Ischemic pre-conditioning of 5 minutes but not of 10 minutes improves lungfunction after warm ischemia in a canine model

Background: Protection from reperfusion injury by ischemic pre-conditioning (IPC) before prolonged ischemia has been proven for the heart and the live r. We now assess the efficacy of IPC to protect lungs from reperfusion inju ry. Methods: Eighteen foxhounds (25 to 30 kg) were anesthetized, intubated, and ventilated with a fraction of inspired oxygen of 0.3 at a volume-controlle d mode to maintain arterial PCO2 of 30 to 40 mm Hg. After left thoracotomy, we peformed warm ischemia for 3 hours by clamping the left hilus, and foll owed with 8 hours of reperfusion (control, n = 6). In the treated groups, I PC was performed either for 5 minutes followed by 15-minute reperfusion (n = 6, IPC-5), or by 2 successive cycles of 10-minute ischemia, followed by 1 0-minute reperfusion (n = 6, IPC-10) before prior to the 3-hours warm-ische mia period. Pulmonary compliance and gas exchange were determined separatel y for each lung, and we recorded pulmonary and systemic hemodynamics. We pe rformed bronchoalveolar lavage (BAL) at the end of the experiment and deter mined total protein concentration as well as tumor necrosis factor alpha (T NF-alpha) mRNA expression in cell-free supernatant and in BAL cells, respec tively. We also assessed the wet/dry ratio of the lung. Results: In the controls, on reperfusion, we encountered a progressive dete rioration of gas exchange, especially of the reperfused left lung, which we could largely avoid using the IPC-5 protocol. Similarly, pulmonary complia nce steadily declined but was much better in the ICP-5 group. Parallel to t he improvement of gas exchange and lung mechanics, we found less total alve olar protein content and TNF-alpha mRNA expression in BAL cells in the IPC- 5 than in the controls. However, we did not find IPC-10 to be paralleled by a significant improvement of lung function. Neither IPC-5 nor IPC-10 influ enced the pulmonary vascular resistance index or the fluid accumulation in the lung. Conclusion: The major finding of the present study was that 5 minutes of IP C improved lung function after 3 hours of warm ischemia of the lung.