Cadaver lungs for transplantation. Effect of ventilation with alveolar gas

Current status and further potential of lung donation after circulatory death

Chronic organ shortage remains the most limiting factor in lung transplantation. To overcome this shortage, a minority of centers have started with efforts to reintroduce donation after circulatory death (DCD). This review aims to evaluate the experimental background, the current international clinical experience, and the further potential and challenges of the different DCD categories. Successful strategies have been implemented to reduce the problems of warm ischemic time, thrombosis after circulatory arrest, and difficulties in organ assessment, which come with DCD donation. From the currently reported results, controlled-DCD lungs are an effective and safe method with good mid-term and even long-term survival outcomes comparable to donation after brain death (DBD). Primary graft dysfunction and onset of chronic allograft dysfunction seem also comparable. Thus, controlled-DCD lungs should be ceased to be treated as marginal and instead be promoted as an equivalent alternative to DBD. A wide implementation of controlled-DCD-lung donation would significantly decrease the mortality on the waiting list. Therefore, further efforts in establishment of legislation and logistics are crucial. With regard to uncontrolled DCD, more data are needed analyzing long-term outcomes. To help with the detailed assessment and improvement of uncontrolled or otherwise questionable grafts after retrieval, ex-vivo lung perfusion is promising.

Donors after cardiocirculatory death and lung transplantation

The number of patients actively awaiting lung transplantation (LTx) is more than the number of suitable donor lungs. The percentage of lung retrieval rate is lower when compared to other solid organs. The use of lungs from donation after cardiocirculatory death (DCD) donors is one of the options to avoid organ shortage in LTx. After extensive experimental research, clinical application of DCD donation is becoming wider. The results from most of the centers show at least equal survival rate compared to donors from brain death. This review paper will summarize experimental background and clinical experience from DCD donors.

An official American Thoracic Society/International Society for Heart and Lung Transplantation/Society of Critical Care Medicine/Association of Organ and Procurement Organizations/United Network of Organ Sharing Statement: ethical and policy considerations in organ donation after circulatory determination of death

RATIONALE

Donation after circulatory determination of death (DCDD) has the potential to increase the number of organs available for transplantation. Because consent and management of potential donors must occur before death, DCDD raises unique ethical and policy issues.

OBJECTIVES

To develop an ethics and health policy statement on adult and pediatric DCDD relevant to critical care and transplantation stakeholders.

METHODS

A multidisciplinary panel of stakeholders was convened to develop an ethics and health policy statement. The panel consisted of representatives from the American Thoracic Society, Society of Critical Care Medicine, International Society for Heart and Lung Transplantation, Association of Organ Procurement Organizations, and the United Network of Organ Sharing. The panel reviewed the literature, discussed important ethics and health policy considerations, and developed a guiding framework for decision making by stakeholders.

RESULTS

A framework to guide ethics and health policy statement was established, which addressed the consent process, pre- and post mortem interventions, the determination of death, provisions of end-of-life care, and pediatric DCDD.

CONCLUSIONS

The information presented in this Statement is based on the current evidence, experience, and clinical rationale. New clinical research and the development and dissemination of new technologies will eventually necessitate an update of this Statement.

A practical approach to clinical lung transplantation from a Maastricht Category III donor with cardiac death

Although donation after cardiac death (DCD) has the potential to provide a novel source of organs for lung transplantation, even in a controlled DCD situation such as a Maastricht Category III donor (withdrawal of treatment), the limited time frame available after the declaration of death to initiate procurement and preservation remains challenging. Indeed, no publication has detailed the exact time frames and technique applicable for successful Maastricht Category III DCD lung procurement. In this patient report, withdrawal of life-support treatment and death certification was performed in the intensive care unit and the lungs were procured in an operating room 49 minutes after cardiac arrest and successfully transplanted (cold ischemia time <6 hours) into a severely ill recipient with primary pulmonary hypertension.

Lung transplantation: donor and recipient critical care aspects

PURPOSE OF REVIEW

The purpose of this paper is to highlight new developments in donor and recipient lung transplant issues for the critical care physician.

