Effect of perfusion pH on rat lung viability of non-heart beating donors

Non-heart beating donors could be an important source of lungs for transplantation. In prior experiments, trypan blue exclusion was used to assess the percentage of viable lung cells after different intervals following circulatory arrest. In this study, we assessed the importance of the trypan blue perfusate pH because in liver preservation studies, pH of the perfusate appears to be very important with the presence of a 'pH paradox'.

Forty Sprague-Dawley rats (n = 5 each group) were sacrificed, left at room temperature, and ventilated with 100% O2 (tidal volume 0.01 cc/g, rate 30/min) for 4 or 8 h after death. Lungs were then flushed with 150 cc of trypan blue in Krebs-Heinseleit buffer via the pulmonary artery, then with 150 cc of fixative (2%) paraformaldehyde + 2% gluteraldehyde). The pH of the trypan blue solution was varied from 6.5 to 7.8. Lungs were sectioned, and cell viability was quantified based on exclusion of trypan blue.

Longer cadaver time was associated with less viability, but pH had no effect on viability. The results were similar in groups ventilated for the same period of time and then flushed with solutions at different pH (4 h, viability 80-84%; 8 h, viability 68-72%). Over the range investigated, the pH of the trypan blue solution had no impact on lung viability in non-heart beating donors and the lungs did not show the 'pH paradox'.

Lung tissue is not susceptible to the 'pH paradox' observed in liver preservation studies. Because more than 80% of lung cells are still viable 4 h after death if the lungs are ventilated with 100% O2 during the cadaveric period, retrieval and transplantation of cadaveric lungs may be feasible and might alleviate the paucity of lung donors.