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What is Vascular Access
Hemodialysis, also called dialysis, is the most common treatment for kidney failure. A dialysis machine is an artificial kidney which cleanses the blood. During dialysis, blood is drawn from the patient into the dialysis machine, circulated through the machine, and then returned to the patient. Two needles are inserted into the patient's bloodstream to allow this process to occur. Hemodialysis is normally performed three times a week and the purpose of vascular access is to provide reliable sites where the bloodstream can be easily accessed each time. There are three major types of vascular access: arteriovenous fistula, arteriovenous graft, and venous catheter. The great majority of vascular accesses are created in the arm, but they can also be created in the leg.
Types of Vascular Access
A surgeon creates an arteriovenous fistula by making a connection between an artery (which carries blood away from the heart) and a vein (which carries blood back to the heart). This artificial connection allows the vein to become larger and for the walls of the vein to thicken, a process termed maturation. A mature fistula makes it easier for the vein to be punctured repeatedly for dialysis. Maturation typically takes three to six months to occur, but in rare cases, can take up to a year. This makes advance planning for an arteriovenous fistula important. When a patient is felt to be approximately a year away from requiring dialysis, the patient should be referred for evaluation for possible creation of an arteriovenous fistula.
An arteriovenous fistula is the preferred type of vascular access due to lower rate of infection and clot formation, resulting in greater longevity than other types of vascular access. However, not everyone is a good candidate for an arteriovenous fistula, particularly older patients and patients with small veins.
If a patient is not a good candidate for an arteriovenous fistula, an arteriovenous graft is considered. An arteriovenous graft is a piece of artificial tubing, generally made out of teflon or fabric, that is attached on one end to an artery, and on the other end to a vein. The tube is placed entirely under the skin and the tube itself is punctured during dialysis. An arteriovenous graft can in general be used two to three weeks after the operation. However, arteriovenous grafts are more prone to infection and clotting than fistulas. The lifespan of an arteriovenous graft is approximately two to three years.
A third type of vascular access is a venous catheter. A venous catheter is a plastic tube which is inserted into a large vein, usually in the neck. An external portion of the catheter is exposed on the chest wall that allows the tubing for the dialysis machine to be connected. Because the catheter is not entirely under the skin, it is prone to infection. Venous catheters also have a high rate of becoming clogged and do not provide for as efficient dialysis as fistulas and grafts.
Venous catheters are generally considered temporary vascular accesses, and are usually only placed when urgent dialysis is needed. In rare cases, a venous catheter may be used as long-term vascular access if no other options are available.
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A final alternative for access creation for patients who are not good candidates for arteriovenous fistula is a device that is a hybrid of an arteriovenous graft and a catheter. This device is especially designed for patients who have a narrowing of the large central veins in the chest that would prevent a fistula or a graft from functioning properly. The entire device is placed underneath the skin and can be used for long-term vascular access. The characteristics of the device are similar to those described above for arteriovenous graft.
How to prepare for creation of a vascular access
In preparation for creation of a vascular access, the patient should reserve one arm which should not be used for blood draws, intravenous lines (IVs) or taking of blood pressure. The vascular surgeon may order imaging of the venous system which may include a duplex ultrasound, which is non-invasive, or a venogram. A venogram is a special type of x-ray in which contrast dye is injected into the veins, allowing a detailed picture to be taken of the veins. In general, a venogram is only needed in patients who have had many previous dialysis access procedures and the venous anatomy is unclear. The vascular surgeon and his staff will advise the patient on how long to fast prior to the procedure, and which medications to take or not take.
What to expect during and after the operation
Most vascular access procedures can be performed on an outpatient basis, under local anesthesia. The anesthesiologist may administer some sedative medication to allow the patient to be relaxed and drowsy, but general anesthesia is usually not required.
After the operation, patients should keep the incision covered and dry for at least two days. The incision should not be soaked or scrubbed until it is completely healed. The arm that the access was created in should be elevated on a few pillows while sitting and sleeping to keep swelling at a minimum. A mild amount of swelling and pain at the incision site is to be expected. If these symptoms become severe, the surgeon should be contacted as soon as possible.
Patients may experience some coolness, numbness or tingling in the fingertips of the arm that the access was created in. This is normal and improves or resolves with time. If these symptoms become severe, a situation termed "steal", contact your physician as soon as possible. This results from the access "stealing" blood away from the hand and there are procedures that can be performed to address this condition.
Complications that can occur include infection and bleeding. The surgeon should be contacted as soon as possible for any fever over 100 degrees Farenheit, drainage from the incision or active bleeding. Steal, as described above, is an uncommon complication.
A potential complication of arteriovenous fistulas is non-maturation. In other words, the vein never enlarges or becomes thick-walled enough to be used for dialysis. In some cases, causes for non-maturation can be identified and corrected, allowing maturation to occur.
After a fistula or graft has been in place for a period of time, it may become abnormally large, or develop an aneurysm. There are procedures that can be performed to correct aneurysmal fistulas.
Arteriovenous fistulas and grafts can develop narrow areas (stenoses) which may decrease the efficiency of dialysis or put the access at risk for developing a clot. Stenoses can be treated with an operation, or with a minimally invasive/endovascular approach. (link to minimally invasive and endovascular therapies here.) After an access has developed a clot, it may or may not be able to be salvaged.
Tips to keep the access healthy
The arm with the access should not be slept on or used to carry heavy items. The arm should also not be used for blood draws or blood pressure measurements and injections should not be given into the access. Clothing or accessories worn on the arm should be loose and non-constricting. The area over the access should be kept clean.
A functioning access will have a vibration that is called a "thrill." The physician or dialysis staff can show the patient how to feel for the thrill. If the patient notices that the thrill has disappeared, he/she should contact the physician as soon as possible.