Mature pulmonary lobar transplants grow in an immature environment.

OBJECTIVE: Mature lobar transplantation will increase the pediatric donor organ pool, but it remains unknown whether such grafts will grow in a developing recipient and provide adequate long-term support. We hypothesized that a mature pulmonary lobar allograft implanted in an immature recipient would grow. METHODS: We investigated our hypothesis in a porcine orthotopic left lung transplant model using animals matched by the major histocompatibility complex to minimize the effects of chronic rejection. Twenty-three immature animals (< 12 weeks of age and < 10 kg total body weight) received either sham left thoracotomy (SH control, n = 4), left upper lobectomy to study compensatory growth (UL control, n = 4), age-matched immature whole left lung transplants (IWL TXP, n = 6), mature (donor > 1 yr in age and > 40 kg in total body weight) left lower lobe transplants (MLL TXP, n = 5), or mature left upper lobe transplants (MUL TXP, n = 4). Twelve weeks after implantation, functional residual capacity of the left lung was measured and arterial blood gas samples were obtained after the native right lung had been excluded. The graft was excised and weighed, and samples for microscopy and wet/dry ratios were collected. RESULTS: Initial and final graft weights were as follows: IWL TXP group (34.6 +/- 1.5 and 107.8 +/- 5.9 gm, p < 0.0001), MLL TXP group (72.4 +/- 6.8 and 111.4 +/- 8.7, p < 0.001), and MUL TXP group (32.8 +/- 1.3 and 92.8 +/- 7.1 gm, respectively, p < 0.004). No significant differences between groups were demonstrated when functional residual capacity, wet/dry ratios, or oxygenation were compared. Immunohistochemical staining for the nuclear antigen Ki-67 demonstrated dividing pneumocytes. CONCLUSIONS: We conclude that a mature lobar graft implanted into an immature recipient grows by pneumocyte division in this model. Mature lobar transplants can be expected to grow and provide adequate long-term function in developing recipients.

Use of over-sized mature pulmonary lower lobe grafts results in superior pulmonary function.

BACKGROUND: Mature lobar transplantation will increase the pediatric donor organ pool; however, issues regarding size discrepancy between donor grafts and recipient lungs remain unresolved. We hypothesized that an oversized mature pulmonary lobar allograft implanted into an immature recipient would provide adequate longterm pulmonary function versus a size-matched mature lobar graft or an immature whole lung. METHODS: We investigated our hypothesis in a porcine orthotopic left lung transplant model in which 19 immature animals made up one control and three recipient groups. Group I underwent sham left thoracotomy (control, n = 4). Group II received age- and size-matched immature whole left lung transplant (n = 6). Group III received mature size-matched left upper lobe transplants (n = 4). Group IV received mature over-sized left lower lobe transplants (n = 5). Twelve weeks after implantation, data were collected after the native right lung was excluded. RESULTS: Graft weight was significantly elevated in group IV as compared with the explanted lung (72.4 +/- 6.8 versus 38.3 +/- 4.5 g; p = 0.003). Pulmonary artery pressure and pulmonary vascular resistance were significantly elevated in group III as compared with the over-sized mature lower lobe transplants (51.8 +/- 2.2 versus 40.4 +/- 2.5 mm Hg [p < 0.0001] and 1,605.9 +/- 117.5 versus 857.6 +/- 133.6 dynes.s.cm-5 [p < 0.0005], respectively). A trend toward decreased oxygenation was identified in group II. CONCLUSIONS: Over-sized mature lobar grafts provide improved hemodynamics as compared with size-matched grafts. Mature left lower lobe grafts are superior to size-matched upper lobe grafts in this model, probably as a result of an augmented vascular bed.

Intratracheal surfactant administration preserves airway compliance during lung reperfusion.

BACKGROUND: Decreased airway compliance after lung transplantation has been observed with severe ischemia-reperfusion injury. Further, it has been shown that the surfactant system is impaired after lung preservation and reperfusion. We hypothesized that surfactant replacement after allograft storage could preserve airway compliance during reperfusion. METHODS: Rabbit lungs were harvested after flush with 50 mL/kg of cold saline solution. Immediate control lungs were studied with an isolated ventilation/perfusion apparatus using venous rabbit blood recirculated at 40 mL/min, room-air ventilation at 20 breaths/min, and constant airway pressure (n = 8). Twenty-four-hour control lungs were preserved at 4 degrees C for 24 hours and then similarly studied (n = 7). Surfactant lungs underwent similar harvest and preservation for 24 hours, but received 1.5 mL/kg of intratracheal surfactant 5 minutes before reperfusion (n = 10). Airway pressure and flow were recorded continuously during 30 minutes of reperfusion. Tidal volume and airway compliance were calculated at 30 minutes. RESULTS: Tidal volume was 33.67 +/- 0.57, 15.75 +/- 5.72, and 29.83 +/- 1.07 mL in the immediate control, 24-hour control, and surfactant groups, respectively (p = 0.004, surfactant versus 24-hour control). Airway compliance was 1.94 +/- 0.27, 0.70 +/- 0.09, and 1.46 +/- 0.10 mL/mm Hg in the immediate control, 24-hour control, and surfactant groups, respectively (p = 0.002, surfactant versus 24-hour control). CONCLUSIONS: We conclude that surfactant administration before reperfusion after 24 hours of cold storage preserves tidal volume and airway compliance in the isolated ventilated/perfused rabbit model of lung reperfusion injury.

