By Dr. Anatole Besarab

Creating and maintaining a good vascular access while on hemodialysis is very important in order to ensure that blood can be removed and returned to a patient's body during dialysis. Until recently, there have only been three vascular access options for patients on hemodialysis. These options include an arteriovenous (AV) fistula, which is formed by connecting an artery to a vein in the arm, an AV graft which is similar to an AV fistula except a piece of synthetic tubing is used to connect the artery to the vein, or a catheter, which is a flexible tube inserted into a vein in your neck or groin.

Unlike the first two options, a catheter has an external portion which sticks out of the patient's body to allow for the nurse to insert a needle directly into the access and then attach the tubing connected to the dialysis machine to a needle. Physicians currently believe that an AV fistula is the best vascular access option since these have a reduced number of complications and the best long-term survival. Unfortunately, an AV fistula cannot always be formed in all patients due to a number of factors. The inability to create an AV fistula in many patients has lead to an increased use of AV grafts and catheters in the United States. While these are useful for many patients, they have an increased potential for complications including clotting and infections. As a result of the need for better options for vascular access in some hemodialysis patients, a new type of access has recently been developed. This new type of access, called a subcutaneous hemodialysis access system, consists of a small metallic device or devices implanted underneath the skin in the upper chest. These devices are connected to two flexible tubes, which are inserted into a large vein to allow for blood access. Unlike catheters, these devices are completely under the skin.

Two different companies have recently developed subcutaneous hemodialysis access devices. The LifeSite® System (Figure 1) has been developed by Vasca, Inc. and the Dialock® System (Figure 2) was developed by Biolink. Of these two devices, the LifeSite® System is currently on the market in the United States and is available to patients. The Dialock® System is undergoing review by the FDA at this time.

A minor surgical procedure is performed to implant these devices usually without the need for the patient to stay overnight in a hospital. It is also possible to use these devices immediately, which means that dialysis can be performed the same day as this surgical procedure. These devices are usually implanted on the right or left side of the upper chest, and because these devices are placed underneath the skin, they produce a small bump in the skin. This helps nurses locate the device prior to a dialysis session. A small scar also forms where the incision was made to place the device under the skin.

The LifeSite® and Dialock® devices each have unique internal mechanisms, which open when a needle is inserted into the device and close when the needle is removed. When this mechanism is open, blood is able to flow from the patient to the hemodialysis machine and returned to the body through the flexible tubes. These tubes lead to the veins, which are connected to the devices.

The needles for the LifeSite® System are similar to the needles which are currently used by nurses for AV fistulas and grafts. These needles are inserted into the same location for each dialysis session and a small hole, called a "buttonhole" develops over time. This buttonhole is very similar to the hole which forms in someone who has pierced ears. After about a week or two, the insertion and removal of the needle will be virtually pain free.

The Dialock® System requires special needles, which are not the same as needles used for standard dialysis. The site where needles are inserted is usually rotated. Both of these devices have mechanisms, which lock the needles into place during dialysis to prevent them from inadvertently falling out during dialysis.

Typically, two LifeSite® devices are implanted (Figure 3) since one is needed for blood coming from the body and the other for returning the blood. Only one Dialock® System is implanted since both tubes are connected to the same device. The use of two separate LifeSite® Systems allows more flexibility for device placement in patients with poor veins in the upper chest and reduces the weight of the device itself. The need for only one device to be implanted for the Dialock® System reduces the time needed for the surgical procedure to place the device.

These new subcutaneous hemodialysis systems allow for patients to receive hemodialysis through a device, which is discreet and usually covered with clothing since it is usually implanted in the upper chest. Patients can also take a bath or swim in a chlorinated pool without damaging the device, provided their physician permits it and the precautions recommended by the manufacturer are followed.

Both of these devices also allow for freedom of movement during the dialysis procedure, since both arms are free. Clinical studies have also been done with these devices which suggest potential benefits to patients. These studies have shown the ability for these devices to provide high blood flows, decreased clotting and decreased rates of infections compared to hemodialysis catheters. This reduction in infections is most likely the result of having the device placed underneath the skin as compared to a typical hemodialysis catheter, which has an external portion. This external portion often allows for germs to contaminate the catheter either as a result of exposure to bacteria through someone or something contaminated touching it or breathing on it.

Since these new subcutaneous hemodialysis access systems are placed entirely underneath the skin, the skin serves as a barrier to bacteria getting to the device and reduces the potential for infection. The LifeSite® System uses an additional procedure to reduce infections. Before and after each hemodialysis session, a small amount of isopropyl alcohol is used to wash out the valve and kill the bacteria or germs which may be there.

The subcutaneous hemodialysis access devices discussed above may be helpful for several types of patients including individuals waiting for a permanent access or transplantation. Since it often takes four months or more before an AV fistula can be used after it is created, patients who need dialysis during this waiting period may be ideal candidates for these new devices as opposed to using a hemodialysis catheter since complications may be less with these new devices. These devices may also be helpful in patients who have had multiple vascular access failures. While both of these devices have been successfully used in some patients for over two years, the potential to use them on a long-term basis still needs to be explored. Overall, the results to date suggest that these new subcutaneous devices offer exciting new vascular access options for the hemodialysis patient.

Dr. Besarab is the Chief, Division of Nephrology at the Robert C. Byrd Medical Center at the University of West Virginia School of Medicine. He is the Vice-Chair of the K-DOQI Vascular Access Work Group.

This article originally appeared in aakpRENALIFE 2001 Special Edition, Vol. 17, No. 2.

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