An arteriovenous (AV) fistula is a surgically created connection between an artery and a vein, typically placed in the arm, that serves as a long-term access point for hemodialysis treatments. This access is often called the patient’s lifeline because its reliable function is necessary for life-sustaining blood filtration. The health and patency of the fistula must be monitored daily to ensure it remains open and effective for use during dialysis sessions. Routine self-monitoring allows the patient to detect potential issues early, which can prevent the complete loss of the access site. Because the fistula’s function relies on a continuous, high volume of blood flow, certain sensations and sounds signal its proper working status.
Understanding the Significance of Bruit and Thrill
The functionality of a mature AV fistula is confirmed by the presence of both a thrill and a bruit. These are direct results of the high-pressure arterial blood being diverted into the lower-pressure venous system, which creates turbulent blood flow through the connected vessels.
The thrill is the vibration that this turbulent flow produces, which can be felt under the skin. It is frequently described as feeling similar to a cat purring or a soft buzzing sensation.
The bruit (pronounced “broo-ee”) is the corresponding auditory phenomenon, defined as the swooshing or whooshing sound made by the same turbulent blood flow. A healthy, functioning fistula will produce a continuous bruit that can be heard throughout both the systolic and diastolic phases of the heartbeat. The presence of both the thrill and the bruit indicates that the fistula is open and the blood is flowing effectively for dialysis. Changes in either the feel of the thrill or the sound of the bruit can be the earliest indicators of a developing problem, such as stenosis (narrowing) or thrombosis (clotting) within the vessel.
Step-by-Step Guide for Checking the Thrill
Checking the thrill is a tactile assessment that should be performed daily as part of the fistula’s self-monitoring routine. The arm containing the fistula should be relaxed and positioned comfortably. This positioning helps ensure that the blood flow is not restricted or altered by muscle tension.
This assessment is best performed using the pads of your fingertips, as they are highly sensitive to vibration. Gently place the pads of two or three fingers directly over the course of the fistula, starting at the site of the surgical connection (anastomosis) and moving along the length of the vein.
You are not checking a pulse but feeling for a continuous, steady vibration under the skin. The pressure should be light; excessive force can compress the vessel and temporarily reduce or eliminate the sensation you are trying to feel.
A normal thrill will feel constant and rhythmic, like a smooth, deep buzz or vibration that persists throughout the cardiac cycle. It is important to become familiar with the unique texture and intensity of your own fistula’s thrill. If the thrill feels weaker, is inconsistent, or is only felt during the systolic phase (heartbeat), it may signal that the blood flow has been compromised by a partial blockage.
Step-by-Step Guide for Checking the Bruit
Listening for the bruit is the auditory component of the daily fistula check, complementing the tactile assessment of the thrill. While a medical professional uses a stethoscope, patients can often listen directly by pressing an ear gently against the skin over the fistula site. The optimal location to listen is usually near the surgical connection, where the sound is typically loudest.
The normal bruit should be a low-pitched, continuous swooshing or whooshing sound, similar to running water or a gentle hum. This sound should be present and steady throughout the entire heartbeat, reflecting uninterrupted blood flow. It is important to distinguish the bruit from a normal heartbeat, which is a separate, more percussive sound.
If a stethoscope is available and its use has been approved and taught by your care team, place the bell or diaphragm over the fistula. Listen for the continuous flow sound, noting its pitch and consistency. A change in the sound, such as a high-pitched whistling or a reduction in sound during the diastolic phase, is often an acoustic sign of a flow-limiting stenosis.
Recognizing Changes and When to Contact Your Care Team
Any deviation from the established normal thrill and bruit for your fistula is a warning sign that requires prompt attention. The most serious finding is the complete absence of the thrill and bruit, which strongly suggests that a thrombosis or clot has formed, stopping blood flow. A sudden loss of either sensation is a time-sensitive medical emergency that risks the access’s viability.
Other changes that warrant contacting your dialysis unit or healthcare provider include a thrill that feels notably weaker, a bruit that has become high-pitched, or a sound that is no longer continuous.
Physical signs of trouble also indicate a potential problem, such as infection or reduced blood flow to the extremity. These physical signs include:
- Swelling.
- Increased warmth.
- Redness near the site.
- Pain in the arm or hand.
These symptoms may signify a narrowing of the vessel or an infection that requires immediate intervention. The patient should never attempt to manipulate or physically clear a suspected blockage; instead, they should immediately notify their care team for professional evaluation and treatment.