Cardiopulmonary bypass

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. 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. Cardiopulmonary bypass is commonly used in coronary bypass heart surgery because of the difficulty of operating on the beating heart. Operations requiring the opening of the chambers of the heart 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. Patients with terminal conditions, cancer, severe nervous system damage, uncontrolled sepsis and other conditions may not be candidates for ECMO. 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. The cannula is connected to tubing filled with isotonic crystalloid solution. Venous blood which is removed from the body by the cannula is filtered, cooled or warmed, oxygenated, and then returned to the body. The cannula used to return oxygenated blood is usually inserted in the ascending aorta, but it may be inserted in the femoral artery. The patient is administered heparin to prevent clotting, and protamine sulfate is given after to reverse effects of heparin. 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 crystalloid solution used to prime the bypass tubing dilutes the blood. An Austrian-German physiologist Maximilian von Frey constructed an early prototype of a heart-lung machine in 1885 at Carl Ludwig’s Physiological Institute of the University of Leipzig.However, such machines were not feasible before the discovery of heparin in 1916 which prevents blood coagulation. A Soviet scientist Sergei Brukhonenko developed a heart-lung machine for total body perfusion in 1926 which was used in experiments with canines. Dr. Clarence Dennis led the team that conducted the first known operation involving open cardiotomy with temporary mechanical takeover of both heart and lung functions on April 5, 1951 at the University of Minnesota Hospital. The patient did not survive due to an unexpected complex congenital heart defect. This followed four years of laboratory experimentation with dogs with a unit called the Iron Heart. A team of scientists at Birmingham University (including Eric Charles, a chemical engineer) were among the pioneers of this technology. Another member of the team was Dr. Russell M. Nelson , current president of The Church of Jesus Christ of Latter-day Saints, who performed the first open heart surgery in Utah. The first successful mechanical support of left ventricular function was performed in July 3, 1952 by Forest Dewey Dodrill using a machine, the Dodrill-GMR co-developed with General Motors. The machine was later used to support right ventricular function. The first successful open heart procedure on a human utilizing the heart lung machine was performed by John Gibbon and Frank F. Allbritten, Jr. on May 6, 1953 at Thomas Jefferson University Hospital in Philadelphia. They repaired an atrial septal defect in an 18-year-old woman. Gibbon's machine was further developed into a reliable instrument by a surgical team led by John W. Kirklin at the Mayo Clinic in Rochester, Minnesota in the mid-1950s. The oxygenator was first conceptualized in the 17th century by Robert Hooke and developed into practical extracorporeal oxygenators by French and German experimental physiologists in the 19th century. Bubble oxygenators have no intervening barrier between blood and oxygen, these are called 'direct contact' oxygenators. Membrane oxygenators introduce a gas-permeable membrane between blood and oxygen that decreases the blood trauma of direct-contact oxygenators. Much work since the 1960s focused on overcoming the gas exchange handicap of the membrane barrier, leading to the development of high-performance microporous hollow-fibre oxygenators that eventually replaced direct-contact oxygenators in cardiac theatres.