Pediatric Cardiopulmonary Bypass | Procedure & Complications

Cardiopulmonary Bypass

What Is Cardiopulmonary Bypass?

To repair most cardiac defects, the cardiothoracic surgeon requires a bloodless, motionless field in which to work. To achieve this, the motion of the heart and lungs must be stopped.

For this to occur, there needs to be a way for blood to circulate throughout the body, delivering the nutrients and oxygen necessary for life, while the heart and lungs are not functioning. This is made possible through a process known as cardiopulmonary bypass (CPB).

Tubing made of clear polyvinyl chloride (PVC) contains the patients' blood as it is diverted from the body. Large bore catheters (called cannula) are placed in the right side of the heart, allowing the desaturated blood from the body to enter the cardiopulmonary bypass circuit.

The PVC tubing runs through a mechanical pump that can be regulated to the proper cardiac output for a given patient.

For example, a 5-year-old child has a much smaller cardiac output than an adult does; thus the pump must run at a higher rate for the adult patient than the child. More PVC tubing delivers blood from the mechanical pump to a gas exchange device called an oxygenator, or artificial lung.

The oxygenator performs the same job as the lungs: oxygenation of the blood as well as removal of carbon dioxide.

This re-oxygenated blood is then returned to the body via another cannula placed in the aorta.

In this way, cardiopulmonary bypass permits the patients' blood to bypass the heart and lungs, achieving the desired bloodless, motionless operative field and still supplying all the other organs of the body with a constant supply of oxygen and nutrient-rich blood.

The sum total of the mechanical pump, oxygenator, cannula and PVC tubing is often referred to as the heart-lung machine, or simply "the pump."

When a patient is being supported by a heart-lung machine, the patient is said to be "on bypass," or "on the pump."

Conversely, when a patient is taken off of this support, it is termed "off bypass," or "off the pump."

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Cardiopulmonary Bypass Risks

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Although the origins of cardiopulmonary bypass can be traced back to the 19th century, the field has developed rapidly in the last 50 years.

The first attempt to use a heart-lung machine for total cardiopulmonary bypass was carried out at the University of Minnesota in 1951. Since that time, cardiopulmonary bypass has become a standard, widely used, low-risk procedure.

It is necessary to recognize some adverse effects may be seen when the circulation of the body is taken over artificially.

Cardiopulmonary bypass has a very wide range of effects on the body. All organ systems are affected by cardiopulmonary bypass, mainly the heart, lungs, brain and kidneys.

These effects can range from mild to severe based on how sick the patient is before surgery, the length of time that a patient is supported by cardiopulmonary bypass and the complexity of the operation being performed.

The function of the heart may be compromised to a degree after bypass surgery. Some patients have subtle neurologic changes after bypass surgery. The occurrence of stroke or seizures during or after bypass remains low, but is a possibility.

The kidney may experience damage ranging from decreased urine output to complete renal failure. Areas of the lung may fail to fully expand after bypass. This condition is known as atelectasis.

During cardiopulmonary bypass, the patients' blood is in contact with the foreign surfaces (PVC tubing) that make up the heart-lung machine. This leads to a reaction by the patient's body that is best characterized as generalized "inflammatory response"; swelling of different body parts, fever and abnormal blood tests partly describe this response. Research has shown this response could be potentially damaging to certain tissues in the body. We try to minimize this inflammatory response with preoperative and intraoperative steroids.

Due to the extra fluid volume needed to fill the cardiopulmonary bypass circuit, the patients' blood volume is diluted. This may require transfusion of blood products to the patient while on cardiopulmonary bypass and blood clotting abnormalities during the post-operative period.

The risk of serious complications related to being placed on cardiopulmonary support depends on the age of the patient, how ill he or she is at the time of the operation and the complexity of the surgery to be performed.

In most cases the risk is below 1 percent, but in higher complexity situations, it may be as high as 10 percent to 20 percent.

Who Operates the Heart-Lung Machine?

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The conduct of cardiopulmonary bypass is a very elaborate process. The cardiovascular perfusionist is the member of the open-heart surgical team responsible for setting up and running the heart-lung machine.

The cardiovascular perfusionist will assemble the proper circuit for a given patient, based on body size and the specific type of operation to be performed.

While a patient is supported by the heart-lung machine, the perfusionist is responsible for monitoring various pressures, ECG, coagulation, blood gases and electrolytes. The goal of the perfusionist is to keep the patient in a normal physiologic state.

Currently there are 18 accredited programs across the United States specializing in perfusion training. Individuals who complete a perfusion training program earn a post-baccalaureate degree. Areas of study include cardiac anatomy, pharmacology, physiology, biochemistry and fluid dynamics.

Cardiovascular perfusionists on staff at Cincinnati Children's Hospital Medical Center are board-certified by the American Board of Cardiovascular Perfusion.

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