Cerebral extracellular chemistry and outcome following traumatic brain injury: a microdialysis study of 223 patients

Preliminary Observations of the Loke Microdialysis in an Experimental Pig Model: Are We Ready for Continuous Monitoring of Brain Energy Metabolism?

BACKGROUND

Brain energy metabolism is often disturbed after acute brain injuries. Current neuromonitoring methods with cerebral microdialysis (CMD) are based on intermittent measurements (1-4 times/h), but such a low frequency could miss transient but important events. The solution may be the recently developed Loke microdialysis (MD), which provides high-frequency data of glucose and lactate. Before clinical implementation, the reliability and stability of Loke remain to be determined in vivo. The purpose of this study was to validate Loke MD in relation to the standard intermittent CMD method.

METHODS

Four pigs aged 2-3 months were included. They received two adjacent CMD catheters, one for standard intermittent assessments and one for continuous (Loke MD) assessments of glucose and lactate. The standard CMD was measured every 15 min. Continuous Loke MD was sampled every 2-3 s and was averaged over corresponding 15-min intervals for the statistical comparisons with standard CMD. Intravenous glucose injections and intracranial hypertension by inflation of an intracranial epidural balloon were performed to induce variations in intracranial pressure, cerebral perfusion pressure, and systemic and cerebral glucose and lactate levels.

RESULTS

In a linear mixed-effect model of standard CMD glucose (mM), there was a fixed effect value (± standard error [SE]) at 0.94 ± 0.07 (p < 0.001) for Loke MD glucose (mM), with an intercept at - 0.19 ± 0.15 (p = 0.20). The model showed a conditional R2 at 0.81 and a marginal R2 at 0.72. In a linear mixed-effect model of standard CMD lactate (mM), there was a fixed effect value (± SE) at 0.41 ± 0.16 (p = 0.01) for Loke MD lactate (mM), with an intercept at 0.33 ± 0.21 (p = 0.25). The model showed a conditional R2 at 0.47 and marginal R2 at 0.17.

CONCLUSIONS

The established standard CMD glucose thresholds may be used as for Loke MD with some caution, but this should be avoided for lactate.

New insights into metabolism dysregulation after TBI

Traumatic brain injury (TBI) remains a leading cause of death and disability that places a great physical, social, and financial burden on individuals and the health system. In this review, we summarize new research into the metabolic changes described in clinical TBI trials, some of which have already shown promise for informing injury classification and staging. We focus our discussion on derangements in glucose metabolism, cell respiration/mitochondrial function and changes to ketone and lipid metabolism/oxidation to emphasize potentially novel biomarkers for clinical outcome prediction and intervention and offer new insights into possible underlying mechanisms from preclinical research of TBI pathology. Finally, we discuss nutrition supplementation studies that aim to harness the gut/microbiome-brain connection and manipulate systemic/cellular metabolism to improve post-TBI recovery. Taken together, this narrative review summarizes published TBI-associated changes in glucose and lipid metabolism, highlighting potential metabolite biomarkers for clinical use, the cellular processes linking these markers to TBI pathology as well as the limitations and future considerations for TBI "omics" work.

NHE1 Protein in Repetitive Mild TBI-Mediated Neuroinflammation and Neurological Function Impairment

Mild traumatic brain injuries (mTBIs) are highly prevalent and can lead to chronic behavioral and cognitive deficits often associated with the development of neurodegenerative diseases. Oxidative stress and formation of reactive oxygen species (ROS) have been implicated in mTBI-mediated axonal injury and pathogenesis. However, the underlying mechanisms and contributing factors are not completely understood. In this study, we explore these pathogenic mechanisms utilizing a murine model of repetitive mTBI (r-mTBI) involving five closed-skull concussions in young adult C57BL/6J mice. We observed a significant elevation of Na+/H+ exchanger protein (NHE1) expression in GFAP+ reactive astrocytes, IBA1+ microglia, and OLIG2+ oligodendrocytes across various brain regions (including the cerebral cortex, corpus callosum, and hippocampus) after r-mTBI. This elevation was accompanied by astrogliosis, microgliosis, and the accumulation of amyloid precursor protein (APP). Mice subjected to r-mTBI displayed impaired motor learning and spatial memory. However, post-r-mTBI administration of a potent NHE1 inhibitor, HOE642, attenuated locomotor and cognitive functional deficits as well as pathological signatures of gliosis, oxidative stress, axonal damage, and white matter damage. These findings indicate NHE1 upregulation plays a role in r-mTBI-induced oxidative stress, axonal damage, and gliosis, suggesting NHE1 may be a promising therapeutic target to alleviate mTBI-induced injuries and restore neurological function.

How to Define and Meet Blood Pressure Targets After Traumatic Brain Injury: A Narrative Review

BACKGROUND

Traumatic brain injury (TBI) poses a significant challenge to healthcare providers, necessitating meticulous management of hemodynamic parameters to optimize patient outcomes. This article delves into the critical task of defining and meeting continuous arterial blood pressure (ABP) and cerebral perfusion pressure (CPP) targets in the context of severe TBI in neurocritical care settings.

METHODS

We narratively reviewed existing literature, clinical guidelines, and emerging technologies to propose a comprehensive approach that integrates real-time monitoring, individualized cerebral perfusion target setting, and dynamic interventions.

RESULTS

Our findings emphasize the need for personalized hemodynamic management, considering the heterogeneity of patients with TBI and the evolving nature of their condition. We describe the latest advancements in monitoring technologies, such as autoregulation-guided ABP/CPP treatment, which enable a more nuanced understanding of cerebral perfusion dynamics. By incorporating these tools into a proactive monitoring strategy, clinicians can tailor interventions to optimize ABP/CPP and mitigate secondary brain injury.

DISCUSSION

Challenges in this field include the lack of standardized protocols for interpreting multimodal neuromonitoring data, potential variability in clinical decision-making, understanding the role of cardiac output, and the need for specialized expertise and customized software to have individualized ABP/CPP targets regularly available. The patient outcome benefit of monitoring-guided ABP/CPP target definitions still needs to be proven in patients with TBI.

CONCLUSIONS

We recommend that the TBI community take proactive steps to translate the potential benefits of personalized ABP/CPP targets, which have been implemented in certain centers, into a standardized and clinically validated reality through randomized controlled trials.

Characterizing Diffusion from Microdialysis Catheters in the Human Brain: A Magnetic Resonance Imaging Study With Gadobutrol

Cerebral microdialysis (CMD) catheters allow continuous monitoring of patients' cerebral metabolism in severe traumatic brain injury (TBI). The catheters consist of a terminal semi-permeable membrane that is inserted into the brain's interstitium to allow perfusion fluid to equalize with the surrounding cerebral extracellular environment before being recovered through a central non-porous channel. However, it is unclear how far recovered fluid and suspended metabolites have diffused from within the brain, and therefore what volume or region of brain tissue the analyses of metabolism represent. We assessed diffusion of the small magnetic resonance (MR)-detectible molecule gadobutrol from microdialysis catheters in six subjects (complete data five subjects, incomplete data one subject) who had sustained a severe TBI. Diffusion pattern and distance in cerebral white matter were assessed using T1 (time for MR spin-lattice relaxation) maps at 1 mm isotropic resolution in a 3 Tesla MR scanner. Gadobutrol at 10 mmol/L diffused from cerebral microdialysis catheters in a uniform spheroidal (ellipsoid of revolution) pattern around the catheters' semipermeable membranes, and across gray matter-white matter boundaries. Evidence of gadobutrol diffusion was found up to a mean of 13.4 ± 0.5 mm (mean ± standard deviation [SD]) from catheters, but with a steep concentration drop off so that ≤50% of maximum concentration was achieved at ∼4 mm, and ≤10% of maximum was found beyond ∼7 mm from the catheters. There was little variation between subjects. The relaxivity of gadobutrol in human cerebral white matter was estimated to be 1.61 ± 0.38 L.mmol-1sec-1 (mean ± SD); assuming gadobutrol remained extracellular thereby occupying 20% of total tissue volume (interstitium), and concentration equilibrium with perfusion fluid was achieved immediately adjacent to catheters after 24 h of perfusion. No statistically significant change was found in the concentration of the extracellular metabolites glucose, lactate, pyruvate, nor the lactate/pyruvate ratio during gadobutrol perfusion when compared with period of baseline microdialysis perfusion. Cerebral microdialysis allows continuous monitoring of regional cerebral metabolism-the volume of which is now clearer from this study. It also has the potential to deliver small molecule therapies to focal pathologies of the human brain. This study provides a platform for future development of new catheters optimally designed to treat such conditions.

Friedman's Gradient-Boosting Algorithm Predicts Lactate-Pyruvate Ratio Trends in Cases of Intracerebral Hemorrhages

OBJECTIVE

The local effects of an intracerebral hemorrhage (ICH) on surrounding brain tissue can be detected bedside using multimodal brain monitoring techniques. The aim of this study is to design a gradient boosting regression model using the R package boostmtree with the ability to predict lactate-pyruvate ratio measurements in ICH.

