Caudoputamen is damaged by hypocapnia during mechanical ventilation in a rat model of chronic cerebral hypoperfusion

Future directions in ventilator-induced lung injury associated cognitive impairment: a new sight

Mechanical ventilation is a widely used short-term life support technique, but an accompanying adverse consequence can be pulmonary damage which is called ventilator-induced lung injury (VILI). Mechanical ventilation can potentially affect the central nervous system and lead to long-term cognitive impairment. In recent years, many studies revealed that VILI, as a common lung injury, may be involved in the central pathogenesis of cognitive impairment by inducing hypoxia, inflammation, and changes in neural pathways. In addition, VILI has received attention in affecting the treatment of cognitive impairment and provides new insights into individualized therapy. The combination of lung protective ventilation and drug therapy can overcome the inevitable problems of poor prognosis from a new perspective. In this review, we summarized VILI and non-VILI factors as risk factors for cognitive impairment and concluded the latest mechanisms. Moreover, we retrospectively explored the role of improving VILI in cognitive impairment treatment. This work contributes to a better understanding of the pathogenesis of VILI-induced cognitive impairment and may provide future direction for the treatment and prognosis of cognitive impairment.

Vascular dementia: A microglia's perspective

Vascular dementia (VaD) is a second most common form of age-related dementia. It is characterized by cognitive impairment associated with vascular pathology, symptoms mainly caused by cerebral damage due to inadequate blood flow to the brain. The pathogenesis of VaD is complex, and a growing body of literature emphasizes on the involvement of microglia in disease development and progression. Here, we review the current knowledge on the role of microglia in regulating neuroinflammation under the pathogenesis of VaD. The commonly used animal and cell models for understanding the disease pathogenesis were summarized. The mechanisms by which microglia contribute to VaD are multifactorial, and we specifically focus on some of the predominant functions of microglia, including chemotaxis, secretory property, phagocytosis, and its crosstalk with other neurovascular unit cells. Finally, potential therapeutic strategies targeting microglia-modulated neuroinflammation are discussed.

Longitudinal Study of the Association between General Anesthesia and Increased Risk of Developing Dementia

The association between exposure to general anesthesia (GA) and the risk of dementia is still undetermined. To investigate a possible link to the development of dementia in older people who have undergone GA, we analyzed nationwide representative cohort sample data from the Korean National Health Insurance Service. The study cohort comprised patients over 55 years of age who had undergone GA between January 2003 and December 2004 and consisted of 3100 patients who had undergone GA and 12,400 comparison subjects who had not received anesthesia. After the nine-year follow-up period, we found the overall incidence of dementia was higher in the patients who had undergone GA than in the comparison group (10.5 vs. 8.8 per 1000 person-years), with the risk being greater for women (adjusted HR of 1.44; 95% CI, 1.19–1.75) and those with comorbidities (adjusted HR of 1.39; 95% CI, 1.18–1.64). Patients who underwent GA showed higher risks for Alzheimer’s disease and vascular dementia (adjusted HR of 1.52; 95% CI, 1.27–1.82 and 1.64; 95% CI, 1.15–2.33, respectively). This longitudinal study using a sample cohort based on a nationwide population sample demonstrated a significant positive association between GA and dementia, including Alzheimer’s disease and vascular dementia.

Angelica sinensis extract promotes neuronal survival by enhancing p38 MAPK-mediated hippocampal neurogenesis and dendritic growth in the chronic phase of transient global cerebral ischemia in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Angelica sinensis (Oliv.) Diels (ASD), commonly known as Dang Gui, is a popular Chinese herb that has long been used to treat ischemic stroke. However, the effects of ASD in chronic cerebral ischemia and its underlying mechanisms still remain unclear.

AIM OF THE STUDY

This study aimed to determine the effects of the ASD extract on hippocampal neuronal survival at 28 d after transient global cerebral ischemia (GCI) and to investigate the precise mechanisms underlying the p38 mitogen-activated protein kinase (MAPK)-related signaling pathway's involvement in hippocampal neurogenesis.

