Ex-vivo perfusion and ventilation of rat lungs from non-heart-beating donors before transplant

Uncontrolled Donation after Circulatory Death Only Lung Program: An Urgent Opportunity

Uncontrolled donation after circulatory death (uDCD) represents a potential source of lungs, and since Steen's 2001 landmark case in Sweden, lungs have been recovered from uDCD donors and transplanted to patients in other European countries (France, the Netherlands, Spain and Italy) with promising results. Disparities still exist among European countries and among regions in Italy due to logistical and organizational factors. The present manuscript focuses on the clinical experiences pertaining to uDCD lungs in North America and European countries and on different lung maintenance methods. Existing experiences (and protocols) are not uniform, especially with respect to the type of lung maintenance, the definition of warm ischemic time (WIT) and, finally, the use of ex vivo perfusion (available in the last several years in most centers). In situ lung cooling may be superior to protective ventilation, but this process may be difficult to perform in the uDCD setting and is also time-consuming. On the other hand, the "protective ventilation technique" is simpler and feasible in every hospital. It may lead to a broader use of uDCD lung donors. To date, the results of lung transplants performed after protective ventilation as a preservation technique are scarce but promising. All the protocols comprise, among the inclusion criteria, a witnessed cardiac arrest. The detectable differences included preservation time (240 vs. 180 min) and donor age (<55 years in Spanish protocols and <65 years in Toronto protocols). Overall, independently of the differences in protocols, lungs from uDCD donors show promising results, and the possibility of optimizing ex vivo lung perfusion may broaden the use of these organs.

Novel Polymerized Human Serum Albumin For Ex Vivo Lung Perfusion

Ex vivo lung perfusion (EVLP) is a method of organ preservation to expand the donor pool by allowing organ assessment and repair. Perfusion solution composition is crucial to maintaining and improving organ function during EVLP. EVLP compared perfusates supplemented with either polymeric human serum albumin (PolyHSA) or standard human serum albumin (HSA). Rat heart-lung blocks underwent normothermic EVLP (37°C) for 120 minutes using perfusate with 4% HSA or 4% PolyHSA synthesized at a 50:1 or 60:1 molar ratio of glutaraldehyde to PolyHSA. Oxygen delivery, lung compliance, pulmonary vascular resistance (PVR), wet-to-dry ratio, and lung weight were measured. Perfusion solution type (HSA or PolyHSA) significantly impacted end-organ metrics. Oxygen delivery, lung compliance, and PVR were comparable among groups ( P > 0.05). Wet-to-dry ratio increased in the HSA group compared to the PolyHSA groups (both P < 0.05) suggesting edema formation. Wet-to-dry ratio was most favorable in the 60:1 PolyHSA-treated lungs compared to HSA ( P < 0.05). Compared to using HSA, PolyHSA significantly lessened lung edema. Our data confirm that the physical properties of perfusate plasma substitutes significantly impact oncotic pressure and the development of tissue injury and edema. Our findings demonstrate the importance of perfusion solutions and PolyHSA is an excellent candidate macromolecule to limit pulmonary edema. http://links.lww.com/ASAIO/A980.

A translational rat model for ex vivo lung perfusion of pre-injured lungs after brain death

The process of brain death (BD) detrimentally affects donor lung quality. Ex vivo lung perfusion (EVLP) is a technique originally designed to evaluate marginal donor lungs. Nowadays, its potential as a treatment platform to repair damaged donor lungs is increasingly studied in experimental models. Rat models for EVLP have been described in literature before, yet the pathophysiology of BD was not included in these protocols and prolonged perfusion over 3 hours without anti-inflammatory additives was not achieved. We aimed to establish a model for prolonged EVLP of rat lungs from brain-dead donors, to provide a reliable platform for future experimental studies. Rat lungs were randomly assigned to one of four experimental groups (n = 7/group): 1) healthy, directly procured lungs, 2) lungs procured from rats subjected to 3 hours of BD and 1 hour cold storage (CS), 3) healthy, directly procured lungs subjected to 6 hours EVLP and 4), lungs procured from rats subjected to 3 hours of BD, 1 hour CS and 6 hours EVLP. Lungs from brain-dead rats showed deteriorated ventilation parameters and augmented lung damage when compared to healthy controls, in accordance with the pathophysiology of BD. Subsequent ex vivo perfusion for 6 hours was achieved, both for lungs of healthy donor rats as for pre-injured donor lungs from brain-dead rats. The worsened quality of lungs from brain-dead donors was evident during EVLP as well, as corroborated by deteriorated ventilation performance, increased lactate production and augmented inflammatory status during EVLP. In conclusion, we established a stable model for prolonged EVLP of pre-injured lungs from brain-dead donor rats. In this report we describe tips and pitfalls in the establishment of the rat EVLP model, to enhance reproducibility by other researchers.

