Hemodialysis uses a machine to clean and filter your blood. This process temporarily removes wastes, extra salt, and excess fluids from your body. Hemodialysis helps control blood pressure and maintain the proper balance of important chemicals such as potassium, sodium, calcium, and bicarbonate.
Hemodialysis uses a special filter called a dialyzer. This filter functions as an artificial kidney to clean your blood. During treatment, your blood travels through tubes into the dialyzer, which filters out wastes and excess fluids. The filtered blood flows through another set of tubes back into your body. The dialyzer is connected to a machine that monitors blood flow and removes wastes from the blood.
Preparation for hemodialysis
Preparations for hemodialysis should be made at least several months before it will be needed. In particular, you will need to have a procedure to create an "access" (described below) several weeks to months before hemodialysis begins.
Vascular access — An access creates a way for blood to be removed from the body, circulate through the dialysis machine, and then return to the body at a rate that is higher than can be achieved through a normal vein. There are three major types of access: primary AV fistula, synthetic AV bridge graft, and central venous catheter. Other names for an access include a fistula or shunt.
The access should be created before hemodialysis begins because it needs time to heal before it can be used. Discussions about the access should begin even earlier, since you will need to avoid injuring blood vessels that will eventually be used for access. Having an intravenous line (IV) or frequent blood draws in the arm that will be used for access can damage the veins, which could prevent them from being used for a hemodialysis access. The access is usually created in the non-dominant arm; for a right-handed person this would be their left arm.
Primary AV fistula — A primary AV fistula is the preferred type of vascular access. It requires a surgical procedure that creates a direct connection between an artery and a vein. This is often done in the lower arm, but can be done in the upper arm as well. Sometimes a vein that would not normally be useful for creating an AV fistula can be moved so that it is more accessible; this is often done in the upper arm.
Regardless of its location or how it is created, the access is located under the skin. During dialysis, two needles are inserted into the access. Blood flows out of the body through one needle, circulates through the dialysis machine, and flows back into the access through the other needle.
A primary AV fistula is usually created two to four months before it will be used for dialysis. During this time, the area can heal and fully develop or "mature".
Synthetic bridge graft — Sometimes, a patient's arm veins are not suitable for creating a fistula. In these cases, a surgeon can use a flexible rubber tube to create a path between an artery and vein. This is called a synthetic bridge graft. The graft sits under the skin and is used in much the same way as the fistula except that the needles used for hemodialysis are placed into the graft material rather than the patient's own vein.
Grafts heal more quickly than fistulas and can often be used about two weeks after they are created. However, complications such as narrowing of the blood vessels and infection are more common with grafts than with AV fistulas.
Central venous catheter — A central venous catheter uses a thin flexible tube that is placed into a large vein (usually in the neck). It may be recommended if dialysis must be started immediately and the patient does not have a functioning AV fistula or graft. This type of access is usually used only on a temporary basis. In some cases, however, there can be problems maintaining an AV fistula or graft, and the central venous route is used for long-term access.
Catheters have the highest risk of infection and the poorest function compared to other access types; they should be used only if a primary fistula or synthetic bridge graft cannot be maintained.