An arteriovenous fistula
is an abnormal channel or passage between an artery and a vein.
An arteriovenous fistula is a disruption of the normal blood flow pattern. Normally, oxygenated blood flows to the tissue through arteries and capillaries. Following the release of oxygen in the tissues, the blood returns to the heart in veins. An arteriovenous fistula is an abnormal connection of an artery and a vein. The blood bypasses the capillaries and tissues, and returns to the heart. Arterial blood has a higher blood pressure than veins and causes swelling of veins involved in a fistula. Although both the artery and the vein retain their normal connections, the new opening between the two will cause some arterial blood to shunt into the vein because of the blood pressure difference.
Causes and symptoms
There are two types of arteriovenous fistulas, congenital and acquired. A congenital arteriovenous fistula is one that formed during fetal development. It is a birth defect. In congenital fistulas, blood vessels of the lower extremity are more frequently involved than other areas of the body. Congenital fistulas are not common. An acquired arteriovenous fistula is one that develops after a person is born. It usually occurs when an artery and vein that are side-by-side are damaged and the healing process results in the two becoming linked. After catheterizations, arteriovenous fistulas may occur as a complication of the arterial puncture in the leg or arm. Fistulas also form without apparent cause. In the case of patients on hemodialysis, physicians perform surgery to create a fistula. These patients receive many needle sticks to flush their blood through dialysis machines and for routine blood analysis testing. The veins used may scar and become difficult to use. Surgery is used to connect an artery and vein so that arterial blood pressure and flow rate widens the vein and decreases the chance of blood clots
forming inside the vein.
The main symptoms of arteriovenous fistulas near the surface of the skin are bulging and discolored veins. In some cases, the bulging veins can be mistaken for varicose veins
. Other fistulas can cause more serious problems depending on their location and the blood vessels involved.
Using a stethoscope, a physician can detect the sound of a pulse in the affected vein (bruit). The sound is a distinctive to-and-fro sound. Dye into the blood can be tracked by x ray to confirm the presence of a fistula.
Small arteriovenous fistulas can be corrected by surgery. Fistulas in the brain or eye are very difficult to treat. If surgery is not possible or very difficult, injection therapy may be used. Injection therapy is the injection of substances that cause the blood to clot at the site of the injection. In the case of an arteriovenous fistula, the blood clot should stop the passage of blood from the artery to the vein. Surgery is usually used to correct acquired fistulas once they are diagnosed.
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Berkow, Robert, ed. Merck Manual of Medical Information. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
Braunwald, E. Heart Disease. Philadelphia: W. B. Saunders Co., 1997.
fistula [fis´tu-lah] (pl. fistulas, fis´tulae) (L.)
any abnormal tubelike passage within body tissue, usually between two internal organs or leading from an internal organ to the body surface. Some fistulas are created surgically for diagnostic or therapeutic purposes; others occur as result of injury or as congenital abnormalities. Among the many kinds of fistulas, the anal type (fistula in ano
) is one of the most common. It generally develops as a result of a break or fissure in the wall of the anal canal or rectum, or an abscess there. Treatment is by surgery.
In women, difficult labor in childbirth may result in formation of a vesicovaginal fistula
between the bladder and the vagina with resulting leakage of urine into the vagina. In a vesicointestinal fistula
, there is leakage of urine from the bladder into the intestine. In a rectovaginal fistula
, feces escape through the wall of the anal canal or rectum into the vagina. This condition, formerly a serious hazard of childbirth, is now rare; like other kinds of fistula, it can be corrected by surgery.
With the types of fistulas described here, typical symptoms are pain in the affected region and an abnormal discharge through the skin near the anus or through the vagina. Fistulas at different places of the body may be caused by tuberculosis
(a fungus infection), the presence of diverticula
, or certain other serious diseases, and the fistula itself may be a site of infection and discomfort.
abdominal fistula one between a hollow abdominal organ and the surface of the abdomen.
anal fistula (fistula in a´no) one opening on the cutaneous surface near the anus, which may or may not communicate with the rectum.
one between an artery and a vein, either pathologic (such as a varicose aneurysm
) or surgically created to ensure an access site for hemodialysis
. The site must be allowed 6 to 8 weeks to mature before it can be cannulated. Such a fistula may be the anastomosis of a natural artery and vein, a bovine graft, or a synthetic polytetrafluoroethylene (PTFE) graft. The bovine graft is taken from the bovine carotid artery and anastomosed to the vein and artery of the patient. In a PTFE graft, fibers are woven into a mesh called Gore-Tex and made into a sleeve and flange; this is available in a variety of sizes.
Precautions necessary to insure patient safety when caring for an individual with an arteriovenous fistula include frequent assessments for adequate circulation in the fistula and the distal extremity. A bruit or thrill can be heard over the access site. Blood pressure measurements, withdrawal of blood, injections, and administration of intravenous fluids should not be done on the extremity with such a fistula.
Internal arteriovenous fistulas.
blind fistula one open at one end only, opening on the skin (external blind fistula) or on an internal surface (internal blind fistula).
bronchopleural fistula one between a bronchus and the pleural cavity, causing an air leak into the pleural cavity; sometimes seen as a complication of empyema, fibrosis, or pneumonia.
cerebrospinal fluid fistula
one between the subarachnoid space and a body cavity, such as from head trauma or bone erosion, with leakage of cerebrospinal fluid, usually in the form of rhinorrhea
complete fistula one extending from the skin to an internal body cavity.
craniosinus fistula one between the cerebral space and a paranasal sinus, permitting escape of cerebrospinal fluid into the nose.
Eck's fistula an artificial communication made between the portal vein and the vena cava.
one connecting some part of the intestine with the urinary bladder; called also vesicoenteric f.
fecal fistula one between the colon and the external surface of the body, discharging feces.
1. one communicating between the stomach and some other body part.
2. a passage created artificially through the abdominal wall into the stomach.
horseshoe fistula one near the anus, having a semicircular tract with both openings on the skin.
rupture of the round window
with leakage of perilymph
into the inner ear, so that changes in middle ear pressure directly affect the inner ear, causing sensorineural deafness
as well as dizziness, vertigo, nausea, and vomiting. Head trauma and dramatic changes in atmospheric pressure are the most common causes. The usual treatment is restriction in activity (sometimes with complete bed rest), so that the fistula can heal. Surgical repair may be necessary, consisting of placement of a graft over the defect.
pulmonary arteriovenous fistula a congenital fistula between the pulmonary arterial and venous systems, allowing unoxygenated blood to enter the systemic circulation.
rectovaginal fistula one between the rectum and vagina.
rectovesical fistula one between the rectum and urinary bladder.
salivary fistula one between a salivary duct or gland and the cutaneous surface, or into the mouth through an abnormal pathway.
thoracic fistula one communicating with the thoracic cavity.
umbilical fistula one communicating with the intestine or urachus at the umbilicus.
urinary fistula any fistula communicating between the urinary tract and another organ or the surface of the body.
vesicovaginal fistula one from the bladder to the vagina.