Incidence and mechanisms of cerebral ischemia in early clinical head injury

Brain energy metabolism: A roadmap for future research

Although we have learned much about how the brain fuels its functions over the last decades, there remains much still to discover in an organ that is so complex. This article lays out major gaps in our knowledge of interrelationships between brain metabolism and brain function, including biochemical, cellular, and subcellular aspects of functional metabolism and its imaging in adult brain, as well as during development, aging, and disease. The focus is on unknowns in metabolism of major brain substrates and associated transporters, the roles of insulin and of lipid droplets, the emerging role of metabolism in microglia, mysteries about the major brain cofactor and signaling molecule NAD+, as well as unsolved problems underlying brain metabolism in pathologies such as traumatic brain injury, epilepsy, and metabolic downregulation during hibernation. It describes our current level of understanding of these facets of brain energy metabolism as well as a roadmap for future research.

The longitudinal biochemical profiling of TBI in a drop weight model of TBI

Traumatic brain injury (TBI) is a major cause of mortality and disability worldwide, particularly among individuals under the age of 45. It is a complex, and heterogeneous disease with a multifaceted pathophysiology that remains to be elucidated. Metabolomics has the potential to identify metabolic pathways and unique biochemical profiles associated with TBI. Herein, we employed a longitudinal metabolomics approach to study TBI in a weight drop mouse model to reveal metabolic changes associated with TBI pathogenesis, severity, and secondary injury. Using proton nuclear magnetic resonance (1H NMR) spectroscopy, we biochemically profiled post-mortem brain from mice that suffered mild TBI (N = 25; 13 male and 12 female), severe TBI (N = 24; 11 male and 13 female) and sham controls (N = 16; 11 male and 5 female) at baseline, day 1 and day 7 following the injury. 1H NMR-based metabolomics, in combination with bioinformatic analyses, highlights a few significant metabolites associated with TBI severity and perturbed metabolism related to the injury. We report that the concentrations of taurine, creatinine, adenine, dimethylamine, histidine, N-Acetyl aspartate, and glucose 1-phosphate are all associated with TBI severity. Longitudinal metabolic observation of brain tissue revealed that mild TBI and severe TBI lead distinct metabolic profile changes. A multi-class model was able to classify the severity of injury as well as time after TBI with estimated 86% accuracy. Further, we identified a high degree of correlation between respective hemisphere metabolic profiles (r > 0.84, p < 0.05, Pearson correlation). This study highlights the metabolic changes associated with underlying TBI severity and secondary injury. While comprehensive, future studies should investigate whether: (a) the biochemical pathways highlighted here are recapitulated in the brain of TBI sufferers and (b) if the panel of biomarkers are also as effective in less invasively harvested biomatrices, for objective and rapid identification of TBI severity and prognosis.

Clinical factors associated with delayed emergency department visit in intracranial traumatic brain injury: from a multicenter injury surveillance registry

INTRODUCTION

Early diagnosis and intervention by visiting the emergency department (ED) are important for traumatic brain injury (TBI). We evaluate the factors associated with delayed ED visits in patients with intracranial TBI.

METHODS

A retrospective multicenter observational study using the ED-based injury in-depth surveillance database (EDIIS) was designed. Patients with intracranial TBI with an alert mentality at ED presentation from 2014 to 2019 were enrolled. Patients were categorized into four groups according to ED visit time after injury (<1 h, 1-3 h, 3-12 h, and >12 h). ED visits after 12 h were defined as delayed ED visits. The factors associated with delayed ED visits were identified using multivariable logistic regression analysis.

RESULTS

Among 15,620 patients with TBI enrolled in the final analysis, 2,190 (14.0%) visited the ED 12 h after injury. Multivariable analysis identified the following factors as independent predictors for delayed ED visit such as unintentionally struck by or against an object or unintentional fall as a trauma mechanism, injury during ordinary activities, indoor injury, injury during nighttime, winter season, combined subdural hemorrhage and epidural hemorrhage.

CONCLUSION

In patients with intracranial TBI with an alert mentality, multiple factors related to patient demographics and injury characteristics were associated with the time interval from injury to ED visit.

The Impact of General Anesthesia on Redox Stability and Epigenetic Inflammation Pathways: Crosstalk on Perioperative Antioxidant Therapy

Worldwide, the prevalence of surgery under general anesthesia has significantly increased, both because of modern anesthetic and pain-control techniques and because of better diagnosis and the increased complexity of surgical techniques. Apart from developing new concepts in the surgical field, researchers and clinicians are now working on minimizing the impact of surgical trauma and offering minimal invasive procedures due to the recent discoveries in the field of cellular and molecular mechanisms that have revealed a systemic inflammatory and pro-oxidative impact not only in the perioperative period but also in the long term, contributing to more difficult recovery, increased morbidity and mortality, and a negative financial impact. Detailed molecular and cellular analysis has shown an overproduction of inflammatory and pro-oxidative species, responsible for augmenting the systemic inflammatory status and making postoperative recovery more difficult. Moreover, there are a series of changes in certain epigenetic structures, the most important being the microRNAs. This review describes the most important molecular and cellular mechanisms that impact the surgical patient undergoing general anesthesia, and it presents a series of antioxidant therapies that can reduce systemic inflammation.

Knockdown of rno_circRNA_009194 Improves Outcomes in Traumatic Brain Injury Rats through Inhibiting Voltage-Gated Sodium Channel Nav1.3

Excessive activation of voltage-gated sodium channel Nav1.3 has been recently reported in secondary traumatic brain injury (TBI). However, the molecular mechanisms underlying regulating voltage-gated sodium channel (Nav1.3) have not been well understood. The present study used a TBI rat model induced by a fluid percussion device and performed a circular RNA (circRNA) microarray (n = 3) to profile the altered circRNAs in the hippocampus after TBI. After polymerase chain reaction (PCR) validation, certain circRNAs were selected to investigate the function and mechanism in regulating Nav1.3 in the TBI rat model by intracerebroventricular injection with lentivirus. The neurological outcome was evaluated by Morris water maze test, modified Neurological Severity Score (mNSS), brain water content measurement, and hematoxylin and eosin staining. The related molecular mechanisms were explored with PCR, Western blotting, luciferase reporter, chromatin immunoprecipitation assay, and electrophoretic mobility shift assay (EMSA). A total of 347 circRNAs were observed to be differentially expressed (fold change [FC] ≥ 1.2 and p < 0.05) after TBI, including 234 up-regulated and 113 down-regulated circRNAs. Among 10 validated circRNAs, we selected circRNA_009194 with the maximized up-regulated fold change (n = 5, FC = 4.45, p < 0.001) for the in vivo functional experiments. Down-regulation of circRNA_009194 resulted in a 27.5% reduced mNSS in rat brain (n = 6, p < 0.01) after TBI and regulated the expression levels of miR-145-3p, Sp1, and Nav1.3, which was reversed by sh-miR-145-3p or Sp1/Nav1.3 overexpression (n = 5, p < 0.05). Mechanistically, circRNA_009194 might act as a sponge for miR-145-3p to regulate Sp1-mediated Nav1.3. This study demonstrated that circRNA_009194 knockdown could improve neurological outcomes in TBI in vivo by inhibiting Nav1.3, directly or indirectly.