RECENT FINDINGS

A shortage of suitable lung donors has led to the use of extended donors and the development of novel techniques such as live-donor lung transplantation and the use of non-heart-beating donors. The increased experience and success with lung transplantation has also resulted in the extension of this therapy to patients previously considered unsuitable for transplantation. Postoperative outcomes can be affected by many of these recent donor and recipient changes. Improved preservation solutions and techniques to reduce reperfusion injury may be able to ameliorate some of the new perioperative graft dysfunction, but morbidity is still potentially significant, and extraordinary interventions such as extracorporeal membrane oxygenation may be required in selected cases.

SUMMARY

Patients undergoing lung transplantation continue to be very challenging in the intensive care unit. A multidisciplinary approach to care, and early recognition of serious problems, will help improve outcomes.

Isoproterenol reduces ischemia-reperfusion lung injury despite beta-blockade

BACKGROUND

If lungs could be retrieved from non-heart-beating donors (NHBDs), the shortage of lungs for transplantation could be alleviated. The use of lungs from NHBDs is associated with a mandatory warm ischemic interval, which results in ischemia-reperfusion injury upon reperfusion. In an earlier study, rat lungs retrieved 2-h postmortem from NHBDs had reduced capillary leak measured by filtration coefficient (Kfc) when reperfused with isoproterenol (iso), associated with an increase in lung tissue levels of cyclic AMP (cAMP). The objective was to determine if this decrease in Kfc was because of beta-stimulation, or would persist despite beta-blockade.

MATERIALS AND METHODS

Donor rats were treated intraperitoneally with beta-blockade (propranolol or pindolol) or carrier, sacrificed, and lungs were retrieved immediately or 2 h postmortem. The lungs were reperfused with or without iso and the beta-blockers in the reperfusate. Outcome measures were Kfc, wet:dry weight ratio (W/D), lung levels of adenine nucleotides and cAMP.

RESULTS

Lungs retrieved immediately after death had normal Kfc and W/D. After 2 h of ischemia, Kfc and W/D were markedly elevated in controls (no drug) and lungs reperfused with beta-blockers alone. Isoproterenol-reperfusion decreased Kfc and W/D significantly (P < 0.01) even in the presence of beta-blockade. Lung cAMP levels were increased only with iso in the absence of beta-blockade.

CONCLUSIONS

The attenuation of ischemia-reperfusion injury because of iso occurs even in the presence of beta-blockade, and may not be a result of beta-stimulated increased cAMP.

Non-heart-beating donors

The widespread application of lung transplantation is limited by the shortage of suitable donor organs resulting in longer waiting times for listed patients with a substantial risk of dying before transplantation. To overcome this critical organ shortage, some transplant programs have now begun to explore the use of lungs from circulation-arrested donors, so called non-heart-beating donors (NHBDs). This review outlines the different categories of NHBDs, the relevant published experimental data that support the use of lungs coming from these donors and the clinical experience worldwide so far. Techniques for NHBD lung preservation and pretransplant functional assessment are reviewed. Ethical issues involved in transplanting lungs from asystolic donors are discussed.

Efeito da ventilação com diferentes frações inspiradas de oxigênio e do alopurinol na isquemia-reperfusão pulmonar em ratos

