Machine perfusion in liver transplantation

BACKGROUND

Liver transplantation is the only chance of cure for people with end-stage liver disease and some people with advanced liver cancers or acute liver failure. The increasing prevalence of these conditions drives demand and necessitates the increasing use of donated livers which have traditionally been considered suboptimal. Several novel machine perfusion preservation technologies have been developed, which attempt to ameliorate some of the deleterious effects of ischaemia reperfusion injury. Machine perfusion technology aims to improve organ quality, thereby improving outcomes in recipients of suboptimal livers when compared to traditional static cold storage (SCS; ice box).

OBJECTIVES

To evaluate the effects of different methods of machine perfusion (including hypothermic oxygenated machine perfusion (HOPE), normothermic machine perfusion (NMP), controlled oxygenated rewarming, and normothermic regional perfusion) versus each other or versus static cold storage (SCS) in people undergoing liver transplantation.

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest search date was 10 January 2023.

SELECTION CRITERIA

We included randomised clinical trials which compared different methods of machine perfusion, either with each other or with SCS. Studies comparing HOPE via both hepatic artery and portal vein, or via portal vein only, were grouped. The protocol detailed that we also planned to include quasi-randomised studies to assess treatment harms.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were 1. overall participant survival, 2. quality of life, and 3. serious adverse events. Secondary outcomes were 4. graft survival, 5. ischaemic biliary complications, 6. primary non-function of the graft, 7. early allograft function, 8. non-serious adverse events, 9. transplant utilisation, and 10. transaminase release during the first week post-transplant. We assessed bias using Cochrane's RoB 2 tool and used GRADE to assess certainty of evidence.

MAIN RESULTS

We included seven randomised trials (1024 transplant recipients from 1301 randomised/included livers). All trials were parallel two-group trials; four compared HOPE versus SCS, and three compared NMP versus SCS. No trials used normothermic regional perfusion. When compared with SCS, it was uncertain whether overall participant survival was improved with either HOPE (hazard ratio (HR) 0.91, 95% confidence interval (CI) 0.42 to 1.98; P = 0.81, I2 = 0%; 4 trials, 482 recipients; low-certainty evidence due to imprecision because of low number of events) or NMP (HR 1.08, 95% CI 0.31 to 3.80; P = 0.90; 1 trial, 222 recipients; very low-certainty evidence due to imprecision and risk of bias). No trials reported quality of life. When compared with SCS alone, HOPE was associated with improvement in the following clinically relevant outcomes: graft survival (HR 0.45, 95% CI 0.23 to 0.87; P = 0.02, I2 = 0%; 4 trials, 482 recipients; high-certainty evidence), serious adverse events in extended criteria DBD liver transplants (OR 0.45, 95% CI 0.22 to 0.91; P = 0.03, I2 = 0%; 2 trials, 156 participants; moderate-certainty evidence) and clinically significant ischaemic cholangiopathy in recipients of DCD livers (OR 0.31, 95% CI 0.11 to 0.92; P = 0.03; 1 trial, 156 recipients; high-certainty evidence). In contrast, NMP was not associated with improvement in any of these clinically relevant outcomes. NMP was associated with improved utilisation compared with SCS (one trial found a 50% lower rate of organ discard; P = 0.008), but the reasons underlying this effect are unknown. We identified 11 ongoing studies investigating machine perfusion technologies.

AUTHORS' CONCLUSIONS

In situations where the decision has been made to transplant a liver donated after circulatory death or donated following brain death, end-ischaemic HOPE will provide superior clinically relevant outcomes compared with SCS alone. Specifically, graft survival is improved (high-certainty evidence), serious adverse events are reduced (moderate-certainty evidence), and in donors after circulatory death, clinically relevant ischaemic biliary complications are reduced (high-certainty evidence). There is no good evidence that NMP has the same benefits over SCS in terms of these clinically relevant outcomes. NMP does appear to improve utilisation of grafts that would otherwise be discarded with SCS; however, the reasons for this, and whether this effect is specific to NMP, is not clear. Further studies into NMP viability criteria and utilisation, as well as head-to-head trials with other perfusion technologies are needed. In the setting of donation following circulatory death transplantation, further trials are needed to assess the effect of these ex situ machine perfusion methods against, or in combination with, normothermic regional perfusion.

