Overview of Hemodialysis (HD)
Hemodialysis removes waste and excess fluid from the blood when the kidneys cannot do so sufficiently. Hemodialysis is the most common method used to treat kidney failure. It may be performed in a hospital or hemodialysis center, or at home.
During hemodialysis, the blood is drawn intravenously, sent through a machine called a dialyzer, and returned to the body through a blood vessel. Inside the dialyzer, the blood is passed over a membrane that filters waste and fluid into a dialysate solution. The dialysate is then pumped out to a disposal tank and new dialysate is pumped in. The process of removing excess fluid is known as ultrafiltration.
The blood is circulated and diffused numerous times during a dialysis session; each circulation through the machine removes more waste and excess fluid. Hemodialysis is usually performed three or more times a week for 4 hours or more.
There are three methods of accessing the bloodstream:
Arteriovenous Fistula (AVF)
The forearm is a common site for intravenous access to the bloodstream. To form a fistula, a vascular surgeon joins an artery and a vein in the forearm, wrist, or upper-arm area on an outpatient basis with local anesthetic. This is done anywhere from 2 months to a year before dialysis, so the fistula can "mature."
As the fistula becomes stronger, a buzz (thrill) can be felt beneath the skin. Eventually, the new vein will bulge, indicating it is mature. After it has matured (usually at least 4 months), the fistula is a stronger, larger vein that can better withstand increased blood flow and the intravenous needles required for dialysis.
At the start of a dialysis session, the access area is anesthetized before the needles are inserted. Blood is directed from the fistula via a needle and tube, into the dialyzer, and returns to the body through a second tube and needle connected to the fistula. The needles are placed carefully to avoid recirculation and recleaning.
The AVF is the most successful mode of access, with the lowest risk of malfunction and infection. It lasts the longest. However, many patients' veins and arteries weaken with age and are not strong enough to support an AVF. Other problems include obesity, medical problems, and small blood vessels that do not mature.
Arteriovenous Graft (AVG)
To form an AVG, the vascular surgeon inserts a plastic (Gortex) tube, usually in the arm, that connects a vein and an artery. The tube accepts the dialysis needles for blood circulation. This is typically done in people whose veins cannot tolerate a fistula. The AVG only requires 10 to 14 days to heal before it can be used, but frequently malfunctions, causes infection, and has a shorter life span than the AVF.
Temporary Venous Dialysis Catheter
A catheter used for hemodialysis is a tube that has a needle at one end and two accessible ports at the other; it is shaped like a "Y." The needle end is inserted through the skin into a vein in the neck (internal jugular vein), chest (subclavian vein), or thigh (femoral vein). The split tubing and two ports remain outside of the body so that the ports can be accessed with the dialysis needles. One tube carries blood to the dialyzer and the other returns it to the bloodstream after it has been cleaned.
The catheter is used in patients who do not have an AVF or AVG but who need hemodialysis urgently. It is used temporarily as a means of access until an AVF or AVG can be inserted. The catheter is used permanently in some people who cannot tolerate the standard methods of access. It poses significant risk for infection and failure and must be replaced often.
There are approximately 300,000 people on dialysis in the United States. Some patients require dialysis in the hospital or clinic and others have in-home dialyzers that they are trained to operate (called home dialysis).
Most of the following complications are due to the repetition of hemodialysis sessions and the continual need to remove fluid that builds up between treatments:
- Back pain (5 percent)
- Chest pain (5 percent)
- Fever, chills (rare)
- Headache (5 percent)
- Hypotension (sudden drop in blood pressure; 20 percent)
- Itching (5 percent)
- Leg cramps (520 percent; treat with hypertonic saline infusion, quinine, klonipin)
- Light-headness (2555 percent; caused by hypotension, treat with fluid replacement)
- Nausea and vomiting (15 percent)
Recent studies have shown that more frequent and prolonged treatments diminish many of these and other chronic symptoms. For example, some evidence suggests that hemodialysis could be done five times a week at a clinic or at night while the patient sleeps. This has prompted new scenarios, such as nocturnal home dialysis and patient monitoring over the Internet.
Rare, Severe Complications of Hemodialysis
- Acute anaphylaxis (allergic reaction to antigens)
- Acute hemolysis (red-blood-cell damage with hemoglobin loss)
- Air embolism (air bubble obstructing a blood vessel)
- Hypoxemia (low of oxygen in the blood)
Chronic Hemodialysis Complications
- Access problems (e.g., clotting, infection, malfunction)
- Amyloidosis (causing carpal tunnel syndrome, shoulder pain)
- Anemia (reduction in red blood cell count)
- Arrhythmia (irregular heart beat)
- Calciphylaxis (calcification of tissue)
- Coronary artery disease
- Infection (causes death in 20 percent of people)
- Malnutrition (along with diet restriction)
- Renal osteodystrophy (bone degeneration with kidney disease)
- Vitamin and mineral deficiencies
In March 2012, the U.S. Food and Drug Administration (FDA) approved peginesatide (Omontys) to treat anemia in adults with chronic kidney disease who are on dialysis. This once-a-month injection helps to stimulate the bone marrow to produce more red blood cells. Side effects include diarrhea, vomiting, high blood pressure and joint pain.