Жүрек-өкпе айналым аппаратының қағидалары мен қолданылуы

Technique that temporarily takes over the function of the heart and lungs during surgery

Cardiopulmonary Bypass (CPB) is a machine that temporarily takes over the function of the heart and lungs during a cardiac surgery by maintaining the circulation of blood and oxygen throughout the body. CPB is used during many heart surgeries to improve the safety of the patient during a heart procedure. The machine mechanically circulates and oxygenates blood throughout the patient's body while bypassing the heart and lungs. Additionally, it maintains perfusion to other body organs and tissues of the patient while the surgeon works in a bloodless surgical field. The CPB is often referred to as a heart lung machine, "the pump," or CPB pumps. CPB is operated by perfusionists, and is a form of extracorporeal circulation.

CPB is commonly used in operations or surgical procedures involving the heart. The technique allows the surgical team to oxygenate and circulate the patient's blood, thus allowing the surgeon to operate safely on the heart. In many operations, such as coronary artery bypass grafting (CABG), the heart is arrested, due to the degree of the difficulty of operating on a beating heart. Operations requiring the opening of the chambers of the heart, for example mitral valve repair or replacement, requires the use of CPB. This is 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 can occur in three to four minutes – death may follow. Similarly, CPB can be used to rewarm individuals who have hypothermia. This rewarming method of using CPB is successful if the core temperature of the patient is above 16 °C.

The blood is cooled during CPB and is 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. Maintaining appropriate blood pressure for organs is a challenge, but it is monitored carefully during the procedure. Hypothermia is also maintained (if necessary), and the body temperature is usually kept at 28 °C to 32 °C (82.4–89.6 °F).

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 for post cardiac surgery patients with cardiac or pulmonary dysfunction, 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 and recover, but is only a temporary solution. Patients with terminal conditions, cancer, severe nervous system damage, uncontrolled sepsis, and other conditions may not be candidates for ECMO.

There are no absolute contraindications to cardiopulmonary bypass. However, there are several factors that need to be considered by the care team when planning an operation. Heparin induced thrombocytopenia (HIT) and heparin induced thrombocytopenia and thrombosis (HITT) are potentially life threatening conditions associated with the administration of heparin. In both of these conditions, antibodies against heparin are formed which causes platelet activation and the formation of blood clots. Because heparin is typically used in CPB, patients who are known to have the antibodies responsible for heparin induced thrombocytopenia and heparin induced thrombocytopenia and thrombosis require alternative forms of anticoagulation. Bivalirudin is the most studied heparin alternative in people with heparin induced thrombocytopenia and heparin induced thrombocytopenia and thrombosis requiring CPB. A small percentage of patients, such as those with an antithrombin III deficiency, may exhibit resistance to heparin. In these patients, patients may need additional heparin, fresh frozen plasma, or other blood products such as recombinant anti thrombin III to achieve adequate anticoagulation. A persistent left superior vena cava (PLSVC) is thoracic system variation in which the left sided vena cava fails to involute during normal development. It is the most common variation of the thoracic venous system, occurring in approximately 0.3% of the population. The abnormality is often detected on pre operative imaging studies, but may also be discovered intra operatively. A persistent left superior vena cava may make it difficult to achieve proper venous drainage or deliver of retrograde cardioplegia. Management of a persistent left superior vena cava during CPB depends on factors such as the size and drainage site of the vena cava variation.

Cardiopulmonary bypass devices consist of two main functional units: the pump and the oxygenator. These units remove oxygen depleted blood from a patient's body and replace it with oxygen rich blood through a series of tubes, also known as hoses. Additionally, a heat exchanger is used to control body temperature by heating or cooling the blood in the circuit. Note: It is important that all components of the circuit are coated internally by heparin or another anticoagulant to prevent clotting within the circuit.

Many CPB circuits now employ a centrifugal pump for the maintenance and control of blood flow during CPB. By altering the speed of revolution (RPM) of the pump head, blood flow is produced by centrifugal force. This type of pumping action is considered to be superior to the roller pump because it is thought to prevent over pressurization, clamping, or kinking of lines, and makes less damage to blood products (hemolysis, etc. ).

CPB requires significant forethought before surgery. In particular, the cannulation, cooling, and cardio protective strategies must be coordinated between the surgeon, anesthesiologist, perfusionist, and nursing staff.

The cannulation strategy varies on several operation specific and patient specific details. Nonetheless, a surgeon will place a cannula in the right atrium, vena cava, or femoral vein to withdraw blood from the body. The cannula used to return oxygenated blood is usually inserted in the ascending aorta, but there is a possibility that it is inserted in the femoral artery, axillary artery, or brachiocephalic artery according to the demand of the surgery. After the cannula is inserted, venous blood is drained from the body by the cannula into a reservoir. This blood is then filtered, cooled, or warmed, and oxygenated before it returns to the body through a mechanical pump.

A CPB circuit must be primed with fluid and all air expunged from the arterial line/cannula before connection to the patient. The circuit is primed with a crystalloid solution and sometimes blood products are also added. Prior to cannulation (typically after opening the pericardium when using central cannulation), heparin or another anticoagulant is administered until the activated clotting time is above 480 seconds. The arterial cannulation site is inspected for calcification or other disease. Preoperative imaging or an ultrasound probe may be used to help identify aortic calcifications that could potentially become dislodged and cause an occlusion or stroke. Once the cannulation site has been deemed safe, two concentric, diamond shaped pursestring sutures are placed in the distal ascending aorta. A stab incision with a scalpel is made within the pursestrings and the arterial cannula is passed through the incision. It is important the cannula is passed perpendicular to the aorta to avoid creating an aortic dissection. Once the patient is ready to come off of bypass support, the cross clamp and cannulas are removed and protamine sulfate is administered to reverse the anticoagulative effects of heparin.

The Austrian German physiologist Maximilian von Frey constructed an early prototype of a heart lung machine in 1885. This was conducted at Carl Ludwig's Physiological Institute of the University of Leipzig. The Soviet scientist Sergei Brukhonenko developed a heart lung machine for total body perfusion in 1926 named the Autojektor, which was used in experiments with canines. Soon after on April 5, 1951, Dr. Clarence Dennis led the team at the University of Minnesota Medical Center, conducted the first human operation involving Cardiotomy. This was a temporary mechanical takeover of both heart and lung functions. The first successful mechanical support of left ventricular function was performed on July 3, 1952, by Forest Dewey Dodrill using a machine co developed with General Motors, the Dodrill GMR. The machine was later used to support the 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. In 1983, Ken Litzie patented a closed emergency heart bypass system which reduced circuit and component complexity. This device improved patient survival after cardiac arrest because it could be rapidly deployed in non surgical settings.