A fistula is a connection between two body parts that are not typically connected. In healthcare, this term often refers to a surgically created connection between an artery and a vein, known as an arteriovenous (AV) fistula. These specialized medical connections are frequently established to provide a reliable access point for essential treatments, such as hemodialysis. Monitoring the function of these fistulas is an important aspect of their care, helping to ensure they continue to work effectively for the patient’s needs.
Understanding a Fistula
AV fistulas are surgically created connections between an artery and a vein, commonly in the arm. Their primary purpose is to provide a durable access point for hemodialysis, a treatment that filters waste from the blood.
During creation, an artery is connected to a neighboring vein. This allows high-pressure arterial blood to flow directly into the lower-pressure vein. The increased blood flow and pressure cause the vein to enlarge and its walls to thicken over several weeks to months, a process known as maturation. A matured fistula becomes robust enough to withstand repeated needle insertions for dialysis, allowing for the rapid blood flow necessary for effective filtration.
The Thrill and The Bruit
A healthy, functioning AV fistula produces two distinct signs: a thrill and a bruit. A thrill is a palpable vibration, a buzzing or rumbling sensation felt by gently touching the skin over the fistula, often compared to a cat’s purr. A bruit (pronounced “broo-ee”) is an audible whooshing or rumbling sound heard when a stethoscope is placed over the fistula.
Both the thrill and the bruit result from altered blood flow dynamics within the surgically connected vessels. In a fistula, high-pressure arterial blood bypasses capillaries and enters the vein directly. This rapid, high-volume flow creates turbulence, generating both the vibration (thrill) and the sound (bruit).
The presence of a continuous thrill and a consistent bruit indicates that blood is flowing properly through the fistula and that the connection remains open. A normal thrill should be felt continuously, having both systolic and diastolic components, meaning it persists throughout the heart’s pumping cycle. Similarly, a healthy bruit is typically a continuous, low-pitched sound. These sensations and sounds are normal and expected signs of a well-functioning AV fistula.
Significance of Changes
Monitoring a fistula’s health involves regularly checking for the thrill and bruit. Any change in their quality, intensity, or presence can indicate a potential problem. For example, a weaker thrill, or one that disappears entirely, can signal reduced blood flow or a blockage. Similarly, a bruit that changes pitch, becomes discontinuous, or is no longer audible suggests an issue.
Such changes often point to complications like stenosis, which is a narrowing of the blood vessel, or thrombosis, the formation of a blood clot within the fistula. Stenosis is a common cause of fistula dysfunction and can lead to inadequate blood flow for dialysis. A complete loss of thrill or bruit can mean the fistula has clotted and stopped working.
Other concerning signs that may accompany changes in thrill or bruit include swelling, redness, warmth, or pain around the fistula site. Prolonged bleeding after dialysis needle removal can also be a symptom of a problem. If any of these changes are noticed, it is important to contact a healthcare provider immediately for evaluation. Prompt medical attention can help address issues early and maintain the fistula’s long-term usability.