MATERIALS AND METHODS

Rats underwent 25 min of four-vessel occlusion. The ASD extract was intragastrically administered at doses of 0.25 g/kg (ASD-0.25 g), 0.5 g/kg (ASD-0.5 g), 1 g/kg (ASD-1 g), 1 g/kg after dimethyl sulfoxide administration (D + ASD-1 g), or 1 g/kg after SB203580 (a p38 MAPK inhibitor) administration (SB + ASD-1 g) at 1, 3, 7, 10, 14, 17, 21, and 24 d after transient GCI.

RESULTS

ASD-0.5 g, ASD-1 g, and D + ASD-1 g treatments had the following effects: upregulation of bromodeoxyuridine (BrdU) and Ki67 expression, and BrdU/neuronal nuclei (NeuN) and Ki67/nestin co-expression in the hippocampal dentate gyrus (DG); upregulation of microtubule-associated protein 2/NeuN co-expression, and NeuN and glial fibrillary acidic protein (GFAP) expression, and downregulation of tumor necrosis factor-α/GFAP co-expression in the hippocampal CA1 region; upregulation of phospho-p38 MAPK (p-p38 MAPK), phospho-cAMP response element-binding protein (p-CREB), brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), and vascular endothelial growth factor A (VEGF-A) expression in the hippocampus. SB + ASD-1 g treatment abrogated the effects of ASD-1 g on the expression of these proteins.

CONCLUSIONS

ASD-0.5 g and ASD-1 g treatments promotes neuronal survival by enhancing hippocampal neurogenesis. The effects of the ASD extract on astrocyte-associated hippocampal neurogenesis and dendritic growth are caused by the activation of p38 MAPK-mediated CREB/BDNF, GDNF, and VEGF-A signaling pathways in the hippocampus at 28 d after transient GCI.

Persistent isoflurane-induced hypotension causes hippocampal neuronal damage in a rat model of chronic cerebral hypoperfusion

BACKGROUND

Postoperative cognitive dysfunction (POCD) is likely to occur in elderly people, who often suffer from cerebral hypoperfusion and white matter lesions even in the absence of cerebral infarctions.

METHODS

Thirty-two adult male rats were randomly assigned to one of four groups: the cerebral normoperfusion + normotension group (n = 8), cerebral normoperfusion + hypotension group (n = 8), chronic cerebral hypoperfusion (CCH) + normotension group (n = 8), and CCH + hypotension group (n = 8). A rat model of CCH was developed via the permanent ligation of the bilateral common carotid arteries, but ligation was avoided in the cerebral normoperfusion groups. Two weeks later, the rats were intubated and mechanically ventilated under isoflurane anesthesia, and their mean arterial blood pressure was maintained over 80 mmHg (normotension) or below 60 mmHg (hypotension) for 2 h. After preparing brain slices, histological cresyl violet staining, ionized calcium binding adaptor molecule 1, a marker of microglial activation, or β amyloid precursor protein, a marker of axonal damage, were performed.

RESULTS AND CONCLUSION

CCH per se caused microglial activation and axonal damage, which was not accentuated by hypotension. CCH alone did not cause neuronal damage, but CCH combined with hypotension caused significant neuronal damage in the hippocampal CA1 region. These results suggest that persistent hypotension during general anesthesia might cause neuronal damage in patients with CCH, such as elderly people, and contribute to prevention against POCD.

To Tube or Not to Tube? The Role of Intubation during Stroke Thrombectomy

In the 10 years since the FDA first cleared the use of endovascular devices for the treatment of acute stroke, definitive evidence that such therapy improves outcomes remains lacking. The decision to intubate patients undergoing stroke thrombectomy impacts multiple variables that may influence outcomes after stroke. Three main areas where intubation may deleteriously affect acute stroke management include the introduction of delays in revascularization, fluctuations in peri-procedural blood pressure, and hypocapnia, resulting in cerebral vasoconstriction. In this mini-review, we discuss the evidence supporting these limitations of intubation during stroke thrombectomy and encourage neurohospitalists, neurocritical care specialists, and neurointerventionalists to carefully consider the decision to intubate during thrombectomy and provide strategies to avoid potential complications associated with its use in acute stroke.

