A Novel Negative Pressure-Flow Waveform to Ventilate Lungs for Normothermic 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.

The impact and relevance of techniques and fluids on lung injury in machine perfusion of lungs

Primary graft dysfunction (PGD) is a common complication after lung transplantation. A plethora of contributing factors are known and assessment of donor lung function prior to organ retrieval is mandatory for determination of lung quality. Specialized centers increasingly perform ex vivo lung perfusion (EVLP) to further assess lung functionality and improve and extend lung preservation with the aim to increase lung utilization. EVLP can be performed following different protocols. The impact of the individual EVLP parameters on PGD development, organ function and postoperative outcome remains to be fully investigated. The variables relate to the engineering and function of the respective perfusion devices, such as the type of pump used, functional, like ventilation modes or physiological (e.g. perfusion solutions). This review reflects on the individual technical and fluid components relevant to EVLP and their respective impact on inflammatory response and outcome. We discuss key components of EVLP protocols and options for further improvement of EVLP in regard to PGD. This review offers an overview of available options for centers establishing an EVLP program and for researchers looking for ways to adapt existing protocols.

A Comparative Study of Ex-Vivo Murine Pulmonary Mechanics Under Positive- and Negative-Pressure Ventilation

Increased ventilator use during the COVID-19 pandemic resurrected persistent questions regarding mechanical ventilation including the difference between physiological and artificial breathing induced by ventilators (i.e., positive- versus negative-pressure ventilation, PPV vs NPV). To address this controversy, we compare murine specimens subjected to PPV and NPV in ex vivo quasi-static loading and quantify pulmonary mechanics via measures of quasi-static and dynamic compliances, transpulmonary pressure, and energetics when varying inflation frequency and volume. Each investigated mechanical parameter yields instance(s) of significant variability between ventilation modes. Most notably, inflation compliance, percent relaxation, and peak pressure are found to be consistently dependent on the ventilation mode. Maximum inflation volume and frequency note varied dependencies contingent on the ventilation mode. Contradictory to limited previous clinical investigations of oxygenation and end-inspiratory measures, the mechanics-focused comprehensive findings presented here indicate lung properties are dependent on loading mode, and importantly, these dependencies differ between smaller versus larger mammalian species despite identical custom-designed PPV/NPV ventilator usage. Results indicate that past contradictory findings regarding ventilation mode comparisons in the field may be linked to the chosen animal model. Understanding the differing fundamental mechanics between PPV and NPV may provide insights for improving ventilation strategies and design to prevent associated lung injuries.

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.

Diagnostic and Therapeutic Implications of Ex Vivo Lung Perfusion in Lung Transplantation: Potential Benefits and Inherent Limitations

Ex vivo lung perfusion (EVLP), a technique in which isolated lungs are continually ventilated and perfused at normothermic temperature, is emerging as a promising platform to optimize donor lung quality and increase the lung graft pool. Over the past few decades, the EVLP technique has become recognized as a significant achievement and gained much attention in the field of lung transplantation. EVLP has been demonstrated to be an effective platform for various targeted therapies to optimize donor lung function before transplantation. Additionally, some physical parameters during EVLP and biological markers in the EVLP perfusate can be used to evaluate graft function before transplantation and predict posttransplant outcomes. However, despite its advantages, the clinical practice of EVLP continuously encounters multiple challenges associated with both intrinsic and extrinsic limitations. It is of utmost importance to address the advantages and disadvantages of EVLP for its broader clinical usage. Here, the pros and cons of EVLP are comprehensively discussed, with a focus on its benefits and potential approaches for overcoming the remaining limitations. Directions for future research to fully explore the clinical potential of EVLP in lung transplantation are also discussed.

Pegylated-Catalase Is Protective in Lung Ischemic Injury and Oxidative Stress

BACKGROUND

Lung transplant ischemia-reperfusion injury is typified by toxic metabolites and oxygen free radicals leading to worse graft function. Catalase is an enzyme involved in oxidative-stress detoxification. We hypothesize that direct delivery of highly concentrated polyethylene glycol-catalase (PEG-CAT) during normothermic ex vivo lung perfusion (EVLP) significantly reduces ischemia-reperfusion injury.

METHODS

To demonstrate protection, primary culture porcine endothelial cells were treated with PEG-CAT (0 to 1250 U/mL) in a model of oxidative stress (400 μM H₂o₂). In vivo, rat lungs were subjected to 0 hours or 1 hour of warm ischemic injury and 2 hours of EVLP with or without PEG-CAT. Perfusate was collected throughout the perfusion duration and tissue was collected at the end. Tissue and perfusate underwent analysis for markers of apoptosis and a biometric signature of lung health.

RESULTS

Uptake of PEG-CAT into primary endothelial cells was demonstrated with Alexa Fluor 488-labeled PEG-CAT. Oxidatively stressed cells pretreated with PEG-CAT had significantly decreased cytotoxicity and caspase 3/7 activity and increased cell viability and cell membrane integrity. In a rat model of warm ischemia with EVLP, PEG-CAT improved allograft viability as measured by indications of cell membrane integrity (lactate dehydrogenase and hyaluronic acid), presence of vasoconstrictive peptides (endothelin-1 and big endothelin-1) released from endothelial cells, and reduced apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling).

CONCLUSIONS

In vitro and ex vivo, PEG-CAT protects against oxidative stress-induced cytotoxicity, maintains cellular metabolism, and mitigates lung ischemia-reperfusion in an experimental model. Together, these data suggest that PEG-CAT is a potential therapeutic target for donor organs at risk for ischemia-reperfusion injury.