When the kidneys fail, hemodialysis is required to filter waste products and excess fluid from the blood using an external machine. This process necessitates a reliable, high-flow connection to the bloodstream. Standard intravenous (IV) lines are insufficient for long-term hemodialysis because they cannot sustain the required high blood flow rate and repeated needle insertions. Therefore, a specialized access point, known as vascular access, must be surgically created. The two most common types of long-term vascular access are the arteriovenous (AV) fistula and the AV graft.
Understanding Vascular Access Options
The choice between an AV fistula and an AV graft depends largely on the condition and suitability of a patient’s natural veins. An arteriovenous fistula (AVF) is created by surgically connecting an artery directly to a nearby vein, typically in the arm or wrist. This connection, known as an anastomosis, redirects the high-pressure, high-volume flow from the artery into the vein. Over time, this increased pressure and flow causes the vein to thicken, enlarge, and become more robust, a process called arterialization, making it ready for repeated needle insertions during dialysis.
The AV fistula is generally the preferred option because it is created entirely from the patient’s own blood vessels, which significantly reduces the risk of infection and blood clotting. Fistulas also tend to last much longer, with some remaining functional for decades, and they provide the best blood flow for effective dialysis sessions. However, a fistula requires several weeks to months to mature before it can be used, and it is not an option for patients whose veins are too small or weak to undergo the necessary enlargement.
When a patient’s native veins are unsuitable for a fistula, an arteriovenous graft (AVG) offers a viable alternative. An AV graft is created using a synthetic, biocompatible tube placed under the skin to connect an artery to a vein, bypassing the need for the vein to enlarge naturally. While grafts can be used much sooner than fistulas, typically within two to four weeks of placement, they carry a higher risk of developing infections and blood clots because they introduce foreign material into the body. Grafts also have a shorter lifespan, often requiring replacement or revision procedures after two to three years of use.
The Creation Process and Maturation Timeline
Creating durable vascular access begins with a detailed pre-operative assessment, often including non-invasive imaging like ultrasound, known as vessel mapping. This mapping identifies the best artery and vein combination, ensuring they have the necessary size and health to support the access. The surgery is usually an outpatient procedure, often performed using local anesthesia with sedation. During the procedure, the artery and vein are exposed through a small incision, and the connection is made, either directly for a fistula or using synthetic tubing for a graft.
Immediately following the procedure, the patient will experience some localized swelling and mild pain at the surgical site, which is managed with prescribed medication and by keeping the arm elevated. The most important phase following surgery is maturation, the period during which the access strengthens sufficiently to handle the demands of dialysis.
For an AV graft, the maturation period is relatively short, usually about two to four weeks, allowing the surrounding tissue time to heal around the synthetic tube. An AV fistula requires a much longer period of structural change, as the high-pressure arterial flow must remodel the vein wall. This natural process takes time, with most fistulas requiring a minimum of six weeks to mature, and often several months, before they meet the criteria for successful cannulation, including a diameter of at least six millimeters. This waiting period is important because using an immature fistula can cause damage and lead to early failure.
Daily Care and Recognizing Issues
Maintaining the health and function of an AV fistula or graft is a continuous, day-to-day responsibility. Routine care starts with meticulous hygiene, requiring the access site to be washed gently with soap and water daily, especially before each dialysis session. To protect the access from damage, patients must never allow blood to be drawn, intravenous (IV) lines to be started, or blood pressure to be taken in the access arm. Additionally, avoiding tight sleeves, jewelry, or carrying heavy objects prevents compression, which can impede blood flow.
Patients should regularly monitor their access by checking for the presence of the “thrill,” a gentle vibration felt over the access point, and the “bruit,” the characteristic swooshing sound heard with a stethoscope. The thrill indicates that blood is flowing properly through the connection, and its consistent presence is a primary sign of a healthy access. A noticeable change or loss of the thrill, or a sudden change in the sound of the bruit, is a serious sign that the access may be clotting or blocked, requiring immediate medical attention.
Recognizing signs of complications is important for long-term safety and function. Signs of an infection include:
- Localized redness
- Unusual warmth
- Tenderness
- The presence of pus at the site
Another potential complication is steal syndrome, where the access diverts too much blood from the hand, leading to symptoms like persistent coldness, numbness, or pain. Any sudden loss of the thrill, persistent swelling in the arm, or signs of infection must be reported immediately to the healthcare team to prevent access failure.