**8. Machine perfusion**

Full discussion about the machine perfusion is beyond the scope of this chapter. Ideally all the organs retrieved should be transplanted immediately or as soon as possible in the same center of the organ procurement. But this is impossible, irrational or illegal in many situations. The donor operation can be easily done in a small rural hospital without any transplant facilities in unstable patients. In such cases transferring the organ to other hospitals is the rule. Another such circumstances is, when histocompatibility (for example for kidney and pancreas), or duration of stay in the waiting list is an important matter for decision making, and transplantation in the same center in such cases is both irrational and illegal. In marginal donors and in cases of donation after cardiac death (DCD), it is very important for the transplant surgeon to predict functionality of the organs. In all such situation, machine perfusion is the best way to know the organ function and increase the time of organ viability before final *in vivo* reperfusion.

In contrast to static cold storage (SCD) which we discussed in all sections of this chapter, dynamic perfusion techniques use a perfusate for active perfusion of the organs *in situ* (*en vivo*) or ex situ (*ex vivo*) [35]. For example, normothermic regional perfusion (NRP) is an *en vivo* method for reconditioning organs for DCD by restoring oxygenated blood flow to the organs before procurement. For such purpose, we need a sophisticated Extracorporeal Machine Oxygenation (ECMO) technology, which is not available in most centers. In contrast to this technique, *ex vivo* machine perfusion is used after organ recovery specially for kidneys and liver. It may be used in a hypothermic (hypothermic machine perfusion or HMP) or normothermic (normothermic machine perfusion or NMP) milieu. For kidney grafts, it is shown that HMP reduced significantly delayed graft function both after DCD and donation after brain death in marginal donors [35]. NMP is an established method for confirming the functionality of marginal liver grafts by showing the function of the graft and preventing ischemic cholangiopathy and it is shown that this method reduced the discard rate by 50% [36]. The results are promising for pancreas and small intestine as well. Machine perfusion of the heart is an essential step in all cases of DCD and for lungs it is essential for uncontrolled DCD cases [37]. In my opinion, future of organ transplantation from marginal donors is in the hand of the engineers who invents better, cheaper and more efficient and reliable machines with simpler use by transplant surgeons, but at these days use of these techniques should be limited to high income countries with an extensive network of transplantation services all around their territories.
