Arteriovenous fistula

Definition

An arteriovenous fistula (AV fistula) is the connection of a vein and an artery, usually in the forearm, to allow access to the vascular system for hemodialysis, a procedure that performs the functions of the kidneys in people whose kidneys have failed. Connecting the vein and artery is a surgical procedure. The fistula develops over a period of months after the surgery.

Purpose

The surgical creation of an AV fistula provides a long-lasting site through which blood can be removed and returned during hemodialysis. The fistula, which allows the person to be connected to a dialysis machine, must be prepared by a surgeon weeks or months before dialysis is started. When the vein and artery are joined, the vein gradually becomes larger and stronger, creating the fistula that provides vascular access years longer than other types of access and with fewer complications.

Sometimes dialysis is only needed temporarily, but some people need it for the rest of their lives or until a kidney is available for a transplant. When kidney failure is diagnosed, time is needed to prepare the patient's body with either an AV fistula or implantable devices that will connect the person to the dialysis machine.

Demographics

At any one time, the number of patients in the United States with kidney failure is approximately two million and rising. According to the National Kidney Foundation, by the year 2008, three million people will be expected to have what is known as end-stage renal (kidney) disease. These people can be of any age, from any background. They are typically suffering from another condition or disease that has led to kidney shutdown, and most will require dialysis. Among dialysis patients, over half will have an AV fistula as vascular access.

Description

Many advances in the treatment of kidney failure have been seen since the first attempts at dialysis treatments were made in the 1920s. At one time dialysis was only thought of as a way to keep people alive until kidney function could be restored. Often the treatment for kidney failure had to be discontinued within several days because patients' veins could not endure the trauma of frequent withdrawing and replacing blood. The first breakthrough came in 1960 with the introduction of an implantable Teflon tube, called a shunt, that was the first effective vascular access device. Since then, the development of the AV fistula has marked another important advance, allowing effective treatment for longer periods of time. The goal of researchers and medical institutions is to continue to improve treatment and improve the length and quality of life for people with chronic kidney failure.

The kidneys are two organs in the mid-abdomen, one on each side of the middle back. Their function is to clean the blood of wastes and regulate fluid and chemical balance in the body. Dialysis performs these functions in place of the failing kidneys. Dialysis cannot restore the kidneys, but it can prolong life, often for years, by preventing the build-up of waste products in the body. Acute kidney failure can happen in many conditions and diseases that place an extra burden on the renal system, such as in advanced kidney and liver diseases; in rapidly progressing terminal illnesses, such as cancer and certain severe anemias; after severe allergic reactions or reactions to drugs or medications; in diseases that involve the vascular system, such as heart and lung diseases or the formation of blood clots (embolism); and often following heart bypass surgery. Diabetes and vascular diseases, especially those with hypertension (high blood pressure), are the two most common underlying diseases contributing to chronic kidney failure.

Hemodialysis

Dialysis is performed as critical life support when someone suffers acute or chronic kidney failure. It is a mechanical way to cleanse the blood and balance body fluids and chemicals when the kidneys are not able to perform these essential functions. Because kidney function can be reversible in some cases, dialysis can provide temporary support until renal function is restored. Dialysis may also be used in irreversible or chronic kidney shutdown when transplantation is the medical goal and the patient is waiting for donated kidneys. Some critically ill patients, with life-threatening illnesses, such as cancer or severe heart disease, are not candidates for transplantation and dialysis may be the only option for treating what is called end-stage renal disease (ESRD).

There are two types of dialysis, hemodialysis and peritoneal dialysis. In hemodialysis, the blood circulates through a machine outside the body and is filtered as it circulates. In peritoneal dialysis, the blood is filtered through a membrane that has been placed in the abdomen. Blood remains in the body and waste material is filtered into an exchange fluid through an opening in the abdomen called a port. Only hemodialysis requires an AV fistula or other vascular access.

Hemodialysis circulates blood through a dialysis machine that contains a filter membrane. The blood is slowly pumped out of the body and into the machine for filtering. After being filtered, the blood is returned to the body through the same vascular access. About one cup of blood is outside the body at any given moment during the continuous circulation process.

Hemodialysis is usually done three times a week, taking between three and five hours each time. Healthcare professionals perform the procedure either at independent dialysis centers or in hospitals or medical centers. Dialysis patients must go to the hemodialysis center where they will sit to receive the treatment. Although they cannot walk around, they can watch television, read, or talk to other patients. The dialysis center offers patient education, including videos and brochures that describe treatment options and self-care. Patients can also be given advice and information about paying for this ongoing treatment through nationally sponsored programs that are available especially for dialysis patients. Often the dialysis center offers emotional support as well, letting people meet and talk with other people who have kidney problems. Some people prefer to perform their own dialysis by having a home dialysis machine. This requires that the dialysis patient and another person, usually a family member, take a three- to six-week training program to learn how to do the treatment.