Initial lung transplantation experience with uncontrolled donation after cardiac death in North America

Uncontrolled donation after cardiac death (uDCD) has the potential to ameliorate the shortage of suitable lungs for transplant. To date, no lung transplant data from these donors are available from North America. We describe the successful use of these donors using a simple method of in situ lung inflation so that the organ can be protected from warm ischemic injury. Forty-four potential donors were approached, and family consent was obtained in 30 cases (68%). Of these, the lung transplant team evaluated 16 uDCDs on site, and 14 were considered for transplant pending ex vivo lung perfusion assessment. Five lungs were ultimately used for transplant (16.7% use rate from consented donors). The mean warm ischemic time was 2.8 hours. No primary graft dysfunction grade 3 was observed at 24, 48, or 72 hours after transplant. Median intensive care unit stay was 5 days (range: 2-78 days), and median hospital stay was 17 days (range: 8-100 days). The 30-day mortality was 0%. Four of 5 patients are alive at a median of 651 days (range: 121-1254 days) with preserved lung function. This study demonstrates the proof of concept and the potential for uDCD lung donation using a simple donor intervention.

Ex Vivo Lung Perfusion in the Rat: Detailed Procedure and Videos

Ex vivo lung perfusion (EVLP) is a promising procedure for evaluation, reconditioning, and treatment of marginal lungs before transplantation. Small animal models can contribute to improve clinical development of this technique and represent a substantial platform for bio-molecular investigations. However, to accomplish this purpose, EVLP models must sustain a prolonged reperfusion without pharmacological interventions. Currently available protocols only partly satisfy this need. The aim of the present research was accomplishment and optimization of a reproducible model for a protracted rat EVLP in the absence of anti-inflammatory treatment. A 180 min, uninjured and untreated perfusion was achieved through a stepwise implementation of the protocol. Flow rate, temperature, and tidal volume were gradually increased during the initial reperfusion phase to reduce hemodynamic and oxidative stress. Low flow rate combined with open atrium and protective ventilation strategy were applied to prevent lung damage. The videos enclosed show management of the most critical technical steps. The stability and reproducibility of the present procedure were confirmed by lung function evaluation and edema assessment. The meticulous description of the protocol provided in this paper can enable other laboratories to reproduce it effortlessly, supporting research in the EVLP field.

Microparticles: A new insight into lung primary graft dysfunction?

Lung transplantation is the only life-saving treatment for end stage respiratory disease. The immediate outcome is still hampered by primary graft dysfunction. The latter is a form of acute lung injury occurring within the 30min following the unclamping of the pulmonary artery that prompts ischemia reperfusion injury. Severe forms may need prolonged mechanical ventilation and extra-corporeal membrane oxygenation. Overall, primary graft dysfunction accounts for at least one third of the deaths during the first post-operative month. Despite increasing experience and knowledge on the underlying cellular events, there is still a lack of an early marker of ischemia reperfusion graft injuries. Microparticles are plasma membrane vesicles that are released from damaged or stressed cells in biological fluids and remodeling tissues, among which the lung parenchyma during acute or chronic injury. We recently evidenced alveolar microparticles as surrogate markers of strong ischemia injury in ex-vivo reperfusion experimental models. We propose herein new insights on how microparticles may be helpful to evaluate the extent of lung ischemia reperfusion injuries and predict the occurrence of primary graft dysfunction.

