Retrograde Flush Following Warm Ischemia in the Non-Heart-Beating Donor Results in Superior Graft Performance at Reperfusion

Lung preservation: from perfusion to temperature

PURPOSE OF REVIEW

This article will review the evidence behind elements of the lung preservation process that have remained relatively stable over the past decade as well as summarize recent developments in ex-vivo lung perfusion and new research challenging the standard temperature for static cold storage.

RECENT FINDINGS

Ex-vivo lung perfusion is becoming an increasingly well established means to facilitate greater travel distance and allow for continued reassessment of marginal donor lungs. Preliminary reports of the use of normothermic regional perfusion to allow utilization of lungs after DCD recovery exist, but further research is needed to determine its ability to improve upon the current method of DCD lung recovery. Also, research from the University of Toronto is re-assessing the optimal temperature for static cold storage; pilot studies suggest it is a feasible means to allow for storage of lungs overnight to allow for daytime transplantation, but ongoing research is awaited to determine if outcomes are superior to traditional static cold storage.

SUMMARY

It is crucial to understand the fundamental principles of organ preservation to ensure optimal lung function posttransplant. Recent advances in the past several years have the potential to challenge standards of the past decade and reshape how lung transplantation is performed.

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.

Warm retrograde perfusion can remove more fat from lung grafts with fat embolism in a porcine model

OBJECTIVE

In lung transplantation, unexpected pulmonary emboli, including thrombi and fat, have been observed with high probability and are associated with potential primary graft dysfunction. We evaluated a new perfusion method using warm retrograde flushing that removes more fat than conventional cold retrograde flushing.

METHODS

We developed a novel porcine donor model for pulmonary fat embolism by administering autologous fat in the left pulmonary artery. The left pulmonary artery and the left superior and inferior pulmonary veins were cannulated for flushing and collecting these solutions. After flushing, the left lung was reperfused under observation for 3 h. Two groups underwent warm and cold additional retrograde flush (WS; warm solution group, CS; cold solution group).

RESULTS

The fat removal rate in the antegrade flush was equal in both groups (3.0 ± 0.6% vs 3.0 ± 0.4%, p = 0.46); however, the rate was significantly greater in the WS group in retrograde flush (25.2 ± 3.2% vs 8.0 ± 1.4%, p = 0.01). Histology with Oil Red O staining and its software analysis showed more residual fat in the CS group (0.12 ± 0.01% vs 0.38 ± 0.07%, p = 0.01). There was no significant difference in the pulmonary function and hemodynamics during the 3-h period after reperfusion.

CONCLUSION

Warm retrograde perfusion can remove more fat from lung grafts with fat embolism in a porcine donor model.

Lungs exposed to 1 hour warm ischemia without heparin before harvesting might be suitable candidates for transplantation

Background

The limiting factor for lung transplantation is the lack of donor organs. The usage of lungs from donation after cardiac death (DCD) would dramatically increase donor availability. In the present paper we wanted to investigate lungs exposed to 1 h of warm ischemia without heparin followed by flush-perfusion and cold storage compared to lungs harvested from heart beating donors (HBD) using standard harvesting technique.

Methods

Twelve Swedish domestic pigs were randomized into two groups. Six pigs (DCD group) underwent ventricular fibrillation and were then left untouched for 1 h after declaration of death. They did not receive heparin. The lungs were then harvested and flush-perfused with Perfadex® solution and the organs were stored at 8 °C for 4 h. Six pigs (HBD group) received heparin and the lungs were harvested and flush-perfused with Perfadex® solution and the organs were stored at 8 °C for 4 h. Lung function was evaluated, using ex vivo lung perfusion (EVLP), with blood gases at different oxygen levels, pulmonary vascular resistance (PVR), lung weight, and macroscopic appearance.

Results

At FiO₂ 1.0, the PaO₂ in the DCD group was 51.7 ± 2.0 kPa and in the HBD group 68.6 ± 2.4 kPa (p < 0.01). Significantly lower PVR levels were measured in the DCD group (372 ± 31 dyne x s/cm⁵) compared to the HBD group (655 ± 45 dyne x s/cm⁵) (p < 0.001). There was no significant difference between groups in weight, compliance or signs of pulmonary thrombosis or embolization.

