Cardiac pump (heart-lung machine)
A cardiac pump or cardiac bypass pump or heart-lung machine temporarily takes over the function of breathing and pumping blood for a patient. It generally has two parts, the pump and the aerator. The pump is usually several motor-driven rollers that perstaltically massage a tube made of silicone rubber. The massage pushes the blood through the tubing. The aerator
varies, but usually is either a drip onto a sterile surface, or passage through a silicone-membrane simulated lung.
Cardiac pumps are most often used in heart surgery, so that a patient's heart can be disconnected from the body for longer than the twenty minutes or so it takes a prepared patient to die. Although unprepared patients get brain damage in three to four minutes, a patient can be prepared by cooling and drugs so that no damage will occur for twenty minutes or more.
Cardiac pumps are also sometimes used to keep babies with birth defects alive, or to aerate bodies with transplantable organs. Chronic use of cardiac pumps is contraindicated because the pressure profile of most practical pumps is believed to cause circulatory damage to the brain, especially in extended use. The pumps generate continuous pressure. When this pressure is set high enough to aerate tissues in the foot, it can easily damage tissue in the brain. Likewise, if set low enough to avoid damaging the brain, it often under-aerates some part of the body, such as the feet.
Heart-lung machine maintains the circulation of the blood and the oxygen content of the body when connected with the arteriovenous system; it is also called the pump oxygenator. The machine is used in open-heart surgery when it is necessary to effect a bypass of the circulatory system of the heart and lungs. The oxygenator repeatedly draws off the blood from the veins, reoxygenates it, and pumps it into the arterial system. The contractions of the heart are halted by running a potassium citrate solution through the coronary vessels. The surgeon is thus enabled to open the heart and make the necessary repairs while the heart is still and his view is not obstructed by blood.