eng. Hassanain Ali Lefta Mossa * , HasAli76@yahoo.com
During an open-heart surgery (such as valve surgery), an extracorporeal (i.e. outside the body) equipment called the heart-lung machine takes over the functions of the heart and lungs, so that the heart can be carefully stopped while the vital organs continue to receive blood and oxygen. The surgeon can then operate in a blood-free surgical field without interference from bleeding or the heart's pumping motion.
The principle of the heart-lung machine (also known cardiopulmonary bypass) is actually quite simple. It permits the heart to be operated on safely by maintaining the circulation of oxygenated blood throughout the cardiovascular system. It represents a continuous loop; as the rich-oxygen blood goes into the body, poor-oxygen blood returns from the body and is drained into the pump completing the circuit.
The 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. Once