A new model for assessment of lung preservation

Ventilation strategy and its influence on the functional performance of lung grafts in an experimental model of single lung transplantation using non-heart-beating donors

OBJECTIVE

To compare the influence of two different ventilation strategies-volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV)-on the functional performance of lung grafts in a canine model of unilateral left lung transplantation using donor lungs harvested after three hours of normothermic cardiocirculatory arrest under mechanical ventilation.

METHODS

The study comprised 40 mongrel dogs, randomized into two groups: VCV and PCV. Of the 20 recipients, 5 did not survive the transplant, and 5 died before the end of the post-transplant assessment period. The remaining 10 survivors (5 in each group) were evaluated for 360 min after lung transplantation. The functional performance of the grafts was evaluated regarding respiratory mechanics, gas exchange, and lung graft histology.

RESULTS

There were no significant differences between the groups regarding respiratory mechanics (peak inspiratory pressure, plateau pressure, mean airway pressure, dynamic compliance, and static compliance) or gas exchange variables (PaO2, venous oxygen tension, PaCO2, venous carbon dioxide tension, and the arterial-venous oxygen content difference). The histopathological findings were consistent with nonspecific acute lung injury and did not differ between the groups.

CONCLUSIONS

This model of lung transplantation showed that the functional performance of lung grafts was not influenced by the ventilation strategy employed during the first six hours after reperfusion.

Glutathione improves the function of porcine pulmonary grafts stored for twenty-four hours in low-potassium dextran solution

BACKGROUND

Flush perfusion with low-potassium dextran is the standard strategy in clinical lung preservation. Despite improved outcome, endothelial cell injury and surfactant dysfunction remain a significant problem after lung transplantation. The radical scavenger glutathione has been shown to be responsible for the efficacy of Celsior solution in lung preservation. We tested the hypothesis that the addition of glutathione to low-potassium dextran might further improve graft function by ameliorating ischemia-reperfusion injury.

METHODS

In 12 domestic pigs, lungs were flush preserved with either low-potassium dextran (n = 6) or low-potassium dextran supplemented by 5 mmol glutathione (n = 6). Left single lung transplantation was performed after 24-hour storage in low-potassium dextran at 8 degrees C. After 15 minutes of reperfusion the right main bronchus and pulmonary artery were crossclamped. Hemodynamic and respiratory measures were recorded in 30-minute intervals for a total observation period of 7 hours. Bronchoalveolar lavage fluid was obtained from the native lung and 2 hours after reperfusion from the graft. Bronchoalveolar lavage fluid and surfactant composition, and surfactant function analyses were performed. Neutrophil sequestration was assessed by myeloperoxidase activity assay. Tissue water content was calculated from wet/dry weight ratios at the end of the experiment.

RESULTS

In the low-potassium dextran group, 2 animals died during reperfusion. After reperfusion, pulmonary vascular resistance (P = .01) and pulmonary artery pressure remained lower in the glutathione/low-potassium dextran group, which was associated with a higher cardiac output (P = .05) in this group. Also, the oxygenation index at the end of the observation period was higher in the glutathione/low-potassium dextran group compared with the low-potassium dextran group (430 +/- 130 vs 338 +/- 184, respectively; P < .05). The graft water content representing postreperfusion lung edema was not different between the 2 study groups. Alteration of surfactant was less in the glutathione/low-potassium dextran group with a significantly decreased small to large aggregate ratio (P = .03) versus low-potassium dextran group. Myeloperoxidase activity was twice as high in the low-potassium dextran group when compared with the glutathione/low-potassium dextran group (glutathione/low-potassium dextran: 134 +/- 110 mU/g vs low-potassium dextran: 274 +/- 168 mU/g, P = .07).

CONCLUSION

The addition of glutathione to low-potassium dextran preservation solution reveals beneficial effects on vascular function and surfactant composition in transplanted lungs. Therefore, glutathione ameliorates ischemia-reperfusion injury in a preclinical model of lung transplantation. Future studies are needed to evaluate this promising modification in clinical lung transplantation.

