Alveolar epithelial fluid transport capacity in reperfusion lung injury after lung transplantation

Reperfusion lung injury Is an important cause of morbidity and mortality af ter orthotopic lung transplantation. The purpose of this study was to inves tigate the function of the alveolar epithelium in the setting of reperfusio n lung injury. Simultaneous samples of pulmonary edema fluid and plasma wer e collected from eight patients with severe post-transplantation reperfusio n edema. The edema fluid to plasma protein ratio was measured, an indicator of alveolar-capillary barrier permeability. The initial edema fluid to pla sma protein ratio was > 0.75 in six of eight patients, confirming the prese nce of increased permeability of the alveolar-capillary barrier. Graft isch emic time was positively correlated with the degree of permeability (r = 0. 77, p < 0.05). In four of six patients with serial samples, there was a hig h rate of alveolar fluid clearance (19 +/- 9%/h, mean +/- SD). Alveolar flu id clearance was calculated from serial samples In six patients. Intact alv eolar fluid clearance correlated with less histologic injury, rapid resolut ion of hypoxemia, and more rapid resolution of radiographic infiltrates. Th e two patients with no net alveolar fluid clearance had persistent hypoxemi a and more severe histologic injury. This study provides the first direct e vidence that increased permeability to protein is the usual cause of reperf usion edema after lung transplantation, with longer ischemic times associat ed with greater permeability to protein in the transplanted lung. The high rates of alveolar fluid clearance indicate that the fluid transport capacit y of the alveolar epithelium may be well preserved in the allograft despite reperfusion lung injury, The ability to reabsorb fluid from the alveolar s pace was a marker of less severe reperfusion injury, whereas the degree of alveolar-capillary barrier permeability to protein was not. Measurement of alveolar fluid clearance may be useful to assess the severity of reperfusio n lung injury and to predict outcome when pulmonary edema develops after lu ng transplantation.