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Management of post-op cardiac surgery patients

Introduction to cardiac surgery

The most common surgical procedure encountered is the Aorto-Coronary Bypass Graft (ACBG) for various indications such as left main coronary artery stenosis, severe triple-vessel disease, angina refractory to medical therapy, or recurrent CHF due to ischemia. Other surgical procedures, concomitantly with ACBG or alone, include valve repair or replacements, repair of congenital or acquired defects (ASD, VSD, etc.), and repair or replacement of the aortic root. Less common are removal of intracardiac tumors and LV aneurysmectomy.

To perform the surgery, the patient is usually put on “pump” or cardiopulmonary bypass (CPB). This involves cannulation of the right atrium and aorta (and later cross-clamping of the aorta), allowing the entire cardiac output to bypass the patient’s heart and lungs. Blood flow is maintained using a pump and the blood is oxygenated via a membrane oxygenator incorporated into the circuit. Several myocardial preservation techniques are used to protect the heart from ischemic damage during this period. Cardioplegic arrest is induced using a hyperkalemic solution to induce asystole and thus decrease myocardial metabolism and oxygen consumption. The heart is usually cooled. The patient is also usually systemically cooled to < 32 C to minimize peripheral oxygen consumption.

While “on pump”, the patient’s BP and cardiac output are controlled by by the perfusionist and also the anesthesiologist by means of vasoactive medications and inotropes. During this time, the patient must by systemically anticoagulated with heparin to an ACT >400 to prevent clotting in the bypass circuit. Long pump times are associated with increased post-operative complications such as bleeding, myocardial stunning, and multi-system organ failure. CPB also seems to be associated with the induction of a systemic inflammatory response syndrome (SIRS). It is sometimes difficult to liberate the patient from CPB or “get him off pump.” That is, to restart the heart contracting normally. Pressors or inotropes are often used in order to aid “coming off pump.” A variety of dysrhythmias also may occur during this period including bradycardias requiring pacing. Most often, these dysrhythmias are transient and resolve.