Arteriovenous Fistula

Definition
Purpose
Demographics
Description
Diagnosis/Preparation
Description
Aftercare
Risks
Normal results
Morbidity and mortality rates

Definition

An arteriovenous fistula (AV fistula) is an abnormal connection between a vein and an artery. The connection can be congenital (present at birth). Occasionally the connection can develop because of trauma such as a knife or bullet wound. Most often, the AV fistula is created surgically to allow access to the vascular system for hemodialysis. When created surgically, the connection of a vein and an artery is usually done in the forearm.

Purpose

Hemodialysis is the process of mechanically cleansing the blood when the kidneys have failed. 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, blood flow increases and the vein gradually becomes larger and stronger, creating a site that provides vascular access years longer than other types of access and with fewer complications. AV fistulas are for people who will need dialysis for long periods—either until a kidney becomes available for transplantation or for the rest of their life. Short-term access to the vascular system for dialysis can be had by the insertion of a venous catheter.

Demographics

According to the National Kidney Foundation, at the end of 2005, 336,000 Americans were receiving dialysis for kidney failure. Typically, another condition or disease caused the kidney shutdown. In the United States, kidney failure is disproportionately high among minority populations with the highest rate being found among African Americans, Hispanic Americans, and Native Americans. Among those receiving dialysis, over half will have an AV fistula as vascular access.

Description

The kidneys are paired organs in the mid-abdo-men, one on each side of the lower back. Their function is to clean the blood of wastes and to regulate fluid and electrolyte balance in the body. Dialysis performs these functions in place of the failing kidneys. Dialysis cannot restore kidney function, but it can prolong life, often for years, by preventing the build-up of waste products in the body.

Acute kidney failure usually happens in circumstances where an extra burden is placed on the renal system. For example, acute kidney failure can occur in advanced liver disease, rapidly progressing terminal illnesses such as cancer and certain severe anemias, after severe allergic reactions, as a reaction to drugs or poisons, in heart and lung diseases, during the formation of blood clots (embolism), and following heart bypass surgery. Diabetes and vascular diseases, especially those with hypertension, are the two most common underlying diseases contributing to chronic kidney failure.

Many advances in the treatment of kidney failure have been made since the first attempts at dialysis treatments in the 1920s. At one time, dialysis was thought of only 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 that occurred with frequent withdrawing and replacing of blood. The first breakthrough came in 1960 with the introduction of an implantable Teflon tube, called a shunt, that became 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.

Hemodialysis

Dialysis is performed as critical life support when a person experiences acute or chronic kidney failure. It is a mechanical way to cleanse the blood and balance body fluids when the kidneys are not able to perform these essential functions. Kidney failure can, in some cases, be reversible, and 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 a donated kidney. Some critically ill patients with life-threatening illnesses such as cancer or severe heart disease are not candidates for transplantation and dialysis for them is the only option for treating permanent kidney failure, also 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.

KEY TERMS

Access— The point where a needle or catheter is inserted for dialysis.

Acute renal (kidney) failure— Abrupt loss of kidney function, possibly temporary.

Artery— Blood vessel that carries blood away from the heart to the body.

Chronic renal (kidney) failure— Progressive loss of kidney function over several years that can result in permanent kidney failure requiring dialysis.

Electrolyte— Ions in the body that participate in metabolic reactions. The major human electrolytes are sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), chloride (Cl^-), phosphate (HPO4^2-), bicarbonate (HCO^3-), and sulfate (SO₄²-0).

Hypertension— High blood pressure.

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 cleansing. After being filtered, the blood is returned to the body through the same vascular access. About one cup (235 mL) 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. Dialysis centers offer patient education, including videos and brochures that describe treatment options and self-care. Patients can also receive advice and information about paying for this ongoing treatment through nationally sponsored programs that are available especially for those who need long-term dialysis. Often the dialysis center offers emotional support as well, letting people meet and talk with others 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: AV fistula, grafts, and catheters.

