Hemodialysis: The What, The Why, And The How It Works

Hemodialysis is a treatment for kidney failure that uses a machine to filter your blood outside your body. At the start of a hemodialysis treatment, a dialysis nurse or technician places two needles into your arm. Once trained by the health care team, some people prefer to insert their own needles. A pump on the hemodialysis machine draws your blood through one of the needles into a tube, a few ounces at a time. Your blood travels through the tube to the filter, called a dialyzer. Inside the dialyzer, your blood flows through thin fibers that filter out

  • wastes
  • extra salt
  • extra fluid


Hemodialysis: How Does It Work?

In hemodialysis, blood is removed from the body and filtered through a man-made membrane called a dialyzer, or artificial kidney, and returned to the body after cleaning. The average human body contains about 10 to 12 pints of blood. Hemodialysis cleans 2 cups of blood at a time.

To perform hemodialysis there needs to be an access created to get the blood from the body to the dialyzer and back to the body. There are three access types for hemodialysis: arteriovenous (AV) fistula, AV graft and central venous catheter. The AV fistula is the vascular access most recommended by the dialysis community.

When a patient goes to hemodialysis, a nurse or technician will check vital signs and get the patient’s weight. The weight gain will tell how much excess fluid the patient has to have removed during the treatment. The patient is then “put on the machine”. Patient with a vascular access (AV fistula or AV graft) will get two needle sticks in their access; one needle takes blood out of the body, the other needle puts it back. Patients with a central venous catheter will have the two tubes from their access connected to the blood tubes that lead to the dialyzer and back to the body. Once the patient is “put on the machine”, the dialysis machine is programmed and then treatment begins.


Hemodialysis: The Machine

Blood never actually goes through the dialysis machine. The dialysis machine is like a big computer and a pump. It keeps track of blood flow, blood pressure, how much fluid is removed and other vital information. It mixes the dialysis solution, which is the fluid bath that goes into the dialyzer. This fluid helps pull toxins from the blood, and then the bath goes down the drain. The dialysis machine has a blood pump that keeps the blood flowing by creating a pumping action on the blood tubes that carry the blood from the body to the dialyzer and back to the body. The dialysis machine also has many safety detection features. If you visit a dialysis center, you will likely hear some of the warning sounds made by a dialysis machine.


Hemodialysis: How often?

Traditional, in-center hemodialysis is generally done three times a week for about four hours each session. Average sessions are usually between 3 to 5 hours, but most common is 4 hours. An alternative is short daily hemodialysis which is performed five or six times per week for about two to three hours each treatment. A third option is nocturnal hemodialysis, where the patient receives dialysis for about eight hours overnight while sleeping. This is a longer, gentler treatment, and patients report fewer problems with cramping and fatigue.

Another type of dialysis called peritoneal dialysis (PD). PD is done by filling the peritoneum in the abdomen with dialysate and using the peritoneal membrane as a semipermeable membrane. There are diet and fluid restrictions with peritoneal dialysis; however, these are usually not as limited as hemodialysis because this therapy is performed every day. PD treatments are performed at home, and so do not require three visits to a treatment center each week. Peritoneal dialysis also has a nighttime treatment option that makes it easier for patients to work, attend school or travel.


Hemodialysis: Advantages

Hemodialysis is an effective treatment for those with end stage renal disease. However, hemodialysis alone will not provide a complete treatment for those with kidney failure. Diet and fluid restrictions need to be followed, and medicines may need to be taken to replace other functions of the kidneys, such as regulating blood pressure and stimulating production of red blood cells to prevent anemia.

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