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.

Impaired bronchial healing after lung donation from non-heart-beating donors.

BACKGROUND: Bronchial viability after lung transplantation remains a concern. Modern preservation methods, surgical technique, and limited cold ischemic periods have decreased the frequency of bronchial complications. However, lungs procured from non-heart-beating donors are subjected to a mandatory period of warm ischemia. We investigated bronchial healing in a porcine survival model of left lung transplantation using organ procurement from non-heart-beating donors after a 60-minute period of warm ischemia. METHODS: Fourteen adult domestic swine underwent left lung transplantation. All lungs were preserved with cold Euro-Collins flush and stored inflated at 4 degrees C. Control lungs (n = 5) were flushed, harvested, and stored for 2 hours before implantation. Experimental lungs (n = 9) were procured from non-heart-beating donors. These lungs were subjected to 60 minutes of warm ischemia before flush and harvest, followed by 2 hours of cold storage before implantation. After 21 days of immunosuppression with prednisone, azathioprine, and cyclosporine, pulmonary function was assessed. Bronchial viability was evaluated with bronchoscopy and, at autopsy, followed by histologic analysis. RESULTS: Implantation time did not differ significantly between the control group and the experimental group (59.6 +/- 2.1 versus 64.4 +/- 2.9 minutes, p = 0.24). Control swine exhibited no evidence of ischemic injury to the donor bronchus. In contrast, six of nine lungs procured from non-heart-beating donors showed evidence of ischemic bronchial injury (p = 0.031 versus control). Findings ranged from hypovascular edematous mucosa to necrosis and sloughing of the mucosa throughout the entire donor bronchial tree. The remaining three non-heart-beating donor lungs exhibited normal lung function and bronchial healing. CONCLUSIONS: We conclude that 60 minutes of warm ischemia for lungs procured from non-heart-beating donors results in impaired bronchial viability with current preservation techniques. Thirty minutes of warm ischemia may be the acceptable limit for lung procurement from non-heart-beating organ donors.

Neutrophil endopeptidase inhibitor improves pulmonary function during reperfusion after eighteen-hour preservation.

BACKGROUND: Reperfusion injury remains a significant problem after lung transplantation and is thought to be in part mediated by neutrophils. Ulinastatin inhibits release of elastase and cathepsin G from neutrophil granules. We hypothesized that inhibition of these neutrophi endopeptidases (proteases) would attenuate pulmonary reperfusion injury. METHODS: With an isolated, whole blood-perfused, ventilated rabbit lung model, we studied the effects of ulinastatin. All lungs were flushed with cold Euro-Collins solution, harvested en bloc, stored inflated at 4 degrees C for 18 hours, and reperfused with whole blood. The 18-hour control lungs (n = 8) were stored and reperfused. Low-dose (n = 8) and high-dose (n = 7) groups were treated with total doses of ulinastatin of 25,000 and 50,000 units, respectively, during flush and reperfusion. An additional control group of lungs (n = 8) was harvested, flushed, and immediately reperfused. RESULTS: The pulmonary artery pressure was significantly lower in the high-dose group than in the 18-hour control group (36.7 +/- 1.8 vs 44.8 +/- 2.9 mm Hg, p = 0.034). The percentage decrease in dynamic airway compliance was significantly less in the high-dose group than in the 18-hour control group (-13.8% +/- 4.4% vs -25.1% +/- 3.7%, p = 0.032). Both low-dose and high-dose ulinastatin treatments did not result in a significant improvement in oxygenation with respect to the 18-hour control group (72.2 +/- 25.8 vs 32.5 +/- 4.9 mm Hg, p = 0.21). CONCLUSIONS: Ulinastatin diminishes reperfusion injury after 18 hours of hypothermic pulmonary ischemia, with resultant improvements in pulmonary artery pressure and airway compliance. Improvement in pulmonary function after preservation and reperfusion with a neutrophil endopeptidase inhibitor confirms the role of endopeptidases in reperfusion injury and suggests an intervention to reduce their detrimental effects on early graft function.

Euro-Collins solution exacerbates lung injury in the setting of high-flow reperfusion.