OBJETIVO: Avaliar o efeito da ventilação associada a frações inspiradas de oxigênio a 0,21 e 1,00 e do alopurinol (antioxidante) na isquemia-reperfusão pulmonar. MÉTODO: Foram utilizados 60 ratos Wistar, distribuídos aleatoriamente em seis grupos. O grupo 1 foi o controle; no grupo 2 os animais foram ventilados durante a isquemia-reperfusão pulmonar com FiO2 de 0,21; e no grupo 3, com FiO2 de 1,00. Os três grupos restantes 1A, 2A e 3A foram medicados com 100 mg/kg de alopurinol no pré-operatório e submetidos a procedimentos semelhantes aos grupos 1, 2 e 3, respectivamente. O modelo utilizado foi de isquemia-reperfusão normotérmica, in situ. O tempo de isquemia foi de 30 minutos, e o de reperfusão, de 10 minutos. Como parâmetros de avaliação foram utilizados a pressão arterial média sistêmica (PAM), a relação da pressão parcial de oxigênio/fração inspirada de oxigênio (PaO2/FiO2), a dosagem das substâncias reativas ao ácido tiobarbitúrico (TBARS) no tecido pulmonar e a relação entre peso pulmonar úmido e peso pulmonar seco. RESULTADOS: Em relação à PAM, ocorreu diminuição significante (p<0,05) entre os grupos 3 x 1, 2 x 2A e 3 x 3A. Na PaO2/FiO2 ocorreu diminuição significante (p<0,05) entre os grupos 3 x 2 e 3 x 3A. Nas TBARS ocorreu diminuição significante (p<0,05) entre os grupos 3 x 3A. Na relação peso pulmonar úmido/seco ocorreu aumento significante (p<0,05) entre os grupos 3 x 2, 2 x 2A e 3 x 3A. CONCLUSÕES: A ventilação com oxigênio a 21%, quando comparada à ventilação com oxigênio a 100%, apresentou diminuição menos acentuada da PAM, melhor relação entre PaO2/FiO2, e menor edema pulmonar. O uso de alopurinol no pré-operatório mostrou uma diminuição menos acentuada da PAM, melhor relação entre PaO2/FiO2, menor produção de TBARS e menor edema pulmonar, quando comparado aos resultados dos grupos que não o utilizaram.

Estudo da fração inspirada de oxigênio na isquemia-reperfusão pulmonar em ratos

OBJETIVO: Estudar o efeito das frações inspiradas de oxigênio (FiO2) a 0,21, 0,40 e 1,00 na isquemia-reperfusão pulmonar. MÉTODOS: Foram utilizados 40 ratos Wistar, distribuídos aleatoriamente em quatro grupos. O grupo I foi o controle e, nos grupos II, III e IV, os animais foram ventilados durante a isquemia-reperfusão com FiO2 a 0,21, 0,40 e 1,00 respectivamente. O modelo utilizado foi de isquemia-reperfusão normotérmica, in situ. O tempo de isquemia foi de 30 minutos e o de reperfusão, de 10 minutos. Como parâmetros de avaliação, utilizou-se a pressão arterial média sistêmica (PAM), a relação entre a pressão parcial de oxigênio e a fração inspirada de oxigênio (PO2/FiO2), a dosagem da glutationa reduzida (GSH) e das substâncias reativas ao ácido tiobarbitúrico (TBARS) no tecido pulmonar e a relação entre o peso pulmonar úmido e o peso pulmonar seco. RESULTADOS: Os resultados mostraram que a ventilação com FiO2 a 0,21, quando comparada à ventilação com FiO2 a 0,40 e 1,00, durante o período de isquemia-reperfusão, apresentou menor diminuição da PAM, melhor relação PO2/FiO2, maior valor na medida da GSH, menor produção das TBARS e menor formação de edema pulmonar. CONCLUSÃO: A ventilação com baixa FiO2 (0,21) mostrou melhores resultados quando comparada àquelas realizadas com FiO2 mais elevadas (0,40 e 1,00) na isquemia-reperfusão pulmonar.

Should we ventilate or cool the pulmonary graft inside the non-heart-beating donor?

BACKGROUND

The ideal preservation method during the warm ischemic period in the non-heart-beating donor (NHBD) remains unclear. In this study we compare the protective effect of ventilation vs cooling of the non-perfused pulmonary graft.

METHODS

Domestic pigs (30.8 +/- 0.35 kg) were divided into 3 groups. In Group I, lungs were flushed with cold Perfadex solution, explanted and stored in saline (4 degrees C) for 4 hours (HBD, n = 5). Pigs in the 2 study groups were killed by myocardial fibrillation and left untouched for 1 hour. Lungs in Group II were ventilated (NHBD-V, n = 5) for 3 hours. Lungs in Group III were topically cooled (NHBD-TC, n = 5) in situ for 3 hours with saline (6 degrees C) infused via intra-pleural drains. Thereafter, the left lungs from all groups were prepared for evaluation. In an isolated circuit the left lungs were ventilated and reperfused via the pulmonary artery (PA) with autologous, hemodiluted, deoxygenated blood. Hemodynamic, aerodynamic and oxygenation parameters were measured at 37.5 degrees C and a PA pressure of 20 mm Hg. The wet:dry weight ratio (W/D) was calculated after reperfusion.

