participated in data collection, data analysis, and critical revision of the article. C.I. and A.G. contributed reagents, analytic tools, and participated in data analysis. M.R. and H.U. participated in data analysis and statistical support. D.Ö. and J.T. supported the study, contributed research advice, and revised the article critically.

Background Given the susceptibility of organs to ischaemic injury, alternative preservation methods to static cold storage (SCS), such as normothermic machine perfusion (NMP) are emerging. The aim of this study was to perform a comparison between NMP and SCS in liver transplantation with particular attention to bile duct lesions. Methods The outcomes of 59 consecutive NMP-preserved donor livers were compared in a 1 : 1 propensity score-matched fashion to SCS control livers. Postoperative complications, patient survival, graft survival and bile duct lesions were analysed. Results While patients were matched for cold ischaemia time, the total preservation time was significantly longer in the NMP group (21 h versus 7 h, P < 0.001). Patient and graft survival rates at 1 year were 81 versus 82 per cent (P = 0.347) and 81 versus 79 per cent (P = 0.784) in the NMP and SCS groups, respectively. The postoperative complication rate was comparable (P = 0.086); 37 per cent NMP versus 34 per cent SCS patients had a Clavien-Dindo grade IIIb or above complication. There was no difference in early (30 days or less) (NMP 22 versus SCS 19 per cent, P = 0.647) and late (more than 30 days) (NMP 27 versus SCS 36 per cent, P = 0.321) biliary complications. However, NMP-preserved livers developed significantly fewer ischaemic-type bile duct lesions (NMP 3 versus SCS 14 per cent, P = 0.047). Conclusion The use of NMP allowed for a significantly prolonged organ preservation with a lower rate of observed ischaemic-type bile duct lesions.

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.

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.

Normothermic machine perfusion (NMP) has emerged as an innovative organ preservation technique. Developing an understanding for the donor organ immune cell composition and its dynamic changes during NMP is essential. We aimed for a comprehensive characterization of immune cell (sub)populations, cell trafficking and cytokine release during liver NMP. Single-cell transcriptome profiling of human donor livers prior to, during NMP and after transplantation shows an abundance of CXC chemokine receptor 1+/2+ (CXCR1+/CXCR2+) neutrophils, which significantly decreased during NMP. This is paralleled by a large efflux of passenger leukocytes with neutrophil predominance in the perfusate. During NMP, neutrophils shift from a pro-inflammatory state towards an aged/chronically activated/exhausted phenotype, while anti-inflammatory/tolerogenic monocytes/macrophages are increased. We herein describe the dynamics of the immune cell repertoire, phenotypic immune cell shifts and a dominance of neutrophils during liver NMP, which potentially contribute to the inflammatory response. Our findings may serve as resource to initiate future immune-interventional studies.

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.

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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.