The chief function of the kidneys is to filter waste products from the blood. When the kidneys fail, hemodialysis is used to clean the blood and remove excess fluid.
Hemodialysis is necessary for patients who have end-stage kidney, and it also can be used in patient's with acute kidney failure. Usually, hemodialysis is required when more than 85 to 90 percent of kidney function has been lost. In some cases, hemodialysis is needed only temporarily until kidney function returns, but in most cases it is required for the rest of the patient's life or until the patient receives a kidney transplant.
Common causes of kidney failure include the following:
- Kidney inflammation
- Blood vessel inflammation
- Genetic kidney diseases
The kidneys can also shut down suddenly after a heart attack or severe injury, or as a result of surgery or severe illness.
What happens during hemodialysis?
During hemodialysis, blood is removed from a patient's vein, circulated through a filtering machine, and returned to the body. Since veins tend to have weak blood flow, a surgeon often connects one of the patient's nearby arteries to the vein being used for dialysis in order to increase blood flow to the vein. This artery-to vein connection can be created either through the use of synthetic material known as a graft, or through a direct surgical connection of one blood vessel to the other, which is known as a fistula.
In cases where creating a fistula or graft is not possible, or in emergency situations, a hemodialysis catheter may be inserted into a vein in the neck or upper leg in order to perform dialysis. These catheters are simliar to large IV's, with 2 ports visible outside the body. One port is used to pull blood from the body to the machine, and the other port is used to return blood to the patient from the machine. Unlike fistulas and grafts, catheters do not require needle sticks to access the patient's blood, but catheters are associated with higher risks of serious infection. Catheters also typically do not clean the blood as efficiently, so patients may require longer dialysis sessions.
What are the differences between grafts and fistulas?
Fistulas are created by a direct surgical connection from an artery to a vein. Arteries take blood from the heart to the rest of the body, and are high flow & high pressure vessels. Veins carry blood back to the heart, and are low flow & low pressure vessels. After the fistula is created, the vein thickens and strengthens in response to the higher blood flow from the artery. This maturation process typically takes 2-3 months for the vein to become stong enough to withstand the needle sticks required to access the bloodstream and move blood to & from the dialysis machine.
Grafts, on the other hand, are synthetic material used to connect the artery to the vein if a direct connection cannot be achieved for a fistula. The graft material can be accessed with needle sticks immediately if needed because no maturation process is needed, but patients often wait until post-operative swelling has improved before using the graft for dialysis. Grafts usually work well, but fistulas generally are the preferred option because of better long term performance and lower infection risk.
Risks of Hemodialysis
Although usually safe, hemodialysis is a complex procedure that has serious risks. Some of these risks include:
- Muscle cramps
- Sleep problems
- Low blood pressure (hypotension)
- Bone diseases
- High blood pressure (hypertension)
- Pulmonary edema (fluid in the lungs)
- High potassium levels
Patient Care During Hemodialysis
While undergoing hemodialysis, it is extremely important to avoid infection. Washing hands, wearing masks, using antiseptic wipes and routinely checking supplies for any signs of contamination are essential. In addition, hemodialysis patients have to carefully monitor their diets. They must make sure that their fluid intake is balanced, that they eat a diet high in protein, and that they restrict their intake of high potassium high phosphorous foods.