METHODS

We performed a retrospective analysis of 6 spontaneous ICH and 6 traumatic ICH patients who underwent surgical removal of the clot with microdialysis catheters placed in the perihematomal zone. Predictors of glucose, lactate, pyruvate, age, sex, diagnosis, and operation status were used to design our model.

RESULTS

In a holdout analysis, the model forecasted lactate-pyruvate ratio trends in a representative in-sample testing set. We anticipate that boostmtree could be applied to designs of similar regression models to analyze trends in other multimodal monitoring features across other types of acute brain injury.

CONCLUSIONS

The model successfully predicted hourly lactate-pyruvate ratios in spontaneous ICH and traumatic ICH cases after the hemorrhage evacuation and displayed significantly better performance than linear models. Our results suggest that boostmtree may be a powerful tool in developing more advanced mathematical models to assess other multimodal monitoring parameters for cases in which the perihematomal environment is monitored.

Sphingolipid changes in mouse brain and plasma after mild traumatic brain injury at the acute phases

BACKGROUND

Traumatic brain injury (TBI) causes neuroinflammation and can lead to long-term neurological dysfunction, even in cases of mild TBI (mTBI). Despite the substantial burden of this disease, the management of TBI is precluded by an incomplete understanding of its cellular mechanisms. Sphingolipids (SPL) and their metabolites have emerged as key orchestrators of biological processes related to tissue injury, neuroinflammation, and inflammation resolution. No study so far has investigated comprehensive sphingolipid profile changes immediately following TBI in animal models or human cases. In this study, sphingolipid metabolite composition was examined during the acute phases in brain tissue and plasma of mice following mTBI.

METHODS

Wildtype mice were exposed to air-blast-mediated mTBI, with blast exposure set at 50-psi on the left cranium and 0-psi designated as Sham. Sphingolipid profile was analyzed in brain tissue and plasma during the acute phases of 1, 3, and 7 days post-TBI via liquid-chromatography-mass spectrometry. Simultaneously, gene expression of sphingolipid metabolic markers within brain tissue was analyzed using quantitative reverse transcription-polymerase chain reaction. Significance (P-values) was determined by non-parametric t-test (Mann-Whitney test) and by Tukey's correction for multiple comparisons.

RESULTS

In post-TBI brain tissue, there was a significant elevation of 1) acid sphingomyelinase (aSMase) at 1- and 3-days, 2) neutral sphingomyelinase (nSMase) at 7-days, 3) ceramide-1-phosphate levels at 1 day, and 4) monohexosylceramide (MHC) and sphingosine at 7-days. Among individual species, the study found an increase in C18:0 and a decrease in C24:1 ceramides (Cer) at 1 day; an increase in C20:0 MHC at 3 days; decrease in MHC C18:0 and increase in MHC C24:1, sphingomyelins (SM) C18:0, and C24:0 at 7 days. Moreover, many sphingolipid metabolic genes were elevated at 1 day, followed by a reduction at 3 days and an absence at 7-days post-TBI. In post-TBI plasma, there was 1) a significant reduction in Cer and MHC C22:0, and an increase in MHC C16:0 at 1 day; 2) a very significant increase in long-chain Cer C24:1 accompanied by significant decreases in Cer C24:0 and C22:0 in MHC and SM at 3 days; and 3) a significant increase of C22:0 in all classes of SPL (Cer, MHC and SM) as well as a decrease in Cer C24:1, MHC C24:1 and MHC C24:0 at 7 days.

CONCLUSIONS

Alterations in sphingolipid metabolite composition, particularly sphingomyelinases and short-chain ceramides, may contribute to the induction and regulation of neuroinflammatory events in the early stages of TBI, suggesting potential targets for novel diagnostic, prognostic, and therapeutic strategies in the future.

PGK1 Is Involved in the HIF-1 Signaling Pathway as a Hub Gene for Ferroptosis After Traumatic Brain Injury

The pathogenesis of ferroptosis in traumatic brain injury (TBI) is unclear; therefore, we aimed to identify key molecules associated with ferroptosis in TBI using bioinformatics analysis to determine its underlying mechanisms. GSE128543 dataset was downloaded from the Gene Expression Omnibus (GEO) database, and TBI-associated modules were obtained by weighted gene co-expression network analysis (WGCNA). We identified 60 differentially expressed genes (DEGs) by intersecting the modules with ferroptosis and glycolysis/gluconeogenesis gene libraries. The hypoxia-inducible factor-1 (HIF-1) signaling pathway was identified to be critical for ferroptosis post-TBI, and protein-protein interaction (PPI) network identified 20 hub genes, including phosphoglycerate kinase 1 (PGK1), ribosomal protein (RP) family, pyruvate kinase M1/2 (PKM), hypoxia-inducible factor 1α subunit (HIF-1α), and MYC genes. In this study, we further explored the role of PGK1, a gene involved in HIF-1 signaling pathway; however, its role and mechanism in TBI are still unclear. Moreover, we constructed a TBI mouse model and examined PGK1 and HIF-1α expression levels, and the results revealed their expressions increased after cortical injury in mice and they co-localized in the same cells. Furthermore, we examined the expressions of PGK1 in the cerebrospinal fluid of 20 clinical patients with different degrees of brain injuries within 48 h of surgery and examined the cognitive function of patients according to the Glasgow Coma Scale (GCS). The results revealed that PGK1 expression level was negatively correlated with the severity of the brain injury. These findings suggest that PGK1 may become a potential hub gene for ferroptosis via the HIF-1 signaling pathway, second to neurological injury after TBI, thereby affecting patient prognosis.

Cerebral perfusion and metabolism with mild hypercapnia vs. normocapnia in a porcine post cardiac arrest model with and without targeted temperature management

Aim

To determine whether targeting mild hypercapnia (PaCO2 7 kPa) would yield improved cerebral blood flow and metabolism compared to normocapnia (PaCO2 5 kPa) with and without targeted temperature management to 33 °C (TTM33) in a porcine post-cardiac arrest model.

Methods

39 pigs were resuscitated after 10 minutes of cardiac arrest using cardiopulmonary bypass and randomised to TTM33 or no-TTM, and hypercapnia or normocapnia. TTM33 was managed with intravasal cooling. Animals were stabilized for 30 minutes followed by a two-hour intervention period. Hemodynamic parameters were measured continuously, and neuromonitoring included intracranial pressure (ICP), pressure reactivity index, cerebral blood flow, brain-tissue pCO2 and microdialysis. Measurements are reported as proportion of baseline, and areas under the curve during the 120 min intervention period were compared.

Results

Hypercapnia increased cerebral flow in both TTM33 and no-TTM groups, but also increased ICP (199% vs. 183% of baseline, p = 0.018) and reduced cerebral perfusion pressure (70% vs. 84% of baseline, p < 0.001) in no-TTM animals. Cerebral lactate (196% vs. 297% of baseline, p < 0.001), pyruvate (118% vs. 152% of baseline, p < 0.001), glycerol and lactate/pyruvate ratios were lower with hypercapnia in the TTM33 group, but only pyruvate (133% vs. 150% of baseline, p = 0.002) was lower with hypercapnia among no-TTM animals.

Conclusion

In this porcine post-arrest model, hypercapnia led to increased cerebral flow both with and without hypothermia, but also increased ICP and reduced cerebral perfusion pressure in no-TTM animals. The effects of hypercapnia were different with and without TTM.(Institutional protocol number: FOTS, id 14931).

Intraoperative application of intelligent, responsive, self-assembling hydrogel rectifies oxygen and energy metabolism in traumatically injured brain

In managing severe traumatic brain injury (TBI), emergency surgery involving the removal of damaged brain tissue and intracerebral hemorrhage is a priority. Secondary brain injury caused by oxidative stress and energy metabolic disorders, triggered by both primary mechanical brain damage and surgical insult, is also a determining factor in the prognosis of TBI. Unfortunately, the effectiveness of traditional postoperative intravenous neuroprotective agents therapy is often limited by the lack of targeting, timeliness, and side effects when neuroprotective agents systemically delivered. Here, we have developed injectable, intelligent, self-assembling hydrogels (P-RT/2DG) that can achieve precise treatment through intraoperative application to the target area. P-RT/2DG hydrogels were prepared by integrating a reactive oxygen species (ROS)-responsive thioketal linker (RT) into polyethylene glycol. By scavenging ROS and releasing 2-deoxyglucose (2DG) during degradation, these hydrogels functioned both in antioxidation and energy metabolism to inhibit the vicious cycle of post-TBI ROS-lactate which provoked secondary injury. In vitro and in vivo tests confirmed the absence of systemic side effects and the neuroprotective function of P-RT/2DG hydrogels in reducing edema, nerve cell apoptosis, neuroinflammation, and maintaining the blood-brain barrier. Our study thus provides a potential treatment strategy with novel hydrogels in TBI.

