Successful canine bilateral single-lung transplantation after 21-hour lung preservation

Therapeutic benefits of nitric oxide in lung transplantation

Lung transplantation is an evolutionary procedure from its experimental origin in the twentieth century and is now recognized as an established and routine life-saving intervention for a variety of end-stage pulmonary diseases refractory to medical management. Despite the success and continuous refinement in lung transplantation techniques, the widespread application of this important life-saving intervention is severely hampered by poor allograft quality offered from donors-after-brain-death. This has necessitated the use of lung allografts from donors-after-cardiac-death (DCD) as an additional source to expand the pool of donor lungs. Remarkably, the lung exhibits unique properties that may make it ideally suitable for DCD lung transplantation. However, primary graft dysfunction (PGD), allograft rejection and other post-transplant complications arising from unavoidable ischemia-reperfusion injury (IRI) of transplanted lungs, increase morbidity and mortality of lung transplant recipients annually. In the light of this, nitric oxide (NO), a selective pulmonary vasodilator, has been identified as a suitable agent that attenuates lung IRI and prevents PGD when administered directly to lung donors prior to donor lung procurement, or to recipients during and after transplantation, or administered indirectly by supplementing lung preservation solutions. This review presents a historical account of clinical lung transplantation and discusses the lung as an ideal organ for DCD. Next, the author highlights IRI and its clinical effects in lung transplantation. Finally, the author discusses preservation solutions suitable for lung transplantation, and the protective effects and mechanisms of NO in experimental and clinical lung transplantation.

Canine Bilateral Lung Transplantation After 18-hour Preservation Using Non–heart-beating Donors

BACKGROUND

We previously reported that lung inflation with oxygen, EPC-K1 (a diester alpha-tocopherol and ascorbic acid), urokinase and low-potassium dextran glucose (LPDG) solution can be beneficial in lung preservation. In the present study, a canine bilateral lung transplantation (BLT) model was used to evaluate long-term lung preservation of non-heart-beating donors (NHBDs).

METHODS

Animals were euthanized without heparinization and left at room temperature for 2 hours until lung extraction. After cardiac arrest, the lungs were kept inflated with 100% oxygen. After extraction, the donor lungs were flushed with LPDG solution containing EPC-K1 (1.0 mg/liter), followed by injection of urokinase (120,000 IU) into the pulmonary artery. Eighteen BLTs were performed after preservation at 4 degrees C. Total ischemic time was scheduled for 12 hours in Group 1 (n = 6), 18 hours in Group 2 (n = 6) and 24 hours in Group 3 (n = 6). After BLT, recipients were followed up for 6 hours. An additional 6 BLTs were performed as a chronic study in the same setting as for Group 2.

RESULTS

All animals in Groups 1 and 2 showed excellent pulmonary function during the 6-hour post-transplant assessment time, in contrast to only 2 dogs from Group 3. In the chronic study, all 6 animals showed excellent pulmonary function for 24 hours (PaO2 = 528 +/- 8 mm Hg with 100% oxygen) and 2 of them survived for >1 week.

CONCLUSION

Successful chronic lung preservation (18 hours) using NHBDs is achievable in a canine BLT model.

Perfadex for clinical lung procurement: is it an advance?

BACKGROUND

Extensive laboratory experience suggested that low potassium dextran lung preservation solution (Perfadex; Medisan, Uppsala, Sweden) is superior to Euro-Collins (EC; Frusen, Hamburg, Germany), the clinical standard. The purpose of this study was to evaluate Perfadex in clinical lung transplantation.

METHODS

A retrospective analysis of the outcome of 69 consecutive lung allografts retrieved and used for transplantation was made. Donor lungs were flushed with EC in 37 patients and Perfadex in 32 patients. The evaluation measurements were quantitative chest roentgenogram score (grade 0 to 4), graft oxygenation, duration of mechanical ventilation, length of intensive care treatment, and survival.

RESULTS

The mean chest roentgenogram score was 1.55 and 1.81 for the EC group compared with 1.18 and 2.09 for the Perfadex group at 1 and 48 hours, respectively (p = 0.1 and 0.8, respectively). Arterial alveolar oxygen tension ratio was similar at 12 and 24 hours (0.61 vs 0.67; p = 0.8; and 0.64 vs 0.53; p = 0.3, respectively). The mean ventilation time was 71.2 +/- 32.3 hours versus 81.9 +/- 43.6 hours for the EC and Perfadex groups, respectively (p = 0.4). The mean intensive therapy unit stay was 3.1 +/- 2.6 days for the EC group compared with 4.1 +/- 3.9 days for the Perfadex group (p = 0.4). Death caused by primary organ failure was 5.1% for the EC group compared with 3.1% for the Perfadex group (p = 0.8).

