Hyperspectral Imaging as a Tool for Viability Assessment During Normothermic Machine Perfusion of Human Livers: A Proof of Concept Pilot Study.

Normothermic machine perfusion (NMP) allows for ex vivo viability and functional assessment prior to liver transplantation (LT). Hyperspectral imaging represents a suitable, non-invasive method to evaluate tissue morphology and organ perfusion during NMP. Liver allografts were subjected to NMP prior to LT. Serial image acquisition of oxygen saturation levels (StO2), organ hemoglobin (THI), near-infrared perfusion (NIR) and tissue water indices (TWI) through hyperspectral imaging was performed during static cold storage, at 1h, 6h, 12h and at the end of NMP. The readouts were correlated with perfusate parameters at equivalent time points. Twenty-one deceased donor livers were included in the study. Seven (33.0%) were discarded due to poor organ function during NMP. StO2 (p < 0.001), THI (p < 0.001) and NIR (p = 0.002) significantly augmented, from static cold storage (pre-NMP) to NMP end, while TWI dropped (p = 0.005) during the observational period. At 12-24h, a significantly higher hemoglobin concentration (THI) in the superficial tissue layers was seen in discarded, compared to transplanted livers (p = 0.036). Lactate values at 12h NMP correlated negatively with NIR perfusion index between 12 and 24h NMP and with the delta NIR perfusion index between 1 and 24h (rs = -0.883, p = 0.008 for both). Furthermore, NIR and TWI correlated with lactate clearance and pH. This study provides first evidence of feasibility of hyperspectral imaging as a potentially helpful contact-free organ viability assessment tool during liver NMP.

Restoring Mitochondrial Function While Avoiding Redox Stress: The Key to Preventing Ischemia/Reperfusion Injury in Machine Perfused Liver Grafts?

Mitochondria sense changes resulting from the ischemia and subsequent reperfusion of an organ and mitochondrial reactive oxygen species (ROS) production initiates a series of events, which over time result in the development of full-fledged ischemia-reperfusion injury (IRI), severely affecting graft function and survival after transplantation. ROS activate the innate immune system, regulate cell death, impair mitochondrial and cellular performance and hence organ function. Arresting the development of IRI before the onset of ROS production is currently not feasible and clinicians are faced with limiting the consequences. Ex vivo machine perfusion has opened the possibility to ameliorate or antagonize the development of IRI and may be particularly beneficial for extended criteria donor organs. The molecular events occurring during machine perfusion remain incompletely understood. Accumulation of succinate and depletion of adenosine triphosphate (ATP) have been considered key mechanisms in the initiation; however, a plethora of molecular events contribute to the final tissue damage. Here we discuss how understanding mitochondrial dysfunction linked to IRI may help to develop novel strategies for the prevention of ROS-initiated damage in the evolving era of machine perfusion.

Prediction of Biliary Complications After Human Liver Transplantation Using Hyperspectral Imaging and Convolutional Neural Networks: A Proof-of-concept Study.

BACKGROUND: Biliary complications (BCs) negatively impact the outcome after liver transplantation. We herein tested whether hyperspectral imaging (HSI) generated data from bile ducts (BD) on reperfusion and machine learning techniques for data readout may serve as a novel approach for predicting BC. METHODS: Tissue-specific data from 136 HSI liver images were integrated into a convolutional neural network (CNN). Fourteen patients undergoing liver transplantation after normothermic machine preservation served as a validation cohort. Assessment of oxygen saturation, organ hemoglobin, and tissue water levels through HSI was performed after completing the biliary anastomosis. Resected BD segments were analyzed by immunohistochemistry and real-time confocal microscopy. RESULTS: Immunohistochemistry and real-time confocal microscopy revealed mild (grade I: 1%-40%) BD damage in 8 patients and moderate (grade II: 40%-80%) injury in 1 patient. Donor and recipient data alone had no predictive capacity toward BC. Deep learning-based analysis of HSI data resulted in >90% accuracy of automated detection of BD. The CNN-based analysis yielded a correct classification in 72% and 69% for BC/no BC. The combination of HSI with donor and recipient factors showed 94% accuracy in predicting BC. CONCLUSIONS: Deep learning-based modeling using CNN of HSI-based tissue property data represents a noninvasive technique for predicting postoperative BC.

Perfusate Enzymes and Platelets Indicate Early Allograft Dysfunction After Transplantation of Normothermically Preserved Livers.