Brain metabolism response to intrahospital transfers in neurocritical ill patients and the impact of microdialysis probe location

Intrahospital transfer (IHT), a routine in the management of neurocritical patients requiring imaging or interventions, might affect brain metabolism. Studies about IHT effects using microdialysis (MD) have produced conflicting results. In these studies, only the most damaged hemisphere was monitored, and those may not reflect the impact of IHT on overall brain metabolism, nor do they address differences between the hemispheres. Herein we aimed to quantify the effect of IHT on brain metabolism by monitoring both hemispheres with bilateral MD. In this study, 27 patients with severe brain injury (10 traumatic brain injury and 17 subarachnoid hemorrhage patients) were included, with a total of 67 IHT. Glucose, glycerol, pyruvate and lactate were measured by MD in both hemispheres for 10 h pre- and post-IHT. Alterations in metabolite levels after IHT were observed on both hemispheres; although these changes were more marked in hemisphere A (most damaged) than B (less damaged). Our results suggest that brain metabolism is altered after an IHT of neurocritical ill patients particularly but not limited to the damaged hemisphere. Bilateral monitorization may be more sensitive than unilateral monitorization for detecting metabolic disturbances not directly related to the course of the disease.

Tracing the path of disruption: 13C isotope applications in traumatic brain injury-induced metabolic dysfunction

Cerebral metabolic dysfunction is a critical pathological hallmark observed in the aftermath of traumatic brain injury (TBI), as extensively documented in clinical investigations and experimental models. An in-depth understanding of the bioenergetic disturbances that occur following TBI promises to reveal novel therapeutic targets, paving the way for the timely development of interventions to improve patient outcomes. The 13C isotope tracing technique represents a robust methodological advance, harnessing biochemical quantification to delineate the metabolic trajectories of isotopically labeled substrates. This nuanced approach enables real-time mapping of metabolic fluxes, providing a window into the cellular energetic state and elucidating the perturbations in key metabolic circuits. By applying this sophisticated tool, researchers can dissect the complexities of bioenergetic networks within the central nervous system, offering insights into the metabolic derangements specific to TBI pathology. Embraced by both animal studies and clinical research, 13C isotope tracing has bolstered our understanding of TBI-induced metabolic dysregulation. This review synthesizes current applications of isotope tracing and its transformative potential in evaluating and addressing the metabolic sequelae of TBI.

Blood-Derived Metabolic Signatures as Biomarkers of Injury Severity in Traumatic Brain Injury: A Pilot Study

Metabolomic biomarkers hold promise in aiding the diagnosis and prognostication of traumatic brain injury. In Canada, over 165,000 individuals annually suffer from a traumatic brain injury (TBI), making it one of the most prevalent neurological conditions. In this pilot investigation, we examined blood-derived biomarkers as proxy measures that can provide an objective approach to TBI diagnosis and monitoring. Using a 1H nuclear magnetic resonance (NMR)-based quantitative metabolic profiling approach, this study determined whether (1) blood-derived metabolites change during recovery in male participants with mild to severe TBI; (2) biological pathway analysis reflects mechanisms that mediate neural damage/repair throughout TBI recovery; and (3) changes in metabolites correlate to initial injury severity. Eight male participants with mild to severe TBI (with intracranial lesions) provided morning blood samples within 1-4 days and again 6 months post-TBI. Following NMR analysis, the samples were subjected to multivariate statistical and machine learning-based analyses. Statistical modelling displayed metabolic changes during recovery through group separation, and eight significant metabolic pathways were affected by TBI. Metabolic changes were correlated to injury severity. L-alanine (R= -0.63, p < 0.01) displayed a negative relationship with the Glasgow Coma Scale. This study provides pilot data to support the feasibility of using blood-derived metabolites to better understand changes in biochemistry following TBI.

Neuromonitoring in Children with Traumatic Brain Injury

Traumatic brain injury remains a major cause of mortality and morbidity in children across the world. Current management based on international guidelines focuses on a fixed therapeutic target of less than 20 mm Hg for managing intracranial pressure and 40-50 mm Hg for cerebral perfusion pressure across the pediatric age group. To improve outcome from this complex disease, it is essential to understand the pathophysiological mechanisms responsible for disease evolution by using different monitoring tools. In this narrative review, we discuss the neuromonitoring tools available for use to help guide management of severe traumatic brain injury in children and some of the techniques that can in future help with individualizing treatment targets based on advanced cerebral physiology monitoring.

In-vitro gadolinium retro-microdialysis in agarose gel-a human brain phantom study

Rationale and objectives

Cerebral microdialysis is a technique that enables monitoring of the neurochemistry of patients with significant acquired brain injury, such as traumatic brain injury (TBI) and subarachnoid haemorrhage (SAH). Cerebral microdialysis can also be used to characterise the neuro-pharmacokinetics of small-molecule study substrates using retrodialysis/retromicrodialysis. However, challenges remain: (i) lack of a simple, stable, and inexpensive brain tissue model for the study of drug neuropharmacology; and (ii) it is unclear how far small study-molecules administered via retrodialysis diffuse within the human brain.

Materials and methods

Here, we studied the radial diffusion distance of small-molecule gadolinium-DTPA from microdialysis catheters in a newly developed, simple, stable, inexpensive brain tissue model as a precursor for in-vivo studies. Brain tissue models consisting of 0.65% weight/volume agarose gel in two kinds of buffers were created. The distribution of a paramagnetic contrast agent gadolinium-DTPA (Gd-DTPA) perfusion from microdialysis catheters using magnetic resonance imaging (MRI) was characterized as a surrogate for other small-molecule study substrates.

Results

We found the mean radial diffusion distance of Gd-DTPA to be 18.5 mm after 24 h (p < 0.0001).

Conclusion

Our brain tissue model provides avenues for further tests and research into infusion studies using cerebral microdialysis, and consequently effective focal drug delivery for patients with TBI and other brain disorders.

Brain Regional Energy Metabolism in Patients with Traumatic Brain Injury: A Cerebral Microdialysis Guided Study

BACKGROUND

In traumatic brain injuries (TBI), cerebral microdialysis (CMD)-derived parameters, especially the lactate to pyruvate ratio (LP ratio), have been utilized for cerebral perfusion optimization. The objectives were to identify cerebral ischemia as measured by CMD in TBI patients requiring decompressive craniectomy and to observe the correlation between cerebral perfusion pressure (CPP), intracranial pressure (ICP), and CMD variables in these patients. Our secondary aim was to observe the effect of CPP augmentation on ischemia biomarkers.

METHODS

After the Institute Ethics Committee approvals, seven adult patients requiring decompressive craniectomy following TBI were enrolled and CMD data were obtained prospectively for 72 h. CPP was augmented by 20% with noradrenaline infusion if LP ratio >40. Correlations were done with bootstrapping (n = 500) to obtain the confidence intervals (CI) due to the small sample size.

RESULTS

One patient had cerebral ischemia (median LP ratio of 265.5 and median pyruvate of 38 μmol/L), while another patient had non-ischemic mitochondrial dysfunction (median LP ratio 40.7 and median pyruvate 278.5). The coefficients of correlation between the LP ratio with CPP and ICP were r = -0.05 (CI = -0.14-0.03) and r = 0.09 (CI = -0.03-0.24), respectively. The coefficient of correlation between cerebral and blood glucose was r = 0.38, (CI - 0.35-0.14). Only two patients needed CPP augmentation, however, postaugmentation cerebral biochemistry did not change appreciably.

CONCLUSION

CMD can identify cerebral ischemia, however, no correlations were observed between the LP ratio and CPP or ICP. CPP augmentation did not improve cerebral biochemistry. More studies are required to understand and treat cerebral metabolism in TBI.

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.

Cerebral Metabolic Crisis in Pediatric Cerebral Malaria

Cerebral metabolic energy crisis (CMEC), often defined as a cerebrospinal fluid (CSF) lactate: pyruvate ratio (LPR) >40, occurs in various diseases and is associated with poor neurologic outcomes. Cerebral malaria (CM) causes significant mortality and neurodisability in children worldwide. Multiple factors that could lead to CMEC are plausible in these patients, but its frequency has not been explored. Fifty-three children with CM were enrolled and underwent analysis of CSF lactate and pyruvate levels. All 53 patients met criteria for a CMEC (median CSF LPR of 72.9 [interquartile range [IQR]: 58.5-93.3]). Half of children met criteria for an ischemic CMEC (median LPR of 85 [IQR: 73-184]) and half met criteria for a nonischemic CMEC (median LPR of 60 [IQR: 54-79]. Children also underwent transcranial doppler ultrasound investigation. Cerebral blood flow velocities were more likely to meet diagnostic criteria for low flow (<2 standard deviation from normal) or vasospasm in children with an ischemic CMEC (73%) than in children with a nonischemic CMEC (20%, p  = 0.04). Children with an ischemic CMEC had poorer outcomes (pediatric cerebral performance category of 3-6) than those with a nonischemic CMEC (46 vs. 22%, p  = 0.03). CMEC was ubiquitous in this patient population and the processes underlying the two subtypes (ischemic and nonischemic) may represent targets for future adjunctive therapies.