Metabolic derangements are associated with impaired glucose delivery following traumatic brain injury

Metabolic derangements following traumatic brain injury are poorly characterized. In this single-centre observational cohort study we combined 18F-FDG and multi-tracer oxygen-15 PET to comprehensively characterize the extent and spatial pattern of metabolic derangements. Twenty-six patients requiring sedation and ventilation with intracranial pressure monitoring following head injury within a Neurosciences Critical Care Unit, and 47 healthy volunteers were recruited. Eighteen volunteers were excluded for age over 60 years (n = 11), movement-related artefact (n = 3) or physiological instability during imaging (n = 4). We measured cerebral blood flow, blood volume, oxygen extraction fraction, and 18F-FDG transport into the brain (K1) and its phosphorylation (k3). We calculated oxygen metabolism, 18F-FDG influx rate constant (Ki), glucose metabolism and the oxygen/glucose metabolic ratio. Lesion core, penumbra and peri-penumbra, and normal-appearing brain, ischaemic brain volume and k3 hotspot regions were compared with plasma and microdialysis glucose in patients. Twenty-six head injury patients, median age 40 years (22 male, four female) underwent 34 combined 18F-FDG and oxygen-15 PET at early, intermediate, and late time points (within 24 h, Days 2-5, and Days 6-12 post-injury; n = 12, 8, and 14, respectively), and were compared with 20 volunteers, median age 43 years (15 male, five female) who underwent oxygen-15, and nine volunteers, median age 56 years (three male, six female) who underwent 18F-FDG PET. Higher plasma glucose was associated with higher microdialysate glucose. Blood flow and K1 were decreased in the vicinity of lesions, and closely related when blood flow was <25 ml/100 ml/min. Within normal-appearing brain, K1 was maintained despite lower blood flow than volunteers. Glucose utilization was globally reduced in comparison with volunteers (P < 0.001). k3 was variable; highest within lesions with some patients showing increases with blood flow <25 ml/100 ml/min, but falling steeply with blood flow lower than 12 ml/100 ml/min. k3 hotspots were found distant from lesions, with k3 increases associated with lower plasma glucose (Rho -0.33, P < 0.001) and microdialysis glucose (Rho -0.73, P = 0.02). k3 hotspots showed similar K1 and glucose metabolism to volunteers despite lower blood flow and oxygen metabolism (P < 0.001, both comparisons); oxygen extraction fraction increases consistent with ischaemia were uncommon. We show that glucose delivery was dependent on plasma glucose and cerebral blood flow. Overall glucose utilization was low, but regional increases were associated with reductions in glucose availability, blood flow and oxygen metabolism in the absence of ischaemia. Clinical management should optimize blood flow and glucose delivery and could explore the use of alternative energy substrates.

Emerging Trends in the Use of Therapeutic Hypothermia as a Method for Neuroprotection in Brain Damage (Review)

The review analyzes current clinical studies on the use of therapeutic hypothermia as a neuroprotective method for treatment of brain damage. This method yields good outcomes in patients with acute brain injuries and chronic critical conditions. There has been shown the interest of researchers in studying the preventive potential of therapeutic hypothermia in secondary neuronal damage. There has been described participation of new molecules producing positive effect on tissues and cells of the central nervous system - proteins and hormones of cold stress - in the mechanisms of neuroprotection in the brain. The prospects of using targeted temperature management in treatment of brain damage are considered.

Sports Related Brain Injury and Neurodegeneration in Athletes

Sports deserve a special place in human life to impart healthy and refreshing wellbeing. However, sports activities, especially contact sports, renders athlete vulnerable to brain injuries. Athletes participating in a contact sport like boxing, rugby, American football, wrestling, and basketball are exposed to traumatic brain injuries (TBI) or concussions. The acute and chronic nature of these heterogeneous injuries provides a spectrum of dysfunctions that alters the neuronal, musculoskeletal, and behavioral responses of an athlete. Many sports-related brain injuries go unreported, but these head impacts trigger neurometabolic disruptions that contribute to long-term neuronal impairment. The pathophysiology of post-concussion and its underlying mechanisms are undergoing intense research. It also shed light on chronic disorders like Parkinson's disease, Alzheimer's disease, and dementia. In this review, we examined post-concussion neurobehavioral changes, tools for early detection of signs, and their impact on the athlete. Further, we discussed the role of nutritional supplements in ameliorating neuropsychiatric diseases in athletes.

Association of Ventilation during Initial Trauma Resuscitation for Traumatic Brain Injury and Post-Traumatic Outcomes: A Systematic Review

OBJECTIVES

In the absence of evidence of acute cerebral herniation, normal ventilation is recommended for patients with traumatic brain injury (TBI). Despite this recommendation, ventilation strategies vary during the initial management of patients with TBI and may impact outcome. The goal of this systematic review was to define the best evidence-based practice of ventilation management during the initial resuscitation period.

METHODS

A literature search of PubMed, CINAHL, and SCOPUS identified studies from 2009 through 2019 addressing the effects of ventilation during the initial post-trauma resuscitation on patient outcomes.

RESULTS

The initial search yielded 899 articles, from which 13 were relevant and selected for full-text review. Six of the 13 articles met the inclusion criteria, all of which reported on patients with TBI. Either end-tidal carbon dioxide (ETCO2) or partial pressure carbon dioxide (PCO2) were the independent variables associated with mortality. Decreased rates of mortality were reported in patients with normal PCO2 or ETCO2.

CONCLUSIONS

Normoventilation, as measured by ETCO2 or PCO2, is associated with decreased mortality in patients with TBI. Preventing hyperventilation or hypoventilation in patients with TBI during the early resuscitation phase could improve outcome after TBI.

Acid-Ion Sensing Channel 1a Deletion Reduces Chronic Brain Damage and Neurological Deficits after Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) causes long-lasting neurodegeneration and cognitive impairments; however, the underlying mechanisms of these processes are not fully understood. Acid-sensing ion channels 1a (ASIC1a) are voltage-gated Na⁺- and Ca²⁺-channels shown to be involved in neuronal cell death; however, their role for chronic post-traumatic brain damage is largely unknown. To address this issue, we used ASIC1a-deficient mice and investigated their outcome up to 6 months after TBI. ASIC1a-deficient mice and their wild-type (WT) littermates were subjected to controlled cortical impact (CCI) or sham surgery. Brain water content was analyzed 24 h and behavioral outcome up to 6 months after CCI. Lesion volume was assessed longitudinally by magnetic resonance imaging and 6 months after injury by histology. Brain water content was significantly reduced in ASIC1a^-/- animals compared to WT controls. Over time, ASIC1a^-/- mice showed significantly reduced lesion volume and reduced hippocampal damage. This translated into improved cognitive function and reduced depression-like behavior. Microglial activation was significantly reduced in ASIC1a^-/- mice. In conclusion, ASIC1a deficiency resulted in reduced edema formation acutely after TBI and less brain damage, functional impairments, and neuroinflammation up to 6 months after injury. Hence, ASIC1a seems to be involved in chronic neurodegeneration after TBI.

Compromised resting cerebral metabolism after sport-related concussion: A calibrated MRI study

Altered resting cerebral blood flow (CBF₀) in the acute phase post-concussion may contribute to neurobehavioral deficiencies, often reported weeks after the injury. However, in addition to changes in CBF₀, little is known about other physiological mechanisms that may be disturbed within the cerebrovasculature. The aim of this study was to assess whether changes in baseline perfusion following sport-related concussion (SRC) were co-localized with changes in cerebral metabolic demand. Forty-two subjects (15 SRC patients 8.0 ± 4.6 days post-injury and 27 age-matched healthy control athletes) were studied cross-sectionally. CBF₀, cerebrovascular reactivity (CVR), resting oxygen extraction (OEF₀) and cerebral metabolic rate of oxygen consumption (CMRO_2|0) were measured using a combination of hypercapnic and hyperoxic breathing protocols, and the biophysical model developed in calibrated MRI. Blood oxygenation level dependent and perfusion data were acquired simultaneously using a dual-echo arterial spin labelling sequence. SRC patients showed significant decreases in CBF₀ spread across the grey-matter (P < 0.05, corrected), and these differences were also confounded by the effects of baseline end-tidal CO₂ (P < 0.0001). Lower perfusion was co-localized with reductions in regional CMRO_2|0 (P = 0.006) post-SRC, despite finding no group-differences in OEF₀ (P = 0.800). Higher CVR within voxels showing differences in CBF was also observed in the SRC group (P = 0.001), compared to controls. Reductions in metabolic demand despite no significant changes in OEF₀ suggests that hypoperfusion post-SRC may reflect compromised metabolic function after the injury. These results provide novel insight about the possible pathophysiological mechanisms underlying concussion that may affect the clinical recovery of athletes after sport-related head injuries.

Spatial and Temporal Pattern of Ischemia and Abnormal Vascular Function Following Traumatic Brain Injury

Question

How does ¹⁵oxygen positron emission tomography characterization of cerebral physiology after traumatic brain injury inform clinical practice?

