Ex vivo evaluation of human lungs for transplant suitability

Background. If lungs could be retrieved from non-heart-beating donors, the critical shortage of lungs for transplant could be alleviated. An obstacle to this approach is the inability to predict these lungs' suitability for transplant. We used human lungs deemed unsuitable for transplant to develop a method to perfuse and ventilate human lungs ex vivo to assess gas exchange and vascular resistance, and to perform bronchoscopic inspection and radiographic evaluation. Methods. Lungs were retrieved from six brain-dead organ donors after cold Perfadex (Vitrolife, Kungsbacka, Sweden) flush, stored cold for 6 to 13 hours (mean, 8.7 hours) then perfused and rewarmed in a modified cardiopulmonary bypass circuit. Circuit perfusate was buffered colloid-crystalloid containing type-specific leukocyte-filtered blood (hematocrit of 10%-12%), circulated through a membrane oxygenator ventilated with CO2 and nitrogen to deoxygenate it. Lungs were ventilated with fraction of inspired oxygen (FIO2) 0.5 when 32 degrees C was reached. Gas exchange and vascular resistance was assessed at 5 L/minute flow at 37 degrees C, FIO2 0.5 and 1.0. Bronchoscopy, plain radiographs, and spiral computed tomographic (CT) scans were performed. Lung biopsies were obtained pre- and post-reperfusion. Results. Ex vivo perfusion did not cause increased wet to dry ratio, or major abnormalities by microscopy but was associated with elevated tissue levels of conjugated dienes. The alveolar-arterial difference in partial pressure of oxygen (PaO2)/FIO2 ratio in the ex vivo circuit was generally higher than in the six donors. Ex vivo radiographs and CT scans were abnormal in all lungs, confirming unsuitability of these lungs for transplant. Conclusions. Ex vivo evaluation of human lungs is feasible and may be useful to evaluate transplant suitability of lungs retrieved after circulatory arrest from non-heart-beating donors.