Quantification of pyruvate in-vitro using mid-infrared spectroscopy: Developing a system for microdialysis monitoring in traumatic brain injury patients

Introduction

Complex metabolic disruption is a major aspect of the pathophysiology of traumatic brain injury (TBI). Pyruvate is an intermediate in glucose metabolism and considered one of the most clinically informative metabolites during neurocritical care of TBI patients, especially in deducing the lactate/pyruvate ratio (LPR) - a widely-used metric for probing the brain's metabolic redox state. LPR is conventionally measured offline on a bedside analyzer, on hourly accumulations of brain microdialysate. However, there is increasing interest within the field to quantify microdialysate pyruvate and LPR continuously in near-real-time within its pathophysiological range. We have previously measured pure standard pyruvate in-vitro using mid-infrared transmission, employing a commercially available external cavity-quantum cascade laser (EC-QCL) and a microfluidic flow cell and reported a limit of detection (LOD) of 0.1 mM.

Research question

The present study was to test whether the current commercially available state-of-the-art mid-infrared transmission system, can detect pyruvate levels lower than previously reported.

Materials and methods

We measured pyruvate in perfusion fluid on the mid-infrared transmission system also equipped with an EC-QCL and microfluidic flow cells, tested at three pathlengths.

Results

We characterised the system to extract its relevant figures-of-merit and report the LOD of 0.07 mM.

Discussion and conclusion

The reported LOD of 0.07 mM represents a clinically recognised threshold and is the lowest value reported in the field for a sensor that can be coupled to microdialysis. While work is ongoing for a definitive evaluation of the system to measuring pyruvate, these preliminary results set a good benchmark and reference against which future developments can be examined.

High-physiological and supra-physiological 1,2-13C2 glucose focal supplementation to the traumatised human brain

How to optimise glucose metabolism in the traumatised human brain remains unclear, including whether injured brain can metabolise additional glucose when supplied. We studied the effect of microdialysis-delivered 1,2-13C2 glucose at 4 and 8 mmol/L on brain extracellular chemistry using bedside ISCUSflex, and the fate of the 13C label in the 8 mmol/L group using high-resolution NMR of recovered microdialysates, in 20 patients. Compared with unsupplemented perfusion, 4 mmol/L glucose increased extracellular concentrations of pyruvate (17%, p = 0.04) and lactate (19%, p = 0.01), with a small increase in lactate/pyruvate ratio (5%, p = 0.007). Perfusion with 8 mmol/L glucose did not significantly influence extracellular chemistry measured with ISCUSflex, compared to unsupplemented perfusion. These extracellular chemistry changes appeared influenced by the underlying metabolic states of patients' traumatised brains, and the presence of relative neuroglycopaenia. Despite abundant 13C glucose supplementation, NMR revealed only 16.7% 13C enrichment of recovered extracellular lactate; the majority being glycolytic in origin. Furthermore, no 13C enrichment of TCA cycle-derived extracellular glutamine was detected. These findings indicate that a large proportion of extracellular lactate does not originate from local glucose metabolism, and taken together with our earlier studies, suggest that extracellular lactate is an important transitional step in the brain's production of glutamine.

3D Printed Customizable Microsampling Devices for Neuroscience Applications

Multifunctional devices that incorporate chemical or physical measurements combined with ways to manipulate brain tissue via drug delivery, electrical stimulation, or light for optogenetics are desired by neuroscientists. The next generation in vivo brain devices will likely utilize the extensive flexibility and rapid processing of 3D printing. This Perspective demonstrates how close we are to this reality for advanced neuroscience measurements. 3D printing provides the opportunity to improve microsampling-based devices in ways that have not been previously available. Not only can 3D printing be used for actual device creation, but it can also allow printing of peripheral objects necessary to assemble functional devices. The most probable 3D printing set up for microsampling devices with appropriate nm to μm feature size will likely require 2-photon polymerization-based printers. This Perspective describes the advantages and challenges for 3D printing of microsampling devices as an initial step to meet the next generation device needs of neuroscientists.

Optimization of Nutrition after Brain Injury: Mechanistic and Therapeutic Considerations

Emerging science continues to establish the detrimental effects of malnutrition in acute neurological diseases such as traumatic brain injury, stroke, status epilepticus and anoxic brain injury. The primary pathological pathways responsible for secondary brain injury include neuroinflammation, catabolism, immune suppression and metabolic failure, and these are exacerbated by malnutrition. Given this, there is growing interest in novel nutritional interventions to promote neurological recovery after acute brain injury. In this review, we will describe how malnutrition impacts the biomolecular mechanisms of secondary brain injury in acute neurological disorders, and how nutritional status can be optimized in both pediatric and adult populations. We will further highlight emerging therapeutic approaches, including specialized diets that aim to resolve neuroinflammation, immunodeficiency and metabolic crisis, by providing pre-clinical and clinical evidence that their use promotes neurologic recovery. Using nutrition as a targeted treatment is appealing for several reasons that will be discussed. Given the high mortality and both short- and long-term morbidity associated with acute brain injuries, novel translational and clinical approaches are needed.

Hyperpolarized 13C metabolic imaging detects long-lasting metabolic alterations following mild repetitive traumatic brain injury

Career athletes, active military, and head trauma victims are at increased risk for mild repetitive traumatic brain injury (rTBI), a condition that contributes to the development of epilepsy and neurodegenerative diseases. Standard clinical imaging fails to identify rTBI-induced lesions, and novel non-invasive methods are needed. Here, we evaluated if hyperpolarized 13C magnetic resonance spectroscopic imaging (HP 13C MRSI) could detect long-lasting changes in brain metabolism 3.5 months post-injury in a rTBI mouse model. Our results show that this metabolic imaging approach can detect changes in cortical metabolism at that timepoint, whereas multimodal MR imaging did not detect any structural or contrast alterations. Using Machine Learning, we further show that HP 13C MRSI parameters can help classify rTBI vs. Sham and predict long-term rTBI-induced behavioral outcomes. Altogether, our study demonstrates the potential of metabolic imaging to improve detection, classification and outcome prediction of previously undetected rTBI.

Cerebro-spinal fluid glucose and lactate concentrations changes in response to therapies in patIents with primary brain injury: the START-TRIP study

INTRODUCTION

Altered levels of cerebrospinal fluid (CSF) glucose and lactate concentrations are associated with poor outcomes in acute brain injury patients. However, no data on changes in such metabolites consequently to therapeutic interventions are available. The aim of the study was to assess CSF glucose-to-lactate ratio (CGLR) changes related to therapies aimed at reducing intracranial pressure (ICP).

METHODS

A multicentric prospective cohort study was conducted in 12 intensive care units (ICUs) from September 2017 to March 2022. Adult (> 18 years) patients admitted after an acute brain injury were included if an external ventricular drain (EVD) for intracranial pressure (ICP) monitoring was inserted within 24 h of admission. During the first 48-72 h from admission, CGLR was measured before and 2 h after any intervention aiming to reduce ICP ("intervention"). Patients with normal ICP were also sampled at the same time points and served as the "control" group.

RESULTS

A total of 219 patients were included. In the intervention group (n = 115, 53%), ICP significantly decreased and CPP increased. After 2 h from the intervention, CGLR rose in both the intervention and control groups, although the magnitude was higher in the intervention than in the control group (20.2% vs 1.6%; p = 0.001). In a linear regression model adjusted for several confounders, therapies to manage ICP were independently associated with changes in CGLR. There was a weak inverse correlation between changes in ICP and CGRL in the intervention group.

CONCLUSIONS

In this study, CGLR significantly changed over time, regardless of the study group. However, these effects were more significant in those patients receiving interventions to reduce ICP.

Invasive Neuromonitoring Modalities in the Pediatric Population

Invasive neuromonitoring has become an important part of pediatric neurocritical care, as neuromonitoring devices provide objective data that can guide patient management in real time. New modalities continue to emerge, allowing clinicians to integrate data that reflect different aspects of cerebral function to optimize patient management. Currently, available common invasive neuromonitoring devices that have been studied in the pediatric population include the intracranial pressure monitor, brain tissue oxygenation monitor, jugular venous oximetry, cerebral microdialysis, and thermal diffusion flowmetry. In this review, we describe these neuromonitoring technologies, including their mechanisms of function, indications for use, advantages and disadvantages, and efficacy, in pediatric neurocritical care settings with respect to patient outcomes.

Traumatic Brain Injury: Intraoperative Management and Intensive Care Unit Multimodality Monitoring

Traumatic brain injury is a devastating event associated with substantial morbidity. Pathophysiology involves the initial trauma, subsequent inflammatory response, and secondary insults, which worsen brain injury severity. Management entails cardiopulmonary stabilization and diagnostic imaging with targeted interventions, such as decompressive hemicraniectomy, intracranial monitors or drains, and pharmacological agents to reduce intracranial pressure. Anesthesia and intensive care requires control of multiple physiologic variables and evidence-based practices to reduce secondary brain injury. Advances in biomedical engineering have enhanced assessments of cerebral oxygenation, pressure, metabolism, blood flow, and autoregulation. Many centers employ multimodality neuromonitoring for targeted therapies with the hope to improve recovery.

