During an open-heart surgery (such as bypass surgery ), the heart-lung machine takes over the functions of the heart and lungs . The use of the machine allows the surgeon to carefully stop the heart while the vital organs continue to receive blood and oxygen. Very delicate work can then be done without interference from bleeding or the heart's pumping motion. When first used successfully in 1953, the machine was truly a revolutionary piece of equipment. Now, new medical technology is allowing for less invasive forms of surgery that involve smaller incisions, less surgical trauma and (in some cases) the continued beating of the heart throughout surgery without the use of the heart-lung machine.
What is a heart-lung machine? During an open-heart surgery (such as valve surgery), the heart-lung machine takes over the functions of the heart and lungs so that the heart can be carefully stopped. The surgeon can then operate in a blood-free surgical field. The heart-lung machine basically consists of a pump (to replace the heart) and an oxygenator (to replace the lungs). Acting as a mechanical heart and lungs, it keeps oxygen-rich blood flowing throughout the body after the patient's heart has been carefully stopped. In a process called perfusion , the machine receives the patient's blood, removes the carbon dioxide and other waste products, adds oxygen, warms (or cools) the blood and pumps it back through the body. Cooling the blood, in turn, lowers body temperature. This helps protect the body's organs while the heart-lung machine is in use. After the surgery is completed, the heart is restarted, the heart-lung machine is stopped and the machine is disconnected from the patient. The heart-lung machine can perform other tasks. For example, it can directly deliver medications into the recirculated blood. It can also minimize blood loss by vacuuming up and recirculating any blood that may get into the surgical field. 
How does a heart-lung machine work? The first step in using a heart-lung machine during open-heart surgery is to give the patient a drug called heparin , which is a powerful anticoagulant . Heparin reduces the blood's ability to clot, reducing the risk of clots forming in the heart-lung machine and within the tubes placed in the heart. Once the medication has taken effect, a tube  (called
a cannula ) from the heart-lung machine is placed in
the upper-right chamber of the heart (the right atrium ), which
contains oxygen-poor blood from the body. Another cannula is
placed in the aorta , a large artery that carries oxygen-rich
blood from the heart to the rest of the body. By setting up
the machine in this way, oxygen-poor blood drains into the machine,
receives fresh oxygen and is returned to the aorta to be carried
to the rest of the body. Once the machine is functioning, the surgeon can carefully stop the heart in order to perform the necessary surgery. When the surgery is complete, the surgeon will restart the heart. Once the surgical team is satisfied that the heart is beating strongly again, the tubes are removed from the right atrium and the aorta. To reverse the effects of the heparin given at the beginning of the process, the patient will be administered another medication called protamine . Throughout this process, the heart-lung machine is operated by a perfusionist , one of several medical specialists on hand in the operating room during open-heart surgery. While the heart is stopped and the machine is working, the perfusionist continually monitors blood pressure , blood oxygen levels, carbon dioxide levels, blood temperature and breathing.
Are there risks of complications with a heart-lung machine? Complications from open-heart surgery tend to be greater when a heart-lung machine is used. For example, a study published in Circulation (August 1999) found that women were more likely to have a stroke after heart surgery than were men. As one possible explanation for this finding, the authors pointed out that female participants had other conditions that increased the risk of stroke following heart surgery. Additional risks for both men and women include the formation of small blood clots in the blood that the machine processes, which (in extreme cases) can cause stroke , heart attack or kidney failure upon return to the body's bloodstream. The machine can also trigger an inflammatory process that can damage many of the body's systems and organs, called postpericardiotomy syndrome . Additionally, post-operative bleeding may be a serious complication, occasionally requiring a return to the operating room. Problems with temporary confusion or memory loss have also been reported in some cases. To avoid these risks, physicians are working to develop minimally invasive techniques for heart surgery that do not involve the use of a heart-lung machine. For more information about minimally invasive techniques to perform bypass surgery, please click on the following link: Minimally Invasive Direct Coronary Artery Bypass. |
