Hemodialysis is a life-sustaining treatment for individuals with kidney failure, functioning by diverting blood outside the body to a machine that filters out waste products and excess fluid. This process, which typically occurs three times a week for several hours, requires a reliable and repeated connection to the patient’s bloodstream. This specialized connection is referred to as vascular access, which is necessary for the efficient delivery of treatment.
The Necessity of Vascular Access for Hemodialysis
A standard intravenous (IV) line, which accesses a small peripheral vein, cannot support the demands of hemodialysis. To effectively clean the blood, the dialysis machine must process a high volume of blood quickly, requiring the access point to sustain high flow rates, often between 400 to 450 milliliters per minute (mL/min). Native veins are too small and fragile to tolerate this high flow rate and the repeated needle insertions required for years of treatment.
Therefore, vascular access is surgically created to allow for the continuous, high-volume flow needed to pass blood through the dialysis filter. This surgical creation strengthens and enlarges the blood vessel, making it durable enough for repeated use.
Distinguishing the Primary Types of Dialysis Access
Hemodialysis access is generally categorized into three main types, each with a distinct structure and intended longevity.
Arteriovenous (AV) Fistula
The Arteriovenous (AV) Fistula is the preferred, long-term access option, created by directly connecting an artery to a vein, usually in the arm. This connection forces arterial blood flow and pressure into the vein, causing the vein to thicken and enlarge, a process called maturation. Because it uses the patient’s own tissue, the AV fistula has the lowest rates of infection and clotting and the longest lifespan, but it requires several months to mature before it can be used.
Arteriovenous (AV) Graft
When a patient’s veins are unsuitable for a fistula, an Arteriovenous (AV) Graft may be created. This involves using a synthetic tube to connect an artery and a vein. The graft is placed under the skin, and needles are inserted directly into the synthetic tube during dialysis. Grafts can typically be used sooner than fistulas, often within two to eight weeks after placement, but they are more susceptible to infection and tend to have a shorter functional lifespan.
Central Venous Catheter (CVC)
The Central Venous Catheter (CVC) is a flexible, Y-shaped tube typically inserted into a large central vein in the neck or chest. This access is generally considered a temporary solution, used for emergency dialysis or as a bridge until a fistula or graft is ready. The CVC has two distinct lumens, one to withdraw blood and one to return the filtered blood. Because a portion of the catheter remains outside the skin, it carries the highest risk of bloodstream infection and may also provide lower blood flow rates, leading to less efficient dialysis.
Management and Maintenance of Dialysis Access
Patients with an AV fistula or graft should regularly check for the presence of a “thrill” (rhythmic vibration felt over the access site) and a “bruit” (swishing sound heard with a stethoscope). The loss of this thrill or bruit is a warning sign of potential clotting or narrowing of the blood vessel (stenosis).
Keeping the access site clean and dry is essential. Patients must avoid having blood pressure measured, blood drawn, or tight clothing worn on the access arm, as this can compress the vessels and impede blood flow. For a CVC, the dressing must be kept clean and dry, and the catheter is often locked with an anticoagulant solution between treatments to prevent clotting.
Common complications across all access types include infection, thrombosis (clotting), and stenosis. Patients must promptly report any prolonged bleeding after dialysis, pain, or a sudden change in the feel of the access to their care team.
Infection
Signs of infection include redness, warmth, swelling, or discharge around the access site, which require immediate medical attention and treatment with antibiotics.
Thrombosis and Stenosis
If clotting occurs, procedures like thrombectomy (clot removal) or angioplasty (widening a narrowed vessel) may be necessary to restore function.