Cardiopulmonary bypass

Cardiopulmonary bypass (CPB) is a technique in which a machine temporarily takes over the function of the heart and lungs during cardiac surgery, maintaining the circulation of blood and oxygen to the body. The CPB pump itself is often referred to as a heart-lung machine or "the pump". Cardiopulmonary bypass pumps are operated by perfusionists. CPB is a form of extracorporeal circulation. Extracorporeal membrane oxygenation (ECMO) is generally used for longer-term treatment.

Cardiopulmonary bypass is used in many heart surgery procedures to improve safety during the surgery. The CPB machine mechanically circulates and oxygenates blood for the patient's body while bypassing the heart and lungs. A heart-lung machine is used to maintain perfusion to other body organs and tissues of the patient while the surgeon works in a bloodless surgical field. The surgeon places a cannula in the right atrium, vena cava, or femoral vein to withdraw blood from the body. Venous blood is drained from the body by the cannula into a reservoir and then filtered, cooled or warmed, and oxygenated before it is returned to the body by a mechanical pump. The cannula used to return oxygenated blood is usually inserted in the ascending aorta, but it can also be inserted in the femoral artery, axillary artery, or brachiocephalic artery (among others) according to the demand of the surgery.

The person is administered heparin to prevent clotting, and protamine sulfate is used as a reversal drug at the end of the surgery. During the procedure, hypothermia may be maintained; body temperature is usually kept at 28 °C to 32 °C (82.4–89.6 °F). The blood is cooled during CPB and returned to the body. The cooled blood slows the body's basal metabolic rate, decreasing its demand for oxygen. Cooled blood usually has a higher viscosity, but the various crystalloid or colloidal solutions that are used to prime the bypass tubing serve to dilute the blood, prevent hemolysis and maintain electrolytic balance. Maintaining appropriate blood pressure for organs is a challenge and this is monitored carefully during the procedure.