Early neurological complications of coronary artery bypass surgery

Perioperative Stroke

PURPOSE OF REVIEW

This review overviews perioperative stroke as it pertains to specific surgical procedures.

RECENT FINDINGS

As awareness of perioperative stroke increases, so does the opportunity to potentially improve outcomes for these patients by early stroke recognition and intervention. Perioperative stroke is defined to be any stroke that occurs within 30 days of the initial surgical procedure. The incidence of perioperative stroke varies and is dependent on the specific type of surgery performed. This chapter overviews the risks, mechanisms, and acute evaluation and management of perioperative stroke in four surgical populations: cardiac surgery, carotid endarterectomy, neurosurgery, and non-cardiac/non-carotid/non-neurological surgeries.

Contemporary Management of Patients with Concomitant Coronary and Carotid Artery Disease

The ideal management of concomitant carotid and coronary artery occlusive disease remains elusive. Although researchers have advocated the potential benefits of varying treatment strategies based on either concomitant or staged surgical treatment, there is no consensus in treatment guidelines among national or international clinical societies. Clinical studies show that coronary artery bypass grafting (CABG) with either staged or synchronous carotid endarterectomy (CEA) is associated with a high procedural stroke or death rate. Recent clinical studies have found carotid artery stenting (CAS) prior to CABG can lead to superior treatment outcomes in asymptomatic patients who are deemed high risk of CEA. With emerging data suggesting favorable outcome of CAS compared to CEA in patients with critical coronary artery disease, physicians must consider these diverging therapeutic options when treating patients with concurrent carotid and coronary disease. This review examines the available clinical data on therapeutic strategies in patients with concomitant carotid and coronary artery disease. A treatment paradigm for considering CAS or CEA as well as CABG and percutaneous coronary intervention is discussed.

Practice Advisory for the Prevention of Perioperative Peripheral Neuropathies 2018

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Carotid artery stenosis as an independent risk factor for perioperative strokes following mitral valve surgical intervention

OBJECTIVE

To examine the role of carotid stenosis (CS) and other independent risk factors of perioperative stroke following either mitral valve repair or replacement.

METHODS

Using data from the National Inpatient Sample (NIS) database for analysis, all patients who underwent either mitral valve repair or replacement were identified using ICD-9 codes.

RESULTS

A total of 79,583 patients who underwent either mitral valve replacement or repair were studied. 3.39% of the total cohort developed perioperative stroke. With a mean age of 62.78±0.23, there was a statistically significant amount of stroke cases in age ranges 65-74 and 75-84 (p<0.05). Risk stratification was done using Van Walraven (VWR) scoring and the cohort had a mean of 2.73±0.06. The following independent predictors were found to be significant: age, female gender, moderate and high VWR risk, both symptomatic and asymptomatic CS, atrial fibrillation, previous h/o smoking, and other cardiac valve procedures performed, and congestive heart failure (CHF).

CONCLUSION

CS is a significant risk factor for perioperative strokes following mitral valve surgery. Further prospective clinical studies are needed that look into risk stratification of patients for better patient selection and the question of whether carotid revascularization procedures will be beneficial in reducing stroke rates.

Perioperative strokes after coronary artery bypass grafting with staged carotid endarterectomy: A nationwide perspective

STUDY OBJECTIVE

To examine the risk of perioperative stroke on in-hospital morbidity and mortality in staged coronary artery bypass grafting (CABG) and carotid endarterectomy (CEA) procedures.

DESIGN

The National Inpatient Sample (NIS) database was used to extract data on all patients who underwent staged CABG CEA procedures. They were identified using the ICD-9 (International Classification of Diseases, Ninth Revision-Clinical Modification) diagnosis and procedure codes.

SETTING

Multi-institutional.

PATIENTS

Patients who underwent staged CABG and CEA from 1999 to 2011.

INTERVENTIONS

Staged CABG and CEA procedures.

MEASUREMENTS

Various pre-operative, and perioperative risk factors and their association with in-hospital mortality and morbidity were studied.

MAIN RESULTS

The study cohort was grouped into 2761 patients who underwent staged CEA and CABG. The average age of the patient population was 69years. An in-hospital mortality of 4.96% (137) was observed. Staged procedures showed a morbidity rate of 69.21%. Patients with perioperative strokes had a mortality rate of 16.73% following staged procedures. Other notable risk factors for mortality and morbidity were post-operative myocardial infarction (MI) and congestive heart failure (CHF).

CONCLUSION

Analysis of 2761 patients over a period of 12years (1999-2011) indicate perioperative stroke to be a strong post-operative predicator of in-hospital mortality and morbidity for staged procedures. Other significant factors such as advancing age, female gender and comorbidities like CHF, left ventricular dysfunction (LVD) and post-operative MI should also be considered when determining patient risk. Further investigative studies on staged CABG and CEA procedures are needed for better patient selection and for implementing preventative strategies such as neuroprotective medication and neuromonitoring to minimize the risk of ischemic strokes.