ARTERIOVENOUS FISTULA. An AV fistula has pro-en to be the best kind of vascular access for people whose veins are large enough, not only because it lasts longer, but also because it is 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 is used to provide temporary vascular access. When kidney disease has progressed quickly, there may not be time to prepare a permanent vascular access site 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 cause the veins to narrow. Long-term catheter access must be used in patients for whom AV 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 evaluate the patient’s general health, 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 electrolytes and other metabolites produced by the body that are normally excreted by the kidneys and passed through urine. The tests can measure effectively if the kidney is filtering out these materials, and how much remains in the blood. These tests include, but are not limited to:

• serum creatinine—found in higher levels in the blood if kidneys fail;
• urinary creatinine—readings are lower in kidney failure;
• urinary output—measuring both fluid intake and allurine produced;
• urinary osmolality—measures the concentration of the urine, an indicator of kidney filtering ability;
• blood urea nitrogen (BUN)—harmful nitrogen waste increases in the blood as kidney function decreases; and
• electrolytes in blood and urine—ions in the blood such as sodium, potassium, magnesium, and chloride are 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 AV fistula is usually doneusing a local anesthetic that is injected into the forearm at the site of the proposed fistula. The procedure is performed in a hospital or at an outpatient surgery if the patient is not already hospitalized and has no serious underlying disease.

After cleaning and sterilizing the site, the surgeon makes a small incision in the forearm sufficient to allow the permanent uniting of a vein and an artery. The blood vessels will be appropriately blocked to stop blood flow while incisions are made to join them. Silk sutures, just as those used in other types of surgical incisions, are used to close incised areas as needed after the vein and artery have been joined. Once joined, blood flow increases. 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 have to learn how to avoid infection and to protect the 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;
• taking care not to bump or cut the access;
• avoiding wearing tight jewelry or clothing near or over the access site;
• avoiding lifting heavy objects or putting pressure on the access arm; and
• 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. Complications include infection around the access area and formation of clots in the fistula. Usually, because they are in the fistula itself, these clots are not life threatening. The greatest danger is that clots may block the fistula and 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.

Other complications from dialysis 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, patients develop 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 when fluid and wastes are removed from the blood too quickly;
• nausea due to changes in blood pressure;

WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?

The surgery to create an AV fistula for vascular access in hemodialysis is performed by a general surgeon or vascular surgeon in a hospital or outpatient surgery center.

• muscle cramps from the removal of too much fluid from the blood;
• headaches near the end of a dialysis session resulting from changes in the concentration of fluid and waste in the blood; or
• 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 it takes to develop the fistula after surgery (usually months) depends upon the size and strength of the patient’s blood vessels and on the person’s health 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 in it. 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 to reduce the chances of being hospitalized with complications. It also gives patients 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 close to the 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

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, reduced incidence of clotting and infection, and longer use than other types of vascular access.

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?

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 about 50% because of the multi-organ dysfunction that has influenced kidney failure.

Resources

BOOKS

Offer, Daniel, Marjorie K. Offer, and Susan O. Szafir. Dialysis without Fear: A Guide to Living Well on Dialysis for Patients and Their Families. New York: Oxford University Press, 2007.

OTHER

“Treatment Methods for Kidney Failure: Hemodialysis.” National Kidney and Urologic Diseases Information Clearinghouse. December 2006. http://kidney.niddk.nih.gov/kudiseases/pubs/hemodialysis/index.htm (February 1, 2008).

“Vascular Access for Hemodialysis.” National Kidney and Urologic Diseases Information Clearinghouse. February 2008. http://kidney.niddk.nih.gov/kudiseases/pubs/vascularaccess/ (February 1, 2008).

“Vascular Access for Hemodialysis.” Texas Heart Institute. July 2007. http://www.texasheartinstitute.org/HIC/Topics/Proced/vascular_access_surgery.cfm (February 1, 2008).

ORGANIZATIONS

National Kidney and Urologic Diseases, 3 Information Way, Bethesda, MD, 20892-3580, (800) 891-5390, http://kidney.niddk.nih.gov.

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

L. Lee Culvert

Tish Davidson, A. M.