Factors causing acute delirium in critically ill adult patients: a systematic review

BACKGROUND

Delirium, also known as acute confusional state, is a clinical syndrome that is typified by a disturbance of consciousness, attention, cognition and perception. It is estimated that the incidence of delirium varies between 28.3% to 80% in intensive care patients. Delirium is most likely to affect older patients above the age of 65 years.

OBJECTIVES

The primary focus of this systematic review was to synthesise the best available evidence to identify the factors which are associated with acute delirium in critically ill adult patients.

SEARCH STRATEGY

A three-step search strategy was utilised in this review. An initial limited search of MEDLINE and CINAHL was undertaken. A search strategy was then developed using identified keywords and MeSH headings. Lastly, the reference lists of all identified studies were examined. All searches were limited to English language studies published between 1990 and 2010.

INCLUSION CRITERIA

The participants of this review were adult patients in a critical care setting who present with acute delirium in the intensive care unit.The review considered studies which examine the factors causing delirium in critically ill adult patients, such as fever, hypoxia and sepsis.This review considered studies that included the incidence of acute delirium as related to the individual factors as an outcome measure.This review considered any high quality quantitative papers that addressed factors causing acute delirium in intensive care unit patients. This review included data from cohort and case control studies.

ASSESSMENT OF METHODOLOGICAL QUALITY

The Joanna Briggs Institute Critical Appraisal Checklist for Cohort / Case Control Studies was used to assess methodological quality.

DATA EXTRACTION/SYNTHESIS

Data were extracted using a standardised Data Extraction Tool from the Joanna Briggs Institute. Due to the heterogeneous nature of the study methods, the findings of this systematic review are presented in a narrative summary.

MAIN RESULTS

Twenty-four papers were included in this review. Some factors were common; however certain factors were exclusive to the type of setting. With regards to pharmacological factors, benzodiazepines were the most likely medications to be associated with delirium as compared to other drugs used in the intensive care unit. With regards to biomarkers, a variety were implicated in causing delirium, such as apolipoprotein 4 genotype, plasma tryptophan, interleukin-6, cortisol and C-reactive protein. Older age was also found to be a common risk factor.

CONCLUSION

With regards to the medical and surgical intensive care units, relatively similar risk factors of older age and co-morbidity are significant. In the cardiac intensive care unit, a variety of risk factors were significant. Benzodiazepines have been singled out as the most likely drug to cause delirium. The biomarkers cortisol and hypoalbuminemia were also shown to be significant risk factors of delirium.

IMPLICATIONS FOR RESEARCH

Future research should use increased sample sizes, recruited from more than one hospital, assessing diverse factors. Future studies could examine the effects of specific biomarkers on delirium.

IMPLICATIONS FOR PRACTICE

By creating a regression model for delirium prediction, clinicians may be able to create a checklist to identify patients at risk of developing delirium. This checklist could assist in monitoring patients at higher risk for developing delirium, allowing measures to be implemented for preventing the incidence or reducing the severity of delirium. The use of benzodiazepines should also be avoided if possible, as they are seen to have a significant association with the incidence of delirium.

Edaravone, a free radical scavenger, mitigates both gray and white matter damages after global cerebral ischemia in rats

Recent studies have shown that similar to cerebral gray matter (mainly composed of neuronal perikarya), white matter (composed of axons and glias) is vulnerable to ischemia. Edaravone, a free radical scavenger, has neuroprotective effects against focal cerebral ischemia even in humans. In this study, we investigated the time course and the severity of both gray and white matter damage following global cerebral ischemia by cardiac arrest, and examined whether edaravone protected the gray and the white matter. Male Sprague-Dawley rats were used. Global cerebral ischemia was induced by 5 min of cardiac arrest and resuscitation (CAR). Edaravone, 3 mg/kg, was administered intravenously either immediately or 60 min after CAR. The morphological damage was assessed by cresyl violet staining. The microtubule-associated protein 2 (a maker of neuronal perikarya and dendrites), the beta amyloid precursor protein (the accumulation of which is a maker of axonal damage), and the ionized calcium binding adaptor molecule 1 (a marker of microglia) were stained for immunohistochemical analysis. Significant neuronal perikaryal damage and marked microglial activation were observed in the hippocampal CA1 region with little axonal damage one week after CAR. Two weeks after CAR, the perikaryal damage and microglial activation were unchanged, but obvious axonal damage occurred. Administration of edaravone 60 min after CAR significantly mitigated the perikaryal damage, the axonal damage, and the microglial activation. Our results show that axonal damage develops slower than perikaryal damage and that edaravone can protect both gray and white matter after CAR in rats.