Conclusions

It seems as if DCD lungs exposed to 1 h of warm ischemia before 4 h of cold storage has satisfying oxygenation capacity, low PVR, normal weight and no signs of thrombosis or embolization. According to our study it seems as lungs exposed to 1 h warm ischemia without heparin might be good candidates for transplantation.

Donor-acquired fat embolism syndrome after lung transplantation

OBJECTIVES

Fat embolism is a known complication of severe trauma and closed chest cardiac resuscitation both of which are more common in the lung transplant donor population and can lead to donor-acquired fat embolism syndrome (DAFES). The objective was to review the diagnosis and management of DAFES in the lung transplantation literature and at our centre.

METHODS

We performed a literature review on DAFES using the Medline database. We then reviewed the transplant record of Brigham and Women's Hospital, a large academic hospital with an active lung transplant programme, for cases of DAFES.

RESULTS

We identified 2 cases of DAFES in our centre, one of which required extracorporeal membrane oxygenation (ECMO) for successful management. In contrast to the broader literature on DAFES, which emphasizes unsuccessfully treated cases, both patients survived.

CONCLUSION

DAFES is a rare but likely underappreciated early complication of lung transplant as it can mimic primary graft dysfunction. Aggressive interventions, including ECMO, may be necessary to achieve a good clinical outcome following DAFES.

Expanding the donor pool: donation after cardiac death

Lung transplantation (LTx) is the definitive treatment of patients with end-stage lung disease. Availability of donor lungs remains the primary limitation and leads to substantial wait-list mortality. Efforts to expand the donor pool have included a resurgence of interest in the use of donation after cardiac death (DCD) lungs. Unique in its physiology, lung viability seems more tolerant to the variable durations of ischemia that occur in DCD donors. Initial experience with DCD LTx is promising and, in combination with ex vivo lung perfusion systems, seems a valuable opportunity to expand the lung donor pool.

Overview of clinical lung transplantation

Since the first successful lung transplant 30 years ago, lung transplantation has rapidly become an established standard of care to treat end-stage lung disease in selected patients. Advances in lung preservation, surgical technique, and immunosuppression regimens have resulted in the routine performance of lung transplantation around the world for an increasing number of patients, with wider indications. Despite this, donor shortages and chronic lung allograft dysfunction continue to prevent lung transplantation from reaching its full potential. With research into the underlying mechanisms of acute and chronic lung graft dysfunction and advances in personalized diagnostic and therapeutic approaches to both the donor lung and the lung transplant recipient, there is increasing confidence that we will improve short- and long-term outcomes in the near future.

Donation after circulatory death: current status

PURPOSE OF REVIEW

Donor shortage has forced transplant teams to explore new methods to increase the potential donor pool. Donation after circulatory death (DCD) has opened new perspectives and could be a valuable option to expand the brain-dead donors. The purpose of this review is to provide an overview of current practice and to identify remaining questions related to ethical and medical issues that should be further addressed in the future.

RECENT FINDINGS

Recent findings demonstrate acceptable outcomes after DCD kidney and lung transplantation but inferior graft survival for liver transplantation. The impact and importance of the agonal phase following withdrawal of treatment in controlled DCD is increasingly recognized. Premortem interventions are currently under debate related to preservation strategies or comfort therapy. New preservation strategies using in-situ/in-vivo extracorporeal membrane oxygenation or ex-vivo machine perfusion have large potential in the future. Finally, organizations and institutions are reporting more uniform guidelines related to declaration of death and DCD organ procurement.

SUMMARY

DCD donation has regained much attention during the last decade and is now part of standard clinical practice albeit this type of donation should not be regarded as an equally acceptable alternative for donation after brain death. It will be important to further explore the potential of DCD, to monitor the long-term outcomes and to further optimize the quality of these grafts. Development and implementation of uniform guidelines will be necessary to guarantee the clinical use of these donor pools.

