolar recruitment, represented by an increase in aerated lung (r = 0.886) and a decrease in nonaerated lung (r = -0.829) during tidal ventilation. The stress index was always >1 and indicated tidal hyperinflation only. Values did not change after the recruitment maneuver and did not correlate with any other lung volume. Parameters derived from the PV curve may help in characterizing the lung aeration of the lung and in indicating recruitment. In the presence of lung-protective ventilator settings, the stress index derived from the Paw-t curve was not able to indicate recruitment.