Histological Analysis of Donor Lung Derived Thrombi

Abstract

<h3>Purpose</h3> Donor lungs often contain clots. Retrograde flush removes a portion of these clots and improves graft quality. It's very likely that some clots remain after retrograde flush and case studies of thrombolytic treatment of donor lungs has shown a beneficial effect. We studied donor lung clots to determine their composition and age. <h3>Methods</h3> At procurement of donor lungs, in situ antegrade flush was followed by a back table retrograde flush. Retrograde flush fluid was collected and filtered using a 0,2mm filter. The material left in the filter was instantly fixed in 4% formalin for at least 24 hours and studied by a haematoxylin-Eosin(HE) stain and with Martius scarlet blue(MSB) stain. The presence and maturity of fibrin and the presence of lines of Zahn were analyzed. Zahn lines are altering bands of light and dark colors indicating the clot was formed in an area of high blood flow. Clots where then classified based on the composition of fibrin. Clot classification was based on the oldest (most dense fibrin) part of the clot. <h3>Results</h3> In the retrograde flush of all included lungs (n=15) clots were found. A total of 129 clots were found in 15 donor lungs. 12 clots were found at a 2^nd retrograde flush at EVLP. Up to 20 clots were seen in a lung varying in size from 0.3 to 70 mm. Composition varied from young, red blood cell-containing clots to more mature dense fibrin meshes (fig 1).A vast majority of clots showed either an outer layer, lines of Zahn or absence of RBC's that we consider characteristics suggestive of formation before death. <h3>Conclusion</h3> All donor lungs contain clots, emphasizing the importance of retrograde flush at retrieval. Of the clots, 39/129 were more mature and had absence of red blood cells and a more mature dense fibrin mesh. These characteristics may render these clots less susceptible to thrombolysis. However, 90/129 clots were more recently formed and might therefore be more accessible to thrombolysis. Further studies are needed to evaluate the effect of thrombolysis on donor lung clots and primary graft function.