Findings

In this single-center observational cohort study of 68 patients and 27 control participants, early ischemia was common in patients, but hyperemia coexisted in different brain regions. Cerebral blood volume was consistently increased, despite low cerebral blood flow.

Meaning

Per this analysis, pathophysiologic heterogeneity indicates that bedside physiological monitoring with devices that measure global (jugular venous saturation) or focal (tissue oximetry) brain oxygenation should be interpreted with caution.

Importance

Ischemia is an important pathophysiological mechanism after traumatic brain injury (TBI), but its incidence and spatiotemporal patterns are poorly characterized.

Objective

To comprehensively characterize the spatiotemporal changes in cerebral physiology after TBI.

Design, Setting, and Participants

This single-center cohort study uses ¹⁵oxygen positron emission tomography data obtained in a neurosciences critical care unit from February 1998 through July 2014 and analyzed from April 2018 through August 2019. Patients with TBI requiring intracranial pressure monitoring and control participants were recruited.

Exposures

Cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral oxygen metabolism (CMRO₂), and oxygen extraction fraction.

Main Outcomes and Measures

Ratios (CBF/CMRO₂ and CBF/CBV) were calculated. Ischemic brain volume was compared with jugular venous saturation and brain tissue oximetry.

Results

A total of 68 patients with TBI and 27 control participants were recruited. Results from 1 patient with TBI and 7 health volunteers were excluded. Sixty-eight patients with TBI (13 female [19%]; median [interquartile range (IQR)] age, 29 [22-47] years) underwent 90 studies at early (day 1 [n = 17]), intermediate (days 2-5 [n = 54]), and late points (days 6-10 [n = 19]) and were compared with 20 control participants (5 female [25%]; median [IQR] age, 43 [31-47] years). The global CBF and CMRO₂ findings for patients with TBI were less than the ranges for control participants at all stages (median [IQR]: CBF, 26 [22-30] mL/100 mL/min vs 38 [29-49] mL/100 mL/min; P < .001; CMRO₂, 62 [55-71] μmol/100 mL/min vs 131 [101-167] μmol/100 mL/min; P < .001). Early CBF reductions showed a trend of high oxygen extraction fraction (suggesting classical ischemia), but this was inconsistent at later phases. Ischemic brain volume was elevated even in the absence of intracranial hypertension and highest at less than 24 hours after TBI (median [IQR], 36 [10-82] mL), but many patients showed later increases (median [IQR] 6-10 days after TBI, 24 [4-42] mL; across all points: patients, 10 [5-39] mL vs control participants, 1 [0-3] mL; P < 001). Ischemic brain volume was a poor indicator of jugular venous saturation and brain tissue oximetry. Patients’ CBF/CMRO₂ ratio was higher than controls (median [IQR], 0.42 [0.35-0.49] vs 0.3 [0.28-0.33]; P < .001) and their CBF/CBV ratio lower (median [IQR], 7.1 [6.4-7.9] vs 12.3 [11.0-14.0]; P < .001), suggesting abnormal flow-metabolism coupling and vascular reactivity. Patients’ CBV was higher than controls (median [IQR], 3.7 [3.4-4.1] mL/100 mL vs 3.0 [2.7-3.6] mL/100 mL; P < .001); although values were lower in patients with intracranial hypertension, these were still greater than controls (median [IQR], 3.7 [3.2-4.0] vs 3.0 [2.7-3.6] mL/100 mL; P = .002), despite more profound reductions in partial pressure of carbon dioxide (median [IQR], 4.3 [4.1-4.6] kPa vs 4.7 [4.3-4.9] kPa; P = .001).

Conclusions and Relevance

Ischemia is common early, detectable up to 10 days after TBI, possible without intracranial hypertension, and inconsistently detected by jugular or brain tissue oximetry. There is substantial between-patient and within-patient pathophysiological heterogeneity; ischemia and hyperemia commonly coexist, possibly reflecting abnormalities in flow-metabolism coupling. Increased CBV may contribute to intracranial hypertension but can coexist with abnormal CBF/CBV ratios. These results emphasize the need to consider cerebrovascular pathophysiological complexity when managing patients with TBI.

Contusion Progression Following Traumatic Brain Injury: A Review of Clinical and Radiological Predictors, and Influence on Outcome

Secondary injuries remain an important cause of the morbidity and mortality associated with traumatic brain injury (TBI). Progression of cerebral contusions occurs in up to 75% of patients with TBI, and this contributes to subsequent clinical deterioration and requirement for surgical intervention. Despite this, the role of early clinical and radiological factors in predicting contusion progression remains relatively poorly defined due to studies investigating progression of all types of hemorrhagic injuries as a combined cohort. In this review, we summarize data from recent studies on factors which predict contusion progression, and the effect of contusion progression on clinical outcomes.

Mismatch between Tissue Partial Oxygen Pressure and Near-Infrared Spectroscopy Neuromonitoring of Tissue Respiration in Acute Brain Trauma: The Rationale for Implementing a Multimodal Monitoring Strategy

The brain tissue partial oxygen pressure (PbtO₂) and near-infrared spectroscopy (NIRS) neuromonitoring are frequently compared in the management of acute moderate and severe traumatic brain injury patients; however, the relationship between their respective output parameters flows from the complex pathogenesis of tissue respiration after brain trauma. NIRS neuromonitoring overcomes certain limitations related to the heterogeneity of the pathology across the brain that cannot be adequately addressed by local-sample invasive neuromonitoring (e.g., PbtO₂ neuromonitoring, microdialysis), and it allows clinicians to assess parameters that cannot otherwise be scanned. The anatomical co-registration of an NIRS signal with axial imaging (e.g., computerized tomography scan) enhances the optical signal, which can be changed by the anatomy of the lesions and the significance of the radiological assessment. These arguments led us to conclude that rather than aiming to substitute PbtO₂ with tissue saturation, multiple types of NIRS should be included via multimodal systemic- and neuro-monitoring, whose values then are incorporated into biosignatures linked to patient status and prognosis. Discussion on the abnormalities in tissue respiration due to brain trauma and how they affect the PbtO₂ and NIRS neuromonitoring is given.

"Omics" in traumatic brain injury: novel approaches to a complex disease

BACKGROUND

To date, there is neither any pharmacological treatment with efficacy in traumatic brain injury (TBI) nor any method to halt the disease progress. This is due to an incomplete understanding of the vast complexity of the biological cascades and failure to appreciate the diversity of secondary injury mechanisms in TBI. In recent years, techniques for high-throughput characterization and quantification of biological molecules that include genomics, proteomics, and metabolomics have evolved and referred to as omics.

METHODS

In this narrative review, we highlight how omics technology can be applied to potentiate diagnostics and prognostication as well as to advance our understanding of injury mechanisms in TBI.

RESULTS

The omics platforms provide possibilities to study function, dynamics, and alterations of molecular pathways of normal and TBI disease states. Through advanced bioinformatics, large datasets of molecular information from small biological samples can be analyzed in detail and provide valuable knowledge of pathophysiological mechanisms, to include in prognostic modeling when connected to clinically relevant data. In such a complex disease as TBI, omics enables broad categories of studies from gene compositions associated with susceptibility to secondary injury or poor outcome, to potential alterations in metabolites following TBI.

CONCLUSION

The field of omics in TBI research is rapidly evolving. The recent data and novel methods reviewed herein may form the basis for improved precision medicine approaches, development of pharmacological approaches, and individualization of therapeutic efforts by implementing mathematical "big data" predictive modeling in the near future.

Silymarin and neurodegenerative diseases: Therapeutic potential and basic molecular mechanisms

BACKGROUND

Neurodegenerative diseases (NDDs) are primarily characterized by selective neuronal loss in the brain. Alzheimer's disease as the most common NDDs and the most prevalent cause of dementia is characterized by Amyloid-beta deposition, which leads to cognitive and memory impairment. Parkinson's disease is a progressive neurodegenerative disease characterized by the dramatic death of dopaminergic neuronal cells, especially in the SNc and caused alpha-synuclein accumulation in the neurons. Silymarin, an extract from seeds of Silybum marianum, administered mostly for liver disorders and also had anti-oxidant and anti-carcinogenic activities.

