Cardiopulmonary bypass (CPB) is a technique in which a machine temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and the oxygen content of the patient's 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 is generally used for longer-term treatment.
CPB mechanically circulates and oxygenates blood for the body while bypassing the heart and lungs. It uses a heart–lung machine to maintain perfusion to other body organs and tissues 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 removed from the body by the cannula 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 may be inserted in the femoral artery, axillary artery, or brachiocephalic artery
Surgical procedures in which cardiopulmonary bypass is used are Coronary artery bypass surgery, Cardiac valve repair and/or replacement (aortic valve, mitral valve, tricuspid valve, pulmonic valve). Repair of large septal defects (atrial septal defect, ventricular septal defect, atrioventricular septal defect), Repair and/or palliation of congenital heart defects (Tetralogy of Fallot, transposition of the great vessels), Transplantation (heart transplantation, lung transplantation, heart–lung transplantation, liver transplantation)
Cardiopulmonary bypass is commonly used in operations involving the heart. The technique allows the surgical team to oxygenate and circulate the patient's blood, thus allowing the surgeon to operate on the heart. In many operations, such as coronary artery bypass grafting (CABG), the heart is arrested (i.e., stopped) because of the difficulty of operating on the beating heart. Operations requiring the opening of the chambers of the heart, for example, mitral valve repair or replacement, requires the use of CPB to avoid engulfing air systemically and to provide a bloodless field to increase visibility for the surgeon. The machine pumps the blood and, using an oxygenator, allows red blood cells to pick up oxygen, as well as allowing carbon dioxide levels to decrease.This mimics the function of the heart and the lungs, respectively.
CPB can be used for the induction of total body hypothermia, a state in which the body can be maintained for up to 45 minutes without perfusion (blood flow).If blood flow is stopped at normal body temperature, permanent brain damage normally occurs in three to four minutes – death may follow shortly afterward. Similarly, CPB can be used to rewarm individuals suffering from hypothermia. This rewarming method of using CPB is successful if the core temperature of the patient is above 16 °C.
Extracorporeal membrane oxygenation (ECMO) is a simplified version of the heart lung machine that includes a centrifugal pump and an oxygenator to temporarily take over the function of heart and/or the lungs. ECMO is useful in post cardiac surgery patients with cardiac or pulmonary dysfunction, in patients with acute pulmonary failure, massive pulmonary embolisms, lung trauma from infections, and a range of other problems that impair cardiac or pulmonary function. ECMO gives the heart and/or lungs time to repair or recover but it's only a temporary solution.