Heart-Lung Machine

The heart and lungs work together to keep the body's cells supplied with oxygen. During circulation, the heart pumps oxygen-depleted blood to the lungs, and then receives oxygenated blood from the lungs for distribution to the rest of the body.

Often times, the heart can become damaged from heart disease or trauma. Open-heart surgery, where the chest is opened and the heart is exposed, may be necessary to repair the damage. During some open-heart procedures, it may be necessary to stop the heart in order to repair the heart's muscle, valves, or other structures. A heart-lung machine allows the surgeon to carefully stop the heart while still maintaining blood circulation.

The machine consists of a pump, which functions as the heart, and an oxygenator, which replaces the function of the lungs.

During a heart-lung bypass, oxygen-poor blood is first diverted from the upper chambers of the heart and is directed to a reservoir in the heart-lung machine. The blood is then transferred to the oxygenator, which infuses the blood with oxygen. Next, a pump returns the blood to the patient's arterial system, where the body can resume blood circulation on its own. Following repair of the heart, the heart is restarted and the heart-lung machine is removed.

The surgeon attaches special tubing to a large blood vessel (like starting a very large IV) that allows oxygen-depleted blood to leave the body and travel to the bypass machine. There, the machine oxygenates the blood and returns it to the body through the second set of tubing, also attached to the body.

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 extra corporeal circulation. Extra corporeal 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 (among others).

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.