Blood-Brain Barrier Disruption After Cardiopulmonary Bypass: Diagnosis and Correlation to Cognition

BACKGROUND

Cardiopulmonary bypass (CPB) elicits a systemic inflammatory response that may impair blood-brain barrier (BBB) integrity. BBB disruption can currently be detected by dynamic contrast enhancement magnetic resonance imaging (MRI), reflected by an increase in the permeability constant (K^trans). We aimed to determine (1) whether CPB induces BBB disruption, (2) duration until BBB disruption resolution, and (3) the obtainable correlation between BBB injury (location and intensity) and neurocognitive dysfunction.

METHODS

Seven patients undergoing CPB with coronary artery bypass grafting (CABG) were assigned to serial cerebral designated MRI evaluations, preoperatively and on postoperative day (POD) 1 and 5. Examinations were analyzed for BBB disruption and microemboli using dynamic contrast enhancement MRI and diffusion-weighted imaging methods, respectively. Neuropsychologic tests were performed 1 day preoperatively and on POD 5.

RESULTS

A significant local K^trans increase (0.03 min^-1 vs 0.07 min^-1, p = 0.033) compatible with BBB disruption was evident in 5 patients (71%) on POD 1. Resolution was observed by POD 5 (mean, 0.012 min^-1). The location of the disruption was most prominent in the frontal lobes (400% vs 150% K^trans levels upsurge, p = 0.05). MRI evidence of microembolization was demonstrated in only 1 patient (14%). The postoperative global cognitive score was reduced in all patients (98.2 ± 12 vs 95.1 ± 11, p = 0.032), predominantly in executive and attention (frontal lobe-related) functions (91.8 ± 13 vs 86.9 ± 12, p = 0.042). The intensity of the dynamic contrast enhancement MRI BBB impairment correlated with the magnitude of cognition reduction (r = 0.69, p = 0.04).

CONCLUSIONS

BBB disruption was evident in most patients, primarily in the frontal lobes. The location and intensity of the BBB disruption, rather than the microembolic load, correlated with postoperative neurocognitive dysfunction.

Strategies to Protect the Brain During Cardiac Surgery

Despite significant advances in cardiopulmonary by pass (CPB) technology, surgical techniques, and anes thetic management, central nervous system (CNS) com plications remain a common and costly problem after CPB. Stroke is often considered a rare and unprevent able complication of cardiac surgery. Recent studies have shown that through the use of echocardiography and historical risk stratification strategies, we can de fine which patients are at substantially greater risk for CNS injury. Through enhanced understanding of the etiology of stroke and perioperative factors, which are associated with potential for neuroprotection or injury extension, there now exists a greater potential than ever to substantially reduce neurological injury associ ated with cardiac surgery. Strategies and theories of stratifying patients at risk and secondarily reducing that risk are described, as well as consideration for early postoperative assessment to allow treatment when events occur.

The Effect of Substrate Load and Blood Glucose Management on Cerebral Dysfunction Following Cardiopulmonary Bypass

Seventy patients undergoing elective coronary artery bypass grafting were prospectively randomized into either of two primes: 5% dextrose or Hartmann's solution. The groups were comparable. Neuropsychological assessment was performed before and eight weeks after surgery. During bypass blood glucose concentrations rose to a mean of 26 mmol/L in the 5% dextrose group and 6 mmol/L in the Hartmann's group. No deaths occurred in either group; 2 clinically evident neurological events were noted, both taking place in the hyperglycemic group. Detailed analysis of the results showed differences between the groups. When score changes between tests were assessed it was found that in 17 of the 18 versions of the tests more patients in the hyperglycemic group deteriorated than the normoglycemic controls. With a two-tailed binomial statistic this difference was significant at the 5% level. Learning ability was likewise found to worsen in the hyperglycemic group after surgery.

Hyperglycemia may be a detrimental factor in the development of postcardiac surgical intellectual dysfunction. The authors would advocate the avoidance of glucose-containing bypass primes and the close monitoring of blood glucose during cardiopulmonary bypass.

Evoked Potentials during Cardiac and Major Vascular Operations

Somatosensory evoked potentials are widely used in spine surgery to prevent injury to the spinal cord. However, their application in cardiac and major vascular surgery is largely unappreciated. This paper will review the unique stresses placed on peripheral nerves, spinal cord, and brain during these operations. In addition, the potential benefits of perioperative somatosensory evoked potentials monitoring are described in detail.

Neuropsychological Testing: Methodology, Interpretation and Outcomes

The outcome most dreaded by patient and surgeon alike is a brain dysfunction. Numerous surveys indicate most patients would prefer death to significant neurological impairment. Cardiac surgery currently enjoys a remarkable safety record in regard to a low death rate and major cerebral infarctions. However, neurobehavioral dysfunction, i.e. memory, coordination, and attention deficits, continues to be an area that is identified in the literature as a major negative outcome associated with cardiac surgery.

If the cardiac surgical community is going to eliminate brain injury associated with interoperative methods and apparatus, then a sensitive, reproducible and quick assessment of brain function that can be reliably correlated with surgical interventions is a basic requirement. This paper discusses the experimental design, environmental and statistical concerns relative to selecting a battery of neurobehavioral assessment tools appropriate for cardiac surgery patients so, as a team, we can make a safe operation safer.

