Cerebral glutamine and glutamate levels in relation to compromised energy metabolism: a microdialysis study in subarachnoid hemorrhage patients

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.

EARLY DECREASED RESPIRATORY CHAIN CAPACITY IN RESUSCITATED EXPERIMENTAL SEPSIS IS A MAJOR CONTRIBUTOR TO LACTATE PRODUCTION

ABSTRACT

Background : Increased plasma lactate levels in patients with sepsis may be due to insufficient oxygen delivery, but mitochondrial dysfunction or accelerated glycolysis may also contribute. We studied the effect of the latter on muscle metabolism by using microdialysis in a sepsis model with sustained oxygen delivery and decreased energy consumption or mitochondrial blockade. Methods : Pigs were subjected to continuous Escherichia coli infusion (sepsis group, n = 12) or saline infusion (sham group, n = 4) for 3 h. Protocolized interventions were applied to normalize the oxygen delivery and blood pressure. Microdialysis catheters were used to monitor muscle metabolism (naïve). The same catheters were used to block the electron transport chain with cyanide or the Na + /K + -ATPase inhibitor, ouabain locally. Results: All pigs in the sepsis group had positive blood cultures and a Sequential Organ Failure Assessment score increase by at least 2, fulfilling the sepsis criteria. Plasma lactate was higher in the sepsis group than in the sham group ( P < 0.001), whereas muscle glucose was lower in the sepsis group ( P < 0.01). There were no changes in muscle lactate levels over time but lactate to pyruvate ratio (LPR) was elevated in the sepsis versus the sham group ( P < 0.05). Muscle lactate, LPR, and glutamate levels were higher in the sepsis group than in the sham group in the cyanide catheters ( P < 0.001, all comparisons) and did not normalize in the former group. Conclusions: In this experimental study on resuscitated sepsis, we observed increased aerobic metabolism and preserved mitochondrial function. Sepsis and electron transport chain inhibition led to increased LPR, suggesting a decreased mitochondrial reserve capacity in early sepsis.

Cerebrospinal Fluid Lactate and Glucose Levels as Predictors of Symptomatic Delayed Cerebral Ischemia in Patients with Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Aneurysmal subarachnoid hemorrhage (aSAH) is a complex neurovascular syndrome with profound systemic effects associated with high rates of disability and mortality. Delayed cerebral ischemia (DCI), which encompasses all neurobiological events occurring in the subacute-late stage after aSAH, has a complex pathogenesis and can occur in the absence of instrumental vasospasm. Our aim was to assess the correlation between cerebrospinal fluid (CSF) lactate and glucose levels measured on the second or third day after aSAH with clinical deterioration caused by DCI and with 3-month functional outcome.

METHODS

This prospective study included all aSAH patients admitted between January 2020 and December 2021 who underwent external ventricular drain placement and CSF lactate and glucose measurement.

RESULTS

Among 133 aSAH patients, 48 had an external ventricular drain placed and early CSF lactate and glucose assessment. Independent predictors of symptomatic DCI were World Federation of Neurosurgical Societies grade IV-V (adjusted odds ratio [aOR] 25.8, 95% confidence interval [CI] 2.9-649.2, P = 0.012), elevated CSF glucose (aOR 28.8, 95% CI 3.3-775.2, P = 0.010), and elevated CSF lactate (aOR 14.7, 95% CI 1.9-205.7, P = 0.018). The only independent predictor of 3-month functional outcome was occurrence of symptomatic DCI (aOR 0.02, 95% CI 0.0-0.2, P = 0.01).

CONCLUSIONS

Elevated CSF lactate and glucose levels in the first 3 days following aSAH were independent predictors of subsequent DCI-related neurological impairment; the presence of instrumental vasospasm was not significantly correlated with DCI after multivariate adjustment. CSF lactate and glucose monitoring may represent a point-of-care test, which could potentially improve prediction of subacute neurological worsening and guide therapeutic choices. Further research with larger prospective cohorts is warranted.

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.

Effects of norepinephrine infusion on cerebral energy metabolism during experimental haemorrhagic shock

BACKGROUND

The use of norepinephrine in the case of life-threatening haemorrhagic shock is well established but widely discussed. The present study was designed to compare the effects of early norepinephrine treatment vs. no treatment on cerebral energy metabolism during haemorrhagic shock.

METHODS

Twelve pigs were subjected to haemorrhagic shock, 4 in the control group and 8 in the norepinephrine (NE) group. Following a 60 min baseline period haemorrhagic shock was achieved by bleeding all animals to a pre-defined mean arterial blood pressure (MAP) of approximately 40 mm Hg. When mean arterial pressure had decreased to 40 mmHg NE infusion started in the treatment group. After 90 min, NE infusion stopped, and all pigs were resuscitated with autologous blood and observed for 2.5 h. During the experiment cerebral tissue oxygenation (PbtO2) was monitored continuously and variables reflecting cerebral energy metabolism (glucose, lactate, pyruvate, glutamate, glycerol) were measured by utilizing intracerebral microdialysis.

RESULTS

All 12 pigs completed the protocol. NE infusion resulted in significantly higher MAP (p < 0.001). During the shock period lactate/pyruvate (LP) ratio group increased from 20 (15-29) to 66 (38-82) (median (IQR)) in the control group but remained within normal limits in the NE group. The significant increase in LP ratio in the control group remained after resuscitation. After induction of shock PbtO2 decreased markedly in the control group and was significantly lower than in the NE group during the resuscitation phase.

CONCLUSION

NE infusion during haemorrhagic shock improved cerebral energy metabolism compared with no treatment.