CONCLUSIONS

There was no difference between Perfadex and EC in clinical lung preservation. This may reflect the difference between controlled laboratory environment and the real world of brain death lung injury. Further studies are required to investigate the impact of Perfadex in the long-term outcome of lung transplantation.

Ischemia-reperfusion-induced lung injury

Ischemia-reperfusion-induced lung injury is characterized by nonspecific alveolar damage, lung edema, and hypoxemia occurring within 72 hours after lung transplantation. The most severe form may lead to primary graft failure and remains a significant cause of morbidity and mortality after lung transplantation. Over the past decade, better understanding of the mechanisms of ischemia-reperfusion injury, improvements in the technique of lung preservation, and the development of a new preservation solution specifically for the lung have been associated with a reduction in the incidence of primary graft failure from approximately 30 to 15% or less. Several strategies have also been introduced into clinical practice for the prevention and treatment of ischemia-reperfusion-induced lung injury with various degrees of success. However, only three randomized, double-blinded, placebo-controlled trials on ischemia-reperfusion-induced lung injury have been reported in the literature. In the future, the development of new agents and their application in prospective clinical trials are to be expected to prevent the occurrence of this potentially devastating complication and to further improve the success of lung transplantation.

Effects of inhaled nitric oxide in a canine living-donor lobar lung transplant model

OBJECTIVE

In living-donor lobar lung transplantation, early severe graft dysfunction can occur if the size or amount of transplanted lung tissue is insufficient. The purpose of this study was to evaluate the effects of inhaled nitric oxide on early pulmonary function in a canine bilateral living-donor lobar lung transplant model.

METHODS

Sixteen pairs of mongrel dogs with a donor/recipient weight ratio less than 1.2 were used. The donor lung bloc was extirpated after heparinization. Right middle, lower and cardiac lobes were implanted as a right lung of the recipient and left lower lobe was implanted as a left lung without cardiopulmonary bypass. In Group 1 (n = 9), nitric oxide gas was administered continuously at a concentration of 40 parts per million prior to reperfusion of the right lung throughout the 6-hour assessment period after transplantation. In Group 2 (n = 7), nitrogen gas was administered in the same manner as nitric oxide, for control.

RESULTS

At the end of assessment, the survival rate was 89% (8/9) in Group 1 and 57% (4/7) in Group 2. The arterial oxygen tension in Group 1 was significantly higher than that in Group 2. The pulmonary arterial pressure and pulmonary vascular resistance index were significantly lower in Group 1 than in Group 2. The aortic pressure and cardiac index did not differ significantly between the two groups. The wet-to-dry weight ratio and myeloperoxidase activity were significantly lower in Group 1 than in Group 2.

CONCLUSIONS

These data suggested that inhaled nitric oxide improved early pulmonary function in living-donor lobar lung transplantation by vasodilatating the pulmonary vasculature and inhibiting neutrophil activation.

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.

Lung procurement by low-potassium dextran and the effect on preservation injury. Munich Lung Transplant Group

BACKGROUND

This clinical study was performed to evaluate the effect of low-potassium dextran (LPD) solution on organ function in human lung transplantation.

METHODS

A total of 80 patients were included in this study. Donor lungs were flushed with Euro-Collins (EC) solution in 48 cases or LPD (Perfadex) in 32 cases. Subsequently, single- (EC: n = 31; LPD: n = 15) or double-lung transplantations (EC: n = 17; LPD: n = 17) were performed. The evaluation parameters of transplant function were the reperfusion injury score (grade I to V); the alveolar/arterial oxygen ratio; the duration of respirator therapy; and the length of intensive care treatment and survival.

