Establecimientos económicos en la Península

The pharmacological management of hyperlipid- emia decreases morbidity and mortality from coro-

nary artery disease (CAD).8,9 _{Desirable lipid levels}

are as follows:

• Total cholesterol less than 200 mg/dL

• Low-density lipoprotein (LDL) cholesterol less than 100 mg/dL (less than 70 mg/dL in very high- risk patients)

• High-density lipoprotein (HDL) cholesterol greater than 60 mg/dL

• Triglycerides less than 150 mg/dL

The primary target of antihyperlipidemic therapy is LDL cholesterol. Drug therapy with LDL-lowering drugs is recommended for patients who meet the following criteria:

• 0 to 1 risk factors for CAD (see Chapter 12, Box 12-3) and an LDL cholesterol level greater than or equal to 190 mg/dL

• 2 or more risk factors for CAD and an LDL choles- terol level greater than or equal to 130 mg/dL • Documented CAD or CAD risk equivalents (eg,

stroke, diabetes, peripheral artery disease) and an LDL cholesterol level greater than or equal to 100 mg/dL

Drug therapy may also be indicated when the tri- glyceride level is 200 mg/dL or greater, and for patients with borderline-high triglycerides (150 to 199 mg/dL) and CAD or CAD risk equivalents. For these patients, drugs to increase HDL cholesterol levels may be given.

There are fi ve major classes of antihyperlipidemic drugs:

• Hydroxymethylglutaryl coenzyme-A (HMG-CoA) reductase inhibitors (statins) decrease total and

Morton_Chap13.indd 162

Patient Management: Cardiovascular System C H A P T E R 1 3 163

Administration of nitroglycerin followed by oral nitrates postoperatively helps decrease the occur- rence of spasm following grafting of the artery.

Patency rates of 89% for 1 year have been reported.3

CABG surgery typically requires a midline sternot- omy. In some cases, surgeons may use less invasive “mini” left or right thoracotomy approaches, known as minimally invasive direct coronary artery bypass grafting (MIDCABG). With MIDCABG, the number of grafts that can be performed is restricted because the small incision does not allow access to the entire heart surface. MIDCABG is most frequently used for grafts to the left anterior descending artery; grafts to the right coronary artery and the posterior descend- ing artery can also be made.

CABG surgery is usually performed with the patient on cardiopulmonary bypass. The cardio- pulmonary bypass machine (also called a pump oxygenator) assumes the job of oxygenating the patient’s blood and circulating it throughout the body (Box 13-3). However, it is also possible to per- form CABG surgery “off pump” (OPCABG). Available data comparing CABG and OPCABG indicates that length of stay in patients after OPCABG surgery is decreased, and patients seem to have fewer neu- rological complications. The stroke rate is similar in both groups of patients; however, in patients undergoing CABG, the symptoms of stroke occur immediately after surgery, and in patients undergo- ing OPCABG, the symptoms of stroke appear later,

48 to 72 hours after surgery.4 _{The explanation for}

this fi nding is that systemic infl ammatory response syndrome (SIRS) causes diffuse microembolic be made in the area of the vein, and a fl exible fi ber-

optic scope is inserted to visualize the vessel and remove it. The fi beroptic method of vein removal is associated with improved wound healing and reduced complications involving the incision site. Only 50% of saphenous vein grafts are patent after 10 years. Three main processes account for saphenous vein failure: thrombosis, fi brointimal hyperplasia, and atherosclerosis. Aspirin is recom- mended postoperatively and should be continued indefi nitely to prevent early saphenous vein graft

closure.2

• Internal mammary artery grafts. The internal mammary artery, the second branch of the sub- clavian artery, is used as a pedicle graft (ie, the proximal end remains attached to the subclavian artery). Both the left and the right internal mam- mary artery can be used. The internal mammary artery descends the anterior chest wall just lat- eral to the sternum behind the costal cartilage. To isolate the internal mammary artery, the pleural space is entered and the internal mammary artery is dissected free from the chest wall. Ninety per- cent of intermal mammary artery grafts are patent 10 years after surgery. As compared with saphe- nous artery grafts, internal mammary artery grafts exhibit less atherosclerosis over time and are associated with lower long-term morbidity and

improved long-term survival.2

• Radial artery grafts. The radial artery, a thick, muscular artery, is prone to spasm with mechani- cal stimulation. To prevent spasm, the artery is perfused with a calcium channel blocker solu- tion during surgery and minimally stimulated.