Vascular access

An access or entry to the vascular system is needed to perform the blood-cleansing role of the kidneys through hemodialysis. There are three types of vascular access: arteriovenous fistula, grafts, and catheters.

ARTERIOVENOUS FISTULA. An AV fistula has proven to be the best kind of vascular access for people whose veins are large enough, not only because it lasts longer but it is also less likely than other types of access to form clots or become infected. If the veins are not large enough, or there is no time to wait for a fistula to develop, a graft or a catheter must be used.

GRAFT. Grafts are often the access of choice when a hemodialysis patient has small veins that will not likely develop properly into a fistula. This type of access uses a synthetic tube implanted under the skin of the arm that can be used repeatedly for needle placement. Unlike a fistula, which requires time to develop, a graft can be used as soon as two to three weeks after placement. Grafts are known to have more problems than fistulas, such as clots and infection, and will likely need replacement sooner.

CATHETER. A catheter may be used to provide temporary vascular access. When kidney disease has progressed quickly, there may not be time to prepare permanent vascular access before dialysis treatments are started. The catheter is a tube that is inserted into a vein in the neck, chest, or in the leg near the groin. Two chambers in the tube allow blood to flow in and out. Once the catheter is in place, needle insertion is not necessary. Catheters are effective for dialysis for several weeks or months while surgery is performed and an AV fistula develops. They are not selected for permanent access because they can clog, become infected, or can cause the veins to narrow. Long-term catheter access must be used in patients for whom fistula or graft surgery has not been successful. If more than three weeks' use is expected, catheters can be made to tunnel under the skin, which increases comfort and reduces complications

Diagnosis/Preparation

Diagnosis

The diagnosis of kidney disease and its progression to kidney failure is typically made by a nephrologist, a specialist in kidney structure and function. The nephrologist will determine whether the patient has acute or chronic kidney failure and if dialysis is appropriate for the patient. If dialysis is recommended, the nephrologist will determine if an AV fistula is the ideal vascular access for the patient. To make these determinations, the nephrologist will need to be aware of the patient's general condition, especially the presence of any underlying disease. Kidney function must be evaluated and determined to be seriously impaired before dialysis is recommended. It is typically started when kidney function is down to about 10% of its normal level. Among other tests that will be performed, such as urinalysis with microscopic examination of the urine, several blood and urine tests can be used to measure a person's kidney function when chronic or acute kidney failure is suspected. Some of the tests measure chemicals produced by the body that are normally excreted (passed in urine) by the kidneys; the tests can measure how much is passing through, and how much remains in the blood, and then determine how well the kidneys are functioning compared to normal. These tests include, but are not limited to:

• Serum creatinine, found in higher levels in the blood if kidneys fail.
• Urinary creatinine, lower in kidney failure.
• Urinary output, measuring both fluid intake and all urine produced.
• Urinary osmolality, measuring the concentration of the urine, an indicator of kidney filtering ability.
• Blood urea nitrogen (BUN), harmful nitrogen waste that increases in the blood as kidney function decreases.
• Electrolytes in blood and urine, minerals that result from the breakdown of salts (sodium, potassium, magnesium, and chloride), often out of balance when kidneys fail. Potassium, for example, increases in the blood during kidney failure and can cause heart irregularities.

Description

Surgery to create an arteriovenous fistula is usually conducted using a local anesthetic, injected at the site of the proposed fistula. The procedure is performed in a hospital or one-day surgery center and can usually be performed on an outpatient basis if the patient is not already hospitalized. After cleaning and sterilizing the site, the surgeon will make a small incision in the forearm sufficient to allow the permanent joining together of a vein and an artery in the arm. The blood vessels will be appropriately blocked to stop blood flow for the procedure and incisions will be made to join them. Silk sutures, just as those used in other types of surgical incisions, will be used to close incised areas as needed after the vein and artery have been joined. Once joined, blood flow will increase, the vein will become thicker, and over a period of months the connection will become strong and develop into the fistula that will allow permanent vascular access.

Aftercare

The hemodialysis patient should expect needle insertion in the AV fistula at every dialysis session. Patients who prefer to insert their own needles or who perform dialysis at home will need training, and all patients will have to learn how to avoid infection and to protect vascular access. Because vascular access problems can lead to treatment failure, the AV fistula requires regular care to make dialysis easier and to help avoid clots, infection, and other complications. Patients can help protect the access by:

• Making sure the access is checked before each treatment.
• Not allowing blood pressure to be taken on the access arm.
• Checking the pulse in the access every day.
• Keeping the access clean at all times.
• Using the access site only for dialysis.
• Being careful not to bump or cut the access.
• Not wearing tight jewelry or clothing near or over the access site.
• Not lifting heavy objects or putting pressure on the access arm.
• Sleeping with the access arm free, not under the head or body.