Raffinose improves the function of rat pulmonary grafts stored for twenty-four hours in low-potassium dextran solution

OBJECTIVES

The perfect strategy for pulmonary graft preservation remains elusive. Experimental work supports the use of perfusates, such as Euro-Collins, University of Wisconsin, and low-potassium dextran solutions. We use low-potassium dextran solution in our clinical program, but we aim for continued improvement. The trisaccharide raffinose has been shown to be responsible for the efficacy of University of Wisconsin perfusate in lung preservation. Raffinose is superior to a variety of other saccharides for this purpose. We tested the hypothesis that the addition of raffinose to low-potassium dextran solution might further improve graft function.

METHODS

In a randomized blinded study with a rat left lung transplant model, donor lungs were flushed with either standard low-potassium dextran solution or low-potassium dextran solution modified by the addition of 30 mmol/L raffinose (n = 5 for each group). Alprostadil (prostaglandin E(1), 500 microg/L) was added to the perfusates in accordance with our clinical practice. Grafts were stored inflated at 4 degrees C for 24 hours. After transplantation, recipients were ventilated with a fraction of inspired oxygen of 1 and a positive end-expiratory pressure of 2 cm H(2)O. Graft function was evaluated by measuring oxygenation at 2 hours after graft reperfusion, peak airway pressure throughout the reperfusion period, and the wet/dry lung weight ratio.

RESULTS

The group receiving low-potassium dextran solution with raffinose demonstrated significantly higher oxygenation (oxygen tension, 370 +/- 45 mm Hg vs 150 +/- 64 mm Hg; P =.0025), lower peak airway pressures at 2 hours after lung reperfusion (11 +/- 2.7 mm Hg vs 16 +/- 2.4 mm Hg; P <.001), and a lower wet/dry weight ratio (4.7 +/- 1.26 vs 11 +/- 5. 0; P =.017).

CONCLUSION

Modification of low-potassium dextran solution with the trisaccharide raffinose resulted in a significant improvement in graft function in this model and merits further evaluation with respect to the mechanisms involved.

Perfusão pulmonar anterógrada "versus" retrógrada na preservação pulmonar para transplante em modelo canino de viabilidade pulmonar pós-morte

A doação pulmonar após parada cardiocirculatória tem sido estudada experimentalmente na obtenção de órgãos para transplante, porém a severa lesão isquêmica/reperfusão exigem métodos de preservação que permitam viabilidade pulmonar. A perfusão do enxerto com solução cristalóide hipotérmica via anterógrada (artéria pulmonar) é o método de preservação mais utilizado, porém esta via não perfunde a circulação brônquica, permitindo a retenção sanguínea neste território capaz de desencadear fenômenos de lesão de reperfusão. Isto nos levou a testar os efeitos da perfusão anterógrada versus retrógrada (via átrio esquerdo, capaz de perfundir a circulação brônquica) em modelo canino de transplante unilateral cujos pulmões foram extraídos 3 horas após parada cardiorrespiratória. Doze cães doadores foram sacrificados com tiopental sódico e mantidos à temperatura ambiente sob ventilação mecânica durante 3 horas, após as quais os animais foram randomizados e os blocos cardiopulmonares perfundidos via retrógrada (n = 6) ou anterógrada (n = 6) com solução de Euro-Collins modificada e extraídos. Os receptores (n = 12) foram anestesiados, pneumonectomizados e submetidos a transplante pulmonar esquerdo recebendo enxertos perfundidos por via retrógrada (grupo I) ou anterógrada (grupo II). Após a reperfusão do enxerto, os animais foram mantidos sob ventilação mecânica (FiO2 = 1) por 6 horas, sendo então sacrificados. Durante este período obtiveram-se medidas hemodinâmicas e gasometrias arteriais, além de amostras de tecido pulmonar para dosagem de ATP intracelular. As medidas hemodinâmicas não diferiram entre os grupos. Nos animais do grupo I a PaO2 e PaCO2 foram superiores às do grupo II (p = 0,016 e p = 0,008, respectivamente). O ATP intracelular não diferiu entre os grupos, embora tenha se reduzido nas amostras obtidas na extração do enxerto do doador quando comparados aos valores após a reperfusão (p = 0,01) e ao término do período de avaliação (p = 0,01). Os autores concluem que, neste modelo experimental, a perfusão retrógrada hipotérmica resulta em função superior do enxerto após 3 horas de isquemia normotérmica sob ventilação mecânica.