TA B L E 1 3 - 3

Common Conduits Used for Coronary Artery Bypass Grafting

Type of Graft Advantages Disadvantages

Saphenous vein • Technically easier to harvest

• Longer length may allow for several grafts

• Less long-term patency compared with internal mammary artery graft

• Leg incision has tendency toward edema and infection; less common with fi beroptic approach

Internal mammary artery

• Vascular endothelium adapted to arterial pressure and high fl ow, resulting in decreased intimal hyperplasia and atherosclerosis • Improved long-term patency

• Retains nerve innervation and therefore its ability to adapt diameter to blood fl ow • No leg incision

• Diameter closer to coronary artery

• Dissection off the chest wall takes more time; long dissection time may increase risk for postoperative bleeding

• Pleural chest tube needed because pleural space violated

• Increased postoperative pain • Use of bilateral internal mammary

arteries may increase risk for infection and sternal infection, especially in patients with diabetes

Radial artery • Technically easier to harvest

• Better patency rate compared with saphenous vein graft

• Vascular endothelium adapted to arterial pressure and high fl ow, resulting in decreased intimal hyperplasia and atherosclerosis

• Tendency to spasm, although this can be treated medically

• Preoperative assessment of ulnar artery’s ability to supply alternative blood fl ow is important

Morton_Chap13.indd 163

B O X 1 3 - 3

Cardiopulmonary Bypass Reservoir Filter Oxygenator Heat exchanger Bubble catcher & filter 1 2 3 4 5 6

A cardiopulmonary bypass machine is used for cardiac surgeries that require the heart to be still and empty. Before the bypass is implemented, the tubing of the machine is primed with a balanced electrolyte solution or blood. The patient’s deoxygenated blood enters the bypass circuit either through one cannula placed in the right atrium or through two cannulae placed in the superior and inferior vena cavae (1), respectively. The blood is temporarily held in the reservoir (2), before moving into the oxygenator (3), which also removes carbon dioxide from the blood. The heat exchanger (4)

cools the blood and then rewarms the blood, and then a series of roller-type pumps (5) pump the blood through the circuit and back to the patient. Oxygenated blood is returned to the ascending aorta (6) by way of a cannula. The fl ow through the bypass pump is nonpulsatile.

During cardiopulmonary bypass, the patient’s core body temperature is lowered to between 82°F and 89°F to reduce the body’s metabolic demands and help protect major organ systems from ischemic injury. Heparin is administered to prevent massive extravas- cular coagulation as the blood circulates through the mechanical parts of the bypass system. Once extracor- poreal circulation is established and systemic hypother- mia is achieved, the aorta is cross-clamped and a cold (39.2°F) cardioplegia solution that is high in potassium is infused into the aortic root. As it circulates through the coronary arteries, the cold cardioplegia solution induces asystole and hypothermia to decrease the metabolic demands of the myocardium. Topical hypo- thermia is also created by pouring iced normal saline slush over the heart. Because cold cardioplegia can be associated with postoperative complications (eg, ven- tricular dysrhythmias, decreased cerebral blood fl ow, reperfusion injury), some surgeons use a normothermic (98.6°F) cardioplegia solution instead.

Following completion of the surgery, the heat exchanger rewarms the blood (if hypothermic tech- niques were used). The aortic cross-clamp is removed so that blood again perfuses the coronary arteries. During perfusion and rewarming, a spontaneous car- diac rhythm may resume, ventricular fi brillation may develop (necessitating internal defi brillation), or pac- ing may be used to initiate a rhythm. After a reliable rhythm and rate are established, total bypass may be reduced to partial bypass (ie, some of the patient’s blood is circulated through the heart and lungs, while some continues to circulate through the pump). After the heart can maintain adequate cardiac output on its own, the cannulae are removed and the heparinization is reversed.

events that take time to develop. Following OPCABG surgery, anticoagulation interventions are aggres- sively implemented to suppress activation of the coagulation cascade. Ongoing nursing assessment of a patient who has undergone OPCABG surgery focuses on detecting embolic events and monitoring for side effects of anticoagulation (eg, gastrointesti- nal bleeding, HIT).

In document Mapa Estratégico de necesidades de la Provincia de Santa Elena (página 104-116)