Chapter 12

Cardiopulmonary bypass for support during cardiac surgery is unique because blood exposed to foreign, nonendothelial cell surfaces is collected and continuously recirculated throughout the body. This contact with synthetic surfaces within the perfusion circuit, as well as open tissue surfaces within the wound triggers a defense reaction that involves at least five plasma protein systems and five types of circulating blood cells. This inflammatory response to cardiopulmonary bypass initiates a powerful thrombotic stimulus and the production, release, and circulation of vasoactive and cytotoxic substances that affect every organ and tissue within the body. Because of this, open- heart surgery using cardiopulmonary bypass is essentially not possible without anticoagulation, usually with heparin; thus the inflammatory response to cardiopulmonary bypass involves the consequences of exposing heparinized blood to foreign surfaces, not lined with endothelial cells.

Although the inflammatory response has been well characterized, the development of a nonthrombogenic artificial surface that would allow heparin-free circulatory support has not yet occurred. This chapter summarizes the application of extracorporeal circulation in adult cardiac surgery, and is divided into three sections. The first section describes the components and operation of perfusion systems and related special topics. The issues of thrombosis and bleeding are addressed in the second section, whereas the humoral response to cardiopulmonary bypass, including the reaction of blood elements and the inflammatory response are presented later in this chapter. The final section, deals with organ damage as a consequences of extracorporeal perfusion.

### Perfusion Systems

#### Components

During cardiopulmonary bypass (CPB) for cardiac surgery, blood is typically drained by gravity into the venous reservoir of the heart-lung machine via cannulas placed in the superior and inferior vena cavae or a single cannula placed in the right atrium. Specialized cannulas can also be placed into the lower IVC through a femoral approach. Blood from the reservoir is then pumped through a hollow fiber oxygenator, and after appropriate gas exchange takes place, into the systemic arterial system through a cannula placed in the distal ascending aorta, the femoral artery, or the axillary artery (Fig. 12-1). This basic extracorporeal perfusion system can be adapted to provide partial or total circulatory and respiratory support or partial support for the left or right heart or for the lungs separately.

###### Figure 12-1

Basic cardiopulmonary bypass circuit with membrane oxygenator and centrifugal pump.

The complete heart-lung machine includes many additional components (Fig. 12-2).1 Most manufacturers consolidate a hollow-fiber oxygenator, venous reservoir, and heat exchanger into a single unit. A microfilter-bubble trap is added to the arterial outflow. Depending on the operation, various suction systems can be used to return blood from the surgical field, cardiac chambers, and/or the aorta, directly back into the cardiotomy reservoir, through a microfilter and then into the venous reservoir. Increasing evidence of the potential harmful effects ...

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