Week 3: Cardiopulmonary Bypass Machine

Hey guys! For my first post this week, I want to talk in detail about the cardiopulmonary bypass machine (heart-lung machine or CPB machine). This machine plays a major role in open heart surgery, and I think that by explaining how the machine works, you will have a better understanding of the process.

The CPB machine essentially consists of parts that assume the functions of your heart and lungs, and is meant to keep blood flowing through the patient's body while his/her heart is stopped during surgery. A surgeon may want to stop the heart for certain medical procedures such as a valve replacement to protect the heart from damage and reach a valve without major blood loss. This can be done by administering cardioplegic solution (high concentration of potassium) into the coronary sinus, a venous channel that empties blood from the coronary vein into the right atrium.

CPB Machine

The main parts of the machine are the oxygenator, pumps, and heat-exchanger (controls temperature of the blood). Venous blood can be taken from the body into the machine via a tube inserted into the right atrium, vena cave, or the femoral vein. A reservoir collects the venous blood, and it is passed to the oxygenator via tubing. The oxygenator allows for the exchange of oxygen and carbon dioxide between the blood flowing through it and the surrounding gas. It then travels through the heat exchanger which cools and rewarms blood, giving the surgeon the option to reduce or stop blood flow around the body since hypothermia reduces the body's oxygen requirement. From there, blood is pumped back via tubing into the femoral artery or ascending aorta to travel around the body.

Overview of blood flow through the CPB machine

The oxygenator, pump, and connecting tubes are filled with physiologically compatible fluid to avoid introducing air bubbles into the blood. Also, when blood comes into contact with foreign surfaces, such as those of the CPB machine, it will naturally clot. This can be avoided by administering heparin, the body's own anticoagulant, to the patient before blood enters the machine. Once the patient is taken off the machine, they are given protamine to neutralize the heparin and restore normal blood clotting mechanisms.

Hopefully this explanation was helpful, and you now have a decent understanding of how the CPB machine takes over the function of the lungs and heart. It is crucial in protecting the heart and allowing the surgeon to work in a clear, "bloodless" field during many open heart surgeries. In my next post, I will talk about the procedures that I will be observing in the next few days. Stay tuned!

Citation:
Heart-lung machines. Retrieved from http://www.surgeryencyclopedia.com/Fi-La/Heart-Lung-Machines.html