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J Thorac Cardiovasc Surg 1999;118:107-114
© 1999 Mosby, Inc.
CARDIOTHORACIC TRANSPLANTATION |
From the University of Rome "La Sapienza," Departments of Thoracic Surgerya and Anesthesia,b Rome, Italy.
Read at the Twenty-fourth Annual Meeting of The Western Thoracic Surgical Association, Whistler, British Columbia, June 24-27, 1998.
Address for reprints: Federico Venuta, MD, Cattedra di Chirurgia Toracica, Policlinico Umberto I, University of Rome "La Sapienza," V. le del Policlinico, 00100 Rome, Italy (E-mail: Fevenuta{at}tin.it).
| Abstract |
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| Introduction |
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We evaluated the role of retrograde pulmonary artery flushing in addition to antegrade pneumoplegia in clinical lung transplantation.
| Patients and methods |
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Data were collected and managed with the aid of a commercial spreadsheet software package (Microsoft Excel 97, version 6.0, Redmond, Wash). All data were expressed as mean ± standard deviation of the mean. The data of the 2 groups were compared with the analysis of variance for repeated measures. Statistical analysis was performed with the GLM procedure of the SAS package (version 6; SAS Institute Inc, Cary, NC).
| Results |
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| Discussion |
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The pulmonary venous circulation is a low resistancehigh capacity network; pneumoplegic solution administered through this route is straightforward and results in a rapid and uniform distribution of the solution.
14 Experimental studies have demonstrated that retrograde pneumoplegia can reach vascular segments that are not flushed by the forward route.
15 Also, less well ventilated areas, such as the posterior segments of the lower lobes, are better flushed.
14,16 Small clots can be removed by the back flow, and even if they remain in place the distal vascular bed can be reached by the retrograde perfusate.
Retrograde pneumoplegia also has the advantage of flushing the bronchial circulation through the bronchopulmonary anastomoses, enhancing airway protection
17; experimental lung transplantation has shown that retrograde flushing improves flow of the perfusate to the trachea and bronchi, whereas antegrade delivery improves flow to the lung parenchyma.
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Many indices have been used to test lung function after transplantation; gas exchange is generally considered a reliable indicator,
18 because early damage may impair the lung exchange capacity without any morphologic alteration.
19 We have shown a significant decrease of the intrapulmonary shunt fraction, alveolar-arterial oxygen gradient, mean airway pressure, and reimplantation response. The extubation time, ICU stay, ratio of arterial oxygen to inspired oxygen fraction, and extravascular lung water index improved in group II, even if the difference was not statistically significant. However, a few points deserve further comments: we expected that the improvement in chest x-ray score, indexed alveolar-arterial PO2 gradient, intrapulmonary shunt fraction, and mean airway pressure would be paralleled by a significant decrease of pulmonary artery pressure, pulmonary vascular resistance, and extravascular lung water. The improved viability of the pulmonary circulation achieved with the retrograde flush should have resulted in a lower pulmonary artery pressure and pulmonary vascular resistance; however, the vasodilating drugs (nitric oxide, alprostadil) routinely administered immediately after reperfusion probably helped to eliminate any possible difference between the 2 groups. Also, the differences in terms of extravascular lung water, which were evident during the operation, were already reduced to nonsignificant levels after a few hours; however, the histologic studies of lung biopsy specimens taken before closing the chest confirmed a mild difference in alveolar edema between the 2 groups. These clinical findings confirm the experimental work published by other authors
20: in well-functioning lungs, the edema related to preservation progressively resolves during the first hours after reperfusion and no irreversible damage results. In DLT we may postulate that, along with the increased viability of the pulmonary vessels, retrograde flushing may have contributed to improved preservation of the second lung, which has prolonged ischemic time. This aspect of lung preservation should be further investigated by administering retrograde pneumoplegia at the time of harvesting. For this reason, we now administer retrograde pneumoplegia immediately after antegrade flushing at the time of lung extraction. An additional advantage of this technique is that any possible emboli in the lung vasculature during antegrade pneumoplegia
6 can be immediately washed out with the retrograde flushing.