PURPOSE

The present comprehensive review summarizes the beneficial effects of Silymarin in-vivo and in-vitro and even in animal models for these NDDs.

METHODS

A diagram model for systematic review is utilized for this search. The research is conducted in the following databases: PubMed, Web of Science, Scopus, and Science Direct.

RESULTS

Based on the inclusion criteria, 83 studies were selected and discussed in this review.

CONCLUSION

Lastly, we review the latest experimental evidences supporting the potential effects of Silymarin, as a neuroprotective agent in NDDs.

The Importance of PbtO2 Probe Location for Data Interpretation in Patients with Intracerebral Hemorrhage

Background/objective

Monitoring of brain tissue oxygen tension (P_btO₂) provides insight into brain pathophysiology after intracerebral hemorrhage (ICH). Integration of probe location is recommended to optimize data interpretation. So far, little is known about the importance of P_btO₂ catheter location in ICH patients.

Methods

We prospectively included 40 ICH patients after hematoma evacuation (HE) who required P_btO₂-monitoring. P_btO₂-probe location was evaluated in all head computed tomography (CT) scans within the first 6 days after HE and defined as location in the healthy brain tissue or perilesional when the catheter tip was located within 1 cm of a focal lesion (hypodense or hyperdense). Generalized estimating equations were used to investigate levels of P_btO₂ in relation to different probe locations.

Results

Patients were 60 [51–66] years old and had a median ICH-volume of 47 [29–60] mL. Neuromonitoring probes remained for a median of 6 [2–11] days. P_btO₂-probes were located in healthy brain tissue in 18/40 (45%) patients and in perilesional brain tissue in 22/40 (55%) patients. In the acute phase after HE (0–72 h), P_btO₂ levels were significantly lower (21 ± 12 mmHg vs. 29 ± 10 mmHg, p = 0.010) and brain tissue hypoxia (BTH) was more common in the perilesional area as compared to healthy brain tissue (46% vs. 19%, adjOR 4.0, 95% CI 1.54–10.58, p = 0.005). Episodes of BTH significantly decreased over time in patients with probes in perilesional location (p = 0.001) but remained stable in normal appearing area (p = 0.485). A significant association between BTH and poor functional outcome was only found when probes were located in the perilesional brain tissue (adjOR 6.6, 95% CI 1.3–33.8, p = 0.023).

Conclusions

In the acute phase, BTH was more common in the perilesional area compared to healthy brain tissue. The improvement of BTH in the perilesional area over time may be the result of targeted treatment interventions and tissue regeneration. Due to the localized measurement of invasive neuromonitoring devices, integration of probe location in the clinical management of ICH patients and in research protocols seems mandatory.

Changes in volumetric and metabolic parameters relate to differences in exposure to sub-concussive head impacts

Structural and calibrated magnetic resonance imaging data were acquired on 44 collegiate football players prior to the season (PRE), following the first four weeks in-season (PTC) and one month after the last game (POST). Exposure data collected from g-Force accelerometers mounted to the helmet of each player were used to split participants into HIGH (N = 22) and LOW (N = 22) exposure groups, based on the frequency of impacts sustained by each athlete. Significant decreases in grey-matter volume specific to the HIGH group were documented at POST (P = 0.009), compared to baseline. Changes in resting cerebral blood flow (CBF0), corrected for partial volume effects, were observed within the HIGH group, throughout the season (P < 0.0001), suggesting that alterations in perfusion may follow exposure to sub-concussive collisions. Co-localized significant increases in cerebral metabolic rate of oxygen consumption (CMRO2|0) mid-season were also documented in the HIGH group, with respect to both PRE- and POST values. No physiological changes were observed in the LOW group. Therefore, cerebral metabolic demand may be elevated in players with greater exposure to head impacts. These results provide novel insight into the effects of sub-concussive collisions on brain structure and cerebrovascular physiology and emphasize the importance of multi-modal imaging for a complete characterization of cerebral health.

Metabolomics analysis of the hippocampus in a rat model of traumatic brain injury during the acute phase

BACKGROUND

Traumatic brain injury (TBI) has increased in rank among traumatic injuries worldwide. Traumatic brain injury is a serious obstacle given that its complex pathology represents a long-term process. Recently, systems biology strategies such as metabolomics to investigate the multifactorial nature of TBI have facilitated attempts to find biomarkers and probe molecular pathways for its diagnosis and therapy.

METHODS

This study included a group of 20 rats with controlled cortical impact and a group of 20 sham rats. We utilized mNSS tests to investigate neurological metabolic impairments on day 1 and day 3. Furthermore, we applied metabolomics and bioinformatics to determine the metabolic perturbation caused by TBI during the acute period in the hippocampus tissue of controlled cortical impact (CCI) rats. Notably, TBI-protein-metabolite subnetworks identified from a database were assessed for associations between metabolites and TBI by the dysregulation of related enzymes and transporters.

RESULTS

Our results identified 7 and 8 biomarkers on day 1 and day 3, respectively. Additionally, related pathway disorders showed effects on arginine and proline metabolism as well as taurine and hypotaurine metabolism on day 3 in acute TBI. Furthermore, according to metabolite-protein database searches, 25 metabolite-protein pairs were established as causally associated with TBI. Further, bioinformation indicated that these TBI-associated proteins mainly take part in 5'-nucleotidase activity and carboxylic acid transmembrane transport. In addition, interweaved networks were constructed to show that the development of TBI might be affected by metabolite-related proteins and their protein pathways.

CONCLUSION

The overall results show that acute TBI is susceptible to metabolic disorders, and the joint metabolite-protein network analysis provides a favorable prediction of TBI pathogenesis mechanisms in the brain. The signatures in the hippocampus might be promising for the development of biomarkers and pathways relevant to acute TBI and could further guide testable predictions of the underlying mechanism of TBI.

Translational approach towards determining the role of cerebral autoregulation in outcome after traumatic brain injury

Cerebral autoregulation is impaired after traumatic brain injury (TBI), contributing to poor outcome. In the context of the neurovascular unit, cerebral autoregulation contributes to neuronal cell integrity and clinically Glasgow Coma Scale is correlated to intactness of autoregulation after TBI. Cerebral Perfusion Pressure (CPP) is often normalized by use of vasoactive agents to increase mean arterial pressure (MAP) and thereby limit impairment of cerebral autoregulation and neurological deficits. However, current vasoactive agent choice used to elevate MAP to increase CPP after TBI is variable. Vasoactive agents, such as phenylephrine, dopamine, norepinephrine, and epinephrine, clinically have not sufficiently been compared regarding effect on CPP, autoregulation, and survival after TBI. The cerebral effects of these clinically commonly used vasoactive agents are incompletely understood. This review will describe translational studies using a more human like animal model (the pig) of TBI to identify better therapeutic strategies to improve outcome post injury. These studies also investigated the role of age and sex in outcome and mechanism(s) involved in improvement of outcome in the setting of TBI. Additionally, this review considers use of inhaled nitric oxide as a novel neuroprotective strategy in treatment of TBI.

Vasoactive agents to improve brain perfusion: pathophysiology and clinical utilization

PURPOSE OF REVIEW

This review highlights the aspects of pathophysiology that make it difficult to predict the effects of any attempt to improve brain perfusion and reviews the options to improve brain perfusion according to the needs of an individual patient, focusing on the choice of a suitable threshold for cerebral perfusion pressure.

RECENT FINDINGS

Typically, vasopressors or vasodilators that do not directly influence the cerebral vascular bed are used to improve cerebral perfusion. Positive inotropic substances are rarely used, as the relationship between cardiac output and cerebral blood flow is complex and difficult to measure. Combining perfusion pressure monitoring with monitoring of brain metabolism or oxygenation to adapt cerebral perfusion to the needs of an individual patient has been disappointing. Recently, attempts to individualize perfusion pressure based on measurements of cerebrovascular autoregulation have shown promising results in the management of traumatic brain injury and during cardiac surgery. Currently, only preliminary data are available linking optimized cerebral perfusion to improved outcome.

SUMMARY

Optimizing cerebral perfusion remains a difficult goal. All our attempts to manipulate brain perfusion are influenced in an unpredictable manner by underlying diseases. Autoregulation-based strategies to individualize cerebral perfusion management warrant further investigation.