The novel in vitro reanimation of isolated human and large mammalian heart-lung blocs

BACKGROUND

In vitro isolated heart preparations are valuable tools for the study of cardiac anatomy and physiology, as well as for preclinical device testing. Such preparations afford investigators a high level of hemodynamic control, independent of host or systemic interactions. Here we hypothesize that recovered human and swine heart-lung blocs can be reanimated using a clear perfusate and elicit viable cardiodynamic and pulmonic function. Further, this approach will facilitate multimodal imaging, which is particularly valuable for the study of both functional anatomy and device-tissue interactions. Five human and 18 swine heart-lung preparations were procured using techniques analogous to those for cardiac transplant. Specimens were then rewarmed and reperfused using modifications of a closed circuit, isolated, beating and ventilated heart-lung preparation. Positive pressure mechanical ventilation was also employed, and epicardial defibrillation was applied to elicit native cardiac sinus rhythm. Videoscopy, fluoroscopy, ultrasound, and infrared imaging were performed for anatomical and experimental study.

RESULTS

Systolic and diastolic left ventricular pressures observed for human and swine specimens were 68/2 ± 11/7 and 74/3 ± 17/5 mmHg, respectively, with associated native heart rates of 80 ± 7 and 96 ± 16 beats per minute. High-resolution imaging within functioning human pulmonary vasculature was obtained among other anatomies of interest. Note that one human specimen elicited poor cardiac performance post defibrillation.

CONCLUSIONS

We report the first dynamic videoscopic images of the pulmonary vasculature during viable cardiopulmonary function in isolated reanimated heart-lung blocs. This experimental approach provides unique in vitro opportunities for the study of novel medical therapeutics applied to large mammalian, including human, heart-lung specimens.

Mechanical circulatory support in lung transplantation: Cardiopulmonary bypass, extracorporeal life support, and ex-vivo lung perfusion

Lung transplant is the standard of care for patients with end-stage lung disease refractory to medical management. There is currently a critical organ shortage for lung transplantation with only 17% of offered organs being transplanted. Of those patients receiving a lung transplant, up to 25% will develop primary graft dysfunction, which is associated with an 8-fold increase in 30-d mortality. There are numerous mechanical lung assistance modalities that may be employed to help combat these challenges. We will discuss the use of mechanical lung assistance during lung transplantation, as a bridge to transplant, as a treatment for primary graft dysfunction, and finally as a means to remodel and evaluate organs deemed unsuitable for transplant, thus increasing the donor pool, improving survival to transplant, and improving overall patient survival.

Animal models of ex vivo lung perfusion as a platform for transplantation research

Ex vivo lung perfusion (EVLP) is a powerful experimental model for isolated lung research. EVLP allows for the lungs to be manipulated and characterized in an external environment so that the effect of specific ventilation/perfusion variables can be studied independent of other confounding physiologic contributions. At the same time, EVLP allows for normal organ level function and real-time monitoring of pulmonary physiology and mechanics. As a result, this technique provides unique advantages over in vivo and in vitro models. Small and large animal models of EVLP have been developed and each of these models has their strengths and weaknesses. In this manuscript, we provide insight into the relative strengths of each model and describe how the development of advanced EVLP protocols is leading to a novel experimental platform that can be used to answer critical questions in pulmonary physiology and transplant medicine.

Successful prolonged ex vivo lung perfusion for graft preservation in rats

OBJECTIVES

Ex vivo lung perfusion (EVLP) strategies represent a new frontier in lung transplantation technology, and there have been many clinical studies of EVLP in lung transplantation. The establishment of a reliable EVLP model in small animals is crucial to facilitating translational research using an EVLP strategy. The main objective of this study was to develop a reproducible rat EVLP (R-EVLP) model that enables prolonged evaluation of the explanted lung during EVLP and successful transplantation after EVLP.

METHODS

The donor heart-lung blocks were procured with cold low-potassium dextran solution and immersed in the solution for 1 h at 4 °C. And then, the heart-lung blocks were flushed retrogradely and warmed up to 37 °C in a circuit perfused antegradely with acellular perfusate. The perfusate was deoxygenated with a gas mixture (6% O2, 8% CO2, 86% N2). The perfusion flow was maintained at 20% of the entire cardiac output. At 37 °C, the lungs were mechanically ventilated and perfusion continued for 4 h. Every hour, the perfused lung was evaluated for gas exchange, dynamic lung compliance (Cdyn) and pulmonary vascular resistance (PVR).

