Selection of Donors
Organ Donation
Sources for transplanted organs include donations from cardiac death donors, brain death donors, and living donors.
Selection of Organs
Due to the shortage of organs, age limits for donors have been progressively relaxed. Typically, the recommended age limits are below 55 years for lung and pancreas donation, 60 years for heart donation, 65 years for kidney donation, and 70 years for liver donation.
Donors with the following conditions are contraindicated for organ transplantation:
- Generalized infections with positive blood cultures that are not fully resolved.
- HIV infection.
- Malignant tumors, with the exception of primary malignant brain tumors.
Organs from donors with hepatitis B or C infections, a history of substance abuse, or relevant organ-related medical histories should be considered cautiously.
Immunological Selection of Organs
To prevent severe or even fatal rejection reactions, certain tests should be performed prior to transplantation.
ABO Blood Group Typing
ABO blood group antigens are expressed not only on red blood cells but also on vascular endothelial cells. Therefore, in allogeneic transplantation, blood group compatibility must generally adhere to the principles of blood transfusion. However, there have been reported successful cases of liver transplantation using ABO-incompatible donors.
Lymphocytotoxic Cross-Match Test
This test involves mixing the recipient's serum with the donor's lymphocytes to investigate serum-to-lymphocyte binding. This test is essential before clinical transplantation. A lymphocytotoxic cross-match result of <10% is considered negative and permits kidney transplantation. In recipients with prior blood transfusions, pregnancies, or allogeneic transplants, anti-HLA antibodies may preexist in their serum, often yielding a positive result. Transplantation in such cases could trigger hyperacute rejection postoperatively.
HLA Typing
International standards require testing for at least HLA-A and HLA-B in class I antigens and HLA-DR in class II antigens in both donor and recipient. Numerous studies have shown that matching these six loci is closely related to long-term survival in kidney and bone marrow transplantation. However, with the clinical application of newer immunosuppressive drugs, the significance of this discrepancy is gradually diminishing.
Organ Harvesting and Preservation
The methods for harvesting and preserving organs vary depending on the type of donor and the specific organ required. The process of obtaining organs typically includes surgical exploration, in situ perfusion, organ removal, preservation, and transportation.
After interruption of an organ’s blood supply during the surgical procedure, cellular viability diminishes rapidly within a short period at 35–37°C. To ensure the quality of donated organs, it is critical to minimize both warm ischemia time and cold ischemia time.
Warm ischemia time refers to the interval between the cessation of blood circulation or localized blood supply in the donor and the initiation of cold perfusion. This period incurs the greatest damage to the organ and is generally restricted to less than 10 minutes.
Cold ischemia time refers to the period from the initiation of cold perfusion to the re-establishment of blood flow in the transplanted organ after the procedure. This includes the organ preservation phase.
It is essential to minimize mechanical damage or harm to donor organs during harvesting. In cases requiring multi-organ procurement, the typical sequence begins with the heart, followed by the small intestine, the liver, and pancreas, and finally the kidneys.
During organ harvesting, specialized organ perfusion solutions are used to rapidly flush the organ, removing blood as thoroughly as possible. The organ is then stored in a container filled with the perfusion solution until transplantation. Among the clinically most common organ perfusion and preservation solutions are UW solution (University of Wisconsin solution), HTK solution (histidine-tryptophan-ketoglutarate solution), and Hartmann's solution.
UW solution mimics intracellular fluid, with a cation concentration similar to that of intracellular environments.
Hartmann’s solution consists of lactated Ringer's solution supplemented with albumin, resembling extracellular fluid.
HTK solution, on the other hand, does not mimic either intracellular or extracellular fluid.
Hartmann’s solution is typically used for the cold perfusion step during organ harvesting, while UW solution and HTK solution are more commonly used for organ preservation.
Theoretical preservation times vary: UW solution can preserve the pancreas and kidneys for up to 72 hours, and the liver for 20–24 hours. However, in clinical practice, maximum preservation times are usually limited to:
- Heart: 5 hours
- Kidneys: <24–30 hours
- Pancreas: <10–12 hours
- Liver: <8–12 hours