Cardiothoracic Anesthesiology - Cardio-pulmonary Bypass (CPB)

Cardio-pulmonary Bypass (CPB)

Cardiopulmonary bypass (CPB) is a technique in which heart-lung machine temporarily takes over the function of the heart and lungs during surgery.

Blood is drained from the venous (deoxygenated) circulation, and is cycled through the CPB machine. While in the machine, the blood is filtered, heated or cooled, and infused with oxygen. Subsequently, it is pumped back into the arterial (oxygenated) circulation, thereby bypassing the heart and lungs and maintaining the perfusion of the vital organs.

While the step by step process for preparation and initiation of CPB can vary between institution and type of surgery, a typical scenario is as follows.

After a median sternotomy, a surgical retractor is placed by the surgeon to optimize exposure of the heart. At this time, heparin is given to thin the blood to prevent thrombus from forming while on CPB. The surgeon places a cannula in the right atrium, vena cava, or femoral vein to withdraw blood from the venous circulation. Gravity is used to drain the venous blood into the CPB machine, and a separate cannula, usually placed in the aorta or femoral artery, is used to return blood to the arterial circulation.

The process of preparation, initiation, and separation of cardiopulmonary bypass is a critical time during cardiac surgery. Some studies have even considered formalizing this period of time, much like the "sterile cockpit" process in critical steps of aviation . The communication, while a team effort, is led and directed by the cardiothoracic anesthesiologist, as the surgeon is focused on acquiring and maintaining adequate exposure. This can even extend to placement of the cannulae for CPB preparation, as the cardiothoracic anesthesiologist often directs the surgical placement via real-time TEE data. As such, this responsibility demands that the cardiothoracic anesthesiologist have a thorough knowledge of the advanced physiology, principles, practical application and management of CPB.

After completion of the "on bypass" surgical correction, preparations are made to separate the patient from CPB. In other words, the heart and lung are prepared to receive, oxygenate, and pump the blood which had immediately previous been done by the CPB machine. Separation can be complicated by the CPB machine, the patient's inherent pathology/physiology, surgical correction, and the dynamic interaction of all three. Cardiopulmonary bypass has effects on the patient's hematology, physiology, and immunology, which must be acutely managed by the cardiothoracic anesthesiologist in order to ensure effective separation from CPB.