Single-lung transplantation has been abandoned for the treatment of pulmonary hypertension by many centers because of overperfusion of the graft following implantation. Euro-Collins solution is currently used for lung preservation despite the vasoconstrictive effect of this intracellular-type solution. We hypothesized that high-flow reperfusion, alone or in combination with Euro-Collins-induced vasoconstriction, may cause lung dysfunction. Twenty-eight New Zealand White rabbit lungs were harvested and studied in an isolated, blood-perfused model of lung function after 4 hours of cold ischemia. Control lungs were preserved with 50 ml/kg cold saline solution flush and reperfused at either normal flow (60 ml/min) or high flow (120 ml/min). Experimental lungs were preserved with 50 ml/kg cold Euro-Collins solution and reperfused at normal or high flow rates. The arteriovenous oxygen gradient at the end of the 30-minute reperfusion period was significantly lower in the high-flow versus the low-flow experimental group (31.1 +/- 4.2 vs 130.6 +/- 41.6 mm Hg, p < 0.05). The pulmonary vascular resistance was increased in the high-flow groups and the experimental groups, with a statistically significant difference between low-flow experimental and control groups (64374.4 +/- 5722.6 vs 37041.5 +/- 2110.9 dynes x sec x cm(-5), p < 0.001). The percentage decrease in dynamic airway compliance in the high-flow experimental group was markedly different from that in the high-flow control group (-51% +/- 13.3% vs -10.15% +/- 3.4%, p < 0.05). Similarly, the wet/dry ratio of the lungs in the high-flow experimental group (13.92 +/- 2.32) was significantly greater than that in the low-flow experimental group (6.27 +/- 0.19, p < 0.01) and than that in the high-flow control group (5.88 +/- 0.23, p < 0.001). These data demonstrate that high-flow reperfusion and preservation with Euro-Collins solution are deleterious to lung function, both individually and in combination, in an ex vivo rabbit lung model. Lung preservation with Euro-Collins solution may not be optimal when high-flow reperfusion is anticipated, as in the setting of unilateral lung transplantation for pulmonary hypertension.

Enhanced isolated lung function after ischemia with anti-intercellular adhesion molecule antibody.

The binding of leukocytes to intercellular adhesion molecules expressed on endothelial surfaces during ischemia and subsequent reperfusion initiates leukocyte-mediated reperfusion injury. Interruption of this leukocyte-endothelium interaction may therefore prevent reperfusion injury. In an isolated, ventilated, blood-perfused rabbit lung preparation, we studied the effect of a monoclonal anti-intercellular adhesion molecule antibody on lung function during reperfusion. Lungs were harvested with 50 ml/kg cold Euro-Collins flush and 30 micrograms prostaglandin E1 before storage for 18 hours at 4 degrees C. Experimental groups received low-dose (100 micrograms) or high-dose (200 micrograms) anti-intercellular adhesion molecule antibody added to the pulmonary flush at harvest and to the initial reperfusate. Eighteen-hour control preparations were preserved for 18 hours and received saline solution vehicle. Immediate control preparations were harvested and immediately reperfused. The oxygen tension in the recirculated pulmonary venous effluent was measured after 30 minutes of reperfusion. Histologic specimens were graded by blinded observers for degree of leukocyte infiltration (0, normal, to 4, severe infiltration). The mean oxygen tensions (+/-standard error of the mean) were 138.29 +/- 6.23, 58.86 +/- 9.14, 86.87 +/- 11.32, and 139.33 +/- 16.15 mm Hg in immediate control preparations, 18-hour control preparations, low-dose antibody group, and high-dose antibody group, respectively (p = 0.0001). The leukocyte grades (mean +/- standard error of the mean) were 1.5 +/- 0.723, 3.0 +/- 0.955, 1.9 +/- 0.899, and 1.2 +/- 0.834, respectively (p = 0.0002). We conclude that anti-intercellular adhesion molecule antibody added to the pulmonary flush and initial reperfusate results in a dose-dependent enhancement of the reperfused lung's ability to oxygenate blood, possibly as a result of decreased leukocyte sequestration.

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.

Pulmonary function after non-heart-beating lung donation in a survival model.

BACKGROUND: Lung procurement from recently deceased cadavers has been suggested to enlarge the limited donor pool. We hypothesized that lungs harvested from non-heart-beating donors (NHBD) would function as well as those harvested from heart-beating donors. METHODS: Sixteen adult swine underwent left lung allotransplantation. Controls received lungs procured from heart-beating donors, NHBD pigs received lungs immediately harvested from donors after death from asphyxiation, and NHBD-15 and NHBD-30 pigs received lungs harvested after 15 and 30 minutes after asphyxiation. RESULTS: After 1 week of survival, mean dynamic airway compliance (mL/cm H2O +/- standard error of the mean) was 16.3 +/- 0.7 in controls, and 17.3 +/- 1.0, 16.4 +/- 6.0, and 7.3 +/- 1.6 in the NHBD, NHBD-15, and NHBD-30 groups, respectively (p = 0.02, NHBD-30 versus others combined). No significant differences were noted in the pulmonary venous partial pressure of oxygen or pulmonary vascular hemodynamics compared with controls. CONCLUSIONS: The decrease in airway compliance noted in the NHBD-30 group may reflect an exacerbation of reperfusion injury caused by 30 minutes of warm ischemia during organ retrieval. We conclude that posttransplantation lung function using an NHBD with up to 15 minutes of warm ischemia is equivalent to lung function after heart-beating harvest.