Permissive hypercapnia to decrease lung injury in ventilated preterm neonates

Lung injury in ventilated premature infants occurs primarily through the mechanism of volutrauma, often due to the combination of high tidal volumes in association with a high end-inspiratory volume and occasionally end-expiratory alveolar collapse. Tolerating a higher level of arterial partial pressure of carbon dioxide (PaCO2) is considered as 'permissive hypercapnia' and when combined with the use of low tidal volumes may reduce volutrauma and lead to improved pulmonary outcomes. Permissive hypercapnia may also protect against hypocapnia-induced brain hypoperfusion and subsequent periventricular leukomalacia. However, extreme hypercapnia may be associated with an increased risk of intracranial hemorrhage. It may therefore be important to avoid large fluctuations in PaCO2 values. Recent randomized clinical trials in preterm infants have demonstrated that mild permissive hypercapnia is safe, but clinical benefits are modest. The optimal PaCO2 goal in clinical practice has not been determined, and the available evidence does not currently support a general recommendation for permissive hypercapnia in preterm infants.

Pathoetiological model of delirium: a comprehensive understanding of the neurobiology of delirium and an evidence-based approach to prevention and treatment

Delirium is the most common complication found in the general hospital setting. Yet, we know relatively little about its actual pathophysiology. This article contains a summary of what we know to date and how different proposed intrinsic and external factors may work together or by themselves to elicit the cascade of neurochemical events that leads to the development delirium. Given how devastating delirium can be, it is imperative that we better understand the causes and underlying pathophysiology. Elaborating a pathoetiology-based cohesive model to better grasp the basic mechanisms that mediate this syndrome will serve clinicians well in aspiring to find ways to correct these cascades, instituting rational treatment modalities, and developing effective preventive techniques.

Delirium in the acute care setting: characteristics, diagnosis and treatment

Delirium is a neurobehavioral syndrome caused by the transient disruption of normal neuronal activity secondary to systemic disturbances. It is also the most common psychiatric syndrome found in the general hospital setting, its prevalence surpassing better known psychiatric disorders. This article reviews the published literature on delirium and addresses the epidemiology, known etiologic factors, presentation and characteristics of delirium, while emphasizing what is known about treatment strategies and prevention. Given increasing evidence that delirium is not always reversible and the many sequelae associated with its development, physicians must do everything possible to prevent its occurrence or shorten its duration, by recognizing its symptoms early, correcting underlying contributing causes, and using treatment strategies proven to help recover functional status.

Measurement of optic nerve blood flow during dissection of parasellar tumors

The authors describe direct measurement of optic nerve blood flow (ONBF) and examine the application of such monitoring to detecting optic nerve ischemia during parasellar tumor surgery. Prospective evaluation was performed for 26 patients requiring surgery for parasellar tumors. Ophthalmologic examination was performed pre- and postoperatively. ONBF was measured using laser Doppler flowmetry before tumor dissection (initial ONBF) and after tumor removal (final ONBF). The waveform was analyzed using a data acquisition system. Initial ONBF could be measured in 16 patients (22 nerves; 8.9 +/- 0.9 ml/100 g/min). Final ONBF could be determined in all 26 patients (42 nerves; 10.8 +/- 0.7 ml/100 g/min). In the 22 nerves with initial measurements, final ONBF (11.3 +/- 0.6 ml/100 g/min) was significantly increased (p < 0.01). In six patients whose optic canal was unroofed, ONBF did not change immediately; nonetheless, an increase was prominent in the final phase (p < 0.05). In another six patients, a small vessel adjacent to the optic nerve was temporarily occluded. ONBF was demonstrably reduced in three patients and recovered quickly after reperfusion. Intraoperative ONBF measurement may be useful as real-time monitoring for prediction and prevention of intraoperative optic nerve ischemia.

