Lowering reperfusion pressure reduces the injury after pulmonary ischemia

Background. Controlled reperfusion with a modified solution limits pulmonar y injury following ischemia. Our initial studies infused this modified repe rfusate at a pressure of 40 to 50 mm Hg to insure distribution. However, pe rhaps a lower pressure, which is closer to the normal physiologic pressure in the lung, would improve results by decreasing sheer stress. Methods. Fifteen adult pigs underwent 2 hours of lung ischemia by clamping the left bronchus and pulmonary artery. Five (group 1) then underwent uncon trolled reperfusion by removing the vascular clamps and allowing unmodified blood to reperfuse the lung at a pulmonary artery pressure of 20 to 30 mm Hg. The other 10 pigs underwent controlled reperfusion by mixing blood from the femoral artery with a crystalloid solution, and infusing this modified reperfusate into the ischemic lung through the pulmonary artery for 10 min utes before removing the arterial clamp. In 5 (group 2), the modified solut ion was infused at a pressure of 40 to 50 mm Hg, and in 5 (group 3) 20 to 3 0 mm Hg. Lung function was assessed 60 minutes after reperfusion and expres sed as percentage of control. Results. Compared to uncontrolled reperfusion (group 1), controlled reperfu sion at a pressure of 40 to 50 mm Hg (group 2) significantly improved postr eperfusion pulmonary compliance (77% versus 86%; p < 0.001 versus group 1), and arterial/alveolar ratio (a/A) ratio (27% versus 52%; p < 0.001 versus group 1); as well as decreased pulmonary vascular resistance (PVR) (198% ve rsus 154%; p < 0.001 versus group 1), lung water (84.3% versus 83.5%; p < 0 .001 versus group 1), and myeloperoxidase (0.35 versus 0.23 optical density /min/mg protein). Reducing the pressure of the modified reperfusate to 20 t o 30 mm Hg further improved postreperfusion compliance (92% +/- 1%; p < 0.0 01 versus groups 1 and 2) and a/A ratio (76% +/- 1%; p < 0.001 versus group s 1 and 2); and lowered PVR (133% +/- 2%; p < 0.001 versus groups 1 and 2), lung water (82.7% +/- 0.1%; p < 0.001 versus groups 1 and 2), and myeloper oxidase (0.16% +/- 0.01%; p < 0.001 versus groups 1 and 2). Conclusions. After 2 hours of pulmonary ischemia, a severe lung injury occu rs following uncontrolled reperfusion, controlled reperfusion with a modifi ed solution reduces this reperfusion injury, and lowering the pressure of t he modified reperfusate to more physiologic levels (20 to 30 mm I-Ig) furth er reduces the reperfusion injury improving pulmonary function. (C) 2000 by The Society of Thoracic Surgeons.