A randomized, double-blind trial comparing the effect of two blood pressure targets on global brain metabolism after out-of-hospital cardiac arrest

PURPOSE

This study aimed to assess the effect of different blood pressure levels on global cerebral metabolism in comatose patients resuscitated from out-of-hospital cardiac arrest (OHCA).

METHODS

In a double-blinded trial, we randomly assigned 60 comatose patients following OHCA to low (63 mmHg) or high (77 mmHg) mean arterial blood pressure (MAP). The trial was a sub-study in the Blood Pressure and Oxygenation Targets after Out-of-Hospital Cardiac Arrest-trial (BOX). Global cerebral metabolism utilizing jugular bulb microdialysis (JBM) and cerebral oxygenation (rSO₂) was monitored continuously for 96 h. The lactate-to-pyruvate (LP) ratio is a marker of cellular redox status and increases during deficient oxygen delivery (ischemia, hypoxia) and mitochondrial dysfunction. The primary outcome was to compare time-averaged means of cerebral energy metabolites between MAP groups during post-resuscitation care. Secondary outcomes included metabolic patterns of cerebral ischemia, rSO₂, plasma neuron-specific enolase level at 48 h and neurological outcome at hospital discharge (cerebral performance category).

RESULTS

We found a clear separation in MAP between the groups (15 mmHg, p < 0.001). Cerebral biochemical variables were not significantly different between MAP groups (LPR low MAP 19 (16-31) vs. high MAP 23 (16-33), p = 0.64). However, the LP ratio remained high (> 16) in both groups during the first 30 h. During the first 24 h, cerebral lactate > 2.5 mM, pyruvate levels > 110 µM, LP ratio > 30, and glycerol > 260 µM were highly predictive for poor neurological outcome and death with AUC 0.80. The median (IQR) rSO₂ during the first 48 h was 69.5% (62.0-75.0%) in the low MAP group and 69.0% (61.3-75.5%) in the high MAP group, p = 0.16.

CONCLUSIONS

Among comatose patients resuscitated from OHCA, targeting a higher MAP 180 min after ROSC did not significantly improve cerebral energy metabolism within 96 h of post-resuscitation care. Patients with a poor clinical outcome exhibited significantly worse biochemical patterns, probably illustrating that insufficient tissue oxygenation and recirculation during the initial hours after ROSC were essential factors determining neurological outcome.

An overview of clinical cerebral microdialysis in acute brain injury

Cerebral microdialysis may be used in patients with severe brain injury to monitor their cerebral physiology. In this article we provide a concise synopsis with illustrations and original images of catheter types, their structure, and how they function. Where and how catheters are inserted, their identification on imaging modalities (CT and MRI), together with the roles of glucose, lactate/pyruvate ratio, glutamate, glycerol and urea are summarized in acute brain injury. The research applications of microdialysis including pharmacokinetic studies, retromicrodialysis, and its use as a biomarker for efficacy of potential therapies are outlined. Finally, we explore limitations and pitfalls of the technique, as well as potential improvements and future work that is needed to progress and expand the use of this technology.

Microdialysis-Based Classifications of Abnormal Metabolic States after Traumatic Brain Injury: A Systematic Review of the Literature

After traumatic brain injury (TBI), cerebral metabolism can become deranged, contributing to secondary injury. Cerebral microdialysis (CMD) allows cerebral metabolism assessment and is often used with other neuro-monitoring modalities. CMD-derived parameters such as the lactate/pyruvate ratio (LPR) show a failure of oxidative energy generation. CMD-based abnormal metabolic states can be described following TBI, informing the etiology of physiological derangements. This systematic review summarizes the published literature on microdialysis-based abnormal metabolic classifications following TBI. Original research studies in which the populations were patients with TBI were included. Studies that described CMD-based classifications of metabolic abnormalities were included in the synthesis of the narrative results. A total of 825 studies underwent two-step screening after duplicates were removed. Fifty-three articles that used CMD in TBI patients were included. Of these, 14 described abnormal metabolic states based on CMD parameters. Classifications were heterogeneous between studies. LPR was the most frequently used parameter in the classifications; high LPR values were described as metabolic crisis. Ischemia was consistently defined as high LPR with low CMD substrate levels (glucose or pyruvate). Mitochondrial dysfunction, describing inability to use energy substrate despite availability, was identified based on raised LPR with near-normal levels of pyruvate. This is the first systematic review summarizing the published literature on microdialysis-based abnormal metabolic states following TBI. Although variability exists among individual classifications, there is broad agreement about broad definitions of metabolic crisis, ischemia, and mitochondrial dysfunction. Identifying the etiology of deranged cerebral metabolism after TBI is important for targeting therapeutic interventions.

Cerebral microdialysis and glucopenia in traumatic brain injury: A review

Traditionally, intracranial pressure (ICP) and partial brain tissue oxygenation (PbtO₂) have been the primary invasive intracranial measurements used to guide management in patients with severe traumatic brain injury (TBI). After injury however, the brain develops an increased metabolic demand which may require an increment in the oxidative metabolism of glucose. Simultaneously, metabolic, and electrical dysfunction can lead to an inability to meet these demands, even in the absence of ischemia or increased intracranial pressure. Cerebral microdialysis provides the ability to accurately measure local concentrations of various solutes including lactate, pyruvate, glycerol and glucose. Experimental and clinical data demonstrate that such measurements of cellular metabolism can yield critical missing information about a patient's physiologic state and help limit secondary damage. Glucose management in traumatic brain injury is still an unresolved question. As cerebral glucose metabolism may be uncoupled from systemic glucose levels due to the metabolic dysfunction, measurement of cerebral extracellular glucose concentrations could provide more predictive information and prove to be a better biomarker to avoid secondary injury of at-risk brain tissue. Based on data obtained from cerebral microdialysis, specific interventions such as ICP-directed therapy, blood glucose increment, seizure control, and/or brain oxygen optimization can be instituted to minimize or prevent secondary insults. Thus, microdialysis measurements of parenchymal metabolic function provides clinically valuable information that cannot be obtained by other monitoring adjuncts in the standard ICU setting.

Technical notes on the placement of cerebral microdialysis: A single center experience

Background

Cerebral microdialysis enables monitoring of brain metabolism and can be an important part of multimodal monitoring strategies in a variety of brain injuries. Microdialysis catheters can be placed in brain parenchyma through a burr hole, a cranial bolt, or directly at the time of an open craniotomy or craniectomy. The location of catheters in relation to brain pathology is important to the interpretation of data and guidance of interventions.

Methods

Here we retrospectively review the use of cerebral microdialysis at a US Regional Medical Center between March 2018 and February 2022 and provide detailed descriptions and technical nuances of the different methods to place microdialysis catheters.

Results

Eighty two unique microdialysis catheters were utilized in 52 patients. 35 (42.68%) were placed via a quad-lumen bolt and 47 (57.32%) were placed through craniotomies. 27 catheters (32.93%) were placed in a perilesional location, 50 (60.98%) were located in healthy tissue, and 6 (7.32%) were mispositioned. No significant difference was seen between placement by bolt or craniotomy in regard to perilesional location, mispositioning, or complications.

Conclusion

With careful planning and thoughtful execution, cerebral microdialysis catheters can be successfully placed though a variety of strategies to optimize and individualize brain monitoring in different clinical settings. This paper provides a detailed guide for the various methods of catheter placement to help providers begin or expand their use of cerebral microdialysis.

Microglial-oligodendrocyte interactions in myelination and neurological function recovery after traumatic brain injury

Differential microglial inflammatory responses play a role in regulation of differentiation and maturation of oligodendrocytes (OLs) in brain white matter. How microglia-OL crosstalk is altered by traumatic brain injury (TBI) and its impact on axonal myelination and neurological function impairment remain poorly understood. In this study, we investigated roles of a Na⁺/H⁺ exchanger (NHE1), an essential microglial pH regulatory protein, in microglial proinflammatory activation and OL survival and differentiation in a murine TBI model induced by controlled cortical impact. Similar TBI-induced contusion volumes were detected in the Cx3cr1-Cre^ERT2 control (Ctrl) mice and selective microglial Nhe1 knockout (Cx3cr1-Cre^ERT2;Nhe1^flox/flox, Nhe1 cKO) mice. Compared to the Ctrl mice, the Nhe1 cKO mice displayed increased resistance to initial TBI-induced white matter damage and accelerated chronic phase of OL regeneration at 30 days post-TBI. The cKO brains presented increased anti-inflammatory phenotypes of microglia and infiltrated myeloid cells, with reduced proinflammatory transcriptome profiles. Moreover, the cKO mice exhibited accelerated post-TBI sensorimotor and cognitive functional recovery than the Ctrl mice. These phenotypic outcomes in cKO mice were recapitulated in C57BL6J wild-type TBI mice receiving treatment of a potent NHE1 inhibitor HOE642 for 1-7 days post-TBI. Taken together, these findings collectively demonstrated that blocking NHE1 protein stimulates restorative microglial activation in oligodendrogenesis and neuroprotection, which contributes to accelerated brain repair and neurological function recovery after TBI.