Genetic Predictors of Perioperative Neurologic and Neuropsychological Injury and Recovery

Central nervous system (CNS) dysfunction after cardio pulmonary bypass represents a continuum from coma and focal stroke to cognitive deficits after surgery. Despite the marked increase in investigation of neuro logic and neurocognitive deficits after cardiac surgery, causative factors fail to predict the majority of the variance in the observed incidence of both early and late neurocognitive decline pointing to some inherent indi vidual susceptibility to injury. The authors' investigative team recently discovered a genetic association be tween late-onset Alzheimer's disease and the apolipo protein E (APOE, gene; apoE, protein) ∈-4 gene. This finding triggered many recent studies that have shown an important role of apoE in the determination of neurologic injury and recovery following a variety of acute ischemic insults including intracerebral hemor rhage, closed-head injury, as well as acute stroke and dementia pugilistica. Most important to the current discussion is the authors' recent report documenting preliminary evidence of an association of APOE4 with neurocognitive decline after cardiac surgery. This re view discusses the authors' hypothesis that the bio chemical products coded by this gene are not available to protect and repair the neurons of the CNS during cardiac surgery resulting in deficits of memory, atten tion, and concentration. Potential mechanisms of apoE's association with acute neurologic injury are discussed including regulation of the inflammatory response. The authors have recently determined that apoE, in vivo, modulates the release of nitric oxide and tumor necro sis factor a. This may compound the autonomic dysreg ulation recently reported in the aging population. The authors' preliminary data associating APOE4 with cogni tive impairment after cardiac surgery support this hy pothesis. The different potential mechanisms of apoE function in neuronal injury and recovery are not mutu ally exclusive, and it is likely that apoE modulates the CNS injury response at several functional levels.

Cerebral blood flow determinants and their clinical implications during cardiopulmonary bypass

Cerebral blood flow (CBF) was measured in 58 patients undergoing elective coronary artery surgery (CABS) prior to, during and following cardiopulmonary bypass. CBF fell significantly during hypothermic bypass and returned to prebypass levels following the end of bypass. At all times CBF, measured as the initial slope index (ISI), was significantly correlated to arterial carbon dioxide tension (PaCO 2) and cerebral oxygen consumption (CMRO2). There was no significant correlation between CBF and changes in arterial blood pressure or, when on bypass, perfusion flow. This supports the notion that CBF autoregulation is maintained during bypass under the conditions of this study.The index of cerebral oxygen supply to demand (CERO2), which reflects the ratio of oxygen consumed by the brain to that supplied by the cerebral circulation, was appropriately matched prior to and following bypass. During bypass the index fell significantly ( p<0.001) to levels consistent with a mismatch of flow and demand indicating relative cerebral hyperperfusion. Acid base maintenance during bypass was consistent with a 'pH stat' protocol with pH on bypass approximating, following temperature adjustment, to 7.40. The maintenance of pH stat requires a higher PaCO2 than does the maintenance of alphastat. It may be that the adoption of an alphastat acid base management protocol, as seen in poikilotherms rather than hibernating mammals, and the resultant reduction in absolute PaCO2 for any given temperature may result in a lowering of CBF and a return to appropriate matching of CBF and demand during bypass. This may be particularly important in relation to the generation of perfusion related, microembolic, cerebral damage during cardiopulmonary bypass.

Circulating non-hematological cells during cardiopulmonary bypass: new findings in cardiac surgery procedures

BACKGROUND

Several factors have been historically advocated to explain the coagulative and inflammatory disorders following cardiopulmonary bypass (CPB). In this paper, we describe the presence of circulating non-hematological cells, introduced within the bloodstream during CPB. We defined the origin of the cells and tested their impact on coagulation.

METHODS

We collected peripheral arterial blood samples in twenty consecutive coronary artery bypass graft cases at four different surgical moments and assessed the presence and nature of circulating cells with the use of the CELLSEARCH® Test, immunocytochemistry and immunofluorescence, evaluating the expression of cytokeratin and calretinin. The effect of the circulating non-hematological cells on coagulation was tested in vitro, using the ROTEM assay.

RESULTS

A mean of 263.85 ± 57.5 (median 258.5) cells were present in the samples following the suction of blood from the surgical field while all the other samples were negative (zero cells) (p<0.00001). Immunologic tests confirmed the mesothelial origin of the cells. The ROTEM® assay of the blood samples contaminated by the mesothelial cells presented longer clotting times (53.4 ± 8.2 secs 48.3 ± 8.9 sec, p=0.05), longer clot formation times (137.1 ± 31.5 sec vs 111.9 ± 25.2 sec, p=0.009), smaller alfa angle amplitudes (66.7 ± 9.1° vs 71.1 ± 5.1°, p=0.04) and maximum clot firmness times (59.0 ± 5.4 sec vs 61.9 ±4.6 sec, p=0.004) than the controls.

CONCLUSION

The presence of circulating non-hematological cells during CPB with a mesothelial immunophenotype alters in vitro coagulation assays. This finding can help to further understand the pathophysiology of CPB.

Saturday Night Retinopathy: Characterization of a Rare Ophthalmic Condition

A 48-year-old, black female with a history of heroin and daily alcohol abuse presented to the emergency room in a lethargic state with severe right eye pain and vision loss. She had been unconscious for 10 hours prior to presentation. On exam she was found to have no light perception vision, severe retinal edema, and complete ophthalmoplegia of the right eye. Imaging and clinical course confirmed the diagnosis of Saturday Night Retinopathy--only the second documented case to be published.

