Overview of Types of Arteriovenous Fistulas
There are nearly 500,000 people who need a treatment called hemodialysis, which is used when your kidneys are no longer able to filter your blood. Each year, around 100,000 new patients are diagnosed with a condition called end-stage kidney disease, which means their kidneys have stopped working completely.
There are different ways to set up the body for hemodialysis, which doctors refer to as “arteriovenous (AV) hemodialysis access”. In 2003, the group that handles Medicare and Medicaid started a program called the “Fistula First Initiative.” The goal of this program was to cut down on the cost and complications often tied to hemodialysis.
Out of all the types of AV access, the most successful type is the “autogenous AV access.” This means a patient’s own blood vessels are used to create an access point for hemodialysis. This method tends to last longer, has fewer complications compared to using artificial blood vessels, and a lower risk of infections compared to temporary central venous catheters (CVCs), which are tubes placed into your veins.
The goal of the Fistula First Initiative was to encourage more people to get AV access when they first start hemodialysis. To ensure the long-term success of this treatment, doctors must conduct a thorough examination before surgery. This is critical in establishing a successful access point for hemodialysis in the long run.
Why do People Need Types of Arteriovenous Fistulas
If a person needs regular blood-cleaning treatments, called hemodialysis, because their kidneys are no longer working effectively, a special passageway called a fistula is often created to make those treatments easier. Kidney specialists, or nephrologists, will keep an eye on certain aspects of a patient’s health to decide when to start hemodialysis.
Usually, people start feeling symptoms when their eGFR, an important measure of how well the kidneys are filtering wastes from the blood, drops below 10 mL per minute per 1.73 m. These symptoms include not eating well, having trouble controlling fluid levels in the body, feeling tired, or having cognitive issues. If the eGFR drops below 5, and the person develops a heart condition known as uremic pericarditis, that is a clear sign that hemodialysis is urgently needed.
Patients with chronic kidney disease are regularly checked for other health problems like acidosis (too much acid in the blood), high levels of potassium (hyperkalemia) and phosphorus (hyperphosphatemia) in the blood. If these conditions continue to get worse, it might be time to consider starting hemodialysis.
The doctors usually use some standard tests to help make this decision. If a person’s creatinine clearance (another measure of kidney function) drops below 25 ml per minute or the amount of a waste product called creatinine in the blood goes above 4 mg/dl, that’s often seen as a sign that dialysis might be needed.
Importantly, if it looks like a person might need hemodialysis within a year, a plan should be put in place to create long-term access for treatment, usually in the form of a fistula.
Preparing for Types of Arteriovenous Fistulas
Before a doctor can start any medical procedure, they need to carry out a complete check-up on the patient. This will include asking about past injuries or treatments that might impact the current medical plan. The doctor will also figure out which arm the patient uses more often. This matters because it might not be the best idea to use that arm for medical procedures.
During the check-up, a special band, much like a blood pressure cuff, is used to look at the veins in the patient’s arm. This helps the doctor to see the cephalic and basilic veins, which are two large veins we have. The doctor will also carefully check the pulse in different parts of the arm, including a test named after Dr. Allen, to make sure that blood is flowing properly all the way to the hand.
Other health issues like the presence of a lot of small blood vessels, swelling, or having had a special type of tube called a central venous catheter (CVC) inserted into the body before could suggest that there may be a narrowing of a blood vessel in the body, which could present challenges if they are planning to create an arteriovenous (AV) access, a connection between an artery and a vein in the body.
The doctor will then perform a venous duplex scan, a special type of ultrasound, to make sure the veins are wide enough and that arteries do not have any narrow sections. Doctors believe that the vein must be at least 2.5 mm wide (with the special band used) to successfully create a mature fistula, which is a new pathway for blood to flow.
Once the doctor is content that the veins and arteries in the pre-planned surgical site are satisfactory, then the surgery can be scheduled.
How is Types of Arteriovenous Fistulas performed
Creating a surgical fistula, or opening, depends on many factors. Doctors generally aim to plan the surgery starting as far away from the body’s core as possible. However, the size of your vein can limit where the fistula can be positioned. The best places for a fistula are in the radial-cephalic (wrist), brachial-cephalic (lower arm), and brachial-basilic (upper arm) areas, in that order. This follows the guidelines set by the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (a group that sets best practice for kidney treatments). Using your own blood vessels for the fistula has been shown to have the highest success rates and fewer complications. If this can’t be done, man-made grafts can be used instead.