Also, it is impossible to establish whether the differences between our 2 groups were simply related to the fact that the lungs in group II were flushed twice (in this case the possible role of a second antegrade flush should be investigated) or to the higher volume of total flushing solution delivered (5.5-6 L in group II vs 3.5-4 L in group I).
The small number of patients enrolled in our study does not allow us to draw definitive conclusions; however, along with the improvement in early lung function, substantiated by a better intrapulmonary shunt fraction, decreased alveolar-arterial oxygen difference, and reduced reperfusion edema at chest radiograph, we have observed blood and clots in the retrograde perfusate of all lung blocks and macroscopic fat emboli in the grafts harvested from donors with multiple bone fractures. However, we cannot postulate what their impact might have been without retrograde flushing.
Retrograde pneumoplegia is not detrimental and seems to improve early graft function. However, the specific role of this technique of preservation should be investigated by further experimental and clinical investigation.
| Appendix: Discussion |
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You remember, of course, that the first lung transplants were combined
with the heart as heart-lung transplants, and at Stanford in 1981 and 1982,
since we were so unsure about the safety of our preservation methods, the
donor was brought into the adjacent operating room to minimize the ischemic
time. You can imagine the difficulties this imposed, especially with the transport
of bodies across state and even international borders. Clearly that was not
going to be supportable in the long term. We then determined that the so-called
modified Euro-Collins solution was a satisfactory solution to be used to flush
the lungs and to get it cold without inducing injury. That was used in our
first clinical case in November 1982. That patient, incidentally, is still
alive, 16
years after the transplant, and is the longest surviving
recipient of a lung transplant. When we used this solution in monkeys, we
found that preservation of the lungs for 24 hours was tolerated. Although
I am sure other solutions might equally well be used and perhaps be even better,
it did not seem fruitful to pursue endlessly various minor variations of chemical
composition. I believed then, and I still believe, that the essential factor
is to get the lungs cold and keep them so until revascularization. In any
event, our group has continued to use the same solution for the past 16 years,
and we have now exceeded 8 hours of ischemia clinically without apparent injury.
Your paper explores a different topic, a different route of administration with the same solution. I think it is a useful contribution. The major point is the ability to flush out particulate material and clot, which in the donors is probably common. This will enhance preservation and also will improve reperfusion after implantation.
I have a number of questions. First, we found in the laboratory many years ago that the use of alprostadil was not helpful, and was possibly harmful, and we abandoned this 15 years ago. Are you sure that it is necessary?
Dr Venuta. A number of papers have been published in the international literature either in favor of or against the use of alprostadil. We have used alprostadil since our first lung transplant 7 years ago, and we have never had any problem. We believe that alprostadil should be used not only because its vasodilating activity compensates the action of the high potassium concentration in the preservation solution, but also because it has other features that can help to improve early lung function and prevent primary graft failure. In fact, we do not use alprostadil only at the time of harvesting; it is part of our routine protocol and is infused for at least 48 hours after the transplant. However, I am aware of the work that you published several years ago. I think the role of alprostadil should be further investigated, especially when retrograde pneumoplegia is used.
Dr Jamieson. I am always concerned about the term pneumoplegia, because, unlike in cardioplegia, the lung is not strictly paralyzed. Did you give the retrograde solution immediately after the antegrade flush solution in the donor operating room? I thought you said that you retrogradely flushed the solution when you brought the lungs to the recipient operating room.
Dr Venuta. You understood correctly; retrograde flushing was administered through the pulmonary veins (each vein separately) when the double lung block arrived at our institution.
Dr Jamieson. I would imagine that it would be most constructive to do it while the donor organs are being harvested, particularly if you wanted to fully revascularize and cool various areas of the lung that had been blocked by particulate debris. One other problem, of course, is that the 2 groups are not strictly compatible because, in effect, you gave your second group a second dose of flush solution, albeit backward.