Granulocyte colony stimulating factor reduces brain injury in a cardiopulmonary bypass-circulatory arrest model of ischemia in a newborn piglet

Ischemic brain injury continues to be of major concern in patients undergoing cardiopulmonary bypass (CPB) surgery for congenital heart disease. Striatum and hippocampus are particularly vulnerable to injury during these processes. Our hypothesis is that the neuronal injury resulting from CPB and the associated circulatory arrest can be at least partly ameliorated by pre-treatment with granulocyte colony stimulating factor (G-CSF). Fourteen male newborn piglets were assigned to three groups: deep hypothermic circulatory arrest (DHCA), DHCA with G-CSF, and sham-operated. The first two groups were placed on CPB, cooled to 18 °C, subjected to 60 min of DHCA, re-warmed and recovered for 8-9 h. At the end of experiment, the brains were perfused, fixed and cut into 10 µm transverse sections. Apoptotic cells were visualized by in situ DNA fragmentation assay (TUNEL), with the density of injured cells expressed as a mean number ± SD per mm(2). The number of injured cells in the striatum and CA1 and CA3 regions of the hippocampus increased significantly following DHCA. In the striatum, the increase was from 0.46 ± 0.37 to 3.67 ± 1.57 (p = 0.002); in the CA1, from 0.11 ± 0.19 to 5.16 ± 1.57 (p = 0.001), and in the CA3, from 0.28 ± 0.25 to 2.98 ± 1.82 (p = 0.040). Injection of G-CSF prior to bypass significantly reduced the number of injured cells in the striatum and CA1 region, by 51 and 37 %, respectively. In the CA3 region, injured cell density did not differ between the G-CSF and control group. In a model of hypoxic brain insult associated with CPB, G-CSF significantly reduces neuronal injury in brain regions important for cognitive functions, suggesting it can significantly improve neurological outcomes from procedures requiring DHCA.

Choroidal changes after cardiopulmonary bypass

AIM

Choroid, which is the vascular tissue responsible for blood supply to the outer parts of the retina, might be affected by hemodynamic events. We aimed to reveal choroidal thickness and ocular pulse amplitude changes after cardiopulmonary bypass in which gross hemodynamic alterations occur.

METHODS

Forty-two eyes of 42 patients who underwent heart surgery with cardiopulmonary bypass were examined in this prospective, cross-sectional case series. The spectral domain optical coherence tomography (Spectralis, Heidelberg, Germany) was used to analyze sub-foveal choroidal thickness. The ocular pulse amplitude, the surrogate of gross choroidal blood flow, was measured with the Pascal dynamic contour tonometer (Pascal DCT, Swiss Microtechnology AG, Port, Switzerland).. The intraocular pressure was also measured with this tonometer. The examinations were performed pre-operatively and post-operatively at the first week and first month.

RESULTS

The mean age of the patients was 58.8 ± 12.4 years. The mean sub-foveal choroidal thickness and ocular pulse amplitude values did not change statistically significantly after the operations at the follow-up visits (p>0.05). Also, there were no important correlations between cardiopulmonary bypass time and mean sub-foveal choroidal thickness and ocular pulse amplitude changes at the post-operative first week (p>0.05). The intraocular pressure values were decreased markedly at the control visits (p<0.05).

CONCLUSIONS

Sub-foveal choroidal thickness and ocular pulse amplitude are unchanged, while intraocular pressure decreases one week and one month after cardiopulmonary bypass.

[Cortical Release Signs in Patients with Schizophrenia, Depressive Disorders, and Bipolar Affective Disorder]

BACKGROUND AND OBJECTIVES

Determining the presence of cortical release signs associated with white matter damage, is a clinically easy method to perform. The objective of this study is to determine the presence of cortical release signs in patients with mental illnesses and cerebrovascular disease, as well as its clinical usefulness, given that it indicates cortical damage.

MATERIAL AND METHODS

A review was made of cortical release signs in patients hospitalized in clinical psychiatry and general hospitals with bipolar affective disorder (40), depression (37), schizophrenia (33), cardiovascular disease (33) and dementia (37).

RESULTS

The signs of cortical release do not have the same importance as cortical damage. For example, the glabellar reflex was found in all the groups, that of paratonia, particularly in the group with schizophrenia, and others signs in the group of patients with dementia.

CONCLUSIONS

It is suggested that these signs imply subcortical white matter damage. The appearance of these signs shows the need for a follow up of patients diagnosed with bipolar affective disorder, depression and schizophrenia.

The assessment of neural injury following open heart surgery by physiological tremor analysis

INTRODUCTION

The appearance of post-operative cognitive dysfunction as a result of open heart surgery has been proven by several studies. Focal and/or sporadic neuron damage emerging in the central nervous system may not only appear as cognitive dysfunction, but might strongly influence features of physiological tremor.

MATERIAL AND METHODS

We investigated 110 patients (age: 34-73 years; 76 male, 34 female; 51 coronary artery bypass grafting (CABG), 25 valve replacement, 25 combined open heart surgery, 9 off-pump CABG) before surgery and after open-heart surgery on the 3(rd) to 5(th) post-operative day. The assessment of the physiological tremor analysis was performed with our newly developed equipment based on the Analog Devices ADXL 320 JPC integrated accelerometer chip. Recordings were stored on a PC and spectral analysis was performed by fast Fourier transformation (FFT). We compared power integrals in the 1-4 Hz, 4-8 Hz and 8-12 Hz frequency ranges and these were statistically assessed by the Wilcoxon rank correlation test.

