Changes in vascular permeability with ischemic time, temperature, and inspired oxygen fraction in isolated rabbit lungs

The capillary filtration coefficient (Kf) is one of the most accurate measures of change in pulmonary vascular permeability and has been used in various models of acute lung injury. To evaluate the isolated effects of ischemia on Kf, we have developed an ex vivo rabbit lung model in which the influences of reperfusion are eliminated. The current study was designed to validate this model by determining the effect of cold flushing with low-potassium-dextran solution containing 1% glucose (LPDG), ischemic time, temperature, and inspired oxygen fraction on Kf. On completion of the ischemic period, the ventilated lungs, with the heart still attached, were suspended from a strain-gauge force transducer. After the lungs were flushed with 50 mL hetastarch solution (6% hetastarch solution with physiologic saline solution), the left atrial drainage cannula was occluded and the pulmonary artery pressure was incrementally increased by elevation of the reservoir. The Kf was calculated as the slope of the line relating the weight gain rate and pulmonary capillary pressure. Our study demonstrated the following: (1) Kf was not altered by flushing the lungs with LPDG at either 1 °C or 10 °C; (2) preservation at 37 °C, even for only 2 hours, demonstrated severe deterioration in Kf; (3) although hypothermia during ischemia suppressed the deterioration of Kf, there were no significant differences in Kf between 1 °C and 10 °C when ischemic time was less than 24 hours; (4) when preservation lasted less than 8 hours, change in Kf was not influenced by the differences in inspired oxygen fraction during the ischemic period; (5) during 24-hour preservation, Kf increased less when the lungs were inflated with room air than when they were inflated with either 100% oxygen or 100% nitrogen. These results indicate that injury occurs primarily during ischemia and increases with ischemic lime even in lungs flushed with LPDG and kept at 1 °C or 10 °C. Inflation with 100% oxygen may cause injury of the pulmonary vascular endothelium during 24-hour preservation, although oxygen supply from airway is essential. This isolated, ex vivo rabbit model examining pulmonary vascular permeability provides a sensitive and reliable means for evaluation of ischemic injury of the preserved lung.