BACKGROUND: Normothermic machine perfusion (NMP) has become a clinically established tool to preserve livers in a near-physiological environment. However, little is known about the predictive value of perfusate parameters toward the outcomes after transplantation. METHODS: Fifty-five consecutive NMP livers between 2018 and 2019 were included. All of the livers were perfused on the OrganOx metra device according to an institutional protocol. Transplant and perfusion data were collected prospectively. RESULTS: Forty-five livers were transplanted after NMP. Five livers stem from donors after circulatory death and 31 (68.9%) from extended criteria donors. Mean (SD) cold ischemia time was 6.4 (2.3) h; mean (SD) total preservation time was 21.4 (7.1) h. Early allograft dysfunction (EAD) occurred in 13 of 45 (28.9%) patients. Perfusate aspartate aminotransferase (P = 0.008), alanine aminotransferase (P = 0.006), lactate dehydrogenase (P = 0.007) and their development over time, alkaline phosphatase (P = 0.013), and sodium (P = 0.016) correlated with EAD. Number of perfusate platelets correlated with cold ischemia time duration and were indicative for the occurrence of EAD. Moreover, von Willebrand Factor antigen was significantly higher in perfusates of EAD livers (P < 0.001), and Δ von Willebrand factor antigen correlated with EAD. Although perfusate lactate and glucose had no predictive value, EAD was more likely to occur in livers with lower perfusate pH (P = 0.008). ΔPerfusate alkaline phosphatase, Δperfusate aspartate aminotransferase, Δperfusate alanine aminotransferase, and Δperfusate lactate dehydrogenase correlated closely with model for early allograft function but not liver graft assessment following transplantation risk score. Bile parameters correlated with extended criteria donor and donor risk index. CONCLUSIONS: Biomarker assessment during NMP may help to predict EAD after liver transplantation. The increase of transaminases and lactate dehydrogenase over time as well as platelets and vWF antigen are important factors indicative for EAD.

Mitochondrial respiration during normothermic liver machine perfusion predicts clinical outcome.

BACKGROUND: Reliable biomarkers for organ quality assessment during normothermic machine perfusion (NMP) are desired. ATP (adenosine triphosphate) production by oxidative phosphorylation plays a crucial role in the bioenergetic homeostasis of the liver. Thus, detailed analysis of the aerobic mitochondrial performance may serve as predictive tool towards the outcome after liver transplantation. METHODS: In a prospective clinical trial, 50 livers were subjected to NMP (OrganOx Metra) for up to 24.ßh. Biopsy and perfusate samples were collected at the end of cold storage, at 1.ßh, 6.ßh, end of NMP, and 1.ßh after reperfusion. Mitochondrial function and integrity were characterized by high-resolution respirometry (HRR), AMP, ADP, ATP and glutamate dehydrogenase analysis and correlated with the clinical outcome (L-GrAFT score). Real-time confocal microscopy was performed to assess tissue viability. Structural damage was investigated by histology, immunohistochemistry and transmission electron microscopy. FINDINGS: A considerable variability in tissue viability and mitochondrial respiration between individual livers at the end of cold storage was observed. During NMP, mitochondrial respiration with succinate and tissue viability remained stable. In the multivariate analysis of the 35 transplanted livers (15 were discarded), area under the curve (AUC) of LEAK respiration, cytochrome c control efficiency (mitochondrial outer membrane damage), and efficacy of the mitochondrial ATP production during the first 6.ßh of NMP correlated with L-GrAFT. INTERPRETATIONS: Bioenergetic competence during NMP plays a pivotal role in addition to tissue injury markers. The AUC for markers of outer mitochondrial membrane damage, ATP synthesis efficiency and dissipative respiration (LEAK) predict the clinical outcome upon liver transplantation. FUNDING: This study was funded by a Grant from the In Memoriam Dr. Gabriel Salzner Stiftung awarded to SS and the Tiroler Wissenschaftsfond granted to TH.

Hyperspectral Imaging and Machine Perfusion in Solid Organ Transplantation: Clinical Potentials of Combining Two Novel Technologies.

Organ transplantation survival rates have continued to improve over the last decades, mostly due to reduction of mortality early after transplantation. The advancement of the field is facilitating a liberalization of the access to organ transplantation with more patients with higher risk profile being added to the waiting list. At the same time, the persisting organ shortage fosters strategies to rescue organs of marginal donors. In this regard, hypothermic and normothermic machine perfusion are recognized as one of the most important developments in the modern era. Owing to these developments, novel non-invasive tools for the assessment of organ quality are on the horizon. Hyperspectral imaging represents a potentially suitable method capable of evaluating tissue morphology and organ perfusion prior to transplantation. Considering the changing environment, we here discuss the hypothetical combination of organ machine perfusion and hyperspectral imaging as a prospective feasibility concept in organ transplantation.

Dealing With Liver Transplantation during Coronavirus Disease 2019 Pandemic: Normothermic Machine Perfusion Enables for Donor, Organ, and Recipient Assessment: A Case Report.

The coronavirus disease 2019 (COVID-19) pandemic has changed life on a global scale. The numbers of transplantations have plummeted as a result of fear of disease transmission, recipient coronavirus disease 2019 infection, priority shift, and resource limitations. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) complicates transplantation because donor testing, (re)allocation of limited resources, and recipient testing may exceed permissible ischemia times. Normothermic machine perfusion (NMP) helps safely prolong liver preservation up to 38 hours. Additional time is essential under the current circumstances. Here we present the case of a 29-year-old liver transplant recipient in whom prolonged liver preservation required for SARS-CoV-2 screening was accomplished through NMP. Donor and recipient test results for SARS-CoV-2 were negative, and intensive care unit capacity was eventually available. The surgical procedure and postoperative course were uneventful. NMP can extend preservation times in liver transplantation while awaiting SARS-CoV-2 test results and available intensive care unit capacity.