Risks

The most frequent complications in hemodialysis relate to the vascular access site where needles are inserted. This can include infection around the access area or the formation of clots in the fistula. Usually, because they are in the fistula itself and do not travel to other parts of the body, these clots are not life-threatening. The greatest danger is that clots may block the fistula and would have to be removed surgically. Frequent clotting may require creating a back-up fistula at another site, to allow dialysis when one access is blocked.

There are other complications from dialysis that are not directly related to the vascular access. For example, when the kidneys have shut down, they produce very little urine. Because dialysis is the only way people with kidney failure can balance fluid levels in their bodies, hemodialysis can cause bloating and fluid overload, indicating that too much fluid remains in the body. If fluid overload occurs, the patient will have swollen ankles, puffy eyes, weight gain, and shortness of breath. Fluid overload can cause heart and circulatory problems and fluctuations in blood pressure. Medications may be prescribed and changes in fluid intake or diet may be made to help balance fluids safely in conjunction with dialysis.

Other problems that can occur during or after hemodialysis include:

• Low blood pressure, if fluid and wastes are removed from the blood too quickly.
• Nausea, because of changes in blood pressure.
• Muscle cramps from the removal of too much fluid from the blood.
• Headaches near the end of a dialysis session, due to changes in the concentration of fluid and waste in the blood.
• Fatigue after treatment, lasting sometimes into the next day.

Normal results

An AV fistula can usually be created and can function well with no adverse affects in a person whose veins are large enough. The amount of time, usually a matter of months, it takes to develop the fistula after surgery will depend upon the size and strength of the patient's blood vessels and on the person's general condition and nutritional status. When the fistula develops, the thickened vein that has been joined to an artery can be seen in the arm and a pulse can be felt. The early development of an AV fistula as access for long-term dialysis has been shown to improve the survival of patients with chronic renal failure, and reduce the chances of being hospitalized with complications. It also gives them a better opportunity to choose self-dialysis as their treatment.

With good nutrition and a fully functioning AV fistula, dialysis patients can be relatively comfortable and free of complications. People may become tired and uncomfortable when it is nearly time for their next dialysis session. This is to be expected because wastes are building up in the blood, and the body senses that it is time to remove them.

Morbidity and mortality rates

The earlier use of dialysis, especially with AV fistula access, has been shown to increase survival in patients with renal failure. The AV fistula is designed to improve the effectiveness of dialysis and is reported to present fewer risks and complications than other vascular access, such as reduced incidence of clotting and infection, and longer use overall.

Kidney failure is reported to account for 1% of hospital admissions in the United States. It occurs in 2–5% of patients hospitalized for other conditions, surgeries, or diseases. In patients undergoing cardiac bypass surgery, 15% are reported to require dialysis for kidney failure. Overall deaths in people undergoing dialysis are reported to be 50% because of the multi-organ dysfunction that has influenced kidney failure.

Resources

ORGANIZATIONS

National Kidney Foundation, Inc. 30 East 33rd Street, New York, NY 10016. (800)622-9010. http://www.kidney.org .

National Kidney and Urologic Diseases Information Clearinghouse. 31 Center Drive, MSC 2560 Building 31, Room 9A-04, Bethesda, MD 20892-2560. (800)891-5390. http://www.niddk.nih.gov .

OTHER

Getting the Most From Your Treatment: What You Need To Know About Hemodialysis Access. Booklet. New York: National Kidney Foundation, Inc. (800)622-9010. http://www.kidney.org .

NIDDK Kidney Failure Series. Booklet. Bethesda, MD: National Kidney and Urologic Diseases Information Clearinghouse. Email: nkudic@info.niddk.nih.gov.

Vascular Access to Hemodialysis. National Kidney and Urologic Diseases Information Clearinghouse, Home Health Information. December 1999. http://www.niddk.nih.gov .

L. Lee Culvert

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?

The surgery to create an arteriovenous fistula for vascular access in hemodialysis is performed by a general surgeon or vascular surgeon in a hospital or one-day surgery center. It requires only local anesthesia and can be performed as an outpatient procedure.

QUESTIONS TO ASK THE DOCTOR

• Why are you recommending an AV fistula instead of another kind of access?
• How will an AV fistula make dialysis easier or better for me?
• How often do you perform this procedure?
• What will the fistula look like? Feel like?
• Should I treat my fistula arm in any special way?
• Are there activities I should avoid?
• How long will the AV fistula last?