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CRITICAL CARE AND TRAUMA

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

Dietrich Henzler, MD, PhD^*, Nadine Hochhausen, MD^*, Rolf Dembinski, MD, PhD, Sandra Orfao, MSc, Rolf Rossaint, MD^*, and Ralf Kuhlen, MD

From the Departments of *Anesthesiology and Surgical Intensive Care Unit, University Hospital, RWTH Aachen; Applied Mathematics II, RWTH Aachen, Aachen, Germany; and Surgical Intensive Care Unit, Klinikum Berlin Buch, Berlin, Germany.

Address correspondence to Dietrich Henzler, MD, PhD, Department of Anesthesiology, University Hospital, RWTH Aachen, Pauwelsstr. 30, D-52074 Aachen, Germany. Address e-mail to mail{at}d-henzler.de.

BACKGROUND: 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.

METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.