Coronary Artery Bypass Grafting
Coronary artery bypass grafting (CABG) circumvents an occluded coronary artery with an autogenous graft (usually a segment of the saphenous vein from the leg or internal mammarian artery), thereby restoring blood flow to the myocardium.
Performed to prevent a myocardial infarction (MI) in a patient with acute or chronic myocardial ischemia, CABG is one of the most commonly performed surgeries today in the United States. The need for CABG is determined from the results of cardiac catheterization and patient symptomology. Prime candidates for CABG include patients who have any of the following: medically uncontrolled angina interfering with the patient’s lifestyle, left main coronary artery stenosis, severe proximal left anterior descending coronary artery stenosis, three-vessel disease with proximal stenoses or left ventricular dysfunction, and three-vessel disease with normal left ventricular function at rest but with inducible ischemia and poor exercise capacity.
If successful, CABG can relieve anginal pain, improve cardiac function, and possibly enhance the patient’s quality of life. CABG techniques vary according to the patient’s condition and the number of arteries being bypassed. (See Mini-CABG.)
Mini-CABG
Two surgical procedures can decrease the risk of cerebral complications and accelerate recovery for selected patients: mini-CABG (minimally invasive coronary artery bypass grafting), which uses a thoracotomy incision rather than a sternotomy; and direct coronary artery bypass, in which grafts are sewn directly to the stabilized, yet beating, heart. Both techniques are used for grafts of only one or two coronary arteries. Nursing care guidelines are the same as those for CABG.
Procedure
After the patient has received general anesthesia, surgery begins with graft harvesting; the surgeon makes a series of incisions in the patient’s thigh or calf and removes a saphenous vein segment for grafting. Most surgeons prefer using a segment of the internal mammarian artery because this provides an artery doing the job of an artery.
Once the autografts are obtained, the surgeon performs a medial sternotomy and exposes the heart. He then initiates cardiopulmonary bypass. (See Understanding cardiopulmonary bypass, pages 208 and 209.)To reduce myocardial oxygen demands during surgery and to protect the heart, he induces cardiac hypothermia and standstill by injecting a cold cardioplegic solution (potassium-enriched saline solution) into the aortic root.
After the patient is fully prepared, the surgeon sutures one end of the venous graft to the ascending aorta and the other end to a patent coronary artery distal to the occlusion. He sutures the graft in a reversed position to promote proper blood flow. He repeats this procedure for each artery he bypasses.
Once the grafts are in place, he flushes the cardioplegic solution from the heart and discontinues cardiopulmonary bypass. He then implants epicardial pacing
electrodes, inserts a chest tube, closes the incision, and applies a sterile dressing.
electrodes, inserts a chest tube, closes the incision, and applies a sterile dressing.
Understanding cardiopulmonary bypass
Open-heart surgery often involves cardiopulmonary bypass, a technique that’s used to divert blood from the heart and lungs to an extracorporeal circuit with a minimum of hemolysis and trauma. As shown in this simplified diagram, the cardiopulmonary bypass (or “heart-lung”) machine uses a mechanical pump to provide ventricular pumping action, an oxygenator to perform gas exchange, and a heat exchanger to cool the blood and lower the metabolic rate during surgery.
To perform this procedure, the surgeon inserts catheters into the right atrium or the inferior or superior vena cava for blood removal and into the ascending aorta for blood return. Then, after heparinizing the patient and priming the pump with fluid to replace diverted venous blood, the surgeon switches on the machine. The pump draws blood from the vena cava catheters into the machine, where it passes through a filter, oxygenator, heat exchanger, and another filter and bubble trap before being returned to arterial circulation. During cardiopulmonary bypass, an anesthesiologist or perfusionist maintains mean arterial pressure by adjusting the rate of perfusion or by infusing fluids or vasopressor drugs.
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