An arteriovenous (AV) fistula is a surgically created connection between an artery and a vein, typically placed in the arm or forearm, designed to provide reliable access to the bloodstream for hemodialysis. By linking a high-pressure artery directly to a lower-pressure vein, the fistula forces the vein to enlarge and strengthen, a process known as maturation. This matured vessel can withstand the repeated needle sticks and high blood flow rates necessary for effective long-term kidney treatment.
The Visual Appearance of a Healthy Fistula
A healthy, matured AV fistula has a distinct appearance in the arm. The most noticeable feature is the surgical scar, which is usually a thin line where the artery and vein were joined, often located near the wrist or elbow crease. This scar remains a marker of the access site.
The vein undergoes significant transformation, becoming visibly enlarged and bulging beneath the skin’s surface. This venous dilation is a sign of successful maturation, as the vein wall thickens and expands to accommodate the substantial increase in blood flow from the artery. The resulting bulge indicates that the fistula is ready to be used for dialysis.
The skin over the fistula should generally appear normal in color, although the underlying enlarged vein may give the area a slightly bluish or purplish hue, similar to a prominent varicose vein. While the vessel is expected to be visible and prominent, the skin should remain intact, smooth, and free from widespread discoloration. The entire access arm may also appear slightly larger than the non-access arm due to the increased blood volume flowing through the limb.
How to Monitor Your Fistula: The Thrill and the Bruit
Monitoring a fistula requires attention to two distinct sensory cues that confirm proper function: the “thrill” and the “bruit.” The thrill is a palpable vibration felt over the fistula, created by the turbulent, high-speed blood flow passing from the artery into the vein. A healthy fistula produces a continuous, soft vibration easily felt by lightly placing two fingertips over the access site.
This sensation confirms that blood is flowing freely through the connected vessels. Patients are instructed to check for this thrill daily, as its presence is the most immediate sign that the fistula is open and working correctly. If the thrill becomes weak, intermittent, or disappears entirely, it signals a potential blockage or clotting issue that requires immediate medical attention.
The second indicator, the bruit, is the distinct whooshing or swishing sound produced by the same turbulent blood flow. While the thrill is felt, the bruit is heard, usually by placing a stethoscope over the fistula. In some cases, the sound may be loud enough to be heard by placing an ear near the access site.
A functioning fistula produces a continuous bruit that can be heard throughout both the systolic and diastolic phases of the heartbeat. Changes in the quality of the bruit, such as a high-pitched whistling sound or a sound only present during the systolic phase, can suggest a narrowing of the vessel, known as stenosis, which can impede blood flow. Teaching patients to listen and feel for these two indicators is fundamental to maintaining the long-term health of the vascular access.
Daily Care and Protection of the Access Site
Maintaining the health of the fistula requires daily care to prevent infection and mechanical damage. Simple hygiene practices include washing the access arm daily with mild soap and water and washing hands thoroughly before touching the site. The skin over the fistula should be kept clean and dry; patients should avoid applying lotions, powders, or creams to the immediate access area.
Protecting the arm from undue pressure or injury is important for preserving the fistula’s patency. Preventing constriction is also necessary for daily protection.
- Avoid sleeping directly on the access arm, as prolonged pressure can compress the vessel and impair blood flow.
- Avoid wearing tight clothing, watches, or jewelry that restrict circulation over the fistula site.
- Avoid heavy lifting or strenuous activities that put excessive strain on the access arm.
- Never draw blood, start an intravenous line, or take a blood pressure reading on the access arm, as these actions can cause clotting or damage the vessel walls.
Identifying Signs of Complications
Recognizing abnormal visual or sensory changes in the fistula allows for the timely diagnosis of complications. The most serious warning sign is the complete loss or significant reduction of the thrill and bruit, which indicates a thrombosis, or blood clot, that has stopped the flow. This change warrants immediate contact with the healthcare team.
Infection typically presents with local signs of inflammation. These include unusual redness, swelling, increased warmth, or pain around the access site. Drainage or pus from previous needle sites, or a fever above 100.3°F (38.0°C), signals an infection requiring prompt treatment.
Other visual warning signs include the development of new lumps or swellings along the vein that are not part of expected maturation. If the hand or fingers in the access arm become cold, numb, or noticeably weaker, it may signal a condition called “steal syndrome,” where the fistula diverts too much blood flow away from the rest of the limb. Persistent bleeding from the access site after dialysis that lasts longer than 20 minutes is also a sign of a problem.