Key Points
- 1.
Despite a progressive decrease in cardiac surgical mortality, the incidence of postoperative neurologic complications has remained relatively unchanged over the decades.
- 2.
The risk for stroke in patients undergoing coronary artery surgery increases progressively with increasing age, ranging from 0.5% for patients younger than 55 years to 2.3% for those older than 75 years.
- 3.
Neurologic events in cardiac surgical patients are associated with increased postoperative mortality, prolonged intensive care unit stay, longer hospital stay, decreased quality of life, and decreased long-term survival.
- 4.
Mechanisms for neurologic injury in cardiac surgery include some combination of cerebral embolism, hypoperfusion, and inflammation, associated vascular disease, and altered cerebral autoregulation, rendering the brain more susceptible to injury.
- 5.
While occlusive carotid disease is associated with increased risk of perioperative stroke, such stroke is not infrequently contralateral, and concomitant perioperative carotid endarterectomy may increase risk of stroke and other major adverse events.
- 6.
Perioperative risk factors for neurologic complications include renal dysfunction, diabetes mellitus, hypertension, prior cerebrovascular disease, aortic atheromatosis, manipulation of ascending aorta, complex surgical procedures, bypass time longer than 2 hours, hypothermic circulatory arrest, hemodynamic instability during and after bypass, new-onset atrial fibrillation, hyperglycemia, hyperthermia, and hypoxemia.
- 7.
Routine epiaortic scanning before instrumentation of the ascending aorta is a sensitive and specific technique used to detect nonpalpable aortic atheromatosis.
- 8.
In patients with significant ascending aorta atheromatosis, avoidance of aortic manipulation (“no-touch technique”) is associated with decreased perioperative stroke.
- 9.
Strategies to decrease the impact of cardiopulmonary bypass (CPB) on embolization, inflammation, and coagulation will decrease neurologic complications.
- 10.
Cerebrovascular disease renders patients who experience wide hemodynamic perturbations during CPB at greater risk for perioperative stroke.
- 11.
Cerebral near-infrared spectroscopy (cerebral oximetry) can detect cerebral ischemia and is associated with decreased incidence of stroke and improved outcomes after cardiac surgery.
- 12.
There is a greater incidence of early postoperative cognitive dysfunction in patients exposed to conventional CPB compared with off-pump and noncardiac surgical patients.
- 13.
The incidence of late cognitive dysfunction and stroke appears to be similar between groups undergoing conventional CPB, percutaneous coronary intervention, or medical management, implying progression of underlying disease and atrial arrhythmias as primary mechanisms of late stroke.
From 2001 to 2011, coronary artery bypass graft (CABG) procedures decreased by nearly 50% to 213,700 procedures, whereas percutaneous coronary intervention (PCI) decreased by more than 25% to 560,500 procedures in 2011. Although these trends may reflect a variety of environmental, lifestyle, and therapeutic factors, overt and subclinical perioperative cerebral injury remains a compelling problem and continues to influence the debate over optimal strategy for coronary revascularization. Accordingly, the risk factors, causes, and potential for mitigation of perioperative stroke and neurobehavioral outcomes associated with cardiac surgery and cardiopulmonary bypass (CPB) are the topic of this chapter.
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Categorization of Central Nervous System Injury
In a seminal study, central nervous system (CNS) injury was classified into two broad categories: type I (focal injury, stupor, or coma at discharge) and type II (deterioration in intellectual function, memory deficit, or seizures). Cerebral injury can also be broadly classified as stroke, delirium (encephalopathy), or postoperative cognitive dysfunction. Stroke is defined clinically as any new focalized sensorimotor deficit persisting longer than 24 hours, identified either on clinical grounds only or, ideally, as confirmed by magnetic resonance imaging (MRI), computed tomography, or other form of brain imaging.
Transient ischemic attack (TIA) is defined as brief neurologic dysfunction persisting for less than 24 hours. Neurologic dysfunction lasting longer than 24 hours but less than 72 hours is termed a reversible ischemic neurologic deficit.
Delirium is described as a transient global impairment of cognitive function, reduced level of consciousness, profound changes in sleep pattern, and attention abnormalities.
Cognitive dysfunction is defined as a decrease in score falling below some predetermined threshold, such as a decrease in postoperative score of magnitude 1 standard deviation or more derived from the preoperative performance.
Seizure is categorized as either convulsive or nonconvulsive and may be related to overt CNS injury or, alternatively, may reflect transient biochemical or pharmacologically mediated neuroexcitation.
Early, Delayed, and Late Stroke
In considering the incidence of perioperative stroke it is apparent that distinguishing stroke as early (ie, neurologic deficit apparent on emergence from anesthesia), delayed (ie, neurologic deficit developing more than 24 hours postoperatively), or late (ie, stroke developing more than 30 days postoperatively) is important to better discriminate causative factors and potential risk reduction strategies. Such an analysis facilitates identification of potentially causal intraoperative events (eg, hypotension, atherosclerotic aorta) from perioperative occurrences (eg, atrial fibrillation) and later progression of underlying disease (eg, cerebrovascular atherosclerosis).
