EXTERNAL COOLING OF WARM ISCHEMIC RABBIT LUNGS AFTER DEATH

Background. If lungs could be retrieved for transplantation after circ ulatory arrest, the shortage of donors might be significantly alleviat ed. However, in such non-heart-beating donors, there is great concern that even a short period of warm ischemia will be deleterious for lung tissue, jeopardizing the transplant recipient. It was the purpose of this study to look for the efficacy of different methods of lung cooli ng inside a cadaver after circulatory arrest. Methods. New Zealand whi te rabbits were sacrificed with an intravenous overdose of pentobarbit al and left at room temperature. Subcutaneous, rectal, lung core, lung surface, and endobronchial temperatures were measured at intervals af ter death. Cooling of the lung during ischemia differed between groups (n = 6 in each group): lungs left deflated at room temperature (24 de grees C) (group 1 = control non-heart-beating donors), lungs ventilate d with cooled (4 degrees C) room air (group 2), lungs left deflated pl us topical cooling (1 degrees C) of both the cadaver and its lungs (gr oup 3), and lungs flushed in situ immediately after circulatory arrest with a cold (4 degrees C) crystalloid solution followed by ex vivo de flated storage in cold (1 degrees C) saline solution (group 4 = contro l heart-beating donors). Results. There was a slow decline in lung cor e, lung surface, and endobronchial temperatures toward room temperatur e in group 1 (1.5 degrees +/- 0.0 degrees C/h, 1.8 degrees +/- 0.2 deg rees C/h, and 1.9 degrees 10.1 degrees C/h, respectively). In contrast , all three lung temperatures immediately (<5 minutes) dropped to less than 10 degrees C in group 4. Hypothermic ventilation (group 2) decre ased endobronchial temperature (p < 0.05 at 30 minutes) but not lung s urface, rectal, or subcutaneous temperature when compared with group 1 . Cooling rate for lung surface and endobronchial temperatures during the first 4 hours after death was faster (p < 0.01) in group 3 (6.6 de grees +/- 0.3 degrees C/h and 6.1 degrees +/- 0.2 degrees C/h, respect ively) when compared with group 2 (2.5 degrees +/- 0.3 degrees C/h and 3.9 degrees +/- 0.1 degrees C/h, respectively), but slower (p < 0.001 ) when compared with group 4 (9.2 degrees +/- 0.1 degrees C/h and 8.7 degrees +/- 0.1 degrees C/h, respectively). Conclusions. These data de monstrate that in the non-heart-beating donor, (1) in situ cold flush will result in immediate cooling of the lung, (2) Ventilation with coo led air will only accelerate the decline in endobronchial temperature but has no effect on lung surface temperature, and (3) topical cooling of the cadaver is more efficacious in decreasing lung temperature tha n hypothermic ventilation.