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Cardiopulmonary bypass

Refers to the technique that temporarily takes over the function of the heart and lungs during surgery.

It maintains the circulation of blood and the oxygen content of the body.

Utilizes a heart–lung machine as a form of extracorporeal circulation operated by perfusionists in association with surgeons who connect the pump to the patient.

Cardiopulmonary bypass consists of two main functional units, the pump and the oxygenator which remove oxygen-deprived blood and replace it with oxygen-rich blood through a series of hoses.

The pump comprises several rotating motor-driven pumps that peristaltically propels the blood through the tubing, and presently many CPB circuits employ a centrifugal pump for the maintenance and control of blood flow.

Centrifugal force pumps are superior to the action of the roller pump as it may produce less blood hemolysis.

The technique mechanically circulates and oxygenates blood for the body while bypassing the heart and lungs, and enables the surgeon to operate in a bloodless surgical field.

Commonly used in heart surgery because of the difficulty of operating on the beating heart, and is required in cardiac surgical procedures where the chambers of the heart are opened to support circulation.

Can be used for the induction of total body hypothermia, and can be used to rewarm individuals suffering from hypothermia state.

A simplified for of CPB is the extracorporeal membrane oxygenation (ECMO), used as life-support for newborns with serious birth defects, or to oxygenate and maintain recipients for organ transplantation until new organs can be found.

A cannula is placed in the right atrium, vena cava, or femoral vein to withdraw blood from the body and it is connected to tubing filled with isotonic crystalloid solution where it is filtered, cooled or warmed, oxygenated, and then returned to the body.

The oxygenated blood is returned by cannula to the ascending aorta, but it may be inserted in the femoral artery.

Heparin is utilized to prevent clotting.

The body temperature is maintained at 28ºC to 32ºC (82.4–89.6ºF) by cooling the circulating blood so that the metabolic rate is slowed and oxygen demand is decreased.

Protamine sulfate is given to reverse effects of heparin.

Surgical procedures in which cardiopulmonary bypass is used include: Coronary artery bypass surgery, cardiac valve repair and/or replacement, repair of septal defects, repair and/or palliation of congenital heart defects, transplantation of heart, lung, or heart–lung, repair of large aneurysms, andpulmonary thrombectomy.

The oxygenator transfers oxygen to infused blood and remove carbon dioxide from the venous blood.

Cardiac surgery was made possible by CPB using bubble oxygenators, but membrane oxygenators are presently used.

Heparin-coated blood oxygenators produce less systemic inflammation and decrease likelihood for blood to clot in the CPB circuit.

A venous cannula removes oxygen deprived blood and an arterial cannula is used to infuse oxygen-rich blood.

A cardioplegia cannula is sewn in the heart to deliver a cardioplegia solution to cause the heart to stop beating.

CPB produces activation of the inflammatory, complement, coagulation, and fibrinolytic systems.

In CPB blood interfaces with non-endothelial surfaces in the extracorporal circulation.

Thrombin generation remains central to the activation of the coagulation and fibrinolytic systems and postoperative blood loss and transfusion correlate directly with thrombin generation during CPB.

Platelets, activated by thrombin and CPB, are removed from circulation, and remaining platelets exhibit decreased responsiveness.

Fibrinolysis is activated during CPB by several mechanisms including Kallikrein and thrombin activation both resultng in release of tissue plasminogen activator, the dominant plasminogen activator during CPB.

Thrombin produces an anticoagulant effect through the protein C pathway.

Thrombin, bound to thrombomodulin, activates protein C, which inactivates factors Va and VIIIa and levels of total protein C decrease during CPB.

Levels of aPC increase during CPB, probably a result of thrombin generation, and increase specifically after release of the aortic cross-clamp.

Correlations exist between the aPC/total protein C ratio in coronary sinus blood and myocardial performance on the first postoperative day, suggesting an important function of this anticoagulant system in suppressing ischemia-induced inflammatory and cytotoxic effects.

Pediatric cardiac surgery patients with low perioperative levels of antithrombin and aPC, as well as patients with resistance to aPC, are at most risk for postoperative central venous thrombosis.

Factor V Leiden carriers have an average of 30% less blood loss after CPB, the magnitude of blood sparing is nearly the same as that provided by the antifibrinolytic drugs aprotinin and ε-aminocaproic acid, and the chance of requiring blood or blood products is signficant lower than in non carriers of the gene.

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