Intensive Care in Traumatic Brain Injury Including Multi-Modal Monitoring and Neuroprotection

Moderate to severe traumatic brain injuries (TBI) require treatment in an intensive care unit (ICU) in close collaboration of a multidisciplinary team consisting of different medical specialists such as intensivists, neurosurgeons, neurologists, as well as ICU nurses, physiotherapists, and ergo-/logotherapists. Major goals include all measurements to prevent secondary brain injury due to secondary brain insults and to optimize frame conditions for recovery and early rehabilitation. The distinction between moderate and severe is frequently done based on the Glascow Coma Scale and therefore often is just a snapshot at the early time of assessment. Due to its pathophysiological pathways, an initially as moderate classified TBI may need the same sophisticated surveillance, monitoring, and treatment as a severe form or might even progress to a severe and difficult to treat affection. As traumatic brain injury is rather a syndrome comprising a range of different affections to the brain and as, e.g., age-related comorbidities and treatments additionally may have a great impact, individual and tailored treatment approaches based on monitoring and findings in imaging and respecting pre-injury comorbidities and their therapies are warranted.

A New Vision for Therapeutic Hypothermia in the Era of Targeted Temperature Management: A Speculative Synthesis

Three decades of animal studies have reproducibly shown that hypothermia is profoundly cerebroprotective during or after a central nervous system (CNS) insult. The success of hypothermia in preclinical acute brain injury has not only fostered continued interest in research on the classic secondary injury mechanisms that are prevented or blunted by hypothermia but has also sparked a surge of new interest in elucidating beneficial signaling molecules that are increased by cooling. Ironically, while research into cold-induced neuroprotection is enjoying newfound interest in chronic neurodegenerative disease, conversely, the scope of the utility of therapeutic hypothermia (TH) across the field of acute brain injury is somewhat controversial and remains to be fully defined. This has led to the era of Targeted Temperature Management, which emphasizes a wider range of temperatures (33–36°C) showing benefit in acute brain injury. In this comprehensive review, we focus on our current understandings of the novel neuroprotective mechanisms activated by TH, and discuss the critical importance of developmental age germane to its clinical efficacy. We review emerging data on four cold stress hormones and three cold shock proteins that have generated new interest in hypothermia in the field of CNS injury, to create a framework for new frontiers in TH research. We make the case that further elucidation of novel cold responsive pathways might lead to major breakthroughs in the treatment of acute brain injury, chronic neurological diseases, and have broad potential implications for medicines of the distant future, including scenarios such as the prevention of adverse effects of long-duration spaceflight, among others. Finally, we introduce several new phrases that readily summarize the essence of the major concepts outlined by this review—namely, Ultramild Hypothermia, the “Responsivity of Cold Stress Pathways,” and “Hypothermia in a Syringe.”

Therapeutic hypercapnia reduces blood-brain barrier damage possibly via protein kinase Cε in rats with lateral fluid percussion injury

Background

This study investigated whether therapeutic hypercapnia (TH) ameliorated blood–brain barrier (BBB) damage and improved the neurologic outcome in a rat model of lateral fluid percussion injury (FPI), and explored the possible underlying mechanism.

Methods

Rats underwent lateral FPI and received inhalation of 30%O₂–70%N₂ or 30%O₂–N₂ plus CO₂ to maintain arterial blood CO₂ tension (PaCO₂) between 80 and 100 mmHg for 3 h. To further explore the possible mechanisms for the protective effects of TH, a PKC inhibitor staurosporine or PKCαβ inhibitor GÖ6976 was administered via intracerebral ventricular injection.

Results

TH significantly improved neurological function 24 h, 48 h, 7 d, and 14 d after FPI. The wet/dry ratio, computed tomography values, Evans blue content, and histological lesion volume were significantly reduced by TH. Moreover, numbers of survived neurons and the expression of tight junction proteins (ZO-1, occludin, and claudin-5) were significantly elevated after TH treatment at 48-h post-FPI. TH significantly increased the expression of protein kinase Cε (PKCε) at 48-h post-FPI, but did not significantly change the expression of PKCα and PKCβII. PKC inhibitor staurosporine (but not the selective PKCαβ inhibitor-GÖ6976) inhibited the protective effect of TH.

Conclusions

Therapeutic hypercapnia is a promising candidate that should be further evaluated for clinical treatment. It not only protects the traumatic penumbra from secondary injury and improves histological structure but also maintains the integrity of BBB and reduces neurologic deficits after trauma in a rat model of FPI.

Management Strategies for Intracranial Pressure Crises in Subarachnoid Hemorrhage

Objectives: Standard management strategies for lowering intracranial pressure (ICP) in traumatic brain injury has been well-studied, but the use of lesser known interventions for ICP in subarachnoid hemorrhage (SAH) remains elusive. Searches were performed in PubMed and EBSCO Host to identify best available evidence for evaluation and management of medically refractory ICP in SAH. The role of standard management strategies such as head elevation, hyperventilation, mannitol and hypertonic saline as well as lesser known management such as sodium bicarbonate, indomethacin, tromethamine, decompressive craniectomy, decompressive laparotomy, hypothermia, and barbiturate coma are reviewed. We also included dose concentrations, dose frequency, infusion volume, and infusion rate for these lesser known strategies. Nonetheless, there is still a gap in the evidence to recommend optimal dosing, timing and its role in the improvement of outcomes but early diagnosis and appropriate management reduce adverse outcomes.

Neuroimaging in the Kleine-Levin Syndrome

PURPOSE OF REVIEW

The purpose was to review the most recent literature on neuroimaging in the Kleine-Levin syndrome (KLS). We aimed to investigate if frontotemporal and thalamic dysfunction are key KLS signatures, and if recent research indicates other brain networks of interest that elucidate KLS symptomatology and aetiology.

RECENT FINDINGS

In a comprehensive literature search, we found 12 original articles published 2013-2018. Most studies report deviations related to cerebral perfusion, glucose metabolism, or blood-oxygen-level-dependent responses in frontotemporal areas and/or the thalamus. Studies also report dysfunction in the temporoparietal junction and the oculomotor network that also were related to clinical parameters. We discuss these findings based on recent research on thalamocortical networks and brain stem white matter tracts. The hypothesis of frontotemporal and thalamic involvement in KLS was confirmed, and additional findings in the temporoparietal junction and the oculomotor system suggest a broader network involvement, which can be investigated by future high-resolution and multimodal imaging.

Patient-Specific Alterations in CO2 Cerebrovascular Responsiveness in Acute and Sub-Acute Sports-Related Concussion

Background

Preliminary studies suggest that sports-related concussion (SRC) is associated with alterations in cerebral blood flow (CBF) regulation. Here, we use advanced magnetic resonance imaging (MRI) techniques to measure CBF and cerebrovascular responsiveness (CVR) in individual SRC patients and healthy control subjects.

Methods

15 SRC patients (mean age = 16.3, range 14–20 years) and 27 healthy control subjects (mean age = 17.6, range 13–21 years) underwent anatomical MRI, pseudo-continuous arterial spin labeling (pCASL) MRI and model-based prospective end-tidal targeting (MPET) of CO₂ during blood oxygenation level-dependent (BOLD) MRI. Group differences in global mean resting CBF were examined. Voxel-by-voxel group and individual differences in regional CVR were examined using statistical parametric mapping (SPM). Leave-one-out receiver operating characteristic curve analysis was used to evaluate the utility of brain MRI CO₂ stress testing biomarkers to correctly discriminate between SRC patients and healthy control subjects.

Results

All studies were tolerated with no complications. Traumatic structural findings were identified in one SRC patient. No significant group differences in global mean resting CBF were observed. There were no significant differences in the CO₂ stimulus and O₂ targeting during BOLD MRI. Significant group and patient-specific differences in CVR were observed with SRC patients demonstrating a predominant pattern of increased CVR. Leave-one-out ROC analysis for voxels demonstrating a significant increase in CVR was found to reliably discriminate between SRC patients and healthy control subjects (AUC of 0.879, p = 0.0001). The optimal cutoff for increased CVR declarative for SRC was 1,899 voxels resulting in a sensitivity of 0.867 and a specificity of 0.778 for this specific ROC analysis. There was no correlation between abnormal voxel counts and Postconcussion Symptom Scale scores among SRC patients.

