Cardiopulmonary Bypass

Much of the surgery necessary in children with congenital and acquired heart disease is done on the inside of the heart and the heart must be stopped during part or all of the surgery. Even when the heart is still beating, it cannot pump blood out to the body. Thus, your child will be placed on a heart-lung machine and cardiopulmonary bypass will be performed. The person who operates the heart-lung machine is called the perfusionist.

The heart-lung machine is a sophisticated machine that has both a pump to move blood around the body in a way similar to how the heart would if it was pumping and an oxygenator, which fills the blood with oxygen and takes the place of the lungs. Since the heart-lung machine does the work of both the heart and the lungs the term Cardiopulmonary Bypass is used to describe this part of the operation. In order to do cardiopulmonary bypass one or more large tubes, called cannulae, are placed in the major veins returning blood to the heart or into the right atrium and this blood, so-called blue blood because it has less oxygen in it, is drawn into the heart-lung machine and goes through an oygenator to be filled with oxygen. The pink blood, blood full of oxygen, is then pumped into the arterial system in the body through a large cannula in the aorta. During this time the blood is also cooled so that there is additional protection for the body.

Sometimes it is not possible to run the heart-lung machine during part of the operation and the heart and the heart-lung machine may be stopped for a limited time and there will be no blood circulating. The patient is cooled down to very low temperatures before this happens. Usually short periods of no circulation at very low body temperatures, called Deep Hypothermic Circulatory Arrest, are well tolerated, but this method is used for as short a period as possible because of potential brain damage.

The heart-lung machine needs to be filled before it is connected to the patient or all of the patient’s blood would end up filling the machine and there would be no blood left in the patient. The machine is filled, or primed, with a mixture of blood and other fluids such as a special mixture of saline and other electrolytes, and this means that there is sufficient fluid to fill both the machine and the body.