Effect of complement inhibition with soluble complement receptor 1 on pig allotransplant lung function

BACKGROUND

Lung dysfunction after transplantation continues to be a significant clinical problem. Soluble complement receptor 1 (sCR1) is a potent inhibitor of complement activation. We evaluated the inhibitory effect of sCR1 on complement activation and reperfusion injury in pig lung allografts.

METHODS

In a randomized and blinded study, left lung transplantation was performed in 13 pigs. Donor lungs were flushed and then stored for 30 hr at 4 degrees C. Control pigs (n=7) received saline, and the treatment group (n=6) received 15 mg/kg sCR1 1 hr before reperfusion. One hour after reperfusion, the right pulmonary artery was clamped for 10 min to assess the function of the transplanted lung. Pulmonary function was assessed again on day 3.

RESULTS

Complement inhibition was 93% in the sCR1 group and returned to baseline (8% inhibition) after 3 days. There was a trend toward a higher partial pressure of oxygen at 1 hr in the sCR1 group compared with the control group (mean +/- SE: 408+/-42 mmHg vs. 288+/-69 mmHg, P = 0.19). Alveolar ventilation was better in the sCR1 group than in the control group (P = 0.01) at 1 hr. Mixed venous saturation was significantly lower in the control group at both 1 hr (P = 0.02) and 3 days (P = 0.001). The wet/dry weight of the lung tissue was lower in the sCR1 group compared with the control group on day 3 (P < 0.05). Chemiluminescence, an index of phagocyte priming, was lower in the sCR1 group when cells were stimulated with complement opsonized zymosan but not when stimulated with zymosan or phorbol myristate acetate.

CONCLUSION

sCR1 improves ventilation, reduces pulmonary edema, and may be beneficial in improving posttransplant lung oxygenation.

Plasma thromboxane B2 concentrations and pulmonary vascular resistance during lung reperfusion

The purpose of this study was to measure the behavior of plasmatic thromboxane B2 (pITxB2) after reperfusion of a glucose-insulin-potassium preserved lung. Seven adult mongrel dogs underwent a left lung allotransplantation. Hemodynamic changes including pulmonary artery pressure and cardiac output were measured. Pulmonary artery vascular resistance, systemic resistance, arterio-venous oxygen difference, and shunt were calculated. Immunoreactive arterial and venous plasma thromboxane B2 concentrations were measured at 0 (basal), 60, 120, and 180 min after reperfusion. Hemodynamic measurements were made after 5 min of occlusion of the right pulmonary artery and ventilation with 100% oxygen. Prepreservation, pre-reperfusion, and posttransplant lung weights were obtained. All animals survived the procedure. Ischemic time was 14.72 (+/-0.31) h. Cardiac output, systemic arterial pressure, and arterio-venous oxygen difference decreased while systemic vascular resistance, pulmonary vascular resistance, and shunt increased during the study. Mean pulmonary artery pressure correlated with pulmonary vascular resistance (p < .01). Oxygen tension diminished significantly at 180 min after reperfusion. Mean basal pulmonary arterial TxB2 was 3589 (+/-424) pg/ml; mean plasma pulmonary venous TxB2 was 6578 (+/-1571) pg/ml. Pulmonary arterial to venous TxB2 ratio (a/vTxB2) increased from 0.70 at basal measurement to 0.83 at 60 min, and 0.99 at 120 and 180 min after reperfusion (p < .05). Pulmonary arterial TxB2 had a positive correlation with mean pulmonary artery pressure (p < .05); also, a/v pITxB2 correlated with pulmonary vascular resistance (r = .616, p < .01). Mean post-reperfusion lung weight increase was 74.88% (45.37 g). In conclusion, pITxB2 a/v ratio ratio increases after reperfusion of a 14-h preserved lung; pulmonary vascular resistance significantly increases after 180 min of reperfusion and correlates with the increase in pITxB2 a/v ratio.

