An arteriovenous (AV) fistula is a surgically created connection between an artery and a vein, typically in the arm. This access point facilitates hemodialysis for individuals with kidney failure. By joining an artery and a vein, the fistula allows arterial blood flow to directly enter the vein, causing it to enlarge and strengthen over several weeks to months. This maturation prepares the vein for the high blood flow rates needed for efficient dialysis. An AV fistula is a preferred method for hemodialysis access due to its durability, lower risk of infection, and reduced likelihood of clotting.
Preparing for Fistula Access
Preparing for AV fistula access involves steps from both the patient and the healthcare professional. Patients maintain good hygiene, washing the fistula arm daily and thoroughly before each dialysis treatment. Avoid tight clothing, jewelry, or anything that could constrict the arm, as this can impede blood flow, and never take blood pressure measurements or blood draws from the fistula arm to prevent damage. Daily self-monitoring involves feeling for a gentle vibration, a “thrill,” and listening for a distinct whooshing sound, a “bruit,” which indicate proper blood flow. Report any changes in these sensations promptly to the healthcare team.
Healthcare professionals assess the fistula by palpating for the thrill and listening for the bruit, and visually inspecting the site for redness, swelling, or pain. Site selection involves choosing clean, straight areas and avoiding aneurysms or previous infiltrations. Access sites are meticulously cleaned and disinfected, often using chlorhexidine or iodine, applied in a circular motion and allowed to air dry. They select the appropriate needle gauge and length based on the fistula’s characteristics and apply a tourniquet to make the vein more prominent. A local anesthetic may be used to numb the skin, reducing patient discomfort during needle insertion.
The Access Procedure
Accessing an AV fistula for hemodialysis requires precise technique and adherence to sterile practices to prevent complications and minimize infection risk. Specialized needles are used for AV fistula access, and they come in various types and sizes. Sharp needles, with a pointed tip, are used for newer fistulas or individuals with firmer skin. Blunt needles, with a rounded tip, are reserved for the “buttonhole” technique, where needles are inserted into the exact same site repeatedly to create a consistent track.
Needle gauge, the needle’s diameter, ranges from 14G to 17G. Larger gauges permit higher blood flow rates but may cause more discomfort. Needle length, usually between 1 inch and 1.25 inches, is chosen based on the depth of the fistula beneath the skin. Many needles also feature a “back-eye” opening near the tip, which optimizes blood flow. A tourniquet is applied to distend the fistula, making cannulation easier.
The standard approach for hemodialysis involves a two-needle technique: an arterial needle draws blood from the patient to the dialysis machine, and a venous needle returns the filtered blood to the body. Needles are inserted with the bevel facing upwards, at an angle around 25 degrees, and advanced carefully into the vessel until a flashback of blood is observed, confirming proper placement. Once inserted, the needles are secured with tape, often using a chevron method, to prevent dislodgement during treatment. The arterial needle is placed retrograde (towards the heart), while the venous needle is inserted antegrade (with the blood flow); a distance of at least 5 centimeters (about 2 inches) between the two needles prevents recirculation. Precise cannulation techniques include the “rope ladder” method, which involves rotating insertion sites along the fistula to preserve vessel health, and the “buttonhole” method for specific patients.
Post-Access Care and Maintenance
Proper care and maintenance of an AV fistula ensure its long-term health and function. Immediately after dialysis, when needles are removed, apply gentle, direct pressure to the insertion sites with sterile gauze for 5 to 10 minutes. Avoid peeking at the site or using clamps, as this can disrupt clot formation. After bleeding stops, apply a clean dressing or small band-aids for several hours. Rest the fistula arm for a few hours following treatment, avoiding heavy lifting or strenuous activities to prevent strain.
Between dialysis sessions, consistent daily care is important. Wash the fistula arm daily with soap and water to maintain cleanliness and reduce infection risk. Continue to avoid tight clothing, jewelry, or any direct pressure on the fistula arm, and also avoid sleeping on the arm or carrying heavy objects with it. Blood pressure measurements and blood draws should always be performed on the non-fistula arm. Regularly inspect the fistula for signs of problems, which could indicate an infection:
- Redness
- Swelling
- Warmth
- Unusual pain
- Discharge
Changes in the thrill or bruit, like a loss of vibration or a different sound, may signal a clot or vessel narrowing (stenosis) and should be reported immediately. Persistent bleeding, unusual bulging, or coldness and numbness in the hand (steal syndrome) also warrant immediate medical attention.