RESULTS

We found significant changes in the power spectrum of physiological tremor. The spectrum in the 8-12 Hz range (neuronal oscillation) decreased and a shift was recognised to the lower spectrum (p < 0.01). The magnitude of the shift was not significantly higher for females than for males (p < 0.157). We found no significant difference between the shift and the cross-clamp or perfusion time (p < 0.6450).

CONCLUSIONS

The assessment of physiological tremor by means of our novel, feasible method may provide a deeper insight into the mechanism of central nervous system damage associated with open heart surgery.

The role of head computed tomography imaging in the evaluation of postoperative neurologic deficits in cardiac surgery patients

BACKGROUND

Computed tomography (CT) scans of the head without contrast are routinely obtained to evaluate neurologic deficits after cardiac surgery, but their utility is unknown. We evaluated our experience with this imaging modality to determine its value.

METHODS

We retrospectively identified cardiac surgery patients with postoperative neurologic deficits occurring during the first week after surgery between January 2000 and December 2012. Stroke was defined by neurologist's determination, whereas a nonfocal deficit (NFD) was defined by the presence of seizure, delirium, or cognitive impairment. We defined early noncontrast head CT as occurring within 7 days of surgery. Outcomes included positive findings on CT, in-hospital mortality, and length of stay. Multivariate logistic regression identified predictors of positive findings on head CT.

RESULTS

Within the population of 11,070 postoperative patients, 451 had early noncontrast head CT scans (4%). Two hundred two (44.7%) were associated with stroke, and 249 (55.2%) were associated with NFD. Among stroke patients, 40 of 202 (20%) showed acute infarction, 17 of 202 (8%) showed subacute infarction, and 5 of 202 (2%) showed hemorrhage. Among NFD patients, 1 of 248 (0.4%) showed acute infarction, 4 of 248 (1.6%) showed subacute infarction, and 1 of 248 (0.4%) showed hemorrhage. There was no difference in in-hospital mortality (stroke, 42 of 201 [21%] versus NFD, 41 of 248 [16%]; p = 0.2) or length of stay (stroke, 24 d versus NFD, 22 d; p = 0.5). On multivariable logistic regression, only focal deficits and aortic procedures predicted a positive finding on CT scan.

CONCLUSIONS

This study reviewed the utility of early postoperative noncontrast head CT in cardiac surgery patients. With focal neurologic deficits, this imaging modality was positive for approximately one third of patients, but rarely positive for NFD. Its use in this setting has limited utility.

Metabotropic actions of the volatile anaesthetic sevoflurane increase protein kinase M synthesis and induce immediate preconditioning protection of rat hippocampal slices

Anaesthetic preconditioning occurs when a volatile anaesthetic, such as sevoflurane, is administered before a hypoxic or ischaemic insult; this has been shown to improve neuronal recovery after the insult. We found that sevoflurane-induced preconditioning in the rat hippocampal slice enhances the hypoxic hyperpolarization of CA1 pyramidal neurons, delays and attenuates their hypoxic depolarization, and increases the number of neurons that recover their resting and action potentials after hypoxia. These altered electrophysiological effects and the improved recovery corresponded with an increase in the amount of a constitutively active, atypical protein kinase C isoform found in brain, protein kinase M zeta (PKMζ). A selective inhibitor of this kinase, zeta inhibitory peptide (ZIP), blocked the increase in the total amount of PKMζ protein and the amount of the activated form of this kinase, phospho-PKMζ (p-PKMζ); it also blocked the altered electrophysiological effects and the improved recovery. We found that both cycloheximide, a general protein synthesis inhibitor, and rapamycin, a selective inhibitor of the mTOR pathway for regulating protein synthesis, blocked the increase in p-PKMζ, the electrophysiological changes, and the improved recovery due to sevoflurane-induced preconditioning. Glibenclamide, a KATP channel blocker, when present only during the hypoxia, prevented the enhanced hyperpolarization, the delayed and attenuated hypoxic depolarization, and the improved recovery following sevoflurane-induced preconditioning. To examine the function of persistent PKMζ and KATP channel activity after the preconditioning was established, we administered 4% sevoflurane for 30 min and then discontinued it for 30 min before 10 min of hypoxia. When either tolbutamide, a KATP channel blocker, or ZIP were administered at least 15 min after the washout of sevoflurane, there was little recovery compared with sevoflurane alone. Thus, continuous KATP channel and PKMζ activity are required to maintain preconditioning protection. We conclude that sevoflurane induces activation of the mTOR pathway, increasing the new protein synthesis of PKMζ, which is constitutively phosphorylated to its active form, leading to an increased KATP channel-induced hyperpolarizaton. This hyperpolarization delays and attenuates the hypoxic depolarization, improving the recovery of neurons following hypoxia. Thus, sevoflurane acts via a metabotropic pathway to improve recovery following hypoxia.

Brain damage and cardiopulmonary bypass: is there really any association?