RESULTS

Pulmonary vascular resistance, oxygenation index and W/D weight ratio were significantly worse in NHBD-V (3,774 +/- 629 dyn sec cm(-5), 3.43 +/- 0.5, 6.98 +/- 0.42, respectively) compared with NHBD-TC (1,334 +/- 140 dyn sec cm(-5), 2.47 +/- 0.14, 5.72 +/- 0.24, respectively; p < 0.01, p < 0.05 and p < 0.05, respectively) and HBD (1,130 +/- 91 dyn sec cm(-5), 2.25 +/- 0.09, 5.23 +/- 0.49, respectively; p < 0.01, p < 0.01 and p < 0.05, respectively groups). No significant differences were observed, however, in any of these parameters between NHBD-TC and HBD (p = 0.46, p = 0.35 and p = 0.12, respectively).

CONCLUSION

These results indicate that cooling of the pulmonary graft inside the cadaver is the preferred method in an NHBD protocol. It is also confirmed that 1 hour of warm ischemia does not diminish graft function upon reperfusion.

How long can we preserve the pulmonary graft inside the nonheart-beating donor?

BACKGROUND

The use of lungs from nonheart-beating donors (NHBD) might significantly alleviate the organ shortage. Extending the preharvest interval in NHBD would facilitate distant organ retrieval. We hypothesized that prolonged topical cooling inside NHBD after 60 minutes of initial warm ischemia would not affect the pulmonary graft.

METHODS

Domestic pigs were anesthetized and divided into three groups (n = 6 in each group). In the control group (HBD), lungs were flushed, explanted, and further stored in low potassium dextran solution (4 degrees C) for 4 hours. In the two study groups pigs were sacrificed by myocardial fibrillation and left untouched for 1 hour. Chest drains were then inserted for topical lung cooling (6 degrees C) for 3 hours (NHBD-TC3) or 6 hours (NHBD-TC6). The left lung in all groups was then prepared for evaluation. In an isolated circuit lungs were ventilated and reperfused through the pulmonary artery. Hemodynamic, aerodynamic, and oxygenation variables were measured 35 minutes after onset of controlled reperfusion. Wet-to-dry weight ratio was calculated.

RESULTS

No significant differences were observed among the three groups in pulmonary vascular resistance (p = 0.38), mean airway pressure (p = 0.39), oxygenation index (p = 0.62), and wet-to-dry weight ratio (p = 0.09).

CONCLUSIONS

These data confirm that 1 hour of warm ischemia does not affect the pulmonary graft from NHBD compared with HBD. The preharvest interval can be safely extended up to 7 hours postmortem by additional topical cooling of the graft inside the cadaver. This technique may facilitate distant organ retrieval in NHBD.

Non-heart-beating donors in thoracic transplantation

Access to lung transplantation is severely limited by a scarcity of suitable donors, resulting in increasing numbers of deaths on the heart and lung transplant waiting lists, and strict selection criteria for recipients. Unlike some other solid organs, the lung may be ideally suited to retrieval for transplant following substantial intervals after circulatory arrest. This may be because lung parenchymal cells do not rely on perfusion for cellular respiration. This review outlines the relevant published experimental data that addresses the concept that lungs might be suitable for transplant even if retrieved from non-heart-beating donors (NHBDs), and the small published clinical experience with NHBDs as lung donors. Aspects of reperfusion injury in this setting are reviewed. The prospect of heart transplant from NHBDs is addressed. The impact of the routine use of NHBDs on lung transplantation is discussed.

Long-term preservation with interim evaluation of lungs from a non-heart-beating donor after a warm ischemic interval of 90 minutes

OBJECTIVE

To investigate the value of in situ preservation and ex vivo evaluation of lungs from a non-heart-beating donor (NHBD) prior to long-term cold storage.

SUMMARY BACKGROUND DATA

The use of pulmonary grafts from NHBD might alleviate the organ shortage. However, viability testing of these grafts is mandatory to transplant only those lungs with excellent function.

METHODS

Pigs were divided into two groups. In the control group, lungs were flushed, explanted, and stored for 4 hours (4 degrees C). In the study group, pigs were killed and left untouched for 90 minutes. Thereafter, the lungs were cooled for 150 minutes via chest drains. Graft function of the left lung in both groups was assessed in an isolated ventilation and reperfusion circuit 4 hours after death. The lung was then cooled and stored. Twenty-four hours after death, the pulmonary graft was reassessed in the same model.

