الفهرس 
Anatomy of the Coronary CirculationOnly 14 pages are availabe for public view
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Abstract
The coronary stent is a relatively new tool used to keep stenotic coronary arteries open, usually following a balloon angioplasty. The number of patients with coronary artery stents presenting for surgery is on the rise.
The peri-operative period for a patient having a coronary artery stent undergoing non-cardiac surgery is especially problematic as surgery induces a hypercoagulable state, while surgeons often prefer to stop anti-platelet drugs pre-operatively to minimize the risk of surgical bleeding in some procedures, thus putting the patient at high risk of stent thrombosis, which carries a mortality on the order of 45%.
On the other hand, the prevention of stent thrombosis is of paramount importance. Initially, it was tackled by the use of complex anticoagulation regimes using aspirin, heparin and warfarin, but in turn this led to high rates of major bleeding, vascular complications and long hospital stays. The development of new anti-platelet agents led to a breakthrough in the use of coronary stents with the adoption of dual anti-platelet regimes combining aspirin with a thienopyridine.
The protective effect of dual anti-platelet therapy in
patients with coronary stents in place has to be balanced against the risk of increased bleeding. It is this balance of risk in the peri-operative period that gives rise to a major clinical dilemma in patients presenting for surgery after the implantation of coronary stents.
Preparation of a patient with coronary artery stent for surgery includes not only management of anti-platelet medications, but also other aspects common to cardiac patients undergoing non-cardiac surgery. Despite sophisticated technologies, history and physical examination of the patient remain the key elements of pre-operative risk assessment. Risk stratification of patients with known or at risk of coronary artery disease is usually based on three elements that include the patient risk factors, functional capacity of the patient, and the risk factors of surgery.
The earlier the surgery is performed after stenting, the higher the risk for stent thrombosis. According to the American College of Cardiology/American Heart Association guidelines, non-cardiac surgery should be ”delayed for at least 2, and ideally 4, weeks after bare-metal stent implantation to allow for at least partial endothelialization of the stent”.
The enhancement of oxygen delivery to the tissues, has been shown to improve outcome of patients deemed to be at high risk from major surgery. Oxygen delivery is dependent on the amount of oxygen in the blood and the cardiac index. Optimization of cardiac index requires fluid and inotrope therapy to increase cardiac contractility.
Intra-operatively monitoring blood pressure, pulse, oximetry, capnography, temperature, urine output, central venous pressure, pulmonary artery pressure, and cardiac output must be achieved. The anesthesiologist should also select the drugs with the objective of minimizing demand and optimum supply of oxygen.
Close postoperative observation and management should be performed. Postoperative pain, respiratory distress, hypovolemia, and anemia are common clinical conditions that may result in excess cardiovascular stress and can result in ischemia or a myocardial infarction. Changes in the ECG may provide an early indication of cardiac compromise. Nitroglycerin is primarily a venodilator at low infused doses and is quite useful in patients with known myocardial ischemia. Postoperative antiplatelet is mandatory as soon as possible.
To conclude, the patient with coronary artery stent that undergoes non-cardiac surgery requires not only optimal timing of surgery, but also needs accurate peri-operative risk assessment, anti-platelet therapy management, and sufficient optimization to enhance the oxygen delivery to the tissues, as well as a strict postoperative management.