Conclusion

Acute and subacute SRCs are associated with alterations in CVR that can be reliably detected by brain MRI CO₂ stress testing in individual patients.

Cerebral Microdialysis Monitoring to Improve Individualized Neurointensive Care Therapy: An Update of Recent Clinical Data

Cerebral microdialysis (CMD) allows bedside semicontinuous monitoring of patient brain extracellular fluid. Clinical indications of CMD monitoring are focused on the management of secondary cerebral and systemic insults in acute brain injury (ABI) patients [mainly, traumatic brain injury (TBI), subarachnoid hemorrhage, and intracerebral hemorrhage (ICH)], specifically to tailor several routine interventions—such as optimization of cerebral perfusion pressure, blood transfusion, glycemic control and oxygen therapy—in the individual patient. Using CMD as clinical research tool has greatly contributed to identify and better understand important post-injury mechanisms—such as energy dysfunction, posttraumatic glycolysis, post-aneurysmal early brain injury, cortical spreading depressions, and subclinical seizures. Main CMD metabolites (namely, lactate/pyruvate ratio, and glucose) can be used to monitor the brain response to specific interventions, to assess the extent of injury, and to inform about prognosis. Recent consensus statements have provided guidelines and recommendations for CMD monitoring in neurocritical care. Here, we summarize recent clinical investigation conducted in ABI patients, specifically focusing on the role of CMD to guide individualized intensive care therapy and to improve our understanding of the complex disease mechanisms occurring in the immediate phase following ABI. Promising brain biomarkers will also be described.

Time spent with impaired autoregulation is linked with outcome in severe infant/paediatric traumatic brain injury

BACKGROUND

It could be shown in traumatic brain injury (TBI) in adults that the functional status of cerebrovascular autoregulation (AR), determined by the pressure reactivity index (PRx), correlates to and even predicts outcome. We investigated PRx, cerebral perfusion pressure (CPP) and intracranial pressure (ICP) and their correlation to outcome in severe infant and paediatric TBI.

METHODS

Seventeen patients (range, 1 day to 14 years) with severe TBI (median GCS at presentation, 4) underwent long-term computerised ICP and mean arterial pressure (MAP) monitoring using dedicated software to determine CPP and PRx and optimal CPP (CPP level where PRx shows best autoregulation) continuously. Outcome was determined at discharge and at follow-up using the Glasgow Outcome Scale.

RESULTS

Favourable outcome was reached in eight patients, unfavourable outcome in seven patients. Two patients died. Nine patients underwent decompressive craniectomy to control ICP during Intensive Care Unit treatment. When dichotomised to outcome, no significant difference was found for overall ICP, CPP and PRx. The time with severely impaired AR (PRx >0.2) was significantly longer for patients with unfavourable outcome (64 h vs 6 h, p = 0.001). Continuously impaired AR of ≥24 h and age <1 year was associated to unfavourable outcome. Children with favourable outcome spent the entire monitoring time at or above the optimal CPP.

CONCLUSIONS

Integrity of AR has a similar role for outcome after TBI in the paediatric population as in adults. The amount of time spent with deranged AR seems to be associated with outcome; a factor especially critical for infant patients. The results of this preliminary study need to be validated in the future.

Normobaric hyperoxia does not improve derangements in diffusion tensor imaging found distant from visible contusions following acute traumatic brain injury

We have previously shown that normobaric hyperoxia may benefit peri-lesional brain and white matter following traumatic brain injury (TBI). This study examined the impact of brief exposure to hyperoxia using diffusion tensor imaging (DTI) to identify axonal injury distant from contusions. Fourteen patients with acute moderate/severe TBI underwent baseline DTI and following one hour of 80% oxygen. Thirty-two controls underwent DTI, with 6 undergoing imaging following graded exposure to oxygen. Visible lesions were excluded and data compared with controls. We used the 99% prediction interval (PI) for zero change from historical control reproducibility measurements to demonstrate significant change following hyperoxia. Following hyperoxia DTI was unchanged in controls. In patients following hyperoxia, mean diffusivity (MD) was unchanged despite baseline values lower than controls (p < 0.05), and fractional anisotropy (FA) was lower within the left uncinate fasciculus, right caudate and occipital regions (p < 0.05). 16% of white and 14% of mixed cortical and grey matter patient regions showed FA decreases greater than the 99% PI for zero change. The mechanistic basis for some findings are unclear, but suggest that a short period of normobaric hyperoxia is not beneficial in this context. Confirmation following a longer period of hyperoxia is required.

Metabolomics Profiling As a Diagnostic Tool in Severe Traumatic Brain Injury

Traumatic brain injury (TBI) is a complex disease with a multifaceted pathophysiology. Impairment of energy metabolism is a key component of secondary insults. This phenomenon is a consequence of multiple potential mechanisms including diffusion hypoxia, mitochondrial failure, and increased energy needs due to systemic trauma responses, seizures, or spreading depolarization. The degree of disturbance in brain metabolism is affected by treatment interventions and reflected in clinical patient outcome. Hence, monitoring of these secondary events in peripheral blood will provide a window into the pathophysiological course of severe TBI. New methods for assessing perturbation of brain metabolism are needed in order to monitor on-going pathophysiological processes and thus facilitate targeted interventions and predict outcome. Circulating metabolites in peripheral blood may serve as sensitive markers of pathological processes in TBI. The levels of these small molecules in blood are less dependent on the integrity of the blood–brain barrier as compared to protein biomarkers. We have recently characterized a specific metabolic profile in serum that is associated with both initial severity and patient outcome of TBI. We found that two medium-chain fatty acids, octanoic and decanoic acids, as well as several sugar derivatives are significantly associated with the severity of TBI. The top ranking peripheral blood metabolites were also highly correlated with their levels in cerebral microdialyzates. Based on the metabolite profile upon admission, we have been able to develop a model that accurately predicts patient outcome. Moreover, metabolomics profiling improved the performance of the well-established clinical prognostication model. In this review, we discuss metabolomics profiling in patients with severe TBI. We present arguments in support of the need for further development and validation of circulating biomarkers of cerebral metabolism and for their use in assessing patients with severe TBI.

State of Cerebrovascular Autoregulation Correlates with Outcome in Severe Infant/Pediatric Traumatic Brain Injury

OBJECTIVE

It could be shown in adults with severe traumatic brain injury (TBI) that the functional status of cerebrovascular autoregulation (AR), determined by the pressure reactivity index (PRx), correlates with and even predicts outcome. We investigated PRx and its correlation with outcome in infant and pediatric TBI. Methods Ten patients (median age 2.8 years, range 1 day to 14 years) with severe TBI (Glasgow Coma Scale score <9 at presentation) underwent long-term computerized intracranial pressure (ICP) and mean arterial pressure (MAP) monitoring using dedicated software for continuous determination of cerebral perfusion pressure (CPP) and PRx. Outcome was determined at discharge and at follow-up at 6 months using the Glasgow Outcome Scale (GOS) score.

RESULTS

Median monitoring time was 182 h (range 22-355 h). Seven patients underwent decompressive craniectomy to control ICP during treatment in the intensive care unit. Favorable outcome (GOS 4 and 5) was reached in 4 patients, an unfavorable outcome (GOS 1-3) in 6 patients. When dichotomized to outcome, no correlation was found with ICP and CPP, but median PRx correlated well with outcome (r = -0.79, p = 0.006) and tended to be lower for GOS 4 and 5 (-0.04) than for GOS 1-3 (0.32; p = 0.067).

CONCLUSION

The integrity of AR seems to play the same fundamental role after TBI in the pediatric population as in adults and should be determined routinely. It carries an important prognostic value. PRx seems to be an ideal candidate parameter to guide treatment in the sense of optimizing CPP, aiming at improvement of cerebrovascular autoregulation (CPPopt concept).