Studies strongly indicate that patient comorbidities, particularly aortic atherosclerosis, in concert with intraoperative factors, whether associated with CABG, OPCAB, or PCI, fundamentally impact the incidence of early stroke and are thus potentially modifiable, whereas late stroke reflects progression of comorbid disease and atrial arrhythmias.
Age-Associated Risk for Central Nervous System Injury
In a review of 67,764 cardiac surgical patients, of whom 4743 were octogenarians, and who underwent cardiac surgery at 22 centers in the National Cardiovascular Network, the incidence of type I cerebral injury was 10.2% in patients older than 80 years versus 4.2% in patients younger than 80. Although global mortality for cardiac surgery in octogenarians was greater than in younger patients, the researchers reported that, when octogenarians without significant comorbidities were considered, their mortality rates were similar to those of younger patients.
In addition to the age-related factor, reports from Europe and North America consistently describe previous cerebrovascular disease, diabetes mellitus, hypertension, peripheral vascular disease (including carotid disease), aortic atherosclerosis, renal dysfunction, infarction or unstable angina within 24 hours before surgery, and intraoperative and postoperative complications as being additional factors increasing the incidence of cerebral injury in cardiac surgical patients ( Box 31.1 ). Determining the impact of age-associated cerebral injury in cardiac surgery is becoming more relevant because of the progressive increase in the average age of the general population and, in particular, of the cardiac surgical population. The presence of preoperative comorbidities is increasingly recognized as the primary determinant of the age-associated risk for CNS complications. As overall survival and quality of life after cardiac surgery continue to improve in older 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.
Age
Aorta atheromatosis
Carotid disease
Diabetes mellitus
Hypertension
Peripheral vascular disease
Renal dysfunction
Stroke or cerebrovascular disease
Recent unstable angina or acute myocardial infarction
Preoperative low output/low ejection fraction
Combined/complex procedures
Redo surgery
Prolonged cardiopulmonary bypass time
Intraoperative hemodynamic instability
Postoperative atrial fibrillation
Risk factors consistently reported for perioperative cerebral injury in cardiac surgery patients; see discussion in the text.
Retrospective Versus Prospective Neurologic Assessment
The detection of CNS injury depends critically on the methodology used, and retrospective studies have been demonstrated as insensitive in various studies. A retrospective chart review is inadequate as an assessment of the overall incidence of postoperative neurologic dysfunction. The reasons for the inability of retrospective chart audit to detect the majority of patients with neurologic dysfunction are readily apparent and include incompleteness of records, a reluctance to document apparently minor complications, and, most important, an insensitivity to subtle neurologic dysfunction. The timing, thoroughness, and reproducibility (single examiner) of the neurologic examinations, as well as the incorporation of a preoperative assessment for comparison, all determine the sensitivity and accuracy with which postoperative CNS injury can be detected. Many of the types of neurologic impairment now being documented are subclinical and not readily detectable by a standard “foot-of-the-bed” assessment and have currently unknown implications for longer-term patient outcomes.
![]()
Categorization of Central Nervous System Injury
In a seminal study, central nervous system (CNS) injury was classified into two broad categories: type I (focal injury, stupor, or coma at discharge) and type II (deterioration in intellectual function, memory deficit, or seizures). Cerebral injury can also be broadly classified as stroke, delirium (encephalopathy), or postoperative cognitive dysfunction. Stroke is defined clinically as any new focalized sensorimotor deficit persisting longer than 24 hours, identified either on clinical grounds only or, ideally, as confirmed by magnetic resonance imaging (MRI), computed tomography, or other form of brain imaging.
Transient ischemic attack (TIA) is defined as brief neurologic dysfunction persisting for less than 24 hours. Neurologic dysfunction lasting longer than 24 hours but less than 72 hours is termed a reversible ischemic neurologic deficit.
Delirium is described as a transient global impairment of cognitive function, reduced level of consciousness, profound changes in sleep pattern, and attention abnormalities.
Cognitive dysfunction is defined as a decrease in score falling below some predetermined threshold, such as a decrease in postoperative score of magnitude 1 standard deviation or more derived from the preoperative performance.
Seizure is categorized as either convulsive or nonconvulsive and may be related to overt CNS injury or, alternatively, may reflect transient biochemical or pharmacologically mediated neuroexcitation.
Early, Delayed, and Late Stroke
In considering the incidence of perioperative stroke it is apparent that distinguishing stroke as early (ie, neurologic deficit apparent on emergence from anesthesia), delayed (ie, neurologic deficit developing more than 24 hours postoperatively), or late (ie, stroke developing more than 30 days postoperatively) is important to better discriminate causative factors and potential risk reduction strategies. Such an analysis facilitates identification of potentially causal intraoperative events (eg, hypotension, atherosclerotic aorta) from perioperative occurrences (eg, atrial fibrillation) and later progression of underlying disease (eg, cerebrovascular atherosclerosis).
