de the body) circulation and hypothermia are acheived, the aorta is cross-clamped just above the coronary arteries. Crystalloids (intravenous fluids) or blood cardioplegia solution is then infused in the aortic root. Once the aorta is cross-clamped, no blood goes through the coronary arteries, so the myocardium is ischemic. Cold cardioplegic solution (4 degrees Celsius or 39.2 degrees Fahrenheit), which is high in potassium, is infused in the aortic root under pressure. The high potassium level causes the heart to stop (asystole). The heart is then relaxed, the combination of asystole and hypothermia protect the heart against myocardial ischemia. Iced normal saline is also placed directly on the heart to make sure all parts of the heart are hypothermic.
Some surgeons also do CABG surgeries keeping the blood at normal body temperature 37 degrees Celsius (98.6 degrees Fahrenheit). This technique is used in simple CABG surgeries, most complicated CABG surgeries use the cold technique. CABG surgeries done a normal body temperature have been shown to have more complications. Because of the increased complications, most CABG surgeries are done using the cold technique.
If the cold technique is used at the end of the CABG surgery, the blood is rewarmed to 37 degrees Celsius (98.6 degrees Fahrenheit) using the heat exchanger in the CBM. The aortic cross clamp is removed so that the blood perfuses coronary arteries, which warms the myocardium. After the heart rhythm is maintained, then the cardiopulmonary bypass is reduced to partial bypass. If the patient tolerates this then the heart assumes total responsibility for cardiac stability and the CBM is discontinued. The cannulas placed in the heart are removed and the patient's chest is closed.
The patient is then taken to a Surgical Intensive Care Unit where postop care is provided. I would also like to add that this CBM's is maintained in the operating room by a perfusionist. A perfusionist is a highly trained specialist who operates the CBM so that the surgeon can focus more on the operative procedure. The article has described what the CBM is used for today. In order to understand how engineering has helped to shape this modern technology, it is necessary to take a look at the history of the development of the CBM.
The first heart-lung machine was built by John Gibbon in 1937. This machine used two roller pumps and the machine had sufficient capacity to replace the heart and lungs of experimental cats. The machine was too small to serve for dogs or humans. Most animals died from the haemolysis( clotting of blood), air embolism introduced into the body, and blood-foreign surface interaction. The problem of haemolysis was alleviated somewhat in 1939 when the anticoagulant Heparin was discovered.
John Gibbon, who was a physician, met an engineer by the name of Thomas Watson in 1946. This engineer was also the chairman of IBM (International Business Machines). Watson was able to provide both financial and technical support to Gibbon to help in the development of heart-lung machine. Watson along with 5 other engineers helped Gibbon to invent a machine that minimized haemolysis and prevented air bubbles from entering the circulation. This heart-lung machine was contained within a cabinet that kept the body at normal temperature and blood flow was carefully controlled to maintain a constant blood volume. With the invention of this new machine, there was only a 10% mortality in dogs, whereas the mortality rate had been 80%.
About the same time as Gibbon was working on his heart-lung machine, Bill Bigelow was also doing open heart operations on dogs but he was using a different approach. Bigelow was using cooling blankets and ice bags to cool the dogs to 20 degrees Celsius (68 degrees Fahrenheit). The oxygen consumption of the heart fell to 15% of normal, thereby allowing the heart to be isolated from circulation for 15 minutes to allow for an operation with a better survival rate than previously found.
Clarence Dennis in 1945 set out to build a mechanical heart-lung appartus that would