RESULTS

R-EVLP was performed for 4 h. Pulmonary oxygenation ability (pO2/pCO2) was stable for 4 h during EVLP. It was noted that Cdyn and PVR were also stable. After 4 h of EVLP, pO2 was 303 ± 19 mmHg, pCO2 was 39.6 ± 1.2 mmHg, PVR was 1.75 ± 0.10 mmHg/ml/min and Cdyn was 0.37 ± 0.03 ml/cmH2O. Lungs that were transplanted after 2 h of R-EVLP resulted in significantly better post-transplant oxygenation and compliance when compared with those after standard cold static preservation.

CONCLUSIONS

Our R-EVLP model maintained stable lung oxygenation, compliance and vascular resistance for up to 4 h of perfusion duration. This reliable model should facilitate further advancement of experimental work using EVLP.

Effect of a vascular endothelial cadherin antagonist in a rat lung transplant model

BACKGROUND

Adherens junctions are critically important in control of endothelial cell permeability. Bβ15-42 is a peptide product of fibrin degradation that binds to vascular endothelial cadherin, the major component of endothelial adherens junctions. We tested the hypothesis that Bβ15-42 improves lung function in our rat lung transplant model.

METHODS

Bβ15-42 was administered to donors before lung retrieval and to recipients by continuous intravenous infusion, or just to recipients, or neither. Recipients were monitored, anesthetized and ventilated, for 6 hours. Outcome measures were indices of lung function (edema [wet-to-dry weight ratio], oxygenation, dynamic compliance) and bronchoalveolar fluid measures of inflammation (protein, cell count, differential, and cytokines).

RESULTS

Bβ15-42 therapy was associated with improved graft lung function, including less edema, and improved oxygenation and airway pressure, particularly if Bβ15-42 was administered to both the donor and recipient. However, Bβ15-42 had little or no effect on bronchoalveolar fluid measures of inflammation. Analysis of bronchoalveolar fluid protein concentration showed Bβ15-42 may enhance alveolar fluid clearance.

CONCLUSIONS

Bβ15-42 may be a useful therapy to reduce edema and improve graft function after lung transplant, alone or as an adjunct to other therapies.

Postmortem and ex vivo carbon monoxide ventilation reduces injury in rat lungs transplanted from non-heart-beating donors

OBJECTIVE

We sought to determine whether ventilation of lungs after death in non-heart-beating donors with carbon monoxide during warm ischemia and ex vivo lung perfusion and after transplant would reduce ischemia-reperfusion injury and improve lung function.

METHODS

One hour after death, Sprague-Dawley rats were ventilated for another hour with 60% oxygen (control group) or 500 ppm carbon monoxide in 60% oxygen (CO-vent group; n=6/group). Then, lungs were flushed with 20 mL cold Perfadex, stored cold for 1 hour, then warmed to 37 °C in an ex vivo lung perfusion circuit perfused with Steen solution. At 37 °C, lungs were ventilated for 15 minutes with alveolar gas with or without 500 ppm carbon monoxide, then perfusion-cooled to 20 °C, flushed with cold Perfadex and stored cold for 2 hours. The left lung was transplanted using a modified cuff technique. Recipients were ventilated with 60% oxygen with or without carbon monoxide. One hour after transplant, we measured blood gases from the left pulmonary vein and aorta, and wet-to-dry ratio of both lungs. The RNA and protein extracted from graft lungs underwent real-time polymerase chain reaction and Western blotting, and measurement of cyclic guanosine monophosphate by enzyme-linked immunosorbent assay.

RESULTS

Carbon monoxide ventilation begun 1 hour after death reduced wet/dry ratio after ex vivo lung perfusion. After transplantation, the carbon monoxide-ventilation group had better oxygenation; higher levels of tissue cyclic guanosine monophosphate, heme oxidase-1 expression, and p38 phosphorylation; reduced c-Jun N-terminal kinase phosphorylation; and reduced expression of interleukin-6 and interleukin-1β messenger RNA.

