High-resolution computed tomography of experimental hydrostatic pulmonary edema.

Abstract

To better understand the distribution and clearance mechanisms of extravascular lung water (EVLW) in pulmonary edema, computed tomographic (CT) scans of isolated canine lungs were obtained. In this model, there is no active lymphatic drainage. Fourteen isolated lobes were inflated with oxygen, and edema was induced by infusion of normal saline solution. Two volumes of saline were used, 50 percent and 150 percent of initial wet lobar weight. Six 10-mm- and 1.5-mm-collimation CT scans were obtained at 10-mm intervals from the hilum to the periphery of the lobe before and after each of the two stages of pulmonary edema. The CT scans were reviewed independently by two chest radiologists and were assessed by CT densitometry. Both subjective analysis and CT densitometry showed a predominantly central peribronchial distribution of EVLW in the isolated lungs. Airway wall thickness also increased from the control value (average thickness, 1.0 mm) to 150 percent edema (average thickness, 1.5 mm) (p less than 0.001). We postulate that the peribronchial distribution of fluid is due to a pressure gradient from the alveolar interstitium to the interstitium around the blood vessels and airways at the hilum. This gradient may play a major role in the characteristic perihilar and peribronchial distribution of EVLW seen radiologically in patients with hydrostatic pulmonary edema.