Brain damage, in the form of stroke and cognitive deficit associated with heart surgery, has long been attributed unquestioningly to cardiopulmonary bypass (CPB). The aim of this paper is to review the randomised control trials (RCT), systematic reviews and meta-analyses of studies, comparing patients who have undergone on- or off-pump coronary artery bypass grafting (CABG) surgeries that have used stroke or cognition as an outcome to determine whether CPB is associated with brain damage. Although not definitive, the evidence base to date strongly suggests that the incidence of stroke and the effect on cognition, if any, are no different whether CABG surgery is undertaken on- or off-pump. In addition and contrary to long-held beliefs, this review leads to the conclusion that CPB may well not be the cause of the brain damage associated with heart surgery.

Paradoxical embolism, stroke and sclerotherapy

Sclerotherapy has been associated with 13 published cases of stroke since 1994. Four earlier reports implicated liquid sclerosants while nine recent cases have followed foam sclerotherapy. This adverse event represents a very rare complication of a very popular procedure. Ten of the 13 reported patients recovered completely with no long-term sequelae. A right-to-left shunt and in particular a patent foramen ovale (PFO) was the most consistent risk factor. Paradoxical gas emboli were observed in the brain-supplying or the intra-cranial arteries of five patients with an immediate onset of stroke after foam sclerotherapy. Paradoxical clot embolism was suspected in three patients with a delayed onset of stroke and concurrent venous thrombosis. In the remaining five cases, which included two cases with an immediate onset after liquid sclerotherapy, no specific cause was identified. Patients with a past history of cryptogenic stroke or a long life history of recurrent classic migraine attacks (with aura) have a higher risk of neurological adverse events and may benefit from preoperative screening and percutaneous closure of PFO.

Intravenous antiarrhythmic doses of lidocaine increase the survival rate of CA1 neurons and improve cognitive outcome after transient global cerebral ischemia in rats

Brain ischemia is often a consequence of cardiac or neurologic surgery. Prophylactic pharmacological neuroprotection would be beneficial for patients undergoing surgery to reduce brain damage due to ischemia. We examined the effects of two antiarrhythmic doses of lidocaine (2 or 4 mg/kg) on rats in a model of transient global cerebral ischemia. The occlusion of both common carotid arteries combined with hypotension for 10 min induced neuronal loss in the CA1 region of the hippocampus (18±12 vs. 31±4 neurons/200 μm linear distance of the cell body layer, X±SD; P<0.01). Lidocaine (4 mg/kg) 30 min before, during and 60 min after ischemia increased dorsal hippocampal CA1 neuronal survival 4 weeks after global cerebral ischemia (30±9 vs. 18±12 neurons/200 μm; P<0.01). There was no significant cell loss after 10 min of ischemia in the CA3 region, the dentate region or the amygdalae; these regions were less sensitive than the CA1 region to ischemic damage. Lidocaine not only increased hippocampal CA1 neuronal survival, but also preserved cognitive function associated with the CA1 region. Using an active place avoidance task, there were fewer entrances into an avoidance zone, defined by relevant distal room-bound cues, in the lidocaine groups. The untreated ischemic group had an average, over the nine sessions, of 21±12 (X±SD) entrances into the avoidance zone per session; the 4 mg/kg lidocaine group had 7±8 entrances (P<0.05 vs. untreated ischemic) and the non-ischemic control group 7±5 entrances (P<0.01 vs. untreated ischemic). Thus, a clinical antiarrhythmic dose of lidocaine increased the number of surviving CA1 pyramidal neurons and preserved cognitive function; this indicates that lidocaine is a good candidate for clinical brain protection.

A severe neurological event during a local anaesthesia phlebectomy

A 58 year old female patient underwent an intervention of phlebectomy below the knee. The patient gradually developed a severe neurological event and the Glasgow Coma Score decreased dramatically. After two and a half hours from onset, general conditions gradually improved and recovered completely. Lidocaine neurotoxicity was excluded. A right side motor deficit strongly suggests a transient ischaemic attack. As to invasivity, phlebectomy can be compared with liquid and foam sclerotherapy so that the simple question arises of also comparing their adverse effects. We have the strong conviction that this case may only be a co-incidental association.

Serum markers of cerebral ischemia

Rapid diagnosis and management of stroke patients is becoming increasingly important with the emergence of new interventional strategies for acute cerebral ischemia. A biochemical surrogate of cerebral ischemia, rapidly detectable in the serum before radiological diagnosis, might have clinical utility in the setting of acute stroke, high-risk cardiovascular procedures, and subarachnoid hemorrhage. Such a marker might also aid in the neurological prognosis of anoxic brain injury. Several serum markers have been evaluated in acute cerebral ischemia. These include neuronal enzymes such as neuron-specific enolase; markers of glial injury and activation, such as protein S100beta; and mediators of inflammation, such as interleukin-6. The clinical and preclinical data supporting the use of these biochemical surrogates of cerebral ischemia are reviewed.

Neuroprotective effect of volatile anesthetic agents: molecular mechanisms

INTRODUCTION

Intra-operative cerebral ischemia can be catastrophic, and volatile anesthetic agents have been recognized for their potential neuroprotective properties since the 1960s. In this review, we examine the neuroprotective effects of five volatile anesthetic agents in current or recent clinical use: isoflurane, sevoflurane, desflurane, halothane and enflurane.