Dr Venuta. I agree with you; it will certainly be more effective to give both antegrade and retrograde flushing in the donor operating room, during harvesting, before taking the lungs out, or at the back table.
Dr Jamieson. I very firmly believe that maintenance of a low inspired oxygen fraction and maintenance of a high hematocrit value are keys to success in the early management of a lung transplant recipient. These are probably some of the most important factors in the assessment of your chest x-ray score. How carefully were you able to compensate for that in both your groups?
Dr Venuta. Fluid restriction is one of the key factors for success in lung transplantation. All patients of this study did well, and we did not observe any primary graft failure or other major problems. Fluid balance was carefully monitored; extravascular lung water was assessed by the COLD system during the operation and after the procedure, in the ICU. All patients were kept extremely dry, allowing a satisfactory hemodynamic performance. Extravascular lung water was higher immediately after reimplantation in the group not receiving retrograde flushing; however, 6 to 8 hours later, in the ICU, extravascular lung water started to decrease, and the differences between the 2 groups were kept at levels that were not statistically significant.
Dr Jamieson. I would like to congratulate you on your paper. You have made a useful contribution that I believe will become a routine measure.
Dr Vaughn A. Starnes (Los Angeles, Calif). I have two questions. First, a high proportion of your patients had cystic fibrosis. Was cardiopulmonary bypass used in all or some of them? How did you do the actual implant? Use or nonuse of bypass would make a difference, and if the techniques differed, there needs to be a variable control for it.
Dr Venuta. We never had to use cardiopulmonary bypass. At our institution bypass is not used electively. It is used only when required to maintain hemodynamic stability and oxygenation.
Dr Starnes. One of the issues that you discussed is that the first lung receives all the cardiac output. In the case of reimplantation, that predisposes it to pulmonary edema. Did you see that in either of your groups? I think the first chest x-ray film that you showed was more indicative of an implantation response.
Dr Venuta. There was a great difference in terms of reimplantation response on the chest x-ray film between group I and II patients. There was, as usual, a more important reimplantation response in the lung transplanted first, probably because it receives all the cardiac output during reimplantation of the second lung. Differences in terms of edema between the 2 groups were confirmed histologically, with biopsy specimens taken from the first reimplanted lung.
Dr Starnes. I have one other comment. Patients with cystic fibrosis come to the operating room in differing conditions. Some are in stable condition, and some have indulin infections. It is not until you start mobilizing the lungs that you observe the endotoxemic effect indicating whether ongoing infection is present. Did you see that in any of your patients? Did some of your patients have to have vasoconstrictors to support their systemic blood pressure during the operation, and was that controlled for?
Dr Venuta. Patients with cystic fibrosis may show different clinical parameters at the time of transplantation. One of our patients arrived already intubated and ventilated in the operating room. Our policy is to perform a careful toilette of the airway with the fiberoptic bronchoscope before starting the operation. We were able to aspirate 200 to 300 mL of dense secretions from the bronchial tree. Most of our patients required extended inotropic support during transplantation to avoid cardiopulmonary bypass. Transesophageal echocardiography was extremely useful to evaluate the morphology and contractility of the right and left sides of the heart during the procedure.
Dr Starnes. In no way do I want to de-emphasize the importance of the paper, because it makes a valuable point. You have treated a very difficult group of patients in whom there would be many factors to control for. It is probably difficult to control for all those in the cystic fibrosis population.
In our living donor series, when those lobes are flushed, there are frequently regions that do not perfuse well. They can be identified simply because they do not lose their color, and continuing the perfusion does not change that. If you then give retrograde pneumoplegia, most of those regions will be perfused, which implies that there may be some advantage in distribution of pneumoplegia with this technique. We have continued to do that.
| Acknowledgments |
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| References |
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