What is kidney transplantation?
Transplantation of a human kidney from a donor to a recipient has been used since the middle of the twentieth century to improve the quality and length of life for people with renal failure. While hemodialysis—or the use of an artificial kidney machine, as it is commonly known—can be used satisfactorily for years, transplantation is often the ultimate goal because it can return the patient to a near-normal life.
The kidneys play a pivotal role in maintaining a stable internal environment by controlling fluid levels, excreting waste products, and regulating the blood concentration of acids and bases and of ions such as sodium and potassium. The kidneys are also responsible for regulating blood pressure by secreting substances that constrict the blood vessels. Clearly, the derangement of such complex functions, as occurs in renal disease, is life-threatening.
There are many reasons for renal failure, but the most frequent are inherited disorders, severe infections, toxic substances, allergic reactions, diabetes mellitus, and hypertension. The latter two, which are common illnesses in the United States, result in renal damage because of long-term injury to the blood vessels. The symptoms of minimally or nonfunctioning kidneys reflect an accumulation of toxic waste products and dramatic changes in the chemical composition of the blood. Every system is affected until coma and death ensue. The process of hemodialysis is used intermittently to cleanse the blood and maintain life. Transplantation in the otherwise healthy person, however, is preferred.
An extraordinary amount of cooperation and preparation is necessary for successful kidney transplantation. The donor organ may come from a living blood relative or from a cadaver within minutes of death. The organ is removed and maintained at low temperature in a special preservative solution for up to forty-eight hours. A suitable recipient is located through a national registry that can rapidly pair a cadaver organ to a waiting patient. The chosen candidate is immediately prepared for surgery, and through an abdominal incision, the kidney is placed in the abdomen and connected to the blood supply by its artery and vein. The ureter, the urine-collecting duct, is attached to the bladder. The recipient’s own diseased kidneys may or may not be removed; their presence does not interfere with the transplanted organ. Within hours, the newly transplanted organ begins to form urine.
All transplanted organs and tissues face both immediate and long-term rejection by the recipient’s immune system. Recognizing the donated kidney as foreign, or “nonself,” the immune system attacks it both physically and chemically. The injury can be so severe as to result in the organ’s death and the need for its surgical removal. In an attempt to prevent this reaction, certain steps are taken both before and after transplantation surgery.
Matching a donor and recipient involves careful selection that must minimize the physiological differences that exist between people. The blood types (the ABO and Rh systems) should be the same. Gene sequences on the sixth chromosome that code for immune system components are also matched as closely as possible in a process known as human leukocyte antigen (HLA) compatibility. Living, first-degree relatives, such as parents or siblings, often provide the best survival rates because of the genetic similarities between donor and recipient. The loss of one kidney in a healthy individual does not appear to affect the body.
The excellent success rates that have been achieved—over 80 percent—are attributable both to preoperative matching and to immunosuppression, which is begun shortly before surgery and continued for many months afterward. Potent drugs are used to inhibit the recipient’s immune system, thereby protecting the new kidney from attack and significantly reducing rejection. Eventually, the drugs are tapered off and stopped, having allowed the body time to adjust to the foreign tissue and the kidney time to heal.
As can be expected in a procedure as difficult as kidney transplantation, the risks and complications are many. In the immediate postoperative period, hemorrhaging from the attached renal artery or vein, leakage from the ureter, organ malfunction, and immediate rejection can occur. Often, difficulties begin weeks or even months later, because of both rejection damage to the kidney and side effects related to severe immunosuppression. Immunosuppression leaves the body prey to bacterial, viral, and fungal infections, as well as cancer. Sometimes, a vicious cycle begins, in which life-threatening infections require the discontinuation of the immunosuppressive drugs, and the probability of organ rejection and irreparable kidney damage is heightened. Continual patient monitoring is absolutely essential to maintain the delicate balance between the risks and benefits involved in this procedure.
Prior to 1962, when immunosuppressive drugs were unavailable and matching could only be based on blood type, kidney transplantation was an experimental procedure usually involving the organ of a living, first-degree relative. In the following decades, an extraordinary surge in information about the immune system and the genes that control the rejection response, as well as the discovery of powerful drugs, made transplantation a successful alternative for patients supported by hemodialysis. It also significantly increased the donor pool of organs by allowing unrelated cadaver kidneys to be used. It is in both areas, more precise matching and the development of less toxic postoperative drugs, that research continues. Contributions made in this field are readily used for research in all other organ transplantation as well.
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