Cardio-Pulmonary Bypass The Perfusionist and the Heart Lung Machine

  • Common questions and their answers

    CoverWe have written this booklet in order to provide some information and answer some questions regarding one aspect of your child's upcoming heart surgery..

    Some parents may have heard of, or know a little about, the heart-lung machine and cardio-pulmonary bypass. This booklet should provide some more details of this integral part of the child's operation, and hopefully, you will be able to understand your child's operation a little better. This is your booklet to keep. Maybe other family members or friends may benefit from reading the booklet, and your child may be interested in it, when he or she is old enough.

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    What part does the Heart-Lung machine play?

    introIn order for the surgeon to actually do the repair, the heart needs to be quite empty, and in most cases, it needs to be stopped for a while. This means that for a short period, during the operation the blood which normally circulated through the heart and lungs, cannot do so. This gives the surgeon the best conditions under which to operate. So, while the heart and lungs are out of action, the Heart-Lung Machine (HLM) takes over. This is called CARDIO-PULMONARY BYPASS.

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    What exactly doe the Heart-Lung machine do?

    The HLM is a very sophisticated machine designed to:

    • take over the job of the heart, and so it pumps blood around the body;
    • take over the job of the lungs, so it adds oxygen to the blood, and removes carbon dioxide

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    What exactly does the Heart-Lung machine look like?

    The machine itself has up to five precision blood pumps. In addition it has a heater / cooler device for temperature control and a series of individual microprocessor units which monitor and control patient temperatures, the gas supply, and the safety systems.

    Below is a diagram of the circuit showing the position of the patient, the oxygenator, the pump and the filter.

    The pump takes over the job of the heart 
    The pump 

    The pump takes over the job of the heart, and pumps the blood through the oxygenator and back into the patient.

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    So that's the basic machine, what else is there?

    Heart machineApart from the machine, we use a disposable oxygenator, and a disposable tubing circuit with the HLM. The oxygenator functions in a similar way to the patient's own lungs, and for a time during the operation will serve as the lungs. As blood flows through the oxygenator, oxygen can be added to the blood, and carbon dioxide can be removed, and the appropriate levels of each gas can be maintained.

    The oxygenator also contains a heat exchanger, which allows the blood temperature, and therefore the patient's temperature to be altered.

    The circuit is made up of a special plastic tubing, and is set up on the HLM. Blood travels from the patient, to the oxygenator, and then is pumped back into the patient's circulation. The circuit also contains a blood filter. We keep the circuit very short, and so the HLM is right next to the operating table.

    The patient is connected to the circuit through plastic cannulae, which the surgeon puts into the large veins and an artery near the heart at the beginning of surgery, and removes them at the end.

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    What kind of things will happen while connected to the Heart-Lung machine?

    Firstly, we fill the tubing circuit with a special solution called the priming solution. The priming solution removes all the air in the circuit, oxygenator and filter, and makes it bubble free. The priming solution is a mixture of donor blood and a type of saline solution. The donor blood is necessary because of the size of children who need cardio-pulmonary bypass and also the volume required to fill the circuit. Almost all children who weigh less than 16 Kg, will need some donor blood (generally, about 500 mls) to prime the tubing circuit.

    During cardio-pulmonary bypass, we need to be able to control the patient's temperature. In most cardiac operations we cool the patient in order to slow and to control the way the body uses oxygen. The level of cooling will be determined by the type of operation, and the body temperature is controlled by altering the blood temperature in the oxygenator. Toward the end of cardio-pulmonary bypass, we warm the patient back up to normal temperature.

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    So who is "driving" the Heart-Lung machine?

    PerfusionistLet's introduce the Perfusionist.

    The perfusionist is the member of the team who is responsible for the operation of the HLM during cardiac surgery. The perfusionist is also responsible for the selection and set-up of the circuit components for the procedure.

    The perfusionist works closely with the surgeon and anaesthetist and is a skilled scientist, with tertiary qualifications which include human physiology and biochemistry, and also has more specialised training in the techniques of artificial blood circulation , commonly known as perfusion science. All our perfusionists are certified by the Australasian Board of Cardio-Vascular Perfusion, and are members of the Australasian Society of Cardio-Vascular Perfusion.

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    How does the PERFUSIONIST keep track of what is happening to the patient's circulation?

    OperatorWe've mentioned the microprocessor control systems which display and aid in the regulation of the temperatures and pressures within the circuit. There is also a monitor which constantly displays the level of oxygen in the blood. The perfusionist takes regular blood samples for biochemical, and blood clotting tests. The analysers are right next to the HLM. The patient's ECG and blood pressure are displayed on a television-type monitor, mounted on the HLM. The whole set-up is similar to a cockpit of an airplane.

    When the surgeon has finished the repair, and the team feels that the heart and lungs can take over from the HLM, the perfusionist slowly weans the patient, and the surgeon removes the cannulae.

    Now you know a little more about cardio-pulmonary bypass, and your child's operations. We perform between 400 & 500 operations requiring cardio-pulmonary bypass every year.