Lasting beneficial effect of short-term inhaled nitric oxide on graft function after lung transplantation. Paris-Sud University Lung Transplantation Group

The combination of ischemia and reperfusion after lung transplantation is characterized by endothelial damage, neutrophil sequestration, and decreased release of endothelial nitric oxide. Because nitric oxide has been shown to selectively dilate the pulmonary vasculature, abrogate neutrophil adherence, and restore endothelial dysfunction, we hypothesized that inhaled nitric oxide given for 4 hours during initial reperfusion might attenuate reperfusion injury in a porcine model of left single-lung transplantation. We tested hemodynamic and gas exchange data, lung neutrophil sequestration, and pulmonary artery endothelial dysfunction after 4 and 24 hours of reperfusion in 12 pigs randomly assigned to nitric oxide and control groups. Harvested lungs were preserved in normal saline solution for 24 hours at 4 degrees C. During transplantation, inflatable cuffs were placed around each pulmonary artery to allow separate evaluation of each lung by occluding flow. Compared with the transplanted lungs in the control group, transplanted lungs in pigs treated with inhaled nitric oxide significantly improved gas exchange, pulmonary vascular resistance, shunt fraction, and oxygen delivery at 4 and 24 hours after reperfusion. Neutrophil sequestration, as measured by the neutrophil-specific enzyme myeloperoxidase and the alveolar leukocyte count per light microscopic field, was significantly lower at 24 hours after reperfusion in the transplanted lungs of the nitric oxide group. The nitric oxide-treated native right lungs exhibited significantly reduced increase in neutrophil accumulation compared with that in control native right lungs. After 24 hours of reperfusion, endothelium-dependent relaxation to acetylcholine was similarly and severely altered in both groups. We conclude that short-term inhaled nitric oxide given during the first 4 hours of reperfusion after lung transplantation significantly attenuates reperfusion injury, improving graft function as long as 24 hours after operation. This effect is probably mediated by a decrease in neutrophil sequestration. A protective effect on the contralateral lung was also observed. Inhaled nitric oxide may be a suitable agent when an acute reperfusion phenomenon is anticipated.

Effects of portal venous inoculation with donor splenocytes on lung allograft survival in dogs

The effects of portal venous inoculation with donor splenocytes on lung allograft survival were evaluated in dogs. Within the dose range examined, portal venous inoculation with donor splenocytes alone did not affect the graft survival time. Although the mean graft survival time was prolonged by FK 506 treatment for 14 days, the transplanted lungs were rejected within 12 days after termination of FK 506 administration. However, when the recipients were given portal venous inoculation with donor splenocytes at the time of transplantation, the graft survival time after termination of FK 506 administration was significantly prolongated. In the recipients that received combined therapy of portal venous inoculation with donor splenocytes and FK 506 treatment, arterial oxygen tension and histologic architecture of the transplanted lungs remained within the normal range for a longer period than these measures did in control animals that received FK 506 treatment alone. Dose-response experiments revealed that 1 x 10(8) cells/recipient was most effective in causing prolonged graft survival after termination of FK 506 treatment. On the basis of these results, perioperative portal venous inoculation with donor splenocytes can enhance the immunosuppressive effect of FK 506 in the canine lung transplantation model.