Alzheimer's disease and anaesthesia: implications for the central cholinergic system

Alzheimer's disease (AD) is associated with a loss of cholinergic neurons resulting in profound memory disturbances and irreversible impairment of cognitive function. The central cholinergic system is involved in the action of general anaesthetic agents. Anaesthetic modulation of cholinergic transmission has profound effects on brain function via a cascade of synaptic and postsynaptic events by binding both nicotinic and muscarinic receptors. During general anaesthesia, decrease in acetylcholine release and depression of cholinergic transmission facilitates the desirable effects of general anaesthetics, such as loss of consciousness, pain, voluntary movements and memory. From this point of view, patients with AD, characterized by a compromised neuronal transmission, represent particular cases in which the choice of anaesthesia drugs may have a negative effect on the postoperative outcome. A future challenge may be the identification of brain targets of general anaesthetics which do not expose patients to postoperative cognitive dysfunction, nor interfere with prognosis of brain degenerative disease.

Astrocytes react to oligemia in the forebrain induced by chronic bilateral common carotid artery occlusion in rats

The effects of oligemia (moderate ischemia) on the brain need to be explored because of the potential role of subtle microvascular changes in vascular cognitive impairment and dementia. Chronic bilateral common carotid artery occlusion (BCCAO) in adult rats has been used to study effects of oligemia (hypoperfusion) using neuropathological and neurochemical analysis as well as behavioral tests. In this study, BCCAO was induced for 1 week, or 2, 4, and 6 months. Sensitive immunohistochemistry with marker proteins was used to study reactions of astrocytes (GFAP, nestin), and lectin binding to study microglial cells during BCCAO. Overt neuronal loss was visualized with NeuN antibodies. Astrocytes reacted to changes in the optic tract at all time points, and strong glial reactions also occurred in the target areas of retinal fibers, indicating damage to the retina and optic nerve. Astrocytes indicated a change in the corpus callosum from early to late time points. Diffuse increases in GFAP labeling occurred in parts of the neocortex after 1 week of BCCAO, in the absence of focal changes of neuronal marker proteins. No significant differences emerged in the cortex at longer time points. Nestin labeling was elevated in the optic tract. Reactions of microglia cells were seen in the cortex after 1 week. Measurements of the basilar artery indicated a considerable hypertrophy, indicative of macrovascular compensation in the chronic occlusion model. These results indicate that chronic BCCAO and, by inference, oligemia have a transient effect on the neocortex and a long-lasting effect on white matter structures.

Anaesthesia in patients with dementia

PURPOSE OF REVIEW

The next couple of decades will be characterized by an increase in life expectancy, leading to an older population. As the incidence of Alzheimer's dementia and vascular dementia is rising with age, the future anaesthesiologist will be increasingly confronted with perioperative care of patients with impaired cognitive function. This paper tries to highlight some topics specifically related to demented patients.

RECENT FINDINGS

Psychometric testing and behaviour vary according to the type of dementia. Neuroanatomical and biochemical correlates for different types of dementia are more precise and better documented. Evidence exists that cognition may be impaired for weeks after anaesthesia, but the mental capacities of those who have undergone surgery are comparable to those of age controls in the long term. Most research efforts are focused on improving the daily functioning of people with cognitive impairment. Several new anticholinesterases are being evaluated. It is advantageous to keep cognition optimal throughout the perioperative period. Neuroleptics may be badly tolerated and, most importantly, pain pathways may be differentially affected in dementia.

SUMMARY

Anaesthesia in the demented patient may be complicated by a number of potential problems, including the comorbid pathology, the concomitant anticholinesterase activity, the need for normoventilation, monitoring of anaesthesia depth and the evaluation of postoperative pain. Anaesthesia in variant Creutzfeldt-Jakob disease is aimed at preventing the spread of the causing prion. There is a broad consensus that early return to the preoperative level of cognition is to be pursued, with the help of short-acting drugs and loco-regional anaesthesia.

