External cooling of warm ischemic rabbit lungs after death

Abstract

Background: If lungs could be retrieved for transplantation after circulatory arrest, the shortage of donors might be significantly alleviated. 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 cooling inside a cadaver after circulatory arrest.

Methods: New Zealand white rabbits were sacrificed with an intravenous overdose of pentobarbital and left at room temperature. Subcutaneous, rectal, lung core, lung surface, and endobronchial temperatures were measured at intervals after death. Cooling of the lung during ischemia differed between groups (n = 6 in each group): lungs left deflated at room temperature (24 degrees C) (group 1 = control non-heart-beating donors), lungs ventilated with cooled (4 degrees C) room air (group 2), lungs left deflated plus topical cooling (1 degree C) of both the cadaver and its lungs (group 3), and lungs flushed in situ immediately after circulatory arrest with a cold (4 degrees C) crystalloid solution followed by ex vivo deflated storage in cold (1 degree C) saline solution (group 4 = control heart-beating donors).

Results: There was a slow decline in lung core, lung surface, and endobronchial temperatures toward room temperature in group 1 (1.5 degrees +/- 0.0 degree C/h, 1.8 degrees +/- 0.2 degree C/h, and 1.9 degrees +/- 0.1 degree 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) decreased endobronchial temperature (p < 0.05 at 30 minutes) but not lung surface, 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 degrees +/- 0.3 degree C/h and 6.1 degrees +/- 0.2 degree C/h, respectively) when compared with group 2 (2.5 degrees +/- 0.3 degree C/h and 3.9 degrees +/- 0.1 degree C/h, respectively), but slower (p < 0.001) when compared with group 4 (9.2 degrees +/- 0.1 degree C/h and 8.7 degrees +/- 0.1 degree C/h, respectively).

Conclusions: These data demonstrate that in the non-heart-beating donor, (1) in situ cold flush will result in immediate cooling of the lung, (2) ventilation with cooled 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 than hypothermic ventilation.