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The artificial circulatory system

What is CPB?

The artificial circulatory system (CPB) is a complex multifunctional system that temporarily takes over the function of the heart and lungs, maintaining adequate blood circulation and proper oxygen content in the body.


What does CPB consist of?

The CPB is a system consisting of pumps that ensure the movement of blood, an oxygenator where gas exchange takes place, a filter, a main line system and a temperature-regulating device. Modern devices, along with mechanical control, have computer software control. The CPB also include systems for monitoring pressure, temperature, oxygen saturation, hemoglobin, blood gases, electrolytes, as well as safety devices such as bubble detectors, oxygen sensors, and low-level liquid detectors in the tank.


Who works with CPB?

In Ukraine, as in the whole world, perfusiologists work with CPB, ensuring the vital activity of the body for the period of surgical intervention. It is worth noting that most often anesthesiologists work as perfusiologists, less often – surgeons who have received appropriate theoretical and practical training. The perfusiologist collects the CPB contour for each patient individually, depending on the size of the body and the specific operation. While the patient’s blood circulation is supported by the CPB, the perfusiologist is responsible for monitoring blood pressure, ECG, coagulation, blood gases and electrolytes, and other vital functions.


When is CPB used?

The CPB is commonly used during heart surgery, in which the presence of heartbeats will significantly complicate surgery (for example, coronary artery bypass grafting). In addition, the CPB is used in surgeries that require opening the heart chambers (for example, mitral or aortic valve prosthetics) or when working on vessels that supply blood to the heart (for example, aortic prosthetics).
In addition, the CPB can be used to induce general hypothermia of the body – a condition in which the body can be maintained for 45 minutes without perfusion (circulation). If blood flow stops at normal body temperature, brain damage usually occurs within three to four minutes -death can occur soon after. Similarly, the CPB can be used to warm people who have suffered from hypothermia.


How does CPB work?

Thanks to the CPB, mechanical circulation and oxygenation of blood are ensured, while bypassing the heart and lungs. The CPB carries blood from the upper right chamber of the heart (right atrium) to a special reservoir called an oxygenator. Inside the oxygenator, oxygen enters the bloodstream through the membrane and binds to hemoglobin in red blood cells. This causes the blood to turn from dark (oxygen-poor) to bright red (oxygen-rich). Then, passing through the filter, blood moves through the contours of the CPB to the body, most often the aorta. From the aorta, blood moves throughout the rest of the body. Thus, while the surgical team works in a bloodless surgical field, CPB allows you to maintain perfusion of other organs of the body and tissues.


How is perfusion performed with CPB?

Before starting the CPB, the patient is given heparin to prevent blood clotting, and after stopping the CPB, protamine sulfate is administered to eliminate its effect. At the same time, to prevent thrombosis, it is important to maintain the activated clotting time (ACT) at a level of more than 480 seconds.

After achieving proper ACT, cannulation is performed depending on the type of operation. Thus, the arterial cannula used to return oxygenated blood is usually inserted first into the CPBending aorta, but it can also be inserted into the femoral artery. The surgeon then places a venous cannula in the right atrium, vena cava, or femoral vein to draw blood from the body. Venous blood that is removed from the body by cannula is filtered, oxygenated, cooled or warmed, and returned to the body.

The blood flow rate of the CPB depends on the patient’s anthropometric data, namely, the surface area of the body. As a rule, the perfusion index during perfusion is 2.4 L/min/m2, which corresponds to the baseline resting heart index.

During the procedure, depending on the surgical intervention, the body is cooled, usually at a level of 32°C to 34°C. Chilled blood slows down the body’s basic metabolic rate, reducing the need for oxygen. Chilled blood tends to have a higher viscosity, but the solutions used to fill the CPB dilute the blood.

The heart can cool down in two ways during AC:

After cooling down, the heart slows down and stops. The introduction of special solutions (cardioplegia) into the heart can speed up this process and completely stop it.


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