Hyperinflation of canine lung allografts during storage increases reperfusion pulmonary edema

The optimal state of inflation for lung allografts during preservation is not known. We previously showed that hyperinflation of canine lung allografts during storage improved posttransplant graft function as measured during 10 minutes of contralateral pulmonary artery occlusion. However, we have also shown that hyperinflation during storage increases pulmonary capillary permeability. It is possible that short-term total cardiac perfusion through the transplanted left lung (for assessment) may not adequately reproduce the clinical situation. The purpose of this study was to assess the effects of hyperinflation during storage in a canine left single-lung transplantation model in which all perfusion was continuously directed to the graft after implantation. Twenty canine left single-lung transplants were done. The lungs of donor animals were ventilated at a tidal volume of 750 ml and an inspired oxygen fraction of 100%. Donor lungs were flushed with modified Euro-Collins solution and the trachea occluded at end inspiration. For donors in groups I and III, the trachea was sealed at that postinflation volume. In groups II and IV, 200 cc of air was withdrawn from the endotracheal tube under positive pressure and the trachea sealed at the lower tidal volume. Lungs were then extracted and stored at 1 degree C for 12 hours. After the preservation period, left lung transplants were performed. After implantation in all groups, the right pulmonary artery was ligated. In groups I and II, the right bronchus was ligated and in groups III and IV the right bronchus was kept open. Subsequent allograft gas exchange and hemodynamics were assessed during a 6-hour period of reperfusion. After assessment, both lungs were excised, wet/dry lung weight ratio was calculated, and histologic examination was done. During the 6-hour assessment, lungs stored in a state of hyperinflation (groups I and III) showed rapid deterioration of gas exchange. At the final assessment, arterial oxygen tension and alveolar-arterial oxygen gradient of groups I and III were significantly worse than those of groups II and IV (group I versus group II: arterial oxygen tension 87.5 +/- 15.0 versus 373.8 +/- 65.5 mm Hg, alveolar-arterial oxygen gradient 564.4 +/- 13.2 versus 298.6 +/- 69.3 mm Hg, p < 0.05; group III versus group IV: arterial oxygen tension 245.4 +/- 33.0 versus 543.6 +/- 41.8 mm Hg, alveolar-arterial oxygen gradient 392.5 +/- 35.6 versus 120.5 +/- 34.7 mm Hg, p < 0.01). We conclude that donor lung hyperinflation during storage does not provide better posttransplant allograft function when perfusion is limited only to the allograft.

Lung transplantation with cardiopulmonary bypass exaggerates pulmonary vasomotor dysfunction in the transplanted lung

Pulmonary vascular resistance is significantly increased in the transplanted lung. If cardiopulmonary bypass is required, the transplanted lung is reperfused with activated blood elements, which might exacerbate the reperfusion injury. The purpose of this study was to examine the influence of cardiopulmonary bypass on the following mechanisms of pulmonary vasomotor control in a dog model of autologous lung transplantation: (1) endothelium-dependent cyclic guanosine monophosphate-mediated relaxation (response to acetylcholine), (2) endothelium-independent cyclic guanosine monophosphate-mediated relaxation (response to nitroprusside), and (3) beta-adrenergic cyclic adenosine monophosphate-mediated relaxation (response to isoproterenol). Autologous right lung transplants were performed with (n = 4 dogs) and without (n = 5 dogs) bypass. Lungs were stored in cold saline solution (4 degrees C, 3 hours) before reimplantation. Pulmonary vasomotor control mechanisms were studied in isolated pulmonary arterial rings immediately after harvest and 1 hour after reimplantation. Ten rings were studied in each group at each time. Statistical analysis was by analysis of variance. Without bypass, endothelium-dependent cyclic guanosine monophosphate-mediated relaxation and beta-adrenergic cyclic adenosine monophosphate-mediated relaxation were significantly impaired, although endothelium-independent cyclic guanosine monophosphate-mediated relaxation was not. Use of bypass produced significantly greater impairment of both endothelium-dependent cyclic guanosine monophosphate-mediated relaxation and beta-adrenergic cyclic adenosine monophosphate-mediated relaxation. In addition, use of bypass produced significant dysfunction of endothelium-independent cyclic guanosine monophosphate-mediated relaxation as well. We conclude that using cardiopulmonary bypass to perform lung transplantation greatly exaggerates pulmonary vasomotor dysfunction in the transplanted lung. This dysfunction may contribute to significantly higher pulmonary vascular resistance in the transplanted lung if cardiopulmonary bypass is used.

