Is it possible to further improve the function of pulmonary grafts by extending the duration of lung reconditioning using ex vivo lung perfusion?

Technical Advances Targeting Multiday Preservation of Isolated Ex Vivo Lung Perfusion

Indications for ex vivo lung perfusion (EVLP) have evolved from assessment of questionable donor lungs to treatment of some pathologies and the logistics. Yet up to 3 quarters of donor lungs remain discarded across the globe. Multiday preservation of discarded human lungs on EVLP platforms would improve donor lung utilization rates via application of sophisticated treatment modalities, which could eventually result in zero waitlist mortality. The purpose of this article is to summarize advances made on the technical aspects of the protocols in achieving a stable multiday preservation of isolated EVLP. Based on the evidence derived from large animal and/or human studies, the following advances have been considered important in achieving this goal: ability to reposition donor lungs during EVLP; perfusate adsorption/filtration modalities; perfusate enrichment with plasma and/or donor whole blood, nutrients, vitamins, and amino acids; low-flow, pulsatile, and subnormothermic perfusion; positive outflow pressure; injury specific personalized ventilation strategies; and negative pressure ventilation. Combination of some of these advances in an automatized EVLP device capable of managing perfusate biochemistry and ventilation would likely speed up the processes of achieving multiday preservation of isolated EVLP.

Significance of Lung Weight in Cellular Ex Vivo Lung Perfusion

BACKGROUND

Currently, pulmonary edema is evaluated via surgical inspection and palpation in donor lungs, and there is no quantitative standard diagnostic tool for evaluating pulmonary edema in donor procurement and ex vivo lung perfusion (EVLP). The purpose of this study was to investigate the significance of lung weight at the donor hospital and lung weight during EVLP as a complementary parameter of transplant suitability in EVLP.

MATERIALS AND METHODS

Twenty-one of rejected human lungs were perfused in cellular EVLP. Transplant suitability was evaluated at 2 h as per standard criteria of Lund-protocol EVLP.

RESULTS

Lung weight at donor hospital was significantly correlated with PaO₂/FiO₂ (P/F) ratio in EVLP (r = -0.44). There was a significant difference in lung weight at donor hospital between suitable cases (n = 13) and nonsuitable cases (n = 8). Light lung group (lung weight at donor hospital < 1280 g; n = 17) was suitable for transplant in 76%, whereas none of heavy lung group (lung weight at donor hospital ≥ 1280 g; n = 4) was suitable (P < 0.05). Lung weight at 2 h and lung weight change during EVLP were significantly associated with P/F ratio at 2 h and transplant suitability (P < 0.05, each).

CONCLUSIONS

Our findings demonstrate that lung weight at donor hospital, lung weight change, and lung weight at 2 h of EVLP might be a predictor of P/F ratio and transplant suitability in cellular EVLP.

One-year experience with ex vivo lung perfusion: Preliminary results from a single center

Objective:

To enlarge the donor pool for lung transplantation, an increasing number of extended criteria donor lungs are used. However, in more than 50% of multi-organ donors the lungs are not used. Ex vivo lung perfusion offers a unique possibility to evaluate and eventually recondition the injured donor lungs. The aim of our study was to assess the enlargement of the donor pool and the outcome with extended criteria donor lungs after ex vivo lung perfusion.

Patients and Methods:

Data were prospectively collected in our lung transplant database. We compared the results of lung transplants after ex vivo lung perfusion with those after conventional cold static preservation. In total, 11 extended criteria donor lungs processed with ex vivo lung perfusion and 41 cold static preservation lungs transplanted consecutively between May 2016 and May 2017 were evaluated. Normothermic ex vivo lung perfusion was performed according to the Toronto protocol for 4 h. Cold static preservation lungs were stored in low-potassium dextran solution.

Results:

Ex vivo lung perfusion lungs before procurement had significantly lower PaO2/FiO2 (P/F) ratios and more X-ray abnormalities. There were no statistically significant differences for pre-donation ventilation time, smoking history, or sex. After reconditioning with ex vivo lung perfusion, 9 out of 11 processed lungs were considered suitable and successfully transplanted. The mean postoperative ventilation time and in-hospital stay were not significantly different in ex vivo lung perfusion and cold static preservation recipients.

Conclusion:

Ex vivo lung perfusion can safely be used in the evaluation of lungs initially considered not suitable for transplantation. The primary outcome was not negatively affected and normothermic ex vivo lung perfusion is a useful tool to increase the usage of potentially transplantable lungs.

Prolonged EVLP Using OCS Lung: Cellular and Acellular Perfusates

BACKGROUND

We report the ability to extend lung preservation up to 24 hours (24H) by using autologous whole donor blood circulating within an ex vivo lung perfusion (EVLP) system. This approach facilitates donor lung reconditioning in a model of extended normothermic EVLP. We analyzed comparative responses to cellular and acellular perfusates to identify these benefits.