CONCLUSIONS

Administration of carbon monoxide to the deceased donor and non-heart-beating donor lungs reduces ischemia-reperfusion injury in rat lungs transplanted from non-heart-beating donors. Therapy to the deceased donor via the airway may improve post-transplant lung function.

Nitric oxide ventilation of rat lungs from non-heart-beating donors improves posttransplant function

Lungs from non-heart-beating donors (NHBDs) would enhance the donor pool. Ex vivo perfusion and ventilation of NHBD lungs allows functional assessment and treatment. Ventilation of rat NHBD lungs with nitric oxide (NO) during ischemia, ex vivo perfusion and after transplant reduced ischemia-reperfusion injury (IRI) and improved lung function posttransplant. One hour after death, Sprague-Dawley rats were ventilated for another hour with either 60% O2 or 60% O2/40 ppm NO. Lungs were then flushed with 20-mL cold Perfadex, stored cold for 1 h, perfused in an ex vivo circuit with Steen solution and warmed to 37 degrees C, ventilated 15 min, perfusion-cooled to 20 degrees C, then flushed with cold Perfadex and stored cold. The left lung was transplanted and ventilated separately. Recipients were sacrificed after 1 h. NO-ventilation was associated with significantly reduced wet:dry weight ratio in the ex vivo circuit, better oxygenation, reduced pulmonary vascular resistance, increased lung tissue levels of cGMP, maintained endothelial NOS eNOS, and reduced increases in tumor necrosis factor alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS). NO-ventilation had no effect on MAP kinases or NF-kappaB activation. NO administration to NHBDs before and after lung retrieval may improve function of lungs from NHBDs.

Novel critical role of Toll-like receptor 4 in lung ischemia-reperfusion injury and edema

Toll-like receptors (TLRs) of the innate immune system contribute to noninfectious inflammatory processes. We employed a murine model of hilar clamping (1 h) with reperfusion times between 15 min and 3 h in TLR4-sufficient (C3H/OuJ) and TLR4-deficient (C3H/HeJ) anesthetized mice with additional studies in chimeric and myeloid differentiation factor 88 (MyD88)- and TLR4-deficient mice to determine the role of TLR4 in lung ischemia-reperfusion injury. Human pulmonary microvascular endothelial monolayers were subjected to simulated warm ischemia and reperfusion with and without CRX-526, a competitive TLR4 inhibitor. Functional TLR4 solely on pulmonary parenchymal cells, not bone marrow-derived cells, mediates early lung edema following ischemia-reperfusion independent of MyD88. Activation of MAPKs and NF-kappaB was significantly blunted and/or delayed in lungs of TLR4-deficient mice as a consequence of ischemia-reperfusion injury, but edema development appeared to be independent of activation of these signaling pathways. Pretreatment with a competitive TLR4 inhibitor prevented edema in vivo and reduced actin cytoskeletal rearrangement and gap formation in pulmonary microvascular endothelial monolayers subjected to simulated warm ischemia and reperfusion. In addition to its well-accepted role to alter gene transcription, functioning TLR4 on pulmonary parenchymal cells plays a key role in very early and profound pulmonary edema in murine lung ischemia-reperfusion injury. This may be due to a novel mechanism: regulation of endothelial cell cytoskeleton affecting microvascular endothelial cell permeability.

Present state of nonheart-beating lung donation

PURPOSE OF REVIEW

Indications for lung transplantation have increased through the years, and currently we have to face a lack of grafts to attend this growing demand with the subsequent increase in waiting-list deaths. Several strategies have been proposed to solve this challenging problem (living-lobe donors, extended donors, size-reduced lung grafts and so on), the use of nonheart-beating donors (NHBDs) being the most promising of them.

RECENT FINDINGS

The last experimental works concerning NHBDs have focused on the improvement of graft preservation in order to minimize warm ischemic injury and the capacity of noninvasive parameters in bronchial lavage to predict good function after implantation. There have also been several reports on the clinical use of controlled and uncontrolled NHBDs with excellent results.

CONCLUSION

Several methods have been effective in protecting these grafts from ischemic damage. Functional predictors will be very useful in the near future allowing us to know in a simple and noninvasive way which grafts are suitable for transplantation. Definitely, NHBDs for lung transplantation are no more a promising source of grafts but a real one, with encouraging short-term and mid-term results.