Mortality rates of severe traumatic brain injury patients: impact of direct versus nondirect transfers

BACKGROUND

Direct transport of patients with severe traumatic brain injury (sTBI) to trauma centers (TCs) that can provide definitive care results in lower mortality rates. This study investigated the impact of direct versus nondirect transfers on the mortality rates of patients with sTBI.

METHODS

Data on patients with TBI admitted between January 1, 2012, and December 31, 2013, to our Level I TC were obtained from the trauma registry. Data included patient age, sex, mechanism, and type of injury, comorbidities, Glasgow Coma Scale, Injury Severity scores, prehospital time, time to request and to transfer, time to initiation of multimodality monitoring and goal-directed therapy protocol, dwell time in the emergency department (EDT), and mortality. Data, reported in means ± standard deviation, were analyzed with the Student t-test and chi-square. Statistical significance was accepted at a P value < 0.05.

RESULTS

sTBI direct transfer to TC versus transfer from non-TCs (NTC): Of the 1187 patients with TBI admitted to our TC, 768 (64.7%) were admitted directly from the scene, whereas 419 (35.3%) were admitted after secondary transfer. One hundred seventy-one (22.2%) of the direct transfers had Glasgow Coma Scale < 8 (sTBI) and 92 (21.9%) of the secondary transfers had sTBI. The transfer time: Time from scene to arrival to the EDT was significantly shorter for TC versus NTCs 43 ± 14 versus 77 ± 26 min, respectively (P < 0.05). EDT dwell time before transfer and time from injury to arrival to TC were 4.2 ± 2.1 and 6.2 ± 8.3 h, respectively. Mortality: There was a statistically significant lower mortality for patients with sTBI transferred directly from the scene to TCs as opposed to patients secondarily transferred, 33/171 (19.3%) versus 33/92 (35.8%), respectively (P < 0.05).

CONCLUSIONS

To decrease TBI-related mortality, patients with suspected sTBI should be taken directly to a Level I or II TC unless they require life-saving stabilization at NTCs.

Aspects on the Physiological and Biochemical Foundations of Neurocritical Care

Neurocritical care (NCC) is a branch of intensive care medicine characterized by specific physiological and biochemical monitoring techniques necessary for identifying cerebral adverse events and for evaluating specific therapies. Information is primarily obtained from physiological variables related to intracranial pressure (ICP) and cerebral blood flow (CBF) and from physiological and biochemical variables related to cerebral energy metabolism. Non-surgical therapies developed for treating increased ICP are based on knowledge regarding transport of water across the intact and injured blood-brain barrier (BBB) and the regulation of CBF. Brain volume is strictly controlled as the BBB permeability to crystalloids is very low restricting net transport of water across the capillary wall. Cerebral pressure autoregulation prevents changes in intracranial blood volume and intracapillary hydrostatic pressure at variations in arterial blood pressure. Information regarding cerebral oxidative metabolism is obtained from measurements of brain tissue oxygen tension (PbtO2) and biochemical data obtained from intracerebral microdialysis. As interstitial lactate/pyruvate (LP) ratio instantaneously reflects shifts in intracellular cytoplasmatic redox state, it is an important indicator of compromised cerebral oxidative metabolism. The combined information obtained from PbtO2, LP ratio, and the pattern of biochemical variables reveals whether impaired oxidative metabolism is due to insufficient perfusion (ischemia) or mitochondrial dysfunction. Intracerebral microdialysis and PbtO2 give information from a very small volume of tissue. Accordingly, clinical interpretation of the data must be based on information of the probe location in relation to focal brain damage. Attempts to evaluate global cerebral energy state from microdialysis of intraventricular fluid and from the LP ratio of the draining venous blood have recently been presented. To be of clinical relevance, the information from all monitoring techniques should be presented bedside online. Accordingly, in the future, the chemical variables obtained from microdialysis will probably be analyzed by biochemical sensors.

Rheological effects of drag-reducing polymers improve cerebral blood flow and oxygenation after traumatic brain injury in rats

Cerebral ischemia has been clearly demonstrated after traumatic brain injury (TBI); however, neuroprotective therapies have not focused on improvement of the cerebral microcirculation. Blood soluble drag-reducing polymers (DRP), prepared from high molecular weight polyethylene oxide, target impaired microvascular perfusion by altering the rheological properties of blood and, until our recent reports, has not been applied to the brain. We hypothesized that DRP improve cerebral microcirculation and oxygenation after TBI. DRP were studied in healthy and traumatized rat brains and compared to saline controls. Using in-vivo two-photon laser scanning microscopy over the parietal cortex, we showed that after TBI, nanomolar concentrations of intravascular DRP significantly enhanced microvascular perfusion and tissue oxygenation in peri-contusional areas, preserved blood-brain barrier integrity and protected neurons. The mechanisms of DRP effects were attributable to reduction of the near-vessel wall cell-free layer which increased near-wall blood flow velocity, microcirculatory volume flow, and number of erythrocytes entering capillaries, thereby reducing capillary stasis and tissue hypoxia as reflected by a reduction in NADH. Our results indicate that early reduction in CBF after TBI is mainly due to ischemia; however, metabolic depression of contused tissue could be also involved.

Role of Microglia Autophagy in Microglia Activation After Traumatic Brain Injury

OBJECTIVE

We evaluated the role of microglia autophagy in microglia activation after traumatic brain injury (TBI) in rats.

METHODS

TBI was induced by a fluid percussion TBI device. All rats were killed 24 hours after TBI. The ipsilateral hippocampus in all rats was analyzed with hematoxylin-eosin staining. Immunohistochemistry and Western blotting of ionized calcium-binding adapter molecule 1 was used to determine changes in microglia activation. Double staining of microtubule-associated protein light chain 3, Beclin-1, and ionized calcium-binding adapter molecule 1 was used to assess changes of microglia autophagy. Enzyme-linked immunosorbent assay of tumor necrosis factor-α and interleukin-1β was used to evaluate changes in inflammatory responses. Terminal deoxyribonucleotidyl transferase-mediated deoxyuridine 5'-triphosphate nick-end labeling staining was used to determine cell death in the ipsilateral hippocampus.

RESULTS

At 24 hours after TBI, microglial cells became activated, and the autophagy inhibitor 3-methyladenine (3-MA) further promoted microglia activation. Protein light chain 3- and Beclin-1-positive microglial cells were increased after TBI, whereas 3-MA decreased the number of positive microglial cells, increasing the expression of tumor necrosis factor-α and interleukin-1β; terminal deoxyribonucleotidyl transferase-mediated deoxyuridine 5'-triphosphate nick-end labeling staining demonstrated that 3-MA could increase the number of terminal deoxyribonucleotidyl transferase-mediated deoxyuridine 5'-triphosphate nick-end labeling-positive cells (16.83 ± 0.83 vs. 11 ± 0.82, P < 0.001).

CONCLUSIONS

Our data demonstrated that TBI induced microglia activation and microglia autophagy. Inhibition of microglia autophagy with 3-MA increased microglia activation and neural apoptosis. These findings indicate that targeting microglia autophagy may be a therapeutic strategy for TBI.

Multimodal neurologic monitoring

Neurocritical care has two main objectives. Initially, the emphasis is on treatment of patients with acute damage to the central nervous system whether through infection, trauma, or hemorrhagic or ischemic stroke. Thereafter, attention shifts to the identification of secondary processes that may lead to further brain injury, including fever, seizures, and ischemia, among others. Multimodal monitoring is the concept of using various tools and data integration to understand brain physiology and guide therapeutic interventions to prevent secondary brain injury. This chapter will review the use of electroencephalography, intracranial pressure monitoring, brain tissue oxygenation, cerebral microdialysis and neurochemistry, near-infrared spectroscopy, and transcranial Doppler sonography as they relate to neuromonitoring in the critically ill. The concepts and design of each monitor, in addition to the patient population that may most benefit from each modality, will be discussed, along with the various tools that can be used together to guide individualized patient treatment options. Major clinical trials, observational studies, and their effect on clinical outcomes will be reviewed. The future of multimodal monitoring in the field of bioinformatics, clinical research, and device development will conclude the chapter.

