How Kidney Dialysis Works

by | Apr 15, 2009 08:00 AM ET

There are a growing number of people in the United States with diabetes, and people with advanced diabetes often experience kidney failure. This page talks about the extent of the problem:

- "Each year in the United States, more than 100,000 people are diagnosed with kidney failure."

- "Most U.S. citizens who develop kidney failure are eligible for federally funded care. In 2005, care for patients with kidney failure cost the United States nearly $32 billion."

Once the kidneys fail, the patient loses the kidneys' ability to clean the blood. This would normally be a fatal problem. Therefore the patient needs to use a dialysis machine to do the kidneys' job.

A dialysis machine (AKA a hemodialyzer or an artificial kidney) takes blood from the body, cleans it and then sends it back to the body, usually through needles/tubes placed in the arm. A patient on kidney dialysis would normally get three treatments per week, and it typically takes several hours to clean the blood. This video explains the process:

This page offers a description of how a dialysis machine works. But another way to understand the process is to think about the first dialysis machine. It used sausage casing and the principle of osmosis to do its job:

Doctor Invented Kidney Dialysis Machine, Artificial Organs

The machine was based on the simple physical principle that substances dissolved in water will move from a place where they are highly concentrated to a place where they are not concentrated if given a chance. When blood containing high concentrations of acid, urea molecules and salts is put in a porous container and placed in a bath of water, those substances will move through the pores and out of the blood.

The sausage casing provided the pores. If you think about blood, you realize that it contains red blood cells (along with white blood cells, platelets, etc.) suspended in plasma. Plasma is mostly water and salt, but without the kidneys to filter it, poisonous chemicals accumulate in the plasma. In a dialysis machine, the harmful chemicals flow across the porous membrane into the dialysate, and the blood is cleaned.

You might wonder, "How does a person have two big needles plunged into his/her arm every other day without damage?" This video demonstrates why that is possible:

A person on dialysis often has a plastic graft or a fistula installed in the arm, and you can see it clearly in the video. It is an artificial vein that can handle all the needle sticks. For more info see: Dialysis Access.

See also: 'DIY' kidney machine saves girl

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