Ischemic preconditioning enhances donor lung preservation in the rabbit

OBJECTIVE

Ischemic preconditioning achieved by brief periods of ischemia followed by reperfusion before a prolonged period of ischemia, is well known to reduce myocardial damage. We investigated whether ischemic preconditioning of the lung could also attenuate ischemia-reperfusion injury following pulmonary preservation.

METHODS

Transient ischemia of the right lung was achieved in rabbits (n = 4 in each group) by occluding the main bronchus and pulmonary artery, followed by reperfusion according to a protocol that differed between study groups: group 1 (control), 45 min ventilation; group 2, 30 min ventilation, 5 min ischemia and 10 min reperfusion; group 3, three periods of 5 min ischemia and 10 min reperfusion; group 4, five periods of 3 min ischemia and 6 min reperfusion. Donor lungs were then flushed with a crystalloid solution followed by inflated storage at 37 degrees C for 2 h. The function of the right lung was assessed during reperfusion for 2 h with homologous, diluted and deoxygenated blood in an isolated, pressure-limited, and room-air ventilated model.

RESULTS

Significant differences (P < 0.0001) were observed between groups 1 and 2 vs. groups 3 and 4 in veno-arterial oxygen pressure gradient (29 +/- 6 and 24 +/- 6 mmHg vs. 124 +/- 24 and 132 +/- 14 mmHg, respectively), and in weight gain (88 +/- 13 and 98 +/- 13% vs. 44 +/- 9 and 29 +/- 3%, respectively) after 1 h of reperfusion, and in wet-to-dry weight ratio (15.5 +/- 1.5 and 14.3 +/- 0.4 vs. 10.1 +/- 1.6 and 9.0 +/- 0.8, respectively) at the end of reperfusion. No significant differences in any of these parameters were observed between group 1 vs. group 2 neither between group 3 vs. group 4.

CONCLUSIONS

These data suggest: (1) That 15 min, but not 5 min of transient ischemia prior to pulmonary preservation can significantly reduce edema in the lung graft upon reperfusion, thus improving oxygenation capacity and (2) although not significant, this beneficial effect seems to be slightly better with more repetitive periods of transient ischemia. Further research is warranted to investigate whether ischemic preconditioning in the human organ donor may become a new strategy to protect lung tissue during a planned ischemic event as in pulmonary transplantation.

Warm ischemic tolerance in collapsed pulmonary grafts is limited to 1 hour

OBJECTIVE

To determine the length of warm ischemic tolerance in pulmonary grafts from non-heart-beating donors.

SUMMARY BACKGROUND DATA

If lungs could be retrieved for transplant after circulatory arrest, the shortage of donors might be significantly alleviated. Great concern, however, exists about the length of tolerable warm ischemia before cold preservation of pulmonary grafts retrieved from such non-heart-beating donors.

METHODS

The authors compared the influence of an increasing postmortem interval on graft function in an isolated, room air-ventilated rabbit lung model during blood reperfusion up to 4 hours. Four groups of cadavers (four animals per group) were studied. In group 1, lungs were immediately reperfused. In the other groups, cadavers with lungs deflated were left at room temperature for 1 hour (group 2), 2 hours (group 3), or 4 hours (group 4).

RESULTS

Pulmonary vascular resistance was enhanced in all ischemic groups compared with the control group. An increase was noted with longer postmortem intervals in peak airway pressure and in weight gain. A concomitant decline was observed in the venoarterial oxygen pressure gradient caused by progressive edema formation, as reflected by the wet-to-dry weight ratio at the end of reperfusion.

CONCLUSIONS

Warm ischemia resulted in increased pulmonary vascular resistance. Graft function in lungs retrieved 1 hour after death was not significantly worse than in nonischemic lungs. Therefore, 60 minutes of warm ischemia with the lung collapsed may be tolerated before cold storage. Further studies are necessary to investigate whether lungs retrieved from non-heart-beating donors will become a realistic alternative for transplant.

Alveolar expansion itself but not continuous oxygen supply enhances postmortem preservation of pulmonary grafts

OBJECTIVE

If lungs could be retrieved for transplant after circulatory arrest, the shortage of donors might be significantly alleviated. Great controversy still exists concerning the optimal mode of preservation of pulmonary grafts in these non-heart-beating donors.