RESULTS

Incidence and severity of reperfusion injury score were more severe in the EC group (31 of 48: grade I: n = 13; II: n = 8; III: n = 5; IV: n = 2; V: n = 3; LPD group: 17 of 32 patients; grade I: n = 12; II: n = 1; III: n = 3; IV: n = 0 grade V: n = 0), leading to death in three patients. In the LPD group, despite of the use of cardiopulmonary bypass, alveolar/arterial oxygen ratio values were significantly (P = 0.009) better during the early postoperative phase. Thirty-day mortality was 12% in the EC group and 6% in the LPD group. The one-year survival rate was 79% after the use of LPD (vs. EC: 62%).

CONCLUSIONS

Graft preservation using LPD leads to better immediate and intermediate graft function after pulmonary transplantation and also results in better long-term survival.

Hypothermic preservation of isolated rat lungs in modified bicarbonate buffer, EuroCollins solution or St Thomas' Hospital cardioplegic solution

OBJECTIVES

Inadequate preservation solutions limit lung storage times and, consequently, transplant programs. To address this problem we established an isolated, ventilated and perfused rat lung preparation. Here we report the effects of hypothermic storage in EuroCollins solution, St Thomas' Hospital cardioplegic solution and a modified bicarbonate buffer solution.

METHODS

Lungs from male Wistar rats (230-330 g) were perfused via the pulmonary artery with modified bicarbonate buffer (37 degrees C, 15 ml/min, constant flow) and ventilated by positive pressure (tidal volume:1.6-1.8 ml, 80 breaths/min). Vascular resistance (pulmonary artery pressure:perfusate flow ratio) and airways compliance (tidal volume:tracheal pressure ratio) were measured. After a control perfusion period (20 min), lungs were flushed with, then immersed in, bicarbonate buffer (4 degrees C) for varying periods (0-24 h). After storage, lung function was assessed during 20 min reperfusion. Having established a suitable period for study, storage in EuroCollins, St Thomas' Hospital cardioplegic solution or bicarbonate buffer were compared.

RESULTS

Pulmonary compliance (ml/cmH2O) was significantly (P < 0.05) reduced in lungs stored for 6 h in modified bicarbonate buffer (0.026 +/- 0.008), EuroCollins solution (0.013 +/- 0.002) or St Thomas' Hospital solution (0.025 +/- 0.005) compared to unstored lungs (0.068 +/- 0.007). Vascular resistance, (1.32 +/- 0.13 cmH2O/ml per min) in unstored lungs, was similar in lungs stored in St Thomas' Hospital solution but increased significantly in lungs stored in modified bicarbonate buffer (3.22 +/- 0.78 cmH2O/ml per min) or EuroCollins solution (4.66 +/- 0.57 cmH2O/ml per min).

CONCLUSIONS

Hypothermic storage of rat lungs for 6 h in modified bicarbonate buffer or St Thomas' Hospital solution causes less increase in vascular resistance on reperfusion than EuroCollins solution.

Both blood and crystalloid-based extracellular solutions are superior to intracellular solutions for lung preservation

OBJECTIVE

Lung transplantation remains limited by donor organ ischemic time, inadequate graft preservation, and reperfusion injury. We evaluated lung preservation with use of an extracellular solution, with or without the addition of blood, as compared with preservation with the intracellular Euro-Collins solution.

METHODS

With use of an isolated, whole blood perfused/ventilated rabbit lung model, we studied three groups of animals. Lungs were flushed with Euro-Collins, low-potassium dextran, or 20% blood-low-potassium dextran solution. Lungs were harvested en bloc, stored inflated at 4 degrees C for 18 hours, and then reperfused at 60 ml/min with whole blood. Continuous measurements of pulmonary artery pressure, pulmonary vascular resistance, and dynamic airway compliance were obtained. Fresh, nonrecirculated venous blood was used to determine the single-pass pulmonary venous-arterial oxygen gradient.

RESULTS

Lungs preserved with Euro-Collins solution demonstrated elevated pulmonary artery pressure and pulmonary vascular resistance when compared with those preserved with low-potassium dextran and 20% blood-low-potassium dextran solutions (pulmonary artery pressure: 40.8 +/- 2.2 mm Hg vs 28.9 +/- 2.4 mm Hg and 28.3 +/- 1.5 mm Hg, respectively, p < 0.001; pulmonary vascular resistance: 46.0 +/- 3.1 x 10(3) dynes x sec x cm(-5) vs 29.0 +/- 4.2 x 10(3) dynes x sec x cm(-5) and 28.8 +/- 2.3 x 10(3) dynes x sec x cm(-5), respectively, p < 0.001). Euro-Collins solution-preserved lungs demonstrated a significant drop in compliance when compared with those preserved with low-potassium dextran and 20% blood-low-potassium dextran (-21.9% +/- 4.7% vs 1.8% +/- 3.3% and 1.4% +/- 6.2%, respectively; p = 0.002). Oxygenation was improved with low-potassium dextran and 20% blood-low-potassium dextran solutions as compared with that with Euro-Collins solution (296.3 +/- 54.6 mm Hg and 290.2 +/- 66.4 mm Hg, respectively, vs 37.2 +/- 4.6 mm Hg; p = 0.001).