METHODS

A review of publications in the National Library of Medicine and National Institutes of Health database from 1970 to 2007 was conducted.

RESULTS

Volatile anesthetic agents have been shown to be neuroprotective in multiple animal works of ischemic brain injury. Short-term neuroprotection (<1 week post-ischemia) in experimental cerebral ischemia has been reported in multiple works, although long-term neuroprotection (> or = 1 week post-ischemia) remains controversial. Comparison works have not demonstrated superiority of one specific volatile agent over another in experimental models of brain injury. Relatively few human works have examined the protective effects of volatile anesthetic agents and conclusive evidence of a neuroprotective effect has yet to emerge from human works.

CONCLUSION

Proposed mechanisms related to the neuroprotective effect of volatile anesthetic agents include activation of ATP-dependent potassium channels, up-regulation of nitric oxide synthase, reduction of excitotoxic stressors and cerebral metabolic rate, augmentation of peri-ischemic cerebral blood flow and up-regulation of antiapoptotic factors including MAP kinases.

Study of distortion-product otoacoustic emissions during hypothermia in humans

Aim

To evaluate the function of cochlear outer hair-cells under the influence of extra-corporeal circulation and moderate hypothermia during cardiac surgery.

Study Design

Prospective clinical study.

Methods

Distortion-product otoacoustic emissions (DPOAE) were registered before surgery, immediately after general anesthesia induction, during extra-corporeal circulation with moderate hypothermia and after the surgical procedure. Results: Comparison of response-amplitudes before and after surgery and before and after general anesthesia initiation did not demonstrate statistical difference. Comparison of amplitudes before and after extra-corporeal circulation with moderate hypothermia demonstrated a statistically significant decrease in responses amplitudes during hypothermia.

Conclusions

The amplitudes of DPOAE decreased during moderate hypothermia induced during extra-corporeal circulation.

Gaseous microemboli sizing in extracorporeal circuits using ultrasound backscatter

This paper describes efforts to estimate the size of gaseous microemboli (GME) in extracorporeal blood circuits based on the amplitude of backscattered ultrasound, starting with analytic modeling of the scattering behavior of GME in blood. After neglecting resonance effects, this model predicts a linear relationship between the amplitude of backscattered echoes and the diameter of GME. Computer simulations based on the cylindrical acoustic finite integration technique were performed to test some of the simplifying assumptions of the analytical model, with the simulations predicting small deviations from the linear approximation that could be treated as random scatter. Ultrasonic and microscopic measurements of injected GME were then performed on a test circuit to determine the linear correlation coefficient between echo amplitude and GME diameter in conditions like those employed in real cardiopulmonary bypass (CPB) circuits. The correlation coefficient determined through this study was further validated in a closed-loop CPB circuit using canine blood. This study shows that the amplitude of ultrasonic backscattered echoes can be used to accurately estimate the size distribution of a population of detected GME when the spacing of emboli is great enough to minimize interference and other multi-path scattering effects. With the high flow rates found in CPB circuits, typically ranging from 2 to 6 L per minute (equivalent to a flow velocity of 0.3 to 1 m/s through the circuit tubing), this assumption will be valid even when hundreds of emboli per second pass through the circuit. Therefore, sizing of GME using the ultrasonic backscatter models described in this paper is a viable method for estimating embolic load delivered to a patient during a CPB procedure.

Technology insight: brain MRI and cardiac surgery--detection of postoperative brain ischemia

Annually, an estimated 1 million patients undergo heart surgery worldwide. Unfortunately, stroke continues to be a frequent complication of cardiac surgery, with the specific cerebrovascular risk depending upon the particular surgical procedure performed. Neuroimaging has an integral role in the initial evaluation and management of patients who present with acute stroke symptoms following cardiac surgery. The aim of this paper is to review the role brain MRI has in detecting postoperative brain ischemia in these patients. Multimodal MRI--using diffusion-weighted MRI (DWI), perfusion-weighted MRI, and gradient-recalled echo imaging--has an excellent capacity to identify and delineate the size and location of acute ischemic strokes as well as intracerebral hemorrhages. This differentiation is critical in making appropriate treatment decisions in the acute setting, such as determining patient eligibility for thrombolytic or hemodynamic therapies. At present, DWI offers prognostic value in patients with strokes following cardiac surgery. Additionally, DWI could be a valuable tool for evaluating stroke preventive measures as well as therapeutic interventions in patients undergoing CABG surgery.

Isolated spinal accessory nerve palsy after coronary artery bypass: an unusual complication

Isolated spinal accessory nerve palsy after coronary artery bypass graft (CABG) surgery is a rare complication. We report a case of a 52-yr-old male patient who presented with right shoulder weakness, drooping of shoulder, and weakness of forward elevation after CABG. A program of neuromuscular electrical stimulation and exercises was started after the diagnosis of right isolated spinal accessory nerve palsy by physical examination and electromyographic study. Involved muscle function recovered after 6 mos of physical therapy and rehabilitation. This case report suggests that isolated spinal accessory nerve palsy should be considered in cases of shoulder pain or weakness after CABG, and conservative treatment is recommended if palsy develops.

