Heart Surgery: Coronary Artery Bypass Grafting (CABG) or Valve Replacement
– Heart surgery is performed for a variety of reasons including myocardial revascularization, valve repair or replacement, repair of congenital or acquired structural abnormalities, placement of a mechanical assist device, and heart transplantation. Two common heart surgeries are coronary artery bypass grafting (CABG), which is done to treat severe coronary artery disease, and heart valve replacement. CABG involves removing a segment of a vein (e.g., saphenous, cephalic) or an artery (e.g., internal mammary, radial, gastro-epiploic) to create an anastomosis between the aorta or other major artery and a point on the coronary artery distal to the obstruction. Heart valve replacement involves replacing the stenotic or regurgitant valve with a mechanical prosthesis or a biologic (tissue) valve (porcine or bovine valve, human valve).
Heart surgery is usually performed through a median sternotomy. Cardiopulmonary bypass (extracorporeal circulation) is maintained during surgery by a machine that diverts the blood from the heart and lungs, oxygenates the blood and removes carbon dioxide, maintains the desired body temperature, filters the blood, and then recirculates the blood into the arterial system. Systemic hypothermia (provided by the cardiopulmonary bypass machine) can reduce tissue oxygen requirements to 50% of normal, which affords the major organs additional protection from ischemic injury. Cold cardioplegia (infusion of a cold, alkaline solution containing potassium into the coronary circulation) is used to precipitate cardiac arrest and provide additional protection to the myocardium during surgery. An isotonic crystalloid solution is used to prime the bypass machine. This dilutes the client’s blood, which improves blood flow and reduces the risk of microemboli formation. Prior to closing the chest, pacing electrodes are usually placed on the epicardial surface of the heart and brought out through the chest wall to be used for temporary pacing if needed. A chest tube is placed in the mediastinum to drain blood and if needed, one is also placed in the pleural space to promote lung re-expansion.
In addition to the traditional sternotomy approach performed on cardiopulmonary bypass (CPB), heart surgery may be performed “off pump” (referred to as off pump coronary bypass [OPCAB]) or using a minimally invasive approach (e.g., small incision in left sternal border, a series of holes or “ports” using video-assisted equipment). Minimally invasive procedures such as a MIDCAB (minimally invasive direct coronary artery bypass) can be performed without cardiopulmonary bypass or with a less invasive, catheter-based system of cardiopulmonary bypass. Several techniques are used to stabilize the operative area during a beating heart procedure (stabilizer device to “still” certain areas of the heart while the rest keeps beating, drugs that decrease the heart rate or cause transient asystole). Because “off pump” and minimally invasive approaches reduce the risk for some of the major complications (e.g., mediastinitis, emboli associated with cross-clamping the aorta) and shorten hospitalization and rehabilitation time, they promise to become more common.
Decreased cardiac output
Risk for impaired respiratory function
ineffective breathing pattern
ineffective airway clearance
impaired gas exchange
Risk for imbalanced fluid and electrolytes
excess fluid volume
third-spacing of fluid
deficient fluid volume
hypokalemia, hypochloremia, and/or metabolic alkalosis
Risk for infection
wound infection and mediastinitis
myocardial infarction (MI)
impaired renal function
Deficient knowledge, Ineffective therapeutic regimen management, or Ineffective health maintenance