[Lung transplantation at the Barnes Hospital in 1992]

Lung transplantation is a constantly changing form of therapy. The St. Louis Work Group is known for its contributions in the area of single lung transplant, with two highly active programs running at present, one for adults and one for children. The Group is also active in research, in the development of various methods for lung preservation, and in medium-and long-term studies. Finally, this team writes and updates the International Register of Lung Transplants, which brings together the vast majority of operations of this type done worldwide. The Register permits control of results of lung transplant operations as well as the assessment of future alternatives.

Lung preservation with low-potassium dextran flush in a primate bilateral transplant model

We used a bilateral lung transplant model to confirm, in primates, the results of lung preservation studies previously obtained in a canine single-lung transplant model. The donor lungs were flushed with low-potassium dextran solution and maintained semiinflated with 100% oxygen at 10 degrees C for a planned ischemic time of 12 hours for the lung implanted first. Of eight experiments performed, results in the 6 operative survivors form the basis of this report. After bilateral lung transplantation, animals were maintained on a ventilator for 6 hours; arterial oxygen tension, pulmonary artery pressure, and pulmonary vascular resistance were determined in the recipients at 2, 4, and 6 hours after transplantation and compared with donor values, which served as controls. Arterial oxygen tension in the recipients did not differ from the controls (p = not significant), whereas the pulmonary artery pressure and pulmonary vascular resistance showed significant elevation (p < 0.05 versus control values). After the 6 hours of assessment, the animals were extubated and 3 survived for 48 to 72 hours with a mean arterial oxygen tension of 69 mm Hg on room air. These results demonstrate excellent lung function after a minimum of 12 hours of preservation in a primate model in which the animal is totally dependent on the function of transplanted lung tissue, and confirm the potential for prolonged clinical lung preservation.

Lung preservation: a review of current practice and future directions

During the past 10 years, pulmonary transplantation has emerged as a successful mode of surgical therapy for suitable patients with end-stage lung disease. Current preservation techniques of donor lungs for subsequent transplantation include core-cooling and single flush perfusion. The relative merits of these are described. These methods are essentially restricted to 6 hours of ischemia. Research in lung preservation is aimed not only at extending the safe period of ischemia but also at improving the quality of preservation. Areas of interest include the ideal composition of the perfusate, relevant pharmacologic additives, and the best conditions for preservation and harvesting. Advantages and disadvantages of the various animal models are listed in addition to the methods used in assessing the quality of preservation. There have been major advances in experimental lung preservation during the past 10 years, and we are possibly on the threshold of incorporating some of these into clinical practice. Among the most important are the adoption of colloid-based perfusates, the more widespread use of free radical scavengers, and the use of leukocyte depletion.

Lung transplantation

The supply of donor organs remains extremely limited, and improved methods of maintaining the lungs of potential donors to allow for transplantation must be developed. Currently the upper limit of donor lung ischemic even with our "best" preservation techniques is approximately 4 to 6 hours. Improved methods for preservation will increase the supply of suitable lungs and will considerably simplify the logistics of transplantation just as has occurred with liver transplantation. Efficient use of donor organs remains of paramount importance. We recently performed two single-lung transplants utilizing lungs from one donor. Likewise, there is no reason why a lung could not be sent to another center for transplantation if the harvesting group uses only one lung. Sufficient progress has been achieved to date to warrant continued application of lung transplantation for end-stage pulmonary disease. With increasing experience, one can anticipate refinement of techniques and broader application of these procedures. Single lung transplantation, initially restricted to patients with end-stage pulmonary fibrosis, has now been successfully applied to patients with emphysema, pulmonary hypertension, and other conditions. Although transplantation currently can offer real benefit only to a limited number of persons, it serves to create hope for many others. An additional benefit may prove to be the interest and attention that transplantation focuses on patients with end-stage lung disease and on the pathophysiology of chronic respiratory failure. Knowledge gained may ultimately result in the prevention of many of the disorders for which lung transplantation currently offers the only hope.