Chapter 29 Central Nervous System Dysfunction after Cardiopulmonary Bypass
Overt and subclinical perioperative cerebral injury remains an unresolved problem. Overall mortality for patients undergoing coronary artery bypass grafting (CABG) has decreased by 23% over the past decade despite a projected risk-adjusted mortality predicting a 33% increase in mortality, but the incidence of stroke has remained relatively unchanged.1
AGE-ASSOCIATED RISK OF CENTRAL NERVOUS SYSTEM INJURY
Current data show a persistent association between increased age and cerebral injury after cardiac surgery. In a review of 67,764 cardiac surgical patients, of whom there were 4743 octogenarians and who underwent cardiac surgery at 22 centers in the National Cardiovascular Network, Alexander and colleagues reported that the incidence of type I cerebral injury, defined as stroke, transient ischemic attack (TIA), or coma, was 10.2% in patients older than 80 years old versus 4.2% in patients younger than 80 years old.2 In addition to the age-related factor, reports from Europe and North America consistently describe previous cerebrovascular disease, diabetes mellitus, hypertension, peripheral vascular disease, aortic atherosclerosis, and intraoperative and postoperative complications as all being additional factors increasing the incidence of cerebral injury in cardiac surgical patients (Box 29-1).
The impact of age-associated cerebral injury in cardiac surgery is becoming more relevant owing to the progressive increase in the average age of the general population and, in particular, of the cardiac surgical population. As overall survival and quality of life after cardiac surgery continue to improve in elderly patients, advanced age alone is no longer considered a deterrent when evaluating a patient for cardiac surgery. The presence and extent of comorbidities should be considered as being of equal or greater importance than age itself as a risk factor for cerebral injury in cardiac surgical patients.3
CENTRAL NERVOUS SYSTEM INJURY
The incidence of stroke or type I injury after closed-chamber cardiac procedures is generally considered to be 1% to 4%, increasing to 8% to 9% in open-chamber (e.g., valvular surgery) or combined/complex procedures. The incidence of cognitive dysfunction (type II) is reported as ranging in incidence from 30% to 80% in the early postoperative period.4 To some extent there is a difference in the incidence of cerebral injury after cardiac surgery related to the type and complexity of the procedure, such as open chamber, combined valvular, and CABG.
Valvular versus Coronary Artery Bypass Graft Surgery
Increasing the complexity or undertaking open chamber-type procedures increases the risk of CNS injury. Ebert and coworkers prospectively studied 42 patients who underwent valve replacement surgery and 42 patients for CABG, with both groups matched post hoc for age, sex, and preoperative cognitive status.5 Patients were investigated preoperatively as well as 2 and 7 days postoperatively with a comprehensive neuropsychological and neuropsychiatric assessment. Valve replacement surgery patients exhibited more severe neuropsychological deficits and showed a slower recovery than patients who underwent CABG. In a study of 64,467 patients who underwent CABG alone and 3297 patients who underwent CABG in conjunction with aortic valve replacement (CABG/AVR) or CABG in conjunction with mitral valve repair or replacement (CABG/MVR), the incidence of type I cerebral injury in patients younger than 80 years of age was 4.2% for CABG, 9.1% for CABG/AVR, and 11.2% for CABG/MVR.2 It should be noted that the total CPB time was 96 minutes for CABG, 148 minutes for CABG/AVR, and 161 minutes for CABG/MVR.
The incidence of subtle neurologic dysfunction and cognitive abnormalities is similar in all adult patients undergoing surgical coronary artery revascularization. Increasing age has been repeatedly shown to be one of the major risk factors for stroke after CABG, likely related to the greater prevalence of severe aortic atherosclerosis in the elderly. This suggests that there may be different factors operative in the production of gross neurologic damage than in the genesis of cognitive dysfunction. Although calcific or atheromatous macroembolic debris from the ascending aorta or aortic arch appears to be a prime factor in the production of clinical stroke syndromes and it was formerly thought that microembolic elements, either gaseous or particulate, produced cognitive dysfunction, studies from beating-heart surgery in which CPB is avoided, despite a much lower incidence of embolic events, appear to have a relatively similar incidence of cognitive dysfunction to CABG using conventional CPB.6
Aortic Atherosclerosis
Atheroembolism from an atheromatous ascending aorta and aortic arch is recognized as a major risk factor in the patient undergoing cardiac surgery and is a widespread problem.7
Atheroembolism in cardiac surgery has a broad spectrum of clinical presentations, including devastating injuries and death; yet its true incidence is probably underestimated. Thoracic aorta atheromatosis is associated with coronary artery disease and stroke in the general population. Yahia and associates prospectively studied patients with diagnoses of TIA or stroke using TEE for assessment of aortic atheromatosis.7 Thoracic aortic atheromas were present in 141 of 237 patients (59%); mild plaque (<2 mm) was present in 5%, moderate plaque (2 to 4 mm) in 21%, severe plaque (≥4 mm) in 33%, and complex plaque in 27%. Plaques were more frequently present in the descending aorta and the arch of the aorta than in the ascending aorta. Overall, atherosclerosis of the ascending aorta is present in 20% to 40% of cardiac surgical patients, with the percentage increasing with age, and it is an independent risk factor for type I cerebral injury.
Transesophageal Echocardiography versus Epiaortic Scanning
Djaiani and colleagues performed TEE and EAS to assess the severity of aortic atherosclerosis in the ascending aorta and the aortic arch.8 Patients were allocated to either low-risk or high-risk groups according to thickness of the intima of the aorta. Transcranial Doppler imaging was used to monitor the middle cerebral artery. Diffusion-weighted magnetic resonance imaging (MRI) was performed 3 to 7 days after surgery. The NEECHAM Confusion Scale was used for assessment and monitoring patient consciousness level. In the high-risk group (intimal thickness > 2 mm), confusion was present in six (16%) patients versus five (7%) patients in the low-risk group, and there was a threefold increase in median embolic count, 223.5 versus 70.0 (P = .0003). Diffusion-weighted MRI–detected brain lesions were only present in patients from the high-risk group, 61.5% versus 0% (P < .0001). There was significant correlation between the NEECHAM scores and embolic count in the high-risk group. Multiple studies have documented that most of the significant atherosclerotic lesions in the ascending aorta are missed by intraoperative palpation by the surgeon, and intraoperative echocardiographic studies of the aorta have been recommended (Fig. 29-1). However, the ability of TEE to reliably detect all ascending aorta and aortic arch lesions is limited.