METHODS

Graft function was measured in an isolated room air-ventilated rabbit lung model during reperfusion with homologous, diluted (Hb +/- 8.0 g/dl) and deoxygenated (PaO2 +/- 40 mmHg) blood up to 4 h. Five groups of cadavers (n = 4 in each group) were studied: In the control group, lungs were immediately reperfused. In the other groups, cadavers were left at room temperature for 4 h after death with lungs either deflated (group 1), inflated with room air (group 2), or ventilated with room air (group 3) or 100% nitrogen (group 4).

RESULTS

After 1 h of reperfusion, significant differences were noted between group 1 and groups 2, 3, and 4 in peak airway pressure (27 +/- 5 cm H2O vs. 15 +/- 1 cm H2O, 17 +/- 2 cm H2O, and 16 +/- 1 cm H2O, respectively; P < 0.05), in weight gain (137 +/- 24 vs. 31 +/- 7, 30 +/- 3, and 30 +/- 2%, respectively; P < 0.05), and in veno-arterial oxygen pressure gradient (9 +/- 5 vs. 95 +/- 13, 96 +/- 7 and 96 +/- 4 mmHg, respectively; P < 0.05). Also, wet-to-dry weight ratio at end of reperfusion was significantly different (10.2 +/- 1.0 vs. 6.0 +/- 0.3. 5.2 +/- 0.3 and 5.4 +/- 0.5, respectively; P < 0.05). No significant differences in any of these parameters were observed between groups 2, 3, and 4.

CONCLUSIONS

These data suggest that: (1) pulmonary edema will develop in atelectatic lungs if reperfusion is delayed for 4 h after death; (2) postmortem room air-inflation is as good as ventilation in prolonging warm ischemic tolerance; (3) ventilation with room air is no different from that with nitrogen; (4) therefore, prevention of alveolar collapse appears to be the critical factor in protecting the warm ischemic lung from reperfusion injury independent of continuous oxygen supply.

Pulmonary cell death in warm ischemic rabbit lung is related to the alveolar oxygen reserve

BACKGROUND

If lungs could be retrieved for transplantation from non-heart-beating cadavers, the shortage of donors might be significantly alleviated.

METHODS

We studied the effect of different postmortem lung conditions on pulmonary cell death. Lungs from 208 New Zealand white rabbits were flushed with trypan blue vital dye solution at intervals after circulatory arrest, fixed, and mounted for histologic examination. Pulmonary cells were judged to be viable on the basis of their ability to exclude trypan blue dye. In the control group, lungs were excised immediately after death and immersed in cold (4 degrees C) saline solution. In the other groups, cadavers were left at room temperature with lungs deflated, ventilated with room air or 100% oxygen or 100% nitrogen, or inflated with room air or 100% oxygen.

RESULTS

There was a gradual increase in percentage (mean +/- SEM) of nonviable cells in the control group from 2.5%+/-0.9% (preischemic value) to 18.1%+/-2.8% at 24 hours after death (p < 0.001). In cadavers with lungs deflated, 79.7%+/-2.1% of cells were nonviable at 24 hours after circulatory arrest (p < 0.001 versus control group). In contrast, room air-ventilated cadavers showed only 21.4%+/-2.7% nonviable cells at this interval (p < 0.001 versus deflated group; not significant versus control group). Values in oxygen-ventilated animals were similar. Nitrogen-ventilated cadavers, however, had significantly more nonviable lung cells (73.8%+/-3.2%; p < 0.001 vs room air and oxygen-ventilated group, not significant vs deflated group). Oxygen-inflated lungs showed a parallel decrease in cell viability up to 4 hours after death when compared with room air-inflated cadaveric lungs, but thereafter more cells became nonviable in the latter group (11.1%+/-0.7% vs 19.6%+/-3.2% at 6 hours and 48.7%+/-7.2% vs 75.5%+/-4.6% at 24 hours, respectively; p < 0.01).

