re spread to expose the anterior mediastinum and pericardium. When the pericardium is opened and the heart and aorta are exposed, the patient is then placed on the CBM, while the CABG surgery is performed. The CBM oygenates blood and circulates is throughout the body. The first step in initiating the CBM is to prime the tubing of the CBM with a balanced electrolyte solution. The patient's blood is then brought to the pump either through one cannula being placed in the right atrial appendage or by two cannulas one being placed in the inferior vena cava and the other in the superior vena cava. In addition, another cannula is placed in the ascending aorta to return oxygenated blood back to the patient's systemic circulation. ( Please see the photo of this basic anatomy of the heart, so as to better visualize how the CBM works.)
Patients are also given an anticoagulant (blood thinner) called Heparin, which helps to prevent massive extravascular coagulation (clotting of the blood while out of the body in the CBM) while the blood is circulating through the mechanical parts of the bypass system. Once the CBM is established, blood is pumped through a circuit by a series of roller-type pumps. Venous blood from the patient flows through a venous cannula to a cardiotomy reservoir and then to the oxygenator where exchange of oxygen and carbon dioxide occurs. Blood goes through the heat exchanger in the CBM, it is cooled initially and then later it is rewarmed. During the CABG surgery, the core body temperature is decreased to 28 to 32 degrees Celsius (82.4 to 89.6 degrees Fahrenheit). This cold temperature of the body, which decreases metabolism, helps to protect major organ systems from ischemic injury (lack of blood flow to an organ of the body that results in damage to that organ). For every 1 degree Celsius drop of body temperature, the metabolic demands of the body are decreased by 7%.
Oxygenated blood is then filtered and returned to the patient's ascending aorta by way of the arterial cannula. Once extracorpeal (outside 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 