Cell-derived microparticles and exosomes in neuroinflammatory disorders

All blood cells and the vascular endothelium shed microparticles (MP) from their plasma membranes when suitably stimulated, and assay of MP in patient blood has found increasing application to the monitoring of disease states. In addition, mounting evidence suggests that MP are not mere epiphenomena but play significant roles in the pathophysiology of thromboses, inflammation, and cancers. This chapter endeavors to summarize the limited number of studies thus far done on MP in neurological disorders such as multiple sclerosis (MS), transient ischemic attacks, and the neurological manifestations of antiphospholipid syndrome (APS). In addition, the chapter offers some plausible hypotheses on possible roles of MP in the pathophsyiology of these disorders, chiefly, the hypothesis that MP are indeed important participants in some neuropathologies, especially those which are ischemic in nature, but probably also inflammatory ones. The chapter also goes over the history and general principles of MP studies (e.g., assay methods and pitfalls), comparison with alternative methods (e.g., soluble markers of disease states), subclasses of MP (such as exosomes), and other topics aimed at helping readers to consider MP studies in their own clinical fields. Tables include a listing of bioactive agents known to be carried on MP, many of which were heretofore considered strictly soluble, and some of which can be transferred from cell to cell via MP vectors, for example certain cytokine receptors.

In vitro evaluation of the air separation ability of four cardiovascular manufacturer extracorporeal circuit designs

Neurologic impairment is a common complication of adult cardiac surgery. Cerebral gaseous microemboli (GME) detected during cardiopulmonary bypass has been associated with cognitive impairment after adult cardiac surgery. Several previous studies have shown that components comprising the extracorporeal circuit (ECC) can affect the ability of the ECC to eliminate air. The differences in the air separation ability of four manufacturer's commonly used ECCs were studied. The air-separating ability of Cobe Cardiovascular, Gish Biomedical, Medtronic, and Terumo Cardiovascular Systems Corp. ECCs were studied in vitro under clinically relevant conditions. Bolus and continuous venous air were introduced and output GME patterns by size, time, and count were measured (using an embolus detection device) and statistically analyzed. Graphic representations depicting elapsed time, GME size, and bubble count helped to visually rank the air-handling performance of the ECCs. There are significant air-handling differences between the ECCs tested. Overall, the blinded results reveal that ECC A and ECC C removed significantly (p < 0.001) more suspended GME than ECC B and ECC D. In the 50-mL venous room-air bolus and the 100 mL/min pulsed air challenges, ECC B and ECC D allowed significantly more GME to pass (p < 0.001) compared with ECC A and ECC C. For example, in a 2-hour pump run ECC C would deliver 480 potential high-intensity transient signals (HITS) compared with the 9600 from the ECC B during venous room air entrainment at 100 mL/min. There are substantial and significant air-handling differences between the ECCs from the four different manufacturers. The results from this work allow for objective characterization of ECCs air-separating ability. This additional information provides an opportunity for clinicians to potentially minimize the risks of arterial air embolization and its associated deleterious neurologic effects, while allowing clinicians to make better-informed consumer decisions.

Magnesium as a neuroprotectant in cardiac surgery: A randomized clinical trial

OBJECTIVE

We sought to evaluate magnesium as a neuroprotectant in patients undergoing cardiac surgery with cardiopulmonary bypass.

METHODS

From February 2002 to September 2003, 350 patients undergoing elective coronary artery bypass grafting, valve surgery, or both were enrolled in a randomized, blinded, placebo-controlled trial to receive either magnesium sulfate to increase plasma levels 1(1/2) to 2 times normal during cardiopulmonary bypass (n = 174) or no intervention (n = 176). Neurologic function, neuropsychologic function, and depression were assessed preoperatively, at 24 and 96 hours after extubation (neurologic) and at 3 months (neuropsychologic, depression). Neurologic scores were analyzed using ordinal longitudinal methods, and neuropsychologic and depression inventory data were summarized by principal component analysis, followed by linear regression analysis using component scores as response variables.

RESULTS

Seven (2%) patients had a postoperative stroke, 2 (1%) in the magnesium and 5 (3%) in the placebo group (P = .4). Neurologic score was worse postoperatively in both groups (P < .0001); however, magnesium group patients performed better than placebo group patients (P = .0001), who had prolonged declines in short-term memory and reemergence of primitive reflexes. Three-month neuropsychologic performance and depression inventory score were generally better than preoperatively, with few differences between groups (P > .6); however, older age (P = .0006), previous stroke (P = .003), and lower education level (P = .0007) were associated with worse performance.

CONCLUSIONS

Magnesium administration is safe and improves short-term postoperative neurologic function after cardiac surgery, particularly in preserving short-term memory and cortical control over brainstem functions. However, by 3 months, other factors and not administration of magnesium influence neuropsychologic and depression inventory performance.

Neurologic complications of cardiovascular surgery

With significant advances in surgical technology and methodology, mortality from congenital heart surgery has been significantly reduced in recent decades. Therefore, focus has naturally turned towards predicting, evaluating, and preventing the neurodevelopmental morbidity associated with congenital heart disease and its treatment. This paper reviews recent publications evaluating preoperative neurologic abnormalities and injuries, current neurodevelopmental outcomes of congenital heart repair, and various neuromonitoring modalities that can be used to monitor neurologic function/dysfunction perioperatively. The rapidly advancing field of clinical neuromonitoring holds the promise of providing modalities that can detect injurious processes acutely to allow for intervention.