Cerebral oxidative metabolism failure in traumatic brain injury: "Brain shock"

Shock is a systemic form of acute circulatory failure leading to cellular dysoxia and death. Such a state of aerobic metabolism failure also underlies neuronal cell death in severe traumatic brain injury. It is becoming increasingly recognized that ischemic hypoxia is not the sole mechanism and that multiple alternate cooperating mechanisms may be responsible for compromising neuronal oxidative metabolism. These different mechanisms can be usefully understood via analysis of the classic subdivisions of tissue hypoxia. This approach could lead to an alternative treatment paradigm toward cerebral oxygen metabolic rate targeting instead of the traditional targets of intracranial and perfusion pressures.

Multi-Disciplinary Management of Athletes with Post-Concussion Syndrome: An Evolving Pathophysiological Approach

Historically, patients with sports-related concussion (SRC) have been managed in a uniform fashion consisting mostly of prescribed physical and cognitive rest with the expectation that all symptoms will spontaneously resolve with time. Although this approach will result in successful return to school and sports activities in the majority of athletes, an important proportion will develop persistent concussion symptoms characteristic of post-concussion syndrome (PCS). Recent advances in exercise science, neuroimaging, and clinical research suggest that the clinical manifestations of PCS are mediated by unique pathophysiological processes that can be identified by features of the clinical history and physical examination as well as the use of graded aerobic treadmill testing. Athletes who develop PCS represent a unique population whose care must be individualized and must incorporate a rehabilitative strategy that promotes enhanced recovery of concussion-related symptoms while preventing physical deconditioning. In this review, we present our evolving evidence-based approach to evaluation and management of athletes with PCS that aims to identify the pathophysiological mechanisms mediating persistent concussion symptoms and guides the initiation of individually tailored rehabilitation programs that target these processes. In addition, we outline the important qualified roles that multi-disciplinary healthcare professionals can play in the management of this patient population, and discuss where future research efforts must be focused to further evaluate this evolving pathophysiological approach.

Evaluating the Role of Reduced Oxygen Saturation and Vascular Damage in Traumatic Brain Injury Using Magnetic Resonance Perfusion-Weighted Imaging and Susceptibility-Weighted Imaging and Mapping

The cerebral vasculature, along with neurons and axons, is vulnerable to biomechanical insult during traumatic brain injury (TBI). Trauma-induced vascular injury is still an underinvestigated area in TBI research. Cerebral blood flow and metabolism could be important future treatment targets in neural critical care. Magnetic resonance imaging offers a number of key methods to probe vascular injury and its relationship with traumatic hemorrhage, perfusion deficits, venous blood oxygen saturation changes, and resultant tissue damage. They make it possible to image the hemodynamics of the brain, monitor regional damage, and potentially show changes induced in the brain's function not only acutely but also longitudinally following treatment. These methods have recently been used to show that even mild TBI (mTBI) subjects can have vascular abnormalities, and thus they provide a major step forward in better diagnosing mTBI patients.

Human Serum Metabolites Associate With Severity and Patient Outcomes in Traumatic Brain Injury

Traumatic brain injury (TBI) is a major cause of death and disability worldwide, especially in children and young adults. TBI is an example of a medical condition where there are still major lacks in diagnostics and outcome prediction. Here we apply comprehensive metabolic profiling of serum samples from TBI patients and controls in two independent cohorts. The discovery study included 144 TBI patients, with the samples taken at the time of hospitalization. The patients were diagnosed as severe (sTBI; n = 22), moderate (moTBI; n = 14) or mild TBI (mTBI; n = 108) according to Glasgow Coma Scale. The control group (n = 28) comprised of acute orthopedic non-brain injuries. The validation study included sTBI (n = 23), moTBI (n = 7), mTBI (n = 37) patients and controls (n = 27). We show that two medium-chain fatty acids (decanoic and octanoic acids) and sugar derivatives including 2,3-bisphosphoglyceric acid are strongly associated with severity of TBI, and most of them are also detected at high concentrations in brain microdialysates of TBI patients. Based on metabolite concentrations from TBI patients at the time of hospitalization, an algorithm was developed that accurately predicted the patient outcomes (AUC = 0.84 in validation cohort). Addition of the metabolites to the established clinical model (CRASH), comprising clinical and computed tomography data, significantly improved prediction of patient outcomes. The identified ‘TBI metabotype’ in serum, that may be indicative of disrupted blood-brain barrier, of protective physiological response and altered metabolism due to head trauma, offers a new avenue for the development of diagnostic and prognostic markers of broad spectrum of TBIs.

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The study reports that serum metabolites are sensitive to severity of TBI as well as predict the patient outcomes.

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The findings are indicative of disruption in blood brain barrier and of protective response and altered TBI metabolism.

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Metabolites significantly improved the prediction of patient outcomes when added to the established clinical model.

Traumatic brain injury (TBI) is an example of a medical condition where there are still major lacks in diagnostics, outcome prediction, and the therapy development. Since the blood-brain barrier prevents diffusion of most water-soluble molecules with molecular mass over 500 Da, here we hypothesized that circulating small molecules (metabolites) are a potential source of TBI markers. Based on serum metabolomic studies in two independent cohorts, we found that metabolites are sensitive to severity of TBI as well as predict the patient outcomes. The findings of this study may pave the way for new diagnostic tools for TBI.

Early Cerebral Circulation Disturbance in Patients Suffering from Severe Traumatic Brain Injury (TBI): A Xenon CT and Perfusion CT Study

Traumatic brain injury (TBI) is widely known to cause dynamic changes in cerebral blood flow (CBF). Ischemia is a common and deleterious secondary injury following TBI. Detecting early ischemia in TBI patients is important to prevent further advancement and deterioration of the brain tissue. The purpose of this study was to clarify the cerebral circulatory disturbance during the early phase and whether it can be used to predict patient outcome. A total of 90 patients with TBI underwent a xenon-computed tomography (Xe-CT) and subsequently perfusion CT to evaluate the cerebral circulation on days 1–3. We measured CBF using Xe-CT and mean transit time (MTT: the width between two inflection points [maximum upward slope and maximum downward slope from inflow to outflow of the contrast agent]) using perfusion CT and calculated the cerebral blood volume (CBV) using the AZ-7000W98 computer system. The relationships of the hemodynamic parameters CBF, MTT, and CBV to the Glasgow Coma Scale (GCS) score and the Glasgow Outcome Scale (GOS) score were examined. There were no significant differences in CBF, MTT, and CBV among GCS3–4, GCS5–6, and GCS7–8 groups. The patients with a favorable outcome (GR and MD) had significantly higher CBF and lower MTT than those with an unfavorable one (SD, VS, or D). The discriminant analysis of these parameters could predict patient outcome with a probability of 70.6%. During the early phase, CBF reduction and MTT prolongation might influence the clinical outcome of TBI. These parameters are helpful for evaluating the severity of cerebral circulatory disturbance and predicting the outcome of TBI patients.

Cerebral and extracerebral vulnerability to hypoxic insults after diffuse traumatic brain injury in rats

The post-traumatic brain vulnerability suggests that after traumatic brain injury (TBI), the brain may be more susceptible to posttraumatic hypoxic insults. This concept could be extended to 'peripheral' organs, as non-neurologic organ failure is common after TBI. This study aims to characterize and quantify cerebral and extracerebral tissue hypoxia with pimonidazole resulting from a standardized hypoxia-hypotension (HH) phase occurring after a diffuse experimental TBI in rats. Rats were allocated to Sham (n=5), TBI (n=7), HH (n=7) and TBI+HH (n=7) groups. Then, pimonidazole was injected and brain, liver, heart and kidneys were analysed. In the cerebral cortex, post-treatment hypoxia was higher in TBI+HH group than Sham group (p=0.003), HH group (p=0.003) and TBI group (p=0.002). Large trends in thalamus, hippocampus and striatum for the TBI+HH group compared to the other groups were observed. For the heart and liver, the 4 groups were comparable. For the kidneys, post-treatment hypoxia was higher in the TBI group compared to the Sham and HH groups, but not more than TBI+HH group. This study reveals that a posttraumatic hypoxic insult occurring after a severe TBI has major hypoxic consequences on brain structures. However, TBI by itself appears to induce renal hypoxia that is not enhanced by posttraumatic hypoxic insult.