Cerebral Autoregulation Monitoring in Traumatic Brain Injury: An Overview of Recent Advances in Personalized Medicine

Impaired cerebral autoregulation (CA) in moderate/severe traumatic brain injury (TBI) has been identified as a strong associate with poor long-term outcomes, with recent data highlighting its dominance over cerebral physiologic dysfunction seen in the acute phase post injury. With advances in bedside continuous cerebral physiologic signal processing, continuously derived metrics of CA capacity have been described over the past two decades, leading to improvements in cerebral physiologic insult detection and development of novel personalized approaches to TBI care in the intensive care unit (ICU). This narrative review focuses on highlighting the concept of continuous CA monitoring and consequences of impairment in moderate/severe TBI. Further, we provide a comprehensive description and overview of the main personalized cerebral physiologic targets, based on CA monitoring, that are emerging as strong associates with patient outcomes. CA-based personalized targets, such as optimal cerebral perfusion pressure (CPPopt), lower/upper limit of regulation (LLR/ULR), and individualized intra-cranial pressure (iICP) are positioned to change the way we care for TBI patients in the ICU, moving away from the "one treatment fits all" paradigm of current guideline-based therapeutic approaches, towards a true personalized medicine approach tailored to the individual patient. Future perspectives regarding research needs in this field are also discussed.

Management of moderate to severe traumatic brain injury: an update for the intensivist

Traumatic brain injury (TBI) remains one of the most fatal and debilitating conditions in the world. Current clinical management in severe TBI patients is mainly concerned with reducing secondary insults and optimizing the balance between substrate delivery and consumption. Over the past decades, multimodality monitoring has become more widely available, and clinical management protocols have been published that recommend potential interventions to correct pathophysiological derangements. Even while evidence from randomized clinical trials is still lacking for many of the recommended interventions, these protocols and algorithms can be useful to define a clear standard of therapy where novel interventions can be added or be compared to. Over the past decade, more attention has been paid to holistic management, in which hemodynamic, respiratory, inflammatory or coagulation disturbances are detected and treated accordingly. Considerable variability with regards to the trajectories of recovery exists. Even while most of the recovery occurs in the first months after TBI, substantial changes may still occur in a later phase. Neuroprognostication is challenging in these patients, where a risk of self-fulfilling prophecies is a matter of concern. The present article provides a comprehensive and practical review of the current best practice in clinical management and long-term outcomes of moderate to severe TBI in adult patients admitted to the intensive care unit.

Serum metabolome associated with severity of acute traumatic brain injury

Complex metabolic disruption is a crucial aspect of the pathophysiology of traumatic brain injury (TBI). Associations between this and systemic metabolism and their potential prognostic value are poorly understood. Here, we aimed to describe the serum metabolome (including lipidome) associated with acute TBI within 24 h post-injury, and its relationship to severity of injury and patient outcome. We performed a comprehensive metabolomics study in a cohort of 716 patients with TBI and non-TBI reference patients (orthopedic, internal medicine, and other neurological patients) from the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) cohort. We identified panels of metabolites specifically associated with TBI severity and patient outcomes. Choline phospholipids (lysophosphatidylcholines, ether phosphatidylcholines and sphingomyelins) were inversely associated with TBI severity and were among the strongest predictors of TBI patient outcomes, which was further confirmed in a separate validation dataset of 558 patients. The observed metabolic patterns may reflect different pathophysiological mechanisms, including protective changes of systemic lipid metabolism aiming to maintain lipid homeostasis in the brain.

Multimodal brain monitoring following traumatic brain injury: A primer for intensive care practitioners

Traumatic brain injury (TBI) is common and potentially devastating. Traditional examination-based patient monitoring following TBI may be inadequate for frontline clinicians to reduce secondary brain injury through individualized therapy. Multimodal neurologic monitoring (MMM) offers great potential for detecting early injury and improving outcomes. By assessing cerebral oxygenation, autoregulation and metabolism, clinicians may be able to understand neurophysiology during acute brain injury, and offer therapies better suited to each patient and each stage of injury. Hence, we offer this primer on brain tissue oxygen monitoring, pressure reactivity index monitoring and cerebral microdialysis. This narrative review serves as an introductory guide to the latest clinically-relevant evidence regarding key neuromonitoring techniques.

Exogenous Ketones and Lactate as a Potential Therapeutic Intervention for Brain Injury and Neurodegenerative Conditions

Metabolic dysfunction is a ubiquitous underlying feature of many neurological conditions including acute traumatic brain injuries and chronic neurodegenerative conditions. A central problem in neurological patients, in particular those with traumatic brain injuries, is an impairment in the utilization of glucose, which is the predominant metabolic substrate in a normally functioning brain. In such patients, alternative substrates including ketone bodies and lactate become important metabolic candidates for maintaining brain function. While the potential neuroprotective benefits of ketosis have been recognized for up to almost a century, the majority of work has focused on the use of ketogenic diets to induce such a state, which is inappropriate in cases of acute disease due to the prolonged periods of time (i.e., weeks to months) required for the effects of a ketogenic diet to be seen. The following review seeks to explore the neuroprotective effects of exogenous ketone and lactate preparations, which have more recently become commercially available and are able to induce a deep ketogenic response in a fraction of the time. The rapid response of exogenous preparations makes their use as a therapeutic adjunct more feasible from a clinical perspective in both acute and chronic neurological conditions. Potentially, their ability to globally moderate long-term, occult brain dysfunction may also be relevant in reducing lifetime risks of certain neurodegenerative conditions. In particular, this review explores the association between traumatic brain injury and contusion-related dementia, assessing metabolic parallels and highlighting the potential role of exogenous ketone and lactate therapies.

Monitoring Neurochemistry in Traumatic Brain Injury Patients Using Microdialysis Integrated with Biosensors: A Review

In a traumatically injured brain, the cerebral microdialysis technique allows continuous sampling of fluid from the brain’s extracellular space. The retrieved brain fluid contains useful metabolites that indicate the brain’s energy state. Assessment of these metabolites along with other parameters, such as intracranial pressure, brain tissue oxygenation, and cerebral perfusion pressure, may help inform clinical decision making, guide medical treatments, and aid in the prognostication of patient outcomes. Currently, brain metabolites are assayed on bedside analysers and results can only be achieved hourly. This is a major drawback because critical information within each hour is lost. To address this, recent advances have focussed on developing biosensing techniques for integration with microdialysis to achieve continuous online monitoring. In this review, we discuss progress in this field, focusing on various types of sensing devices and their ability to quantify specific cerebral metabolites at clinically relevant concentrations. Important points that require further investigation are highlighted, and comments on future perspectives are provided.

Neuromonitoring in Severe Traumatic Brain Injury: A Bibliometric Analysis

Traumatic brain injury (TBI) is the leading cause of mortality and disability among trauma-related injuries. Neuromonitoring plays an essential role in the management and prognosis of patients with severe TBI. Our bibliometric study aimed to identify the knowledge base, define the research front, and outline the social networks on neuromonitoring in severe TBI. We conducted an electronic search for articles related to neuromonitoring in severe TBI in Scopus. A descriptive analysis retrieved evidence on the most productive authors and countries, the most cited articles, the most frequently publishing journals, and the most common author's keywords. Through a three-step network extraction process, we performed a collaboration analysis among universities and countries, a cocitation analysis, and a word cooccurrence analysis. A total of 1884 records formed the basis of our bibliometric study. We recorded an increasing scientific interest in the use of neuromonitoring in severe TBI. Czosnyka, Hutchinson, Menon, Smielewski, and Stocchetti were the most productive authors. The most cited document was a review study by Maas et al. There was an extensive collaboration among universities. The most common keywords were "intracranial pressure," with an increasing interest in magnetic resonance imaging and cerebral perfusion pressure monitoring. Neuromonitoring constitutes an area of active research. The present findings indicate that intracranial pressure monitoring plays a pivotal role in the management of severe TBI. Scientific interest shifts to magnetic resonance imaging and individualized patient care on the basis of optimal cerebral perfusion pressure.

Current state of high-fidelity multimodal monitoring in traumatic brain injury

INTRODUCTION

Multimodality monitoring of patients with severe traumatic brain injury (TBI) is primarily performed in neuro-critical care units to prevent secondary harmful brain insults and facilitate patient recovery. Several metrics are commonly monitored using both invasive and non-invasive techniques. The latest Brain Trauma Foundation guidelines from 2016 provide recommendations and thresholds for some of these. Still, high-level evidence for several metrics and thresholds is lacking.

