Hemodialysis involves cleansing a person's blood via a kidney machine, because their own kidneys are no longer able to do the job. A person undergoing hemodialysis is connected to a kidney machine, through which their blood is passed and cleansed for a period of approximately 4 hours, usually 3 times weekly. Hemodialysis can be undertaken either in hospital or at home. Home dialysis requires motivation and a competent attendant. For most people, in-hospital or in a center dialysis staffed by experienced nurses, is generally preferable. Many people on hemodialysis are waiting for a kidney transplant. However, some people are unsuitable for transplantation and remain on dialysis for the rest of their lives.
Research into how much dialysis is required has shown that under-dialysis carries a significant mortality. It is important to understand that a dialysis prescription of, say, 4 hours, 3 times per week is the minimum necessary to maintain long-term health. In the early days of dialysis, people used to suffer serious complications with their first dialyzes, because treatment was started late and the changes in their chemistry were very drastic. Today, these types of problems are usually avoided by introducing dialysis treatment earlier and more gently.
How is hemodialysis done?
Because repeated access to the person's blood stream is required, an artificial connection between an artery and a vein (arteriovenous fistula) is made, using a small surgical procedure. The preferred method is an arteriovenous fistula in the forearm. This results in expansion (dilatation) of the vein so it can easily be punctured with a large needle each time dialysis is undertaken. An alternative is an implanted plastic arteriovenous shunt that is again, usually placed in the forearm, though they can be placed in other locations. Blood flowing through a tube from the patient is pumped through the dialysis machine, called a dialyzer (see figure 1).
The dialyzer separates the blood from dialysis fluid via a membrane. This allows substances that would normally be excreted by the kidney to cross from the patient's blood into the dialysis fluid, and also allows other adjustments such as removal of salt and water from the patient during the dialysis process. The dialysis fluid becomes waste. Dialyzers come in different sizes and degrees of efficiency. The newer units allow blood to flow fast, shortening dialysis time to 2 to 3 hours, 3 times a week. The older units however, can take 3 to 5 hours, 3 times a week.
People who are on dialysis have essentially no kidney function in the period between each dialysis, and therefore need to be on a regulated diet. Most importantly, they need to control their intake of salt, water, and of potassium, otherwise dangerous complications can arise before their next dialysis treatment. Regulating blood pressure in people on dialysis can also be problematic.
What are the complications of hemodialysis?
People on dialysis do not maintain normal blood chemistry. Significant fluctuations occur pre- and post-dialysis that sometimes cause symptoms. However, some people have maintained reasonable health on chronic dialysis for more than a decade.
Many people on hemodialysis are able to hold down jobs and live relatively normal lives, except for the inconvenience of the regular treatment. Complications of long-term hemodialysis include difficulties with access (fistula of shunt), anemia, now generally managed by administering erythropoietin injections, and less commonly, as in untreated renal failure, problems with bones, nerves, and other organs.
People on either hemodialysis or peritoneal dialysis usually require medication for phosphate control, as phosphate is not efficiently removed by dialysis. Medications for blood pressure and erythropoietin to prevent severe anemia are also required.