Intravital Microscopy of Pulmonary Microcirculation After Single Lung Transplantation in Pigs F.-U. Sack, R. Dollner, B. Reidenbach, A. Koch, M.M. Gebhard, and S. Hagl ABSTRACT Background. Pulmonary reperfusion injury is a significant risk factor following lung transplantation (LTx). Unfortunately, in vivo observations and quantitative analyses of the pulmonary microcirculation following LTx are technically demanding. Methods. Pigs, weighing 18 to 22 kg, served as the laboratory animals. The left lung was harvested and preserved using donor aortic vessel segments, the pulmonary artery, and the cuff of the lung veins were extended. After 4 hours of ischemia, the lungs were transplanted by direct connection of the conduits to the left atrial appendage and the left pulmonary artery of the recipient. The lungs were placed extrathoracically and ventilated. The recipient left lung was excluded. With this procedure, mechanical trauma to the lung and moving artefacts were avoided. Intravital microscopic observation became feasible. Results. Following reperfusion, oxygenation of pulmonary venous blood was excellent. However, blood flow distribution was significantly reduced to the transplanted lung compared with the native right recipient lung. Pulmonary vascular resistance was significantly increased, dropping from 3500 to 1000 dynes  s  cm -5 during reperfusion compared to a value of 500 for the native right lung. The pulmonary microcirculation showed a significant number of no-reflow areas with extremely reduced red blood cell velocities. Greater than 90% of microvessels (30 m) showed velocities below 0.1 mm/sec. In conclusion, microvascular injury seems to be a major pathogeneic factor for the development reperfusion failure. Quantification of alterations within the microvasculature may shed light on various treatment modalities that reduce perfusion failure. L UNG TRANSPLANTATION is often the only thera- peutic option in end-stage disease. Following lung transplantation, the postischemic development of pulmo- nary reperfusion injury is one of the major causes of early graft failure. 1,2 The primary target for different mechanisms leading to ischemia reperfusion (I/R) failure is the micro- circulation phenomena known as no-reflow and the reflow paradox. 3,4 This effect has been demonstrated in a variety of tissue and organ systems. 5 However, there is still a lack of knowledge about the pathogenic role of pulmonary micro- circulation. A variety of small animal models exists to study lung microcirculation. However, the clinical situation of single lung transplantation is usually not reflected ade- quately. Besides the macrohemodynamics and oxygenation capability of the transplanted lung, observations of the pulmonary microcirculation are technically demanding. The sensitive lung surface as well as motion artifacts owing to the beating heart and ventilation are major causes for the lack of adequate animal models for intravital microscopic studies of the microcirculation of the transplanted lung. Therefore, we developed a large animal model for intravital microscopic observations of the lung surface following single lung transplantation and reperfusion. MATERIAL AND METHODS Sixteen pigs (eight donor and eight recipient animals) weighing 18 to 22 kg received care according to the government law of animal protection. After induction of anesthesia with azaperon (Stresnil, 8 mg/kg IM), ketamine-hydrochloride (Ketanest, 5 mg/kg IV) and dehydrobenzperidol (DHB, 0.25 mg/kg IV), continuous application From the Department of Cardiac Surgery (F.-U.S., R.D., B.R., A.K., S.H.) and the Department of Experimental Surgery (M.M.G.), University of Heidelberg, Heidelberg, Germany. Address reprint requests to Falk-Udo Sack, MD, PhD, Depart- ment of Cardiac Surgery, INF 110, D-69120 Heidelberg, Germany. E-mail: falk-udo.sack@urz.uni-heidelberg.de © 2006 by Elsevier Inc. All rights reserved. 0041-1345/06/$–see front matter 360 Park Avenue South, New York, NY 10010-1710 doi:10.1016/j.transproceed.2006.01.060 Transplantation Proceedings, 38, 737–740 (2006) 737