Machine perfusion of the liver: Which is the best technique to mitigate ischaemia-reperfusion injury?

Table 1 Advantages and disadvantages of different modalities of machine perfusion of the liver

	Advantage	Disadvantage
Machine perfusion of the liver (All modalities)	Continuous circulation-improved preservation of the microcirculation; Nutrients and oxygen delivery for cellular metabolism; Removal of metabolic waste products; Delivery of cytoprotective agents and/or metabolic-modulating agents	Costly procedure; Requires specialised team
Techniques leading to reperfusion of the liver during machine perfusion (In situ normothermic regional perfusion; Ex situ normothermic machine perfusion)	Support organ full metabolism; Assessment of organ viability Assessment of hepatocellular injury; Potential to extend the period of organ storage; Possibility to shorten the ischaemic period of the livers	Persuade reperfusion on the machine; Risk of organ injury in case of organ failure or unrecognised problems with cannulation of the vessels; Require the use of an oxygen carrier in the perfusate
Techniques that do not lead to reperfusion of the liver during machine perfusion (Hypothermic oxygenated machine perfusion; dual-vessel hypothermic oxygenated perfusion; subnormothermic machine perfusion; controlled oxygenated rewarming)	Assessment of hepatocellular injury; Enhancement of mitochondrial function and replenishment of cellular energy stores; Lower rates of intra-hepatic biliary complications post-transplantation; Does not require oxygen carriers in the perfusate	Limited metabolic rate of the organs does not favour assessment of organ viability; Definition of the biomarkers to individualise perfusion times and assess responses to treatment in real-time is still pending
Ischaemia-free organ transplantation	Potential to abolish completely ischaemia-reperfusion injury	Limited application to donation after brainstem death thus far; Challenging procedure; Logistically challenging in a multivisceral retrieval setting; Just a single case reported