METHODS

Twelve pairs of swine lungs were retrieved after cardiac arrest and studied for 24H on the Organ Care System (OCS) Lung EVLP platform. Three groups (n = 4 each) were differentiated by perfusate: (1) isolated red blood cells (RBCs) (current clinical standard for OCS); (2) whole blood (WB); and (3) acellular buffered dextran-albumin solution (analogous to STEEN solution).

RESULTS

Only the RBC and WB groups met clinical standards for transplantation at 8 hours; our primary analysis at 24H focused on perfusion with WB versus RBC. The WB perfusate was superior (vs RBC) for maintaining stability of all monitored parameters, including the following mean 24H measures: pulmonary artery pressure (6.8 vs 9.0 mm Hg), reservoir volume replacement (85 vs 1607 mL), and PaO2:FiO2 ratio (541 vs 223). Acellular perfusion was limited to 6 hours on the OCS system due to prohibitively high vascular resistance, edema, and worsening compliance.

CONCLUSIONS

The use of an autologous whole donor blood perfusate allowed 24H of preservation without functional deterioration and was superior to both RBC and buffered dextran-albumin solution for extended lung preservation in a swine model using OCS Lung. This finding represents a potentially significant advance in donor lung preservation and reconditioning.

Comparison of two strategies for ex vivo lung perfusion

BACKGROUND

Two clinically used strategies for ex vivo lung perfusion (EVLP) were compared in a porcine model with respect to lung function, metabolism, inflammatory response, oxidative stress, and cell viability.

METHODS

Porcine lungs (n = 20) were preserved, harvested, and kept cooled for 2 hours. After randomization, EVLP was performed using a cellular perfusate and open left atrium (COA group) or an acellular perfusate and a closed left atrium (ACA group). Oxygenation (partial pressure of arterial oxygen/fraction of inspired oxygen), compliance, dead space, weight, and perfusate oncotic pressure were registered before and after a 4-hour period of reconditioning. Lung tissue samples were collected before and after EVLP for quantitative polymerase chain reaction analysis of gene expression for inflammatory markers, measurement of tissue hypoxia (hypoxia inducible factor-1α) and oxidative stress (ascorbyl radical), and viability (trypan blue staining) and lung histopathology.

RESULTS

In 3 of 10 lungs undergoing EVLP in the ACA group, EVLP was terminated prematurely because of severe lung edema and inability to perfuse the lungs. There were no significant differences in changes of lung oxygenation or pulmonary vascular resistance between groups. Compliance decreased and lung weights increased in both groups, but more in the ACA group (p = 0.083 and p = 0.065, respectively). There was no obvious difference in gene expression for hypoxia inducible factor-1α, inflammatory markers, free radicals, or lung injury between groups.

CONCLUSIONS

Lung edema formation and decreased lung compliance occurs with both EVLP techniques but were more pronounced in the ACA group. Otherwise, there were no differences in lung function, inflammatory response, ischemia/reperfusion injury, or histopathologic changes between the EVLP techniques.

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.

Ex Vivo Perfusion With Adenosine A2A Receptor Agonist Enhances Rehabilitation of Murine Donor Lungs After Circulatory Death

BACKGROUND

Ex vivo lung perfusion (EVLP) enables assessment and rehabilitation of marginal donor lungs before transplantation. We previously demonstrated that adenosine A2A receptor (A2AR) agonism attenuates lung ischemia-reperfusion injury. The current study utilizes a novel murine EVLP model to test the hypothesis that A2AR agonist enhances EVLP-mediated rehabilitation of donation after circulatory death (DCD) lungs.

METHODS

Mice underwent euthanasia and 60 minutes warm ischemia, and lungs were flushed with Perfadex and underwent cold static preservation (CSP, 60 minutes). Three groups were studied: no EVLP (CSP), EVLP with Steen solution for 60 minutes (EVLP), and EVLP with Steen solution supplemented with ATL1223, a selective A2AR agonist (EVLP + ATL1223). Lung function, wet/dry weight, cytokines and neutrophil numbers were measured. Microarrays were performed using the Affymetrix GeneChip Mouse Genome 430A 2.0 Array.

RESULTS

Ex vivo lung perfusion significantly improved lung function versus CSP, which was further, significantly improved by EVLP + ATL1223. Lung edema, cytokines, and neutrophil counts were reduced after EVLP and further, significantly reduced after EVLP + ATL1223. Gene array analysis revealed differential expression of 1594 genes after EVLP, which comprise canonical pathways involved in inflammation and innate immunity including IL-1, IL-8, IL-6, and IL-17 signaling. Several pathways were uniquely regulated by EVLP + ATL1223 including the downregulation of genes involved in IL-1 signaling, such as ADCY9, ECSIT, IRAK1, MAPK12, and TOLLIP.

CONCLUSIONS

Ex vivo lung perfusion modulates proinflammatory genes and reduces pulmonary dysfunction, edema, and inflammation in DCD lungs, which are further reduced by A2AR agonism. This murine EVLP model provides a novel platform to study rehabilitative mechanisms of DCD lungs.

