ORGAN PRESERVATION
Solid organ harvesting and transplantation invariably cause injury
to the donor organ. Three main distinct periods have been identified that contribute
to injury: (1) storage of harvested organs ex vivo during transport (generally under
hypothermic conditions) from the donor to the recipient, (2) the implantation phase
(rewarming phase) without reperfusion, and (3) the initial reperfusion phase with
the reintroduction of oxygen. Each period contributes to deterioration of the organ
through a different pathway. Ex vivo storage involves immediate cooling and flushing
of the organ after harvesting with different available preservation solutions.[27]
Currently, most organs are stored at 4°C without continuous perfusion after
initial flushing. However, at some centers and organ procurement organizations,
organs are continuously perfused, in some cases with normothermic preservation.
Various cold storage solutions used worldwide include Collins, Euro-Collins (Fresenius,
Germany), Bretschneider/Histidin-Tryptophan-Ketogluterat (HTK) (Franz Koehler Chemie,
Germany), Celsior (Sangstat Medical Corporation, United States), Perfadex (Vitrolife,
Sweden), and University of Wisconsin (UW) (Du Pont, United States) solution.[28]
[29]
The UW solution is probably the most frequently
used solution, especially for intra-abdominal organs. Most solutions are modified
with additives (e.g., oxygen radical scavengers) that are believed to improve organ
storage conditions. The content of the various organ preservation solutions varies
widely, as does the amount used. For example, UW solution contains 120 mmol/L of
potassium versus only 10 mmol/L in the HTK solution. These differences may have
clinical implications, such as a greater potential for hyperkalemia after reperfusion
of organs preserved in UW solution. However, hyperkalemia is seen mainly in cases
in which the preservation solution is not adequately flushed with colloids before
implantation. Organ-specific flush solution is commonly used with Euro-Collins solution,
and more recently, Perfadex solution is being used for lung storage. The heart is
frequently stored in Celsior preservation solution, but medical centers may occasionally
have center-specific cardioplegia solutions. Sometimes perfluorocarbons are used
as a component of the two-layer method for preservation of the pancreas.[30]
Organ preservation solutions are under constant review and undergo frequent modifications.
The maximum cold preservation time varies between organs and solutions used. Typically,
kidneys can be stored in cold preservation solution for 1 to 2 days before transplantation,
whereas hearts are transplanted within hours of retrieval. Continuous machine perfusion
(as opposed to cold storage) of the organ has attracted some attention.[31]
However, this method is not widely adopted currently, and large randomized trials
are necessary to demonstrate its feasibility.[32]
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