The “go-to” location for a fistula is at the wrist, where the radial artery and the cephalic vein meet. This type is often called a “Cimino fistula”, named after Dr James Cimino who designed it in 1966. This is a relatively simple procedure to perform. The success rate after 1 year is roughly 50% to 80%. However, this location can limit the amount of blood flow available for dialysis. Despite this, using this location means that other veins in your arm are saved for future attempts if needed.
If a fistula at the wrist isn’t possible, doctors consider using the lower or upper arm. In these cases, they create a fistula between the brachial artery and either the cephalic vein in the forearm, or the basilic vein in the upper arm. In these locations, a man-made graft can be used as an alternative method. These types of fistulas have a success rate around 70% to 85% after a year. However, the brachial-basilic fistula is more complicated as the blood vessels are deeper, and often requires a second procedure to bring the fistula closer to the skin surface. Fistulas in these “proximal” locations, closer to the body, have a higher risk of complications, such as the fistula not maturing properly, steal syndrome (blood being diverted from normal pathways), narrowing of the vessels, blood clotting, and changes in heart output.
The process of creating any fistula includes prepping and evaluating the blood vessels, potentially harvesting a blood vessel, creating a connection between an artery and vein, tying off branch vessels, and closing the wound. The connection between the artery and vein can either be side-to-side, or the end of the artery to the side of the vein, depending on the location and size of the blood vessels. It’s no longer common practice to join the artery and vein end-to-end, as this can cause complications.
The maturing of a fistula, or when it’s ready for use, follows the “Rule of 6s”. This includes a blood flow of more than 600 mL per minute, a fistula diameter of more than 6mm, a depth under the skin of less than 6mm, a vein length of at least 6 cm for use, and a detailed check-up and expected readiness in about 6 weeks.
Possible Complications of Types of Arteriovenous Fistulas
After some surgeries to create an arteriovenous (AV) fistula (which is a connection between an artery and a vein), a blood clot (thrombosis) might form early on. This can be caused by issues with the flow in or out of the fistula, narrowing of the artery, or a small vein. Doctors usually need to perform another surgery to correct this problem. Planning carefully before the operation can minimize these risks.
A clot can also form much later, usually due to the inner layer of blood vessels (intima) growing too much. In such cases, doctors can perform angioplasty (a procedure to open up blood vessels), remove the clot, or use tissue plasminogen activator (tPA) to dissolve it.
Some patients may develop a condition known as venous hypertension after surgery. This is where the pressure in their veins is too high and this can happen because of a narrowing down of the central blood vessels. It can lead to symptoms like swelling in the limbs, varicose veins, prolonged bleeding after dialysis, or higher pressures during dialysis–a treatment that filters waste products from your blood when your kidneys can’t do the job adequately. To treat this, doctors may perform an angioplasty and place a stent (a small, mesh tube) in the vein to open it up. If this doesn’t work, doctors may close off (ligate) and use another limb instead.
Arterial steal syndrome can occur when blood supply gets redirected away from the hand. Symptoms can vary and may only present during dialysis. Treatment depends on the severity. Mild cases may get better with time, but if symptoms are drastic, the doctors may have to close (ligate) off the access.
Ischemic monomelic neuropathy (IMN) is another potential issue. IMN involves acute pain, abnormal sensations (paresthesia), weakness, or paralysis, and typically happens right after creating the AV fistula. This condition comes about because of limited blood flow (ischemia) to the nerves. To prevent progression and permanent nerve damage, doctors may need to close off (ligate) the AV fistula.
Repeated puncture at the same site might cause a pseudoaneurysm, a false aneurysm where the blood vessels’ wall or a graft gets destroyed, leading to thinning of the skin. To avoid this, it’s suggested to vary the puncture sites. Although most can be kept under observation safely, severe cases need surgery that involves removing the affected area and repairing with a transposed vein or graft.
After any surgery, including creating an AV fistula, there’s a risk of complications like bleeding, infections, and the build-up of serous fluid (a pale yellow and transparent fluid), called a seroma. Bleeding can get worse in patients with kidney issues and may require a specific medication called DDAVP to help control the bleeding.
What Else Should I Know About Types of Arteriovenous Fistulas?
Fistulas, which are special connections made between two body parts, are often created as part of a long-term plan for people who need regular hemodialysis – a process that cleans the blood when the kidneys cannot. Hemodialysis is commonly needed by patients with End Stage Renal Disease (ESRD), which is the last stage of chronic kidney disease. The process of planning, creating, and maintaining these fistulas is managed by a team of different healthcare professionals.