Hemofiltration in ex vivo lung perfusion-a study in experimentally induced pulmonary edema

OBJECTIVES

Ex vivo lung perfusion (EVLP) can potentially reduce pulmonary edema. In a pig model with induced pulmonary edema, we evaluated the effect of hemofiltration (HF) during EVLP on lung function, perfusate oncotic pressure, and lung weight.

METHODS

In anesthetized pigs (n = 14), pulmonary edema was induced by a balloon in the left atrium, combined with crystalloid infusion (20 mL/kg), for 2 hours. The lungs were harvested, stored cold for 2 hours, and randomized to EVLP, with or without a hemofilter (HF and noHF groups, respectively, n = 7 for each). EVLP was performed with cellular perfusate at a hematocrit of 10% to 15%. Oncotic pressure, lung performance, and weight were measured before and after 180 minutes of EVLP reconditioning with or without HF.

RESULTS

After in vivo induction of edema, arterial oxygen tension (Pao2)/inspired oxygen fraction (Fio2), and compliance decreased by 63% and 16%, respectively. Pao2/Fio2 was considerably improved at first evaluation ex vivo in both groups. HF increased oncotic pressure by 43% and decreased lung weight by 15%. The effects were negligible in the noHF group. Compliance decreased in both groups during reconditioning, although less so in the HF group (P < .05). Pao2/Fio2, shunt fraction, and oxygen saturation remained unchanged in both groups. Pulmonary flow index decreased in both groups, and was partially reversed by nitroglycerin. Dorsal atelectatic consolidations were seen in both groups.

CONCLUSIONS

In this lung-edema model, EVLP reconditioning with hyperoncotic solution did not affect the degree of lung edema. HF during EVLP increased perfusate oncotic pressure, decreased lung weight with beneficial effects on compliance, but did not improve lung oxygenation capacity.

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.

Do we need to cool the lung graft after ex vivo lung perfusion? A preliminary study

BACKGROUND

After normothermic ex vivo lung perfusion (EVLP), pulmonary grafts are usually flush-cooled and stored on ice until implantation although evidence for this practice lacks. We compared outcomes between 2 post-EVLP preservation strategies in a porcine left single-lung transplantation model.

MATERIAL AND METHODS

After cold flush and 2-h EVLP, donor lungs were prepared and split. In [C], (n = 5) lungs cooled on device to 15°C were preserved in ice-water; in [W] (n = 5), lungs were disconnected from EVLP at 37°C and kept at room temperature. The left lung was transplanted in a recipient animal. Posttransplant, 6 h-monitoring included hourly assessment of pulmonary vascular resistance, pulmonary artery pressure, plateau airway pressure, compliance, and oxygenation before and after exclusion of the right lung. Lung biopsies and bronchoscopy with bronchoalveolar lavage (BAL) were performed at retrieval, at the end of EVLP (R lung), and 1 and 6 h after reperfusion (L lung).

RESULTS

Lungs in [W] showed the highest compliance (P < 0.05) and the lowest plateau airway pressure (not statistically significant) throughout the whole reperfusion period. Oxygenation and pulmonary artery pressure were similar between groups. Pulmonary vascular resistance was stable in [C], but rose after reperfusion in [W]. Histologic signs of lung injury and BAL neutrophilia were more pronounced in [C] at 1 h (not statistically significant and P < 0.05, respectively). BAL cytokine levels and lung tissue expression of intercellular adhesion molecule 1 did not differ between groups.

CONCLUSIONS

Normothermic preparation after EVLP results in similar graft performances compared with lung cooling after EVLP.

Plasmin administration during ex vivo lung perfusion ameliorates lung ischemia-reperfusion injury

BACKGROUND

Donor lung thrombus is considered a significant etiology for primary graft dysfunction (PGD). We hypothesized that thrombolysis in ex vivo lung perfusion (EVLP) before lung transplantation could alleviate ischemia-reperfusion injury (IRI), resulting in a decreased incidence of PGD.

METHODS

Rats were divided into control (n = 5), non-plasmin (n = 7) and plasmin (n = 7) groups. In the non-plasmin and plasmin groups, cardiac arrest was induced by withdrawal of ventilation without heparinization. After 120 minutes of warm ischemia, the lungs were ventilated and flushed. Hearts and both lungs were excised en bloc. The lungs were perfused and ventilated in the EVLP for 30 minutes, and plasmin or placebo was administered on EVLP initiation. The lungs were then stored at 4°C for 90 minutes and finally perfused with rat blood for 80 minutes. We assessed physiologic and histologic findings during reperfusion and the correlation between physiologic data during EVLP and after reperfusion.

RESULTS

Physiologic results were better in the plasmin group than in the non-plasmin group. The plasmin group lungs had fewer signs of histologic injury. Caspase-3 and -7 activity in the plasmin group was lower in the non-plasmin group. Pulmonary vascular resistance (PVR) during EVLP correlated with that at the end of reperfusion.

CONCLUSIONS

Plasmin administration during EVLP protected the donor lungs after reperfusion. We also found that several physiologic values in EVLP may be predictive markers of lung function after reperfusion.