Studies strongly indicate that patient comorbidities, particularly aortic atherosclerosis, in concert with intraoperative factors, whether associated with CABG, OPCAB, or PCI, fundamentally impact the incidence of early stroke and are thus potentially modifiable, whereas late stroke reflects progression of comorbid disease and atrial arrhythmias.
Age-Associated Risk for Central Nervous System Injury
In a review of 67,764 cardiac surgical patients, of whom 4743 were octogenarians, and who underwent cardiac surgery at 22 centers in the National Cardiovascular Network, the incidence of type I cerebral injury was 10.2% in patients older than 80 years versus 4.2% in patients younger than 80. Although global mortality for cardiac surgery in octogenarians was greater than in younger patients, the researchers reported that, when octogenarians without significant comorbidities were considered, their mortality rates were similar to those of younger patients.
In addition to the age-related factor, reports from Europe and North America consistently describe previous cerebrovascular disease, diabetes mellitus, hypertension, peripheral vascular disease (including carotid disease), aortic atherosclerosis, renal dysfunction, infarction or unstable angina within 24 hours before surgery, and intraoperative and postoperative complications as being additional factors increasing the incidence of cerebral injury in cardiac surgical patients ( Box 31.1 ). Determining the impact of age-associated cerebral injury in cardiac surgery is becoming more relevant because of the progressive increase in the average age of the general population and, in particular, of the cardiac surgical population. The presence of preoperative comorbidities is increasingly recognized as the primary determinant of the age-associated risk for CNS complications. As overall survival and quality of life after cardiac surgery continue to improve in older 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.
Age
Aorta atheromatosis
Carotid disease
Diabetes mellitus
Hypertension
Peripheral vascular disease
Renal dysfunction
Stroke or cerebrovascular disease
Recent unstable angina or acute myocardial infarction
Preoperative low output/low ejection fraction
Combined/complex procedures
Redo surgery
Prolonged cardiopulmonary bypass time
Intraoperative hemodynamic instability
Postoperative atrial fibrillation
Risk factors consistently reported for perioperative cerebral injury in cardiac surgery patients; see discussion in the text.
Retrospective Versus Prospective Neurologic Assessment
The detection of CNS injury depends critically on the methodology used, and retrospective studies have been demonstrated as insensitive in various studies. A retrospective chart review is inadequate as an assessment of the overall incidence of postoperative neurologic dysfunction. The reasons for the inability of retrospective chart audit to detect the majority of patients with neurologic dysfunction are readily apparent and include incompleteness of records, a reluctance to document apparently minor complications, and, most important, an insensitivity to subtle neurologic dysfunction. The timing, thoroughness, and reproducibility (single examiner) of the neurologic examinations, as well as the incorporation of a preoperative assessment for comparison, all determine the sensitivity and accuracy with which postoperative CNS injury can be detected. Many of the types of neurologic impairment now being documented are subclinical and not readily detectable by a standard “foot-of-the-bed” assessment and have currently unknown implications for longer-term patient outcomes.
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Neuropsychologic Dysfunction
Compared with stroke, cognitive dysfunction (neurocognitive dysfunction) is a considerably more frequent sequela of cardiac surgery and has been demonstrated in up to 80% of patients early after surgery. The pathogenesis of cognitive dysfunction after cardiac surgery is still uncertain. Variables that have been postulated to explain the development of postoperative neurocognitive decline include advanced age, concomitant cerebrovascular disease, and severity of cardiovascular disease, as well as progression of underlying disease. Various intraoperative factors, such as cerebral emboli, hypoperfusion or hypoxia, activation of inflammatory processes, aortic cross-clamp or CPB time, low mean arterial pressure (MAP), and cerebral venous hypertension, have all been implicated. In many instances, subtle signs of neuropsychological dysfunction are detectable only with sophisticated cognitive testing strategies, although depression and personality changes may be noted by family members. It should be recognized that formalized cognitive testing is reproducible and quantifiable and represents an objective outcome measure; as such, it can act as a benchmark to assess various therapeutic interventions (eg, the efficacy of putative cerebroprotectants, equipment modifications, pH management strategies). In addition, a number of studies have made correlations between early postoperative cognitive dysfunction and intraoperative cerebral oxygen desaturation, as well as new ischemic lesions on MRI. Assessment of early cognitive dysfunction can be used to discriminate between various intraoperative treatment modalities (eg, pH management, use of cell saver, epiaortic scanning [EAS]). However, whether early postoperative cognitive dysfunction represents permanent neurologic damage remains controversial.
Several more recent studies have demonstrated similar incidences of later cognitive dysfunction whether patients underwent CABG, off-pump surgery, PCIs, or were managed medically. These results strongly imply that underlying comorbidities and progression of cerebrovascular disease are the most relevant factors in late postoperative cognitive dysfunction rather than cardiac surgery per se.
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