When a patient experiences renal failure, their kidneys no longer function. Normally, kidneys work by constantly filtering the blood, removing excess water, and nitrogen based waste. They also work to regulate the electrolytes in the body. When the kidneys fail, these functions are no longer performed by the kidney. This leads to a buildup of waste, excess fluid, and imbalances in electrolytes, and this can cause dealth within a matter of days.
Dialysis is a process where blood from a patient's body is filtered for the patient, removing these waste products, balancing the electrolytes, and removing excess fluid. The dialysis machine exists outside the patient's body, so blood has to be removed from the body, sent through the machine to be filtered, and then returned back to the body. This is usually done 2-4 times per week, for about 3-4 hours a session. This way, patients can live for many years, despite having kidneys which no longer function.
In order to filter the blood, vascular surgeons create either an arteriovenous fistula or graft. An AV fistula is a direct connection between a vein and an artery. A graft is a tube which is connected at one end to an artery, and at the other end to a vein.
When these connections are created between a large artery and a large vein, blood flow through the graft or fistula increases tremendously, because of the pressure differences between an artery and a vein. This increased blood flow is important, because it allows dialysis to occur. In dialysis, two large needles are placed into the graft or fistula. The first needle pulls the blood out of the body, sending it to the dialyzer for filtration. The second needle returns the filtered blood to the body. The increased flow in the fistula is what allows this filtration to occur at a pace that filters all the blood in just a few hours. This would be impossible in an ordinary small vein or small artery.
Preparing for your procedure
The choice to receive dialysis is a difficult one, but it is one that should be addressed along with the counseling of your primary care doctor as well as your nephrologist (your kidney doctor). Ideally, a dialysis access (an AV fistula or an AV graft) should be considered several weeks before it is time to begin dialysis.
When you are seen by the vascular surgeon, options for dialysis access will be discussed. Determination of whether to place a graft or a fistula depends on the quality and size of the veins in your arm. Usually fistulas are preferred over grafts, because they have a lower chance of becoming infected, and because on average, they last much longer. On the flip side, a graft may be preferable if the veins are not large enough to create a fistula, or if dialysis is imminent, since grafts usually can be used after only a few weeks, whereas fistulas take several weeks to mature (for the vein to get larger) prior to being used.
Pre operative planning
In order to determine which surgery will be done, several factors are considered. Fistulas and grafts do not last forever, and often more than one will need to be made over time. Therefore, planning is critical. Surgeons usually place the first fistula or graft in the non-dominant arm (if you are right handed, the first fistula is placed in the left arm, for example). It is usually placed as low as possible in the arm (in the forearm instead of the upper arm).
In order to decide what surgery is best for you, an ultrasound will usually be done. The ultrasound shows the surgeon the quality and size of the veins in both arms, and allows her to plan the best procedure for you, given all the information. Sometimes we also use the ultrasound to evaluate the quality of the arteries in the arm as well.
The patient also has a very important role in the weeks leading to dialysis. In order to have a successful dialysis access, the arm veins and arteries must be in good condition. It is critical that the patient protect his or her dialysis arm, both before and after the dialysis access is placed. This means avoiding blood draws in this arm at all times. Blood pressure cuffs should also be avoided (have the doctor or nurse take your blood pressure in the arm that doesn't have the dialysis graft). It is important not to sleep with this arm underneath your head or neck, cutting off the circulation. It is also important to avoid wearing tight clothing or jewelry on this arm, and to avoid using the armexcessively.
Dialysis access surgery
Usually the procedure consists of one or two small incisions. In the case of a graft, the gortex tube is connected at one end to a vein, and at another end to the artery. The graft itself is implanted just under the skin, allowing the nurses to place needles easily into the length of the graft for dialysis.
In the case of a fistula, an incision is made over the artery and vein, the vein is harvested, and divided. One end of the vein is then attached to the side of the artery. In this case, the needles for dialysis will eventually be placed in the vein itself, to pull blood out and put blood back into the body. After surgery, the vein will grow slowly over several weeks, until it is quite prominent under the skin, and big enough to get the needle in every time.
The surgery itself is usually done on an outpatient basis. After the surgery is performed, the patient will feel a "thrill" over the graft or fistula. A "thrill" is caused by the increased flow of blood that occurs when blood goes from a high pressure arterial system to a low pressure venous system. It shows us that the fistula or graft is functioning correctly. The patient should feel for the "thrill" every day, and contact us immediately if they cannot feel it, since that may mean the fistula or graft is no longer functioning.
Usually dialysis grafts can be used a few weeks after the procedure is performed, and a dialysis fistula can be used about 8-12 weeks after it is made.
Maintaining your dialysis access
After dialysis grafts and fistulas are made, the flow through them is tested periodically by the dialysis center in order to make sure they continue to function well. If a graft or fistula is showing signs of decreasing flow, or increasing pressure, the patient is again referred back to the vascular surgeon for evaluation. In this case, a narrowing may have occurred in the graft or fistula.
At our office, we are very invested in making sure that our dialysis access lasts as long as possible. Dialysis patients usually become like members of our own family, and we take care of them accordingly! Therefore, after an access is made, regular ultrasounds are scheduled for the patient in order for us to regularly see our work. This way, if we see a narrowing or any other problem in our graft or fistula, we can act quickly to fix it, before the access fails.
Treatment of failing fistulas or grafts
If testing reveals problems in the fistula or graft, every effort is made to correct that problem, and keep the access working. Usually, problems with flow are caused by a narrowing within the vein portion of the fistula or graft. These narrowings are usually treated with an angioplasty and/or stent.
In this procedure, the patient is brought to the hospital, and a fistulogram is done. The fistulogram is done by injecting a small amount of dye into the fistula, and taking pictures. This will show us the narrowing in the vein. We then place a balloon at the exact location of the narrowing (also called "stenosis"), and inflate it. The balloon is then removed. When necessary, stents are also used to correct these problems. A stent is a small metal tube which is deployed at the location of the vein stenosis, and left in place to hold the vessel open.
After this procedure is done, the patient is usually sent home the same day, and their dialyisis regimen continues on the same schedule.
If a graft fails (becomes clotted), then a patient is sent directly to the hospital for evaluation and treatment. The surgeon will decide if the graft needs to have the clot removed, or if a new graft or fistula is needed. Ultrasounds will be obtained if needed, and fistulograms are employed when appropriate. If a new access needs to be done, this will be done in the operating room, much like the initial procedure.
Because dialysis needs to be done every two days, an adequate access must always exist for dialyisis. If there is any question regarding the use of a graft or fistula, a dialysis catheter will be inserted.
A dialysis catheter is like a giant IV which is placed in one of the biggest veins in the body (usually the jugular vein in the neck). This IV is very long, and its tip is placed in the right atrim of the heart. In this way, dialysis nurses are able to use one port of the catheter to pull blood out of the body, and another port to put blood back into the body.
Dialysis catheters work well, but they are prone to infection. They also can hurt the large veins in the body, causing narrowing over time. Therefore, these catheters are only used for short time periods, until a more suitable access is ready to be used.