Hemodialysis

By SickKids staff

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Learn how hemodialysis removes waste products from the blood when the kidneys fail.

Key points

Hemodialysis uses a mechanical kidney, called a dialyzer, to clean the blood when the kidneys can no longer do so.
Blood travels to and from the dialyzer through a central venous line or fistula.
Hemodialysis can be done at home or in the hospital.

Introduction

Healthy kidneys clean the blood by removing waste products and unwanted fluid and flushing them out of the body through urine. When the kidneys fail, hemodialysis takes over the job that they can no longer do.

During hemodialysis, blood is removed from your child's body through a tube. It then goes to a mechanical kidney called a dialyzer. The dialyzer cleans the blood by removing waste products and unwanted fluid. The blood then returns to your child's body through another tube.

This type of dialysis can be done at home or in the hospital and is safe, efficient and usually painless. It may be done several times a week.

Blood travelling out the body into the dialyzer to be cleaned and then travelling back into the body — Simple illustration of hemodialysis

About the treatment

How hemodialysis works

Hemodialysis works on two principles:

osmosis
diffusion

Osmosis is the ability of water to pass through the wall of a cell. This wall is called a semi-permeable membrane and acts like a filter.

Diffusion is the natural movement of particles from an area with lots of particles to an area with fewer particles.

In hemodialysis, the dialyzer (mechanical kidney) acts as the semi-permeable membrane.

Blood flows along one side of the membrane and a special dialysis solution called dialysate flows on the other side.
The waste products removed from your child's body diffuse, or spread, from the blood (an area with lots of waste products) into the dialysate (an area with no waste products).
The substances that the body needs cannot pass through the semi-permeable membrane. These stay in the blood that is returned to your child's body.

How hemodialysis takes blood from the body and returns it

Blood is taken out and returned through a central venous line or fistula.

The central venous line is a tube that is inserted in your child's body during a minor operation under general anesthetic. The tube is put into the major blood vessels leading to your child's heart and sits at the top of the right side of the heart.

A fistula is created by sewing together an artery and a vein in the arm during surgery. Two needles are inserted into your child's arm: one sends blood to the dialyzer for cleaning and another returns the blood to your child's body. Over time, the vein becomes bigger, which creates easier access for the dialysis needles.

Last updated: July 30th 2014