Page 621 - Cardiac Nursing

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C HAPTER 2 5 / Cardiac Surgery 597
should be infused antegrade or retrograde, and timing of infusion
(intermittent or continuous). Most cardiac surgery programs use CARDIAC SURGERY
a combination of the myocardial protection techniques discussed PROCEDURES FOR CORONARY
here. ARTERY REVASCULARIZATION
Cardioplegia solutions are made of crystalloid, oxygenated
crystalloid, or crystalloid–blood mixtures. Although cardioplegic Coronary Artery Bypass Surgery
solutions vary widely, typical components include potassium,
magnesium, or procaine to provide immediate diastolic arrest; Indications for Surgical Revascularization
oxygen, glucose, glutamate, or aspartate as energy substrate; bi- CABG surgery is done primarily to alleviate anginal symptoms as
carbonate or phosphate to buffer acidosis; and calcium, steroids, well as improve survival. CABG surgery is among the most com-
or procaine to stabilize membranes. The solution should be mon surgical procedures preformed worldwide. The American
hyperosmolar to edema. Cardioplegia is infused continuously or College of Cardiology and the American Heart Association Task
intermittently. Force on Practice Guidelines was formed to recommend appro-
Cardioplegia can be normothermic or hypothermic. Hy- priate use ofdiagnostic tests and therapies. Based on bothlitera-
pothermic techniques were originally used as a means to reduce ture review and expert opinion, the ACC/AHA updated the
metabolic demands during arrest. A cooled nonbeating heart uses guidelines for CABG in 2004. Class I guideline indications for
less oxygen than a warm-beating or fibrillating heart. Cold car- CABG are described as conditions for which there is evidence
dioplegic solutions are commonly cooled to 15 C to 20 C to re- and/or general agreement that a given procedure or treatment is
duce oxygen demand. Normothermic cardioplegia has been used useful and effective. Class I recommendations for CABG surgery
at both the induction of cardioplegic arrest and at the termination include: significant left main coronary artery stenosis or equiva-
of arrest. Warm, oxygenated, hyperkalemic blood cardioplegia lent; three-vessel coronary disease; two-vessel coronary disease and
maintains arrest while supplying oxygenated blood to myocardial an ejection fraction less than 50%; one- or two-vessel disease with
cells. “Hot shots” are warm cardioplegic infusions administered at a large amount of viable myocardium at risk; and one- or two-ves-
the end of the surgical procedure, before removal of the aortic sel disease with severe angina despite maximal medical therapy. 10
cross-clamp. Other class I indications for CABG include failed angioplasty
Cardioplegia solution can be delivered antegrade into the as- withpersistent pain or hemodynamic instability, postinfraction
cending aorta, after which it flows through the coronary circula- ventricular septaldefect (VSD) or postinfarction mitral insuffi-
10
tion and returns to the heart through the coronary sinus. Al- ciency, cardiogenic shock in patients less than age 75. In com-
though antegrade cardioplegia has been the standard in cardiac parison withdrug-eluting stents for patients with multivessel
surgery for many years, its delivery may be inadequate. Antegrade coronary disease, CABG is associated withlower mortality rates
cardioplegia infusion through coronary arteries that are severely andlower rates of repeat revascularization. 11
stenosed or occluded is uneven. Hearts with left ventricular hy-
pertrophy may receive incomplete delivery to the subendo- Relative Contraindications
cardium. In patients with aortic insufficiency, the left ventricle Conditions that greatly increase the mortality risk during surgery
may become distended because of the retrograde flow of cardio- and anatomic limitations are relative contraindications to CABG
plegia across the valve. Although cardioplegia can be delivered surgery. Lack of adequate conduit, coronary arteries distal to the
through saphenous vein grafts, it cannot be delivered through stenosis smaller than 1 to 1.5 mm, and severe aortic atherosclero-
IMA grafts. Insufficient delivery of cardioplegia results in poor sis are anatomic abnormalities that may limit the success of the
myocardial protection, which results in postoperative myocardial revascularization for technical reasons. Severe left ventricular fail-
damage and dysfunction. Because of inadequate delivery using an- ure and coexisting pulmonary, renal, carotid, and peripheral vas-
tegrade techniques, retrograde delivery systems were developed. cular disease may significantly increase the risk of surgery by pre-
Retrograde cardioplegia is infused under low pressure through disposing to complications during the perioperative period.
catheters inserted directly into the coronary sinus. Cardioplegia Patients with low ejection fraction are sicker at baseline and more
flows retrograde through the coronary veins to capillaries to the than four times the mortality than patients with high ejection
coronary arterial bed, and exits at the coronary ostia, where efflu- fraction. 12
ent is removed by vent and suction. Retrograde and combined ret-
rograde–antegrade techniques allow for optimal delivery and my- Bypass Conduits
ocardial protection. Coronary artery revascularization is accomplished most com-
monly with the IMA in combination with saphenous vein grafts.
Deep Hypothermic Circulatory Arrest Because of the excellent patency associated with IMA grafts, other
arterial conduits are now accepted for bypass surgery. Use of the
Circulatory arrest (interruption of circulation through the as- right GEA as a pedicle graft to the right coronary or as a free graft
cending aorta for an extended period of time) may be necessary to the left coronary system requires a more extensive surgery be-
in procedures involving the ascending aorta and aortic arch. Pro- cause the abdomen must be entered. Radial artery grafts were ini-
found hypothermia is used to protect the brain and other vital or- tially used in the early 1970s but were abandoned because of their
gans. The patient’s body temperature is lowered to 18 C and tendency to spasm and their poor short-term patency. With the
CPB is stopped. Operative procedures are performed expediently advent of calcium-channel blockers, radial artery grafts have en-
because of the interruption of circulation to vital organs. In gen- joyed renewed interest. Greater saphenous vein from the legs is
eral, deep hyperthermic arrest can be used up to 60 minutes. 8 the most commonly used venous conduit. Because of patient
After repair, the patient is placed back on CPB and is gradually anatomy, history of vein stripping, or previous revascularizations,
rewarmed. alternative conduits may be necessary. Veins harvested from the