Invasive Multimodal Neuromonitoring in Aneurysmal Subarachnoid Hemorrhage: A Systematic Review

BACKGROUND AND PURPOSE

Aneurysmal subarachnoid hemorrhage is a devastating disease leaving surviving patients often severely disabled. Delayed cerebral ischemia (DCI) has been identified as one of the main contributors to poor clinical outcome after subarachnoid hemorrhage. The objective of this review is to summarize existing clinical evidence assessing the diagnostic value of invasive neuromonitoring (INM) in detecting DCI and provide an update of evidence since the 2014 consensus statement on multimodality monitoring in neurocritical care.

METHODS

Three invasive monitoring techniques were targeted in the data collection process: brain tissue oxygen tension (p_tiO₂), cerebral microdialysis, and electrocorticography. Prospective and retrospective studies as well as case series (≥10 patients) were included as long as monitoring was used to detect DCI or guide DCI treatment.

RESULTS

Forty-seven studies reporting INM in the context of DCI were included (p_tiO₂: N=21; cerebral microdialysis: N=22; electrocorticography: N=4). Changes in brain oxygen tension are associated with angiographic vasospasm or reduction in regional cerebral blood flow. Metabolic monitoring with trend analysis of the lactate to pyruvate ratio using cerebral microdialysis, identifies patients at risk for DCI. Clusters of cortical spreading depolarizations are associated with clinical neurological worsening and cerebral infarction in selected patients receiving electrocorticography monitoring.

CONCLUSIONS

Data supports the use of INM for the detection of DCI in selected patients. Generalizability to all subarachnoid hemorrhage patients is limited by design bias of available studies and lack of randomized trials. Continuous data recording with trend analysis and the combination of INM modalities can provide tailored treatment support in patients at high risk for DCI. Future trials should test interventions triggered by INM in relation to cerebral infarctions.

Early High Cerebrospinal Fluid Glutamate: A Potential Predictor for Delayed Cerebral Ischemia after Aneurysmal Subarachnoid Hemorrhage

Delayed cerebral ischemia (DCI) is an important complication after aneurysmal subarachnoid hemorrhage (aSAH). Early identification of cerebrospinal fluid (CSF) markers is helpful for warning of impending DCI. This study assessed whether early high CSF glutamate levels can be observed in aSAH patients who later developed DCI. In this prospective clinical study, patients with normal pressure hydrocephalus or aSAH were enrolled. We found that the early CSF levels of glutamate were significantly elevated in aSAH patients compared to patients with normal pressure hydrocephalus. There was a significant difference in early CSF levels of glutamate between aSAH patients without DCI and with DCI. The early CSF levels of glutamate are significantly related to the Hunt and Hess grade, the World Federation of Neurological Surgeons (WFNS) grade, and the modified Fisher score on admission and occurrence of DCI in aSAH patients. Preliminary evidence of this study suggests that early high CSF glutamate levels are correlated with DCI in aSAH patients.

Selective mGluR1 Negative Allosteric Modulator Reduces Blood-Brain Barrier Permeability and Cerebral Edema After Experimental Subarachnoid Hemorrhage

The blood-brain barrier (BBB) disruption leads to the vasogenic brain edema and contributes to the early brain injury (EBI) after subarachnoid hemorrhage (SAH). However, the mechanisms underlying the BBB damage following SAH are poorly understood. Here we reported that the neurotransmitter glutamate of cerebrospinal fluid (CSF) was dramatically increased in SAH patients with symptoms of cerebral edema. Using the rat SAH model, we found that SAH caused the increase of CSF glutamate level and BBB permeability in EBI, intracerebroventricular injection of exogenous glutamate deteriorated BBB damage and cerebral edema, while intraperitoneally injection of metabotropic glutamate receptor 1(mGluR1) negative allosteric modulator JNJ16259685 significantly attenuated SAH-induced BBB damage and cerebral edema. In an in vitro BBB model, we showed that glutamate increased monolayer permeability of human brain microvascular endothelial cells (HBMEC), whereas JNJ16259685 preserved glutamate-damaged BBB integrity in HBMEC. Mechanically, glutamate downregulated the level and phosphorylation of vasodilator-stimulated phosphoprotein (VASP), decreased the tight junction protein occludin, and increased AQP4 expression at 72 h after SAH. However, JNJ16259685 significantly increased VASP, p-VASP, and occludin, and reduced AQP level at 72 h after SAH. Altogether, our results suggest an important role of glutamate in disruption of BBB function and inhibition of mGluR1 with JNJ16259685 reduced BBB damage and cerebral edema after SAH.

Cerebral Metabolic Changes Related to Oxidative Metabolism in a Model of Bacterial Meningitis Induced by Lipopolysaccharide

BACKGROUND

Cerebral mitochondrial dysfunction is prominent in the pathophysiology of severe bacterial meningitis. In the present study, we hypothesize that the metabolic changes seen after intracisternal lipopolysaccharide (LPS) injection in a piglet model of meningitis is compatible with mitochondrial dysfunction and resembles the metabolic patterns seen in patients with bacterial meningitis.

METHODS

Eight pigs received LPS injection in cisterna magna, and four pigs received NaCl in cisterna magna as a control. Biochemical variables related to energy metabolism were monitored by intracerebral microdialysis technique and included interstitial glucose, lactate, pyruvate, glutamate, and glycerol. The intracranial pressure (ICP) and brain tissue oxygen tension (PbtO₂) were also monitored along with physiological variables including mean arterial pressure, blood glucose, lactate, and partial pressure of O₂ and CO₂. Pigs were monitored for 