The Critical Role of Retrograde Flush in Lung Procurement and Thromboembolic Mitigation

 

 

The scarcity of viable donor organs remains a restrictive bottleneck in thoracic transplantation. To expand the donor pool, transplant networks increasingly utilize «extended-criteria» or marginal donor lungs. However, brain-dead or circulatory-death donors exist in a hypercoagulable, prothrombotic state due to systemic inflammation, prolonged immobilization, and invasive central venous access. 
Studies indicate that macro- or microscopic pulmonary embolism (PE) is incidentally detected in 35% to 38% of donor lungs. When a donor lung containing unrecognized thromboemboli is implanted, the consequences for the recipient can be catastrophic. The primary defense against this surgical complication is the retrograde flush (backflush) performed during organ procurement and back-table preparation. 
The Pathophysiological Threat of Donor Thromboembolism
Antegrade preservation flush—administered via the main pulmonary artery trunk—is highly effective at cooling the pulmonary parenchyma and clearing mobile blood elements. However, if an organized or semi-adherent thrombus is lodged in the pulmonary arterial tree, antegrade pressure acts like a piston, driving the clot deeper into the narrowing subsegmental branches and capillaries.
Upon implantation and reperfusion in the recipient, these trapped clots lead to severe graft injury:
Mechanical Occlusion: Blocked microvasculature forces the recipient’s entire right ventricular output through a restricted vascular bed, sparking acute pulmonary hypertension and right heart strain.
Ischemia-Reperfusion Injury (IRI): Areas distal to the emboli experience profound ischemia. Reperfusion induces a massive inflammatory cascade characterized by oxygen free-radical generation, endothelial cellular swelling, and capillary leak.
Primary Graft Dysfunction (PGD): Microvascular plugging is a leading trigger for severe PGD (Grade 3), presenting as severe hypoxemia, diffuse alveolar infiltrates, and a high risk of early mortality.
Long-Term Allograft Loss: Trapped thromboemboli accelerate endothelial injury, which is strongly associated with acute cellular rejection and the subsequent development of Chronic Lung Allograft Dysfunction (CLAD). 
Mechanics of the Retrograde Flush
The retrograde flush reverses the hydrodynamic vector of the preservation solution. Instead of entering the arterial system, cold preservation fluid (e.g., extracellular low-potassium dextran solution) is instilled under controlled pressure directly into the pulmonary veins via the left atrial cuff or individual venous orifices.