CONCLUSIONS

Extracellular solutions provided superior preservation of pulmonary function in this rabbit lung model of ischemia-reperfusion. However, the addition of blood does not confer any demonstrable advantage over low-potassium dextran solution alone with use of an 18-hour period of cold ischemia.

Gene therapy in lung transplantation: feasibility of ex vivo adenovirus-mediated gene transfer to the graft

Lung transplantation is associated with complications such as reperfusion injury and graft rejection. Gene therapy targeted to the graft offers a promising approach to the prevention of these complications. Because adenovirus vectors can transfer genes in vivo to the lung vasculature, we evaluated the feasibility of adenovirus-mediated gene transfer to the lung graft in a porcine model of left lung allotransplantation. Following removal of the donor lung, an adenovirus vector encoding the beta-galactosidase (beta-Gal) gene was injected ex vivo into the lumen of the upper lobe pulmonary artery of the graft. After 2 hr of incubation at 10 degrees C, the lung graft was implanted into the recipient animal. Three days later, the animals were sacrificed and the lung graft was evaluated for beta-Gal activity. No beta-Gal activity was detected in the left lower lobe used as a control. In contrast, beta-Gal activity was detected in endothelial cells of the left upper lobe pulmonary circulation, and was also observed in airway and alveoli epithelial cells. However, less than 1% of cells of the graft expressed beta-Gal. In vitro experiments showed that this may be explained in part by the low temperature and the short duration of adenovirus incubation within the graft, and by the low susceptibility of porcine cells to human adenovirus. Furthermore, expression of the exogenous gene occurred in several organs of recipient animals. Thus, adenovirus-mediated gene transfer to the lung graft is feasible ex vivo, but several parameters limit gene transfer efficiency and need to be improved before clinical application is attempted.

Low-potassium solution for lung preservation in the setting of high-flow reperfusion

BACKGROUND

We previously demonstrated that standard preservation using Euro-Collins solution impairs lung function in the setting of high-flow reperfusion because of potassium-induced vasoconstriction. Preservation strategies for single-lung transplantation are an important factor in patients with pulmonary hypertension. This study investigates the hypothesis that low-potassium preservation solution will improve function of lungs subjected to high-flow reperfusion.

METHODS

Twenty-one New Zealand white rabbit lungs were harvested and studied on an isolated, blood-perfused model of lung function after 4 hours of cold ischemia at 4 degrees C. Control lungs were preserved with 50 mL/kg of cold saline solution flush (group I). Experimental lungs were preserved with low-potassium solution (group II) or Euro-Collins solution (group III) at similar temperatures and volumes.

RESULTS

The pulmonary arteriovenous oxygen gradient at the end of the 30-minute high-flow reperfusion period was significantly higher in group II compared with group III (121.3 +/- 19.2 mm Hg versus 31.1 +/- 4.2 mm Hg; p < 0.001). The pulmonary vascular resistance was significantly lower in group II than in group III (46.3 +/- 1.8 x 10(3) dynes x s x cm(-5) versus 79.8 +/- 8.4 x 10(3) dynes x s x cm(-5); p < 0.01. The percent decrease in dynamic airway compliance in group III was significantly greater than in group I and II (-51.0% +/- 13.3% versus -10.2% +/- 3.4% and -11.2% +/- 2.8%, respectively; p < 0.001). Similarly, the wet to dry ratio of the lungs in group III was significantly greater than in groups I and II (13.9 +/- 2.3 versus 5.9 +/- 0.2 and 6.0 +/- 0.4, respectively; p < 0.001).

CONCLUSIONS

These data demonstrate that a low-potassium preservation solution yields improved lung function after high-flow reperfusion in an ex vivo rabbit lung model. Lung preservation should be aimed at the clinical setting.