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Weaning from cardiopulmonary bypass (CPB)

Michael G Fitzsimons, MD
Section Editor
Jonathan B Mark, MD
Deputy Editor
Nancy A Nussmeier, MD, FAHA


Cardiopulmonary bypass (CPB) is a form of extracorporeal circulation in which the patient's blood is diverted from the heart and lungs and rerouted outside of the body. The normal physiological functions of the heart and lungs, including circulation of blood, oxygenation, and ventilation, are temporarily assumed by surrogate technology. This allows a surgeon to operate on a non-beating heart in a field largely devoid of blood while maintaining complete control of tissue oxygenation and perfusion.

This topic will discuss the general principles and physiology of CPB, preparations for weaning from CPB, the process of weaning, problems that may be encountered during and after the weaning process, and management of failure to wean.


Components of the cardiopulmonary bypass (CPB) machine include pumps, tubing, artificial organs, and monitoring systems (figure 1A). Modern CPB circuits are also equipped with several safety features, including continuous vascular pressure monitoring; blood gas, hemoglobin, and electrolyte monitoring; air detection systems; and blood filters.

Physiology — During CPB, venous blood is intercepted as it returns to the right atrium and is diverted through the venous line of the CPB circuit to a venous reservoir (figure 1A-B). The arterial pump functions as an artificial heart by withdrawing blood from this reservoir and propelling it through an artificial lung (oxygenator or gas exchanger), a heat exchanger, and finally an arterial line filter. The blood then returns to the patient's arterial system through an arterial line positioned in the ascending aorta or other major artery. Additional CPB circuit components and pumps are employed as needed to remove fluid (hemoconcentration), suction blood from the surgical field, deliver cardioplegia solution to produce cardiac electromechanical silence, and decompress the heart (venting). The functions of the heart, lungs, and, to a lesser extent, the kidneys are temporarily replaced.

CPB is associated with an intense inflammatory response that is primarily induced by contact of blood with non-endothelial extracorporeal surfaces [1]. This results in platelet activation, initiation of the coagulation cascade, and decreased levels of coagulation factors. Endothelial cells and leukocytes are activated, releasing more mediators and resulting in capillary leakage and tissue edema. Many of the challenges encountered during weaning from CPB and the postbypass period (eg, myocardial dysfunction, vasodilation, and bleeding) are thought to be consequences of this inflammatory sequence [2-4].


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Literature review current through: Sep 2016. | This topic last updated: Jun 6, 2016.
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