CONCLUSIONS

Postmortem room air ventilation is as good as oxygen ventilation in delaying pulmonary cell death, and its effect is comparable to cold storage; nitrogen ventilation, however, is ineffective and not different from deflation; oxygen inflation will preserve ischemic cells for longer intervals as opposed to room air inflation. Therefore the alveolar oxygen reserve seems to be the critical factor to protect-the lung parenchyma from warm ischemic damage.

Extended preservation of ischemic pulmonary graft by postmortem alveolar expansion

BACKGROUND

If lungs could be retrieved for transplantation from non-heart-beating cadavers, the shortage of donors might be significantly alleviated.

METHODS

Peak airway pressure, mean pulmonary artery pressure, pulmonary vascular resistance, and wet to dry weight ratio were measured during delayed hypothermic crystalloid flush in rabbit lungs (n = 6) at successive intervals after death comparing cadavers with lungs left deflated (group 1), inflated with room air (group 2) or 100% oxygen (group 4), or ventilated with room air (group 3), or 100% nitrogen (group 5), or 100% oxygen (group 6).

RESULTS

There was a gradual increase in mean pulmonary artery pressure and pulmonary vascular resistance with longer postmortem intervals in all study groups (p = not significant, group 1 versus group 2 versus group 3). There was also a gradual increase in peak airway pressure and wet-to-dry weight ratio over time in all groups, which reflected edema formation during flush (airway pressure, from 14.5 +/- 1.0 cm H2O to 53.7 +/- 12.2 cm H2O, and wet-to-dry weight ratio, from 3.6 +/- 0.1 to 11.5 +/- 1.2, in group 1 at 0 and 6 hours postmortem, respectively; p < 0.05). Compared with group 1, however, the increase in groups 2 and 3 was much slower (airway pressure, 20.9 +/- 0.5 cm H2O and 18.8 +/- 1.2 cm H2O, and wet-to-dry weight ratio, 5.2 +/- 0.3 and 4.6 +/- 0.4 at 6 hours postmortem, respectively; p < 0.05 versus group 1 and p = not significant, group 2 versus group 3). Airway pressure and wet-to-dry weight ratio did not differ between groups 2 and 4 or between groups 3, 5, and 6.

CONCLUSIONS

These data suggest that (1) pulmonary edema will develop in atelectatic lungs if hypothermic flush is delayed for 2 hours after death, (2) postmortem inflation is as good as ventilation in prolonging warm ischemic tolerance, (3) inflation with oxygen or ventilation with nitrogen or oxygen is no different from that with room air, and (4) therefore, prevention of alveolar collapse appears to be the critical factor in protecting the lung from warm ischemic damage independent of continued oxygen delivery.

External cooling of warm ischemic rabbit lungs after death

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.

Delay of adenosine triphosphate depletion and hypoxanthine formation in rabbit lung after death

BACKGROUND

If lungs could be retrieved for transplantation from non-heart-beating cadavers, the shortage of donors might be significantly alleviated.

METHODS

Adenosine triphosphate (ATP) and hypoxanthine levels were measured postmortem in rabbit lungs comparing deflation (group 1), ventilation with room air (group 2), inflation with room air (group 3), ventilation with oxygen (group 4), ventilation with cooled air (group 5), deflation plus cadaver cooling (group 6), and cooling by pulmonary arterial flush (group 7).

RESULTS

The level of ATP dropped to 25.9% and HYP increased elevenfold at 30 minutes in group 1 but remained constant during 24 hours in group 7. The ATP catabolism beyond 2 hours postmortem appeared less in group 2 compared with group 3 (3.58 +/- 1.24 versus 0.39 +/- 0.08 mumol/g dry weight for ATP and 3.03 +/- 0.49 versus 7.64 +/- 0.94 mumol/g dry weight for hypoxanthine at 24 hours, respectively; p < 0.05). Cadaver cooling significantly slowed ATP catabolism. Changes in ATP level were similar in groups 2, 4, and 5.

CONCLUSIONS

These data suggest that in the non-heart-beating cadaver (1) cooling, ventilation, and inflation can delay ATP catabolism; (2) postmortem ventilation but not inflation for more than 2 hours will inhibit further ATP breakdown; (3) ventilation with either oxygen or cooled air is not more beneficial than room air ventilation; and (4) cold flush more than cadaver cooling will prevent ATP depletion.