Cardiopulmonary bypass (CPB) is a form of extracorporeal circulation that diverts the patient’s blood from the heart and lungs, rerouting it, and assuming control of the normal physiological functions of the heart and lungs, including maintaining whole body blood perfusion pressure, oxygenation, and CO2 elimination during cardiovascular and thoracic surgery. CPB allows surgeons to operate on a nonbeating heart in the setting of a bloodless field while maintaining adequate whole body tissue oxygenation and perfusion.
CARDIOPULMONARY BYPASS CIRCUIT
The CPB circuit serves five major functions: circulation of blood, oxygenation, ventilation, systemic cooling and rewarming, and diversion of blood from the heart to provide a bloodless surgical field. During CPB, venous blood is drained passively from the right atrium into a venous reservoir via a venous return cannula (Figure 56-1). The reservoir is placed below the level of the patient to allow for gravity drainage, and serves as a large mixing chamber for all blood return (e.g., cardiotomy suction, aortic root and left atrial vents) as well as for additional fluids and medications. In most cases, negative pressure is not used. Therefore, the amount of venous drainage is accounted for by the central venous pressure (CVP), the resistance to flow in the venous circuitry, and the column height between the patient and reservoir.
CPB circuit. (Reproduced with permission from Cohn LH, Edmunds LH Jr, eds. Cardiac Surgery in the Adult, 4th ed. New York: McGraw-Hill, 2012.)
The arterial pump functions as an artificial heart by pulling blood from this reservoir and driving it through the oxygenator or gas exchanger (artificial lung), a heat exchanger, and an arterial line filter. The oxygenated, warm blood then returns to the patient’s arterial system via an arterial line typically positioned in the ascending aorta. Additional components of the circuit include pumps and tubing for cardiotomy suction, venting, and cardioplegia delivery and recirculation, along with air bubble detectors, blood sampling ports, pressure monitors, and in-line blood gas monitors (Figure 56-2).
Intracardiac and vascular cannulae utilized during cardiopulmonary bypass. (Reproduced with permission from Miller RD. Miller’s Anesthesia, 7th ed. Philadelphia: Elsevier; 2010.)
The cannulation sites depend on the type of operation planned. Most cardiac procedures use full CPB, which involves blood that is drained from the right atrium and returned to the ascending aorta. Aorto-atriocaval cannulation is the preferred method; however, if emergent access is needed, femoral arteriovenous cannulation may be the technique of choice. Some procedures, including surgeries involving the thoracic aorta, are performed using partial bypass, which is a technique that removes a portion of oxygenated blood from the left side of the heart and returned to the femoral artery. Partial bypass allows for perfusion of the ...