Use of Extracorporeal Circulation During Cardiac Surgery
It is almost impossible to repair intracardiac defects surgically while the heart is still pumping. Therefore, many types of artificial heart-lung machines have been developed to take the place of the heart and lungs during the course of operation. Such a system is called extracorporeal circulation. The system consists princi-pally of a pump and an oxygenating device. Almost any type of pump that does not cause hemolysis of the blood seems to be suitable.
Methods used for oxygenating blood include (1) bubbling oxygen through the blood and removing the bubbles from the blood before passing it back into the patient, (2) dripping the blood downward over the sur-faces of plastic sheets in the presence of oxygen, (3) passing the blood over surfaces of rotating discs, or (4) passing the blood between thin membranes or through thin tubes that are permeable to oxygen and carbon dioxide.
The different systems have all been fraught with many difficulties, including hemolysis of the blood, development of small clots in the blood, likelihood of small bubbles of oxygen or small emboli of antifoam agent passing into the arteries of the patient, necessity for large quantities of blood to prime the entire system, failure to exchange adequate quantities of oxygen, and necessity to use heparin to prevent blood coagulation in the extracorporeal system. Heparin also interferes with adequate hemostasis during the surgi-cal procedure. Yet despite these difficulties, in the hands of experts, patients can be kept alive on artifi-cial heart-lung machines for many hours while opera-tions are performed on the inside of the heart.