METHODS

Regarding invasive brain monitoring, intracranial pressure (ICP) forms the cornerstone, and pressures above 22 mmHg should be avoided. From ICP, cerebral perfusion pressure (CPP) (mean arterial pressure (MAP)-ICP) and pressure reactivity index (PRx) (a correlation between slow waves MAP and ICP as a surrogate for cerebrovascular reactivity) may be derived. In terms of regional monitoring, partial brain tissue oxygen pressure (PbtO₂) is commonly used, and phase 3 studies are currently ongoing to determine its added effect to outcome together with ICP monitoring. Cerebral microdialysis (CMD) is another regional invasive modality to measure substances in the brain extracellular fluid. International consortiums have suggested thresholds and management strategies, in spite of lacking high-level evidence. Although invasive monitoring is generally safe, iatrogenic hemorrhages are reported in about 10% of cases, but these probably do not significantly affect long-term outcome. Non-invasive monitoring is relatively recent in the field of TBI care, and research is usually from single-center retrospective experiences. Near-infrared spectrometry (NIRS) measuring regional tissue saturation has been shown to be associated with outcome. Transcranial doppler (TCD) has several tentative utilities in TBI like measuring ICP and detecting vasospasm. Furthermore, serial sampling of biomarkers of brain injury in the blood can be used to detect secondary brain injury development.

CONCLUSIONS

In multimodal monitoring, the most important aspect is data interpretation, which requires knowledge of each metric's strengths and limitations. Combinations of several modalities might make it possible to discern specific pathologic states suitable for treatment. However, the cost-benefit should be considered as the incremental benefit of adding several metrics has a low level of evidence, thus warranting additional research.

Focally administered succinate improves cerebral metabolism in traumatic brain injury patients with mitochondrial dysfunction

Following traumatic brain injury (TBI), raised cerebral lactate/pyruvate ratio (LPR) reflects impaired energy metabolism. Raised LPR correlates with poor outcome and mortality following TBI. We prospectively recruited patients with TBI requiring neurocritical care and multimodal monitoring, and utilised a tiered management protocol targeting LPR. We identified patients with persistent raised LPR despite adequate cerebral glucose and oxygen provision, which we clinically classified as cerebral 'mitochondrial dysfunction' (MD). In patients with TBI and MD, we administered disodium 2,3-¹³C₂ succinate (12 mmol/L) by retrodialysis into the monitored region of the brain. We recovered ¹³C-labelled metabolites by microdialysis and utilised nuclear magnetic resonance spectroscopy (NMR) for identification and quantification.Of 33 patients with complete monitoring, 73% had MD at some point during monitoring. In 5 patients with multimodality-defined MD, succinate administration resulted in reduced LPR(-12%) and raised brain glucose(+17%). NMR of microdialysates demonstrated that the exogenous ¹³C-labelled succinate was metabolised intracellularly via the tricarboxylic acid cycle. By targeting LPR using a tiered clinical algorithm incorporating intracranial pressure, brain tissue oxygenation and microdialysis parameters, we identified MD in TBI patients requiring neurointensive care. In these, focal succinate administration improved energy metabolism, evidenced by reduction in LPR. Succinate merits further investigation for TBI therapy.

Association of Age and Sex With Multi-Modal Cerebral Physiology in Adult Moderate/Severe Traumatic Brain Injury: A Narrative Overview and Future Avenues for Personalized Approaches

The impact of age and biological sex on outcome in moderate/severe traumatic brain injury (TBI) has been documented in large cohort studies, with advanced age and male sex linked to worse long-term outcomes. However, the association between age/biological sex and high-frequency continuous multi-modal monitoring (MMM) cerebral physiology is unclear, with only sparing reference made in guidelines and major literature in moderate/severe TBI. In this narrative review, we summarize some of the largest studies associating various high-frequency MMM parameters with age and biological sex in moderate/severe TBI. To start, we present this by highlighting the representative available literature on high-frequency data from Intracranial Pressure (ICP), Cerebral Perfusion Pressure (CPP), Extracellular Brain Tissue Oxygenation (PbtO₂), Regional Cerebral Oxygen Saturations (rSO₂), Cerebral Blood Flow (CBF), Cerebral Blood Flow Velocity (CBFV), Cerebrovascular Reactivity (CVR), Cerebral Compensatory Reserve, common Cerebral Microdialysis (CMD) Analytes and their correlation to age and sex in moderate/severe TBI cohorts. Then we present current knowledge gaps in the literature, discuss biological implications of age and sex on cerebrovascular monitoring in TBI and some future avenues for bedside research into the cerebrovascular physiome after TBI.

Metabolic reprogramming mediates hippocampal microglial M1 polarization in response to surgical trauma causing perioperative neurocognitive disorders

Background

Microglial polarization toward pro-inflammatory M1 phenotype are major contributors to the development of perioperative neurocognitive disorders (PNDs). Metabolic reprogramming plays an important role in regulating microglial polarization. We therefore hypothesized that surgical trauma can activate microglial M1 polarization by metabolic reprogramming to induce hippocampal neuroinflammation and subsequent postoperative cognitive impairment.

Methods

We used aged mice to establish a model of PNDs, and investigated whether surgical trauma induced metabolic reprograming in hippocampus using PET/CT and GC/TOF–MS based metabolomic analysis. We then determined the effect of the glycolytic inhibitor 2-deoxy-d-glucose (2-DG) on hippocampal microglial M1 polarization, neuroinflammation, and cognitive function at 3 d after surgery.

Results

We found that surgery group had less context-related freezing time than either control or anesthesia group (P < 0.05) without significant difference in tone-related freezing time (P > 0.05). The level of Iba-1 fluorescence intensity in hippocampus were significantly increased in surgery group than that in control group (P < 0.05) accompanied by activated morphological changes of microglia and increased expression of iNOS/CD86 (M1 marker) in enriched microglia from hippocampus (P < 0.05). PET/CT and metabolomics analysis indicated that surgical trauma provoked the metabolic reprogramming from oxidative phosphorylation to glycolysis in hippocampus. Inhibition of glycolysis by 2-DG significantly alleviated the surgical trauma induced increase of M1 (CD86⁺CD206⁻) phenotype in enriched microglia from hippocampus and up-regulation of pro-inflammatory mediators (IL-1β and IL-6) expression in hippocampus. Furthermore, glycolytic inhibition by 2-DG ameliorated the hippocampus dependent cognitive deficit caused by surgical trauma.

Conclusions

Metabolic reprogramming is crucial for regulating hippocampal microglial M1 polarization and neuroinflammation in PNDs. Manipulating microglial metabolism might provide a valuable therapeutic strategy for treating PNDs.

Surgical trauma impaired the hippocampus-dependent contextual memory in age mice.

Surgical trauma induced microglial M1 polarization and subsequent neuroinflammation.

Metabolic reprogramming was crucial for regulating microglial M1 polarization in PNDs.

Modulating microglial metabolism might provide a valuable approach for treating PNDs.

Impact of Age and Biological Sex on Cerebrovascular Reactivity in Adult Moderate/Severe Traumatic Brain Injury: An Exploratory Analysis

Age and biological sex are two potential important modifiers of cerebrovascular reactivity post-traumatic brain injury (TBI) requiring close evaluation for potential subgroup responses. The goal of this study was to provide a preliminary exploratory analysis of the impact of age and biological sex on measures of cerebrovascular function in moderate/severe TBI. Forty-nine patients from the prospectively maintained TBI database at the University of Manitoba with archived high-frequency digital cerebral physiology were evaluated. Cerebrovascular reactivity indices were derived as follows: PRx (correlation between intracranial pressure [ICP] and mean arterial pressure [MAP]), PAx (correlation between pulse amplitude of ICP [AMP] and MAP), and RAC (correlation between AMP and cerebral perfusion pressure [CPP]). Time above clinically significant thresholds for each index was calculated over different periods of the acute intensive care unit stay. The association between PRx, PAx, and RAC measures with age was assessed using linear regression, and an age trichotomization scheme (<40, 40-60, >60) using Kruskal-Wallis testing. Similarly, association with biological sex was tested using Mann-Whitney U testing. Biological sex did not demonstrate an impact on any measures of cerebrovascular reactivity. Linear regression between age and PAx and RAC demonstrated a statistically significant positive linear relationship. Median PAx and RAC measures between trichotomized age categories demonstrated statistically significant increases with advancing age. The PRx failed to demonstrate any statistically significant relationship with age in this cohort, suggesting that in elderly patients with controlled ICP, PAx and RAC may be better metrics for detecting impaired cerebrovascular reactivity. Biological sex appears to not be associated with differences in cerebrovascular reactivity in this cohort. The PRx performed the worst in detecting impaired cerebrovascular reactivity in those with advanced age, where PAx and RAC appear to have excelled. Future work is required to validate these findings and explore the utility of different cerebrovascular reactivity indices.

Cerebral perfusion and metabolism with mean arterial pressure 90 vs. 60 mmHg in a porcine post cardiac arrest model with and without targeted temperature management

AIM

To determine whether targeting a mean arterial pressure of 90 mmHg (MAP90) would yield improved cerebral blood flow and less ischaemia compared to MAP 60 mmHg (MAP60) with and without targeted temperature management at 33 °C (TTM33) in a porcine post-cardiac arrest model.