Postmortem microbiological findings of two total artificial heart recipients

This report describes the postmortem microbiological findings and related gross pathology from two patients who had the longest survival after implantation of the Jarvik-7-100 total artificial heart. We documented extensive polymicrobial colonization at the site of the device and adjacent structures; however, the internal drive lines were remarkably free of bacterial colonization despite evidence of infection at the skin junction and in close proximity to the artificial heart. The polyurethane polymer (Biomer) on the external surface of the device was discolored and pitted in appearance and the Velcro material that attaches the two ventricles together was eroded. A nonspecific mass of tissue that was adherent to the device and to portions of the drive lines contained inflammatory cells, fibrinous debris, and colonies of microorganisms.

Biomaterial-centered sepsis and the total artificial heart. Microbial adhesion vs tissue integration

The principal barrier to the extended use of the total artificial heart is infection that is centered on the biomaterial constituting the prosthetic device and exacerbated by the surrounding damaged tissue. Ultrastructural studies of total artificial hearts removed from two patients indicate a failure of true tissue integration and diffuse, adhesive bacterial colonization of biomaterial surfaces. Biomaterials are, in part, susceptible to infection because, at the present state of the art, they are usually not well integrated with host tissue or, if hemodynamic, not optimally biocompatible or antiadhesive.

Infectious complications in four long-term recipients of the Jarvik-7 artificial heart

This article describes the infectious complications that occurred among four of the longest-term recipients of the Jarvik-7 artificial heart. Infection arising from the drive lines, with spread to the mediastinal periprosthetic space, was the major limiting factor in long-term use of the device in these patients. Periprosthetic infections were due to coagulase-negative staphylococci, Staphylococcus aureus, Pseudomonas aeruginosa, and other Pseudomonas species. Other infectious complications incurred by some of the patients included pneumonia, empyema, urinary tract infection, and intravascular line sepsis with Candida. Intensive antimicrobial therapy for prolonged periods seemed to suppress but not to eradicate infection and was accompanied by the appearance of multiresistant bacterial strains. Complications of antimicrobial therapy included diarrhea secondary to overgrowth with Clostridium difficile in two patients. Use of the current device for more than 30 days should be considered extraordinary and should be reserved for patients for whom no other form of life support is available.

Thromboembolic and infectious complications of total artificial heart implantation

Thromboembolic and infectious events were found to be major complications of long-term total artificial heart implantation in two patients. Similar complications have been reported in other patients, as well as in animal studies. The thromboembolic events and the infectious complications appear to be interrelated. On the one hand, thrombi located on the valves and at the vascular anastomoses of the artificial heart were found to be infected at autopsy; such infections are known to exacerbate formation of thromboemboli. On the other hand, the generation of microthrombi may have contributed to the RES blockade seen in our patients. We hypothesize that this RES blockade led to a progressive decrease in lymphoid system function and impaired the patients' capacity to clear microorganisms from the circulation. These phenomena arose, in part, from the design of the artificial heart and were exacerbated by associated therapy, such as blood transfusions. Our data suggest several measures that might be taken in order to reduce the severity of both the thrombogenic and infectious complications. Improved anticoagulation regimens, which increase the ability of the physician to maintain the proper balance between thrombotic and hemorrhagic potential, are needed. This may require not only improved methods of monitoring anticoagulation and predicting changes in the effectiveness of various agents as other events supervene, but also new anticoagulant and antithrombotic drugs, for example, low molecular weight heparins and prostacyclin derivatives. It is also clear that the design of the artificial heart should be modified in order to improve fluid dynamics so that they will approximate as closely as possible those of the natural heart. This includes redesigning the mounting of the valves to eliminate crevices and discontinuities that allow stagnant flow and predispose to thrombus formation as well as imposing a dP/dt that minimizes shear-related hemolysis, thereby minimizing the need for blood transfusions. Prevention of infections presents a more difficult problem. Transcutaneous lines (regardless of their use) are an obvious route for infection, and attention should be given to minimizing the number and length of use of monitoring lines. However, until a totally implantable drive system is available, the drive lines will remain a potential avenue for the introduction of infections. The risk may be minimized by rigorous attention to care of the exit sites and by improved designs that will provide a better mechanical barrier by, for example, enhancing epithelial ingrowth into the materials of the drive line.(ABSTRACT TRUNCATED AT 250 WORDS)