Lowering reperfusion pressure reduces the injury after pulmonary ischemia

Background. Controlled reperfusion with a modified solution limits pulmonary injury following ischemia. Our initial studies infused this modified reperfusate at a pressure of 40 to 50 mm Hg to insure distribution. However, perhaps 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 uncontrolled 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 minutes before removing the arterial clamp. In 5 (group 2), the modified solution was infused at a pressure of 40 to 50 mm Hg, and in 5 (group 3) 20 to 30 mm Hg. Lung function was assessed 60 minutes after reperfusion and expressed as percentage of control. Results. Compared to uncontrolled reperfusion (group 1), controlled reperfusion at a pressure of 40 to 50 mm Hg (group 2) significantly improved postreperfusion 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% versus 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 to 30 mm Hg further improved postreperfusion compliance (92% +/- 1%; p < 0.001 versus groups 1 and 2) and a/A ratio (76% +/- 1%; p < 0.001 versus groups 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 myeloperoxidase (0.16% +/- 0.01%; p < 0.001 versus groups 1 and 2). Conclusions. After 2 hours of pulmonary ischemia, a severe lung injury occurs following uncontrolled reperfusion, controlled reperfusion with a modified solution reduces this reperfusion injury, and lowering the pressure of the modified reperfusate to more physiologic levels (20 to 30 mm I-Ig) further reduces the reperfusion injury improving pulmonary function. (C) 2000 by The Society of Thoracic Surgeons.