Ketamine attenuates hypocapnia-induced neuronal damage in the caudoputamen in a rat model of chronic cerebral hypoperfusion

We previously demonstrated that the caudoputamen was exclusively further damaged by hypocapnia in a rat with chronic cerebral hypoperfusion which is characterized by white matter lesions (WML) and a well-established model for patients with cerebrovascular diseases and/or dementia, and suggest that this process may be the cause of long lasting postoperative delirium or brain dysfunction in such patients. In the present study, we investigated whether ketamine, a non-competitive N-methyl-D-aspartate receptor antagonist, could attenuate the neuronal damage in the caudoputamen. Ketamine, at doses of 10 and 20 mg/kg, which was given intraperitoneally before hypocapnia induction, attenuated the aggravation of WML score, neuronal damage, and astroglial proliferation in the rat caudoputamen. These results suggest that ketamine may be beneficial for preventing postoperative brain dysfunction, especially in patients with cerebrovascular diseases and/or dementia induced by hypocapnia, which is likely to occur in the mechanical ventilation used during surgery.

Inhibitory effect of propofol on ketamine-induced c-Fos expression in the rat posterior cingulate and retrosplenial cortices is mediated by GABAA receptor activation

BACKGROUND

Non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists, including ketamine, have psychotomimetic activities and cause neuronal damage in the posterior cingulate and retrosplenial cortices (PC/RS), which are suggested to be the brain regions responsible for their psychotomimetic activities. We previously demonstrated that ketamine induced marked c-Fos (c-fos protein) expression in the rat PC/RS, which was inhibited by propofol, and the expression was closely related to ketamine-induced abnormal behavior. In the present study, we investigated whether the inhibition by propofol was mediated by GABAA receptor receptor activation.

METHODS

Using Wistar rats, propofol alone, propofol with bicuculline or propofol with flumazenil was injected intravenously and then continuously infused. Fifteen minutes later, 100 mg kg-1 of ketamine or normal saline was injected intraperitoneally. Two hours after the ketamine or saline injection, the brain was extracted and brain sections were prepared, and c-Fos expression was detected using immunohistochemical methods.

RESULTS

Ketamine induced marked c-Fos expression in the PC/RS (171 +/- 9/0.4 mm2), which was significantly inhibited by propofol (5 +/- 5/0.4 mm2). The inhibition by propofol was disinhibited dose-dependently by both bicuculline (0.5 and 1.0 mg kg-1 bicuculline groups: 46 +/- 15 and 143 +/- 16, respectively) and flumazenil (0.1 and 1.0 mg kg-1 flumazenil groups: 79 +/- 6 and 130 +/- 15, respectively).

CONCLUSION

These results demonstrate that the inhibitory effect of propofol on ketamine-induced c-Fos expression in the PC/RS is mediated by GABAA receptor activation, and suggests that ketamine-induced psychoneuronal adverse effects may be suppressed by propofol via the activation of GABAA receptors.

Permissive hypercapnia

Although lifesaving, mechanical ventilation can result in lung injury and contribute to the development of bronchopulmonary dysplasia. The most critical determinants of lung injury are tidal volume and end-inspiratory lung volume. Permissive hypercapnia offers to maintain gas exchange with lower tidal volumes and thus decrease lung injury. Further physiologic benefits include improved oxygen delivery and neuroprotection, the latter through both avoidance of accidental hypocapnia, which is associated with a poor neurologic outcome, and direct cellular effects. Clinical trials in adults with acute respiratory failure indicated improved survival and reduced incidence of organ failure in subjects managed with low tidal volumes and permissive hypercapnia. Retrospective studies in low birth weight infants found an association of bronchopulmonary dysplasia with low PaCO(2). Randomized clinical trials of low birth weight infants did not achieve sufficient statistical power to demonstrate a reduction of BPD by permissive hypercapnia, but strong trends indicated the possibility of important benefits without increased adverse events. Herein, we review the mechanisms leading to lung injury, the physiologic effects of hypercapnia, the dangers of hypocapnia, and the available clinical data.