Coronary Artery Bypass Graft Surgery

Coronary artery bypass graft (CABG) surgery is the most frequently performed cardiac surgery in North America,


with nearly 400,000 procedures performed annually in the United States and Canada. '751 Early retrospective studies of open heart surgery found that stroke and anoxic encephalopathy were common postoperative neurological complications occurring in more than 20 percent of patients. Improvement in surgery and extracorporeal circulation may have initially reduced the frequency of permanent, disabling neurological sequelae. Nevertheless, subsequent prospective studies have shown that neurological complications account for the major adverse sequelae of this procedure. Because these problems can be severe, they must be taken into account when decisions are weighed as to whether medical or surgical therapy would be more appropriate in a given case.


Stroke as a complication of CABG procedures occurs in 0.9 to 5.9 percent of cases. y Most territorial infarcts result from macroemboli from diseased valves, left ventricular thrombus, or atheromatous emboli from a rigid ascending aorta. Stroke occurs more frequently with valvular heart surgery than with coronary artery bypass grafting operations. A permanent neurological disability after valve replacement occurs in 5 to 10 percent of patients. In contrast, the risk of a severe disability complicating CABG surgery is less than 2 to 5 percent. y , y The difference is due to the greater risk of cardiac macroemboli with operations that require opening of the heart chambers. Removal or repair of diseased, calcified mitral or aortic valves is associated with the dispersion of tissue and surgical debris in the cardiac chambers. Extracranial carotid artery disease is often suggested as an important cause of stroke during CABG surgery. This theory proposes that severe carotid occlusive disease, combined with intraoperative hypotension, results in cerebral ischemia. However, most perioperative strokes occur in the absence of carotid occlusive disease or have their onset in the postoperative period. Most studies have failed to demonstrate a correlation between perioperative stroke and asymptomatic carotid artery stenosis. Nevertheless, it is common practice in some hospitals to perform a prophylactic staged or combined carotid endarterectomy in asymptomatic patients discovered to have carotid stenosis. y Although CABG surgery frequently results in a tendency for bleeding (as a result of heparin administration, low fibrinogen levels, and thrombocytopenia induced by hemodilution and sequestration) and occasional disseminated intravascular coagulation, intracranial hemorrhage is an infrequent cause of stroke. y

Attempts to prevent neurological sequelae after cardiac surgery have focused on improved surgical and cardiopulmonary bypass techniques, as well as identifying the high-risk patient. Age, preoperative stroke (within 3 months), severe aortic atheroma, opening of cardiac chambers, and sustained mean arterial pressure of less than 30 to 40 mm Hg are probable risk factors for postoperative neurological sequelae. Less proven but still possible risk factors are prolonged cardiopulmonary bypass, severe carotid or cerebrovascular disease, postoperative atrial fibrillation, congestive heart failure, and diabetes mellitus. '751 , y

Minor cognitive impairment following CABG procedures occurs in as many as 75 percent of patients tested 8 days postoperatively and may be present in up to a third of patients, even 1 year after surgery. These patients show a reduction of one standard deviation in neurocognitive testing postoperatively. '751 The pathogenesis of the cognitive decline following CABG is believed to be secondary to disseminated brain microemboli occurring during cardiac surgery. An alkaline phosphatase map of the afferent cerebral microvasculature has revealed thousands to millions of focal, small capillary and arteriolar dilatations in patients and dogs who have recently undergone CABG. These capillary and arteriolar dilatations are usually empty, suggesting that gas bubbles or fat emboli are a prime cause. Some authors believe that membrane oxygenators and 40-p arterial line filters are an essential part of protecting the brain against microembolic events, although this remains to be proved in practice. '751

The global encephalopathy that can follow heart surgery varies from confusion to coma or a psychotic delirium. Nonmetabolic coma is a rare complication of open heart surgery, occurring in less than 1 percent of patients. It may be due to global anoxia-ischemia, massive stroke, or multiple strokes. On the other hand, the incidence of clinically detectable diffuse encephalopathy varies from 3 to 12 percent. '751 Post-CABG encephalopathy is often multifactorial and can be related to medications, hypoxia, fever, sepsis, metabolic derangements, hemodynamic instability, and intensive care unit psychosis. These patients may be slow to emerge from anesthesia, are often agitated or restless, and have poor visual fixation, small reactive pupils, and occasionally, Babinski sign. Improvement usually occurs during the first postoperative week. In otherwise uncomplicated cardiac surgery, disseminated microemboli during extracorporeal circulation may be the cause of this encephalopathy.^1 Seizures occur in less than 1 percent of patients and can accompany coma, encephalopathy, or delirium, or they may occur independently. The vast majority occur within the first 24 hours after surgery.


In a prospective analysis of 412 consecutive patients undergoing coronary bypass surgery, 55 (13 percent) developed new peripheral nervous system complications postoperatively. y The most common complication was brachial plexopathy, occurring in 23 patients. Most frequently the lower trunk or the medial cord of the brachial plexus was involved. The plexus injuries may be due to torsional traction, compression, or cannulation of the jugular vein. Male gender and hypothermia during surgery were associated with an increased risk. The usual clinical presentation involves intrinsic hand weakness and a decreased or absent triceps reflex. Sensory loss is sometimes present in the affected hand; some patients have prominent pain, and a minority of them have a Horner's syndrome. Most brachial plexus injuries are reversible within 1 to 3 months, implicating conduction block as the primary pathophysiological mechanism. Such injuries may be prevented by minimizing the opening of the sternal retractor, placing the retractor in the most caudal location, and avoiding asymmetrical traction. Unilateral phrenic nerve injuries with hemidiaphragmatic


paralysis occur in at least 10 percent of patients during open heart surgery and can be manifested as atelectasis or persistent singultus. Finally, mononeuropathies resulting from compression or trauma during surgery may involve the accessory, facial, lateral femoral cutaneous, peroneal, radial, recurrent laryngeal, saphenous, and ulnar nerves.y

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