METHODS

After 10 min of cardiac arrest, 41 swine of either sex were resuscitated until return of spontaneous circulation (ROSC). They were randomised to TTM33 or no-TTM, and MAP60 or MAP90; yielding four groups. Temperatures were managed with intravasal cooling and blood pressure targets with noradrenaline, vasopressin and nitroprusside, as appropriate. After 30 min of stabilisation, animals were observed for two hours. Cerebral perfusion pressure (CPP), cerebral blood flow (CBF), pressure reactivity index (PRx), brain tissue pCO2 (PbtCO2) and tissue intermediary metabolites were measured continuously and compared using mixed models.

RESULTS

Animals randomised to MAP90 had higher CPP (p < 0.001 for both no-TTM and TTM33) and CBF (no-TTM, p < 0.03; TH, p < 0.001) compared to MAP60 during the 150 min observational period post-ROSC. We also observed higher lactate and pyruvate in MAP60 irrespective of temperature, but no significant differences in PbtCO2 and lactate/pyruvate-ratio. We found lower PRx (indicating more intact autoregulation) in MAP90 vs. MAP60 (no-TTM, p = 0.04; TTM33, p = 0.03).

CONCLUSION

In this porcine cardiac arrest model, targeting MAP90 led to better cerebral perfusion and more intact autoregulation, but without clear differences in ischaemic markers, compared to MAP60.

INSTITUTIONAL PROTOCOL NUMBER

FOTS, id 8442.

Cerebral Microdialysate Metabolite Monitoring using Mid-infrared Spectroscopy

The brains of patients suffering from traumatic brain-injury (TBI) undergo dynamic chemical changes in the days following the initial trauma. Accurate and timely monitoring of these changes is of paramount importance for improved patient outcome. Conventional brain-chemistry monitoring is performed off-line by collecting and manually transferring microdialysis samples to an enzymatic colorimetric bedside analyzer every hour, which detects and quantifies the molecules of interest. However, off-line, hourly monitoring means that any subhourly neurochemical changes, which may be detrimental to patients, go unseen and thus untreated. Mid-infrared (mid-IR) spectroscopy allows rapid, reagent-free, molecular fingerprinting of liquid samples, and can be easily integrated with microfluidics. We used mid-IR transmission spectroscopy to analyze glucose, lactate, and pyruvate, three relevant brain metabolites, in the extracellular brain fluid of two TBI patients, sampled via microdialysis. Detection limits of 0.5, 0.2, and 0.1 mM were achieved for pure glucose, lactate, and pyruvate, respectively, in perfusion fluid using an external cavity-quantum cascade laser (EC-QCL) system with an integrated transmission flow-cell. Microdialysates were collected hourly, then pooled (3-4 h), and measured consecutively using the standard ISCUSflex analyzer and the EC-QCL system. There was a strong correlation between the compound concentrations obtained using the conventional bedside analyzer and the acquired mid-IR absorbance spectra, where a partial-least-squares regression model was implemented to compute concentrations. This study demonstrates the potential utility of mid-IR spectroscopy for continuous, automated, reagent-free, and online monitoring of the dynamic chemical changes in TBI patients, allowing a more timely response to adverse brain metabolism and consequently improving patient outcomes.

Integrative Neuroinformatics for Precision Prognostication and Personalized Therapeutics in Moderate and Severe Traumatic Brain Injury

Despite changes in guideline-based management of moderate/severe traumatic brain injury (TBI) over the preceding decades, little impact on mortality and morbidity have been seen. This argues against the "one-treatment fits all" approach to such management strategies. With this, some preliminary advances in the area of personalized medicine in TBI care have displayed promising results. However, to continue transitioning toward individually-tailored care, we require integration of complex "-omics" data sets. The past few decades have seen dramatic increases in the volume of complex multi-modal data in moderate and severe TBI care. Such data includes serial high-fidelity multi-modal characterization of the cerebral physiome, serum/cerebrospinal fluid proteomics, admission genetic profiles, and serial advanced neuroimaging modalities. Integrating these complex and serially obtained data sets, with patient baseline demographics, treatment information and clinical outcomes over time, can be a daunting task for the treating clinician. Within this review, we highlight the current status of such multi-modal omics data sets in moderate/severe TBI, current limitations to the utilization of such data, and a potential path forward through employing integrative neuroinformatic approaches, which are applied in other neuropathologies. Such advances are positioned to facilitate the transition to precision prognostication and inform a top-down approach to the development of personalized therapeutics in moderate/severe TBI.

Repeated 31P-MRS in severe traumatic brain injury: Insights into cerebral energy status and altered metabolism

Phosphorous magnetic resonance spectroscopy (31P-MRS) is suited to non-invasively investigate energy metabolism and to detect molecules containing phosphorus in the human brain. The aim of this longitudinal study was to perform 31P-MRS at two different time points (within 72 hours and between day 10-14) after severe traumatic brain injury (sTBI) to reveal alterations in cerebral energy metabolism. Twenty-six ventilated sTBI patients, aged between 20 to 75 years, with a median initial GCS of 5 were prospectively analyzed. 31P-MRS data of the structurally more affected side were compared to data from contralateral normal appearing areas and to data of age- and gender-matched healthy controls. There were no significant intraindividual differences between the lesioned and the less affected side at either of time points. In the acute phase, PCr/ATP and PCr/Pi were significantly elevated whereas PME/PDE and Pi/ATP were significantly decreased in contrast to healthy controls. In the subacute phase these differences gradually dissipated, remaining lower Pi/ATP ratio, and only partly altered levels of PCr/Pi and PME/PDE. Our data affirm that cerebral metabolism is globally altered after sTBI, demonstrating the diffuse impairment of brain bioenergetics at multiple levels, with resultant developments in terms of time.

Duraplasty in Traumatic Thoracic Spinal Cord Injury: Impact on Spinal Cord Hemodynamics, Tissue Metabolism, Histology, and Behavioral Recovery Using a Porcine Model

After acute traumatic spinal cord injury (SCI), the spinal cord can swell to fill the subarachnoid space and become compressed by the surrounding dura. In a porcine model of SCI, we performed a duraplasty to expand the subarachnoid space around the injured spinal cord and evaluated how this influenced acute intraparenchymal hemodynamic and metabolic responses, in addition to histological and behavioral recovery. Female Yucatan pigs underwent a T10 SCI, with or without duraplasty. Using microsensors implanted into the spinal cord parenchyma, changes in blood flow (ΔSCBF), oxygenation (ΔPO₂), and spinal cord pressure (ΔSCP) during and after SCI were monitored, alongside metabolic responses. Behavioral recovery was tested weekly using the Porcine Injury Behavior Scale (PTIBS). Thereafter, spinal cords were harvested for tissue sparing analyses. In both duraplasty and non-animals, the ΔSCP increased ∼5 mm Hg in the first 6 h post-injury. After this, the SCP appeared to be slightly reduced in the duraplasty animals, although the group differences were not statistically significant after controlling for injury severity in terms of impact force. During the first seven days post-SCI, the ΔSCBF or ΔPO₂ values were not different between the duraplasty and control animals. Over 12 weeks, there was no improvement in hindlimb locomotion as assessed by PTIBS scores and no reduction in tissue damage at the injury site in the duraplasty animals. In our porcine model of SCI, duraplasty did not provide any clear evidence of long-term behavioral or tissue sparing benefit after SCI.

Relationship Between Glycosylated Hemoglobin and Short-Term Mortality of Spontaneous Intracerebral Hemorrhage

Background: The relationship between glycosylated hemoglobin (HbA1c) and prognosis of spontaneous intracerebral hemorrhage (SICH) patients has not been fully elucidated. This study aimed to reveal the relationship between HbA1c levels and short-term mortality after patient admission with SICH. Methods: It was a large-scale, multicenter, cross-sectional study. From August 1, 2015, to July 31, 2019, a total of 41910 SICH patients were included in the study from the Chinese Stroke Center Alliance (CSCA) program. Finally, we comprehensively analyzed the data from 21,116 patients with SICH. HbA1c was categorized into four groups by quartile. Univariate and multivariate logistic regression analyses were used to assess the association between HbA1c levels and short-term mortality in SICH patients. Results: The average age of the 21,116 patients was 62.8 ± 13.2 years; 13,052 (61.8%) of them were male, and 507 (2.4%) of them died. Compared to the higher three quartiles of HbA1c, the lowest quartile (≤5.10%) had higher short-term mortality. In subgroup analysis with or without diabetes mellitus (DM) patients, the mortality of the Q3 group at 5.60-6.10% was significantly lower than that of the Q1 group at ≤5.10%. After adjustment for potential influencing factors, the ROC curve of HbA1c can better predict the short-term mortality of patients with SICH (AUC = 0.6286 P < 0.001). Conclusions: Therefore, we concluded that low or extremely low HbA1c levels (≤5.10%) after stroke were associated with higher short-term mortality in SICH patients, with or without DM.