To elucidate the underlying pathophysiological mechanisms, we conducted two sets of experiments. This effect was attenuated when the lung was ventilated with a gas mixture containing 5% CO 2. In dogs, ligation of the left pulmonary artery and the left main bronchus led to massive hemorrhagic lung injury, shock, and death. Severe, bilateral pulmonary hypoperfusion during veno-arterial bypass has been associated with massive pulmonary infarction and ARDS-like changes in lambs. While reduction of the ventilatable volume and unphysiological stress and strain has been extensively investigated, the effects of occluded lung perfusion have received much less attention. If capillary permeability is altered, increased blood flow may induce or increase edema. The total amount of edema in the two lungs differed because of differences in lung size. The right and left perfusion blocks caused the same “intensity” of edema in conditioned lungs. Pulmonary artery pressure, PaO 2/FiO 2, dead space, and lung mechanics were more markedly affected in animals with left perfusion block, while the gas/tissue ratios were similar in the non-occluded lobes. The lobes with perfusion block were not affected (gas/tissue ratio right 1.6 ± 0.9 left 1.7 ± 0.5, respectively). In conditioned lungs, the left perfusion block caused more edema in the contralateral lung (777 ± 62 g right lung vs 484 ± 204 g left p < 0.05) than the right perfusion block did (581 ± 103 g right lung vs 484 ± 204 g left p n.s.). Perfusion block did not damage healthy lungs.
After an 8-h observation period, CT scans were obtained at 0 and 15 cmH 2O airway pressure. Gas exchange, respiratory mechanics, and hemodynamics were measured hourly.
Nineteen pigs (61.2 ± 2.5 kg) were randomized to five groups: controls ( n = 3), the right lower lobe block alone ( n = 3), lavage and high V T ( n = 4), lung lavage, and high V T plus perfusion block of the right ( n = 5) or left ( n = 4) lower lobe. We studied the effects of regional perfusion block in normal lungs and in the lungs that had been conditioned by lavage with 500 ml saline and high V T (20 ml kg −1) ventilation. Severe hypoperfusion can cause lung damage.
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