RESULTS

We did not observe a statistical significant difference between the two groups in pulmonary vascular resistance, mean airway pressure, and partial oxygen tension at each time point. There was also no statistical significant difference in wet-to-dry weight ratio. Finally, no statistical difference was found within both groups comparing the assessment at 24 hours with the interim evaluation at 4 hours.

CONCLUSIONS

These data demonstrate that: 1) 90 minutes of warm ischemia and 150 minutes of intrapleural cooling do not affect pulmonary graft function; and 2) NHBD lungs can be safely preserved up to 24 hours. Finally, we have demonstrated that interim ex vivo evaluation of NHBD lungs is a valid and safe method to assess graft function.

Effects of cold and warm ischemia on the mitochondrial oxidative phosphorylation of swine lung

BACKGROUND

The aim of the study was to investigate the consequence of warm and cold ischemia on lung mitochondria in order to define bioenergetic limits within lung could be suitable for pulmonary transplantation.

METHODS

Twenty-two pigs underwent lung harvesting after lung flush with Euro-Collins solution. Mitochondria were isolated from fresh lungs, from lungs submitted to 24 or 48 hr of cold ischemia, to 30 or 45 min of warm ischemia, and to 30 min of warm ischemia followed by 24 or 48 hr of cold ischemia. Mitochondrial oxidative phosphorylation parameters were determined in isolated mitochondria by in vitro measurement of oxygen consumption.

RESULTS

Relative to controls, mitochondria submitted to cold ischemia showed an alteration in the oxidoreductase activities of the respiratory chain but no membrane permeability alteration. After 48 hr of cold ischemia, there was a decrease in the yield of the oxidative phosphorylation. Thirty minutes of warm ischemia did not alter the mitochondrial respiratory parameters. However, lung submitted to 45 min of warm ischemia showed mitochondrial damage as a decrease in the oxidative phosphorylation efficiency and ADP availability but no change in the oxidoreductase activities. Relative to cold ischemia alone, 30 min of warm ischemia preceding cold ischemia promoted no significant change in the respiratory parameters.

CONCLUSIONS

On bioenergetic basis, lung submitted to warm ischemia could be suitable for transplantation if the warm ischemia duration does not exceed 30 min. This could be a major concern in lung procurement from non-heart beating donors.

Pre-arrest heparinization and ventilation during warm ischemia preserves lung function in non-heart-beating donors

BACKGROUND/PURPOSE

To solve the problem of donor scarcity, many attempts have been made including improved community education, relaxed organ acceptance criteria, increased reliance on single lung transplantation, and the use of partial organ donation. Unfortunately, these efforts have produced only modest increases in lung allograft availability; therefore, the so-called non-heart-beating organ donation must be considered. The aim of this study is to assess the viability of the non-heart-beating donor (NHBD) lung transplant rat model and determine the best strategy to manage the donor before and after cardiac arrest.

METHODS

Fifty-five inbred Fischer rats were used as donors and recipients in an isogenic model of left lung transplantation. The rats were divided into 6 groups (n = 5): group I, normal controls without transplant; group II, heart-beating donor controls (HBD); group III, NHBD, no heparin, no ventilation during warm ischemia; group IV, NHBD, heparin, no ventilation; group V, NHBD, no heparin, ventilation; group VI, NHBD, heparin, ventilation. All lungs were stored at 4 degrees C for 4 hours. Animals were killed 24 hours after implantation. Gas exchange, pulmonary artery pressure, compliance, chest x-ray score, and histological score were assessed.

RESULTS

Heparinized and ventilated animals during warm ischemia (group VI) had similar performance than those transplanted without warm ischemia time in a scenario of heart-beating donor (group II). Groups III, IV, and V transplanted lungs showed severe damage.

CONCLUSIONS

The authors conclude that the rat lung transplantation model is useful to study the phenomena that occur in a setting of transplantation using NHBD and that heparinization and ventilation before cardiac arrest is the best strategy to manage non-heart-beating donors in this model.

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.

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.