Reconditioning lungs donated after cardiac death using short-term hypothermic machine perfusion

BACKGROUND

Hypothermic machine perfusion (HMP) is widely used to preserve kidneys and livers for transplantation. This study investigated whether short-term HMP could improve the quality of lungs donated after cardiac death (DCD).

METHODS

In a clinically relevant uncontrolled DCD model, beagles were divided into two groups (n=5 each): 4 hr warm ischemia + 14 hr static cold storage (SCS group) or 4 hr warm ischemia + 12 hr SCS followed by 2 hr HMP (HMP group). HMP was performed using centrifugal perfusion with STEEN solution at approximately 10°C. In both groups, the left lungs were then transplanted and reperfused for 4 hr to evaluate the posttransplantation lung functions.

RESULTS

HMP was performed safely, not inducing any oxidative damage. The dynamic pulmonary compliance was stable during HMP, whereas the pulmonary vascular resistance significantly decreased. HMP microscopically eliminated residual microthrombi in the donor lungs just before transplantation. The lung tissue adenosine triphosphate levels 4 hr after reperfusion were significantly higher in the HMP group compared with the SCS group. The serum malondialdehyde levels and proinflammatory cytokine levels in the bronchoalveolar lavage fluid 4 hr after reperfusion were significantly lower in the HMP group than in the SCS group. The physiologic lung functions during reperfusion were significantly better in the HMP group compared with the SCS group. HMP also significantly reduced ischemia-reperfusion injury in the microscopic findings.

CONCLUSIONS

Short-term HMP could resuscitate ischemically damaged DCD lungs and ameliorate ischemia-reperfusion injury.

Donor management and lung preservation for lung transplantation

Although lung transplantation has become a life-saving option for patients with end-stage lung disease, this intervention is hampered by a shortage of lungs in view of the growing number of people on the waiting list. Lungs are retrieved from only a small percentage of multiorgan donors, and the transplantation and intensive-care communities have recognised the need to develop innovative methods to expand the donor pool. Advancements in lung-preservation techniques in the preretrieval and postretrieval periods have increased the pool of available donors, and novel research and discoveries in this area have steadily improved post-transplantation adverse events. This Review summarises current best practice and the latest research on intensive-care management of a potential lung donor. We also discuss lung-preservation techniques, including advancements in normothermic ex-vivo lung perfusion, and the potential for a personalised medicine approach to the organ.

Reconditioning of lungs donated after circulatory death with normothermic ex vivo lung perfusion

BACKGROUND

The use of donation-after-circulatory-death (DCD) donors for lung transplantation has come into practice. In this study we investigated whether DCD lungs can be resuscitated after warm ischemia with normothermic ex vivo lung perfusion (EVLP).

METHODS

Four hours after cardiac arrest, beagle dogs were divided into two groups (n = 6 each): those with static cold storage (SCS group) and those with normothermic EVLP (EVLP group), for 3.5 hours. Physiologic lung functions were evaluated during EVLP. In both groups, the left lungs were then transplanted and reperfused for 4 hours to evaluate post-transplant lung functions. Lung tissue adenosine triphosphate (ATP) levels were measured at given time-points.

RESULTS

Lung oxygenation was significantly improved with EVLP (p < 0.01), and lung oxygenation at the end of EVLP significantly reflected post-transplant lung oxygenation (r = 0.99, p < 0.01). Post-transplant lung oxygenation was significantly better in the EVLP group than in the SCS group (p < 0.05). Both dynamic pulmonary compliance and wet-to-dry lung weight ratio 4 hours after transplantation were also significantly better in the EVLP group than in the SCS group (p < 0.05). Microthrombi in the donor lungs before transplantation were microscopically detected more often in the SCS group. The lung tissue ATP levels 4 hours after transplantation were significantly higher in the EVLP group compared with the SCS group (p = 0.03).

CONCLUSIONS

Normothermic ex vivo lung perfusion could resuscitate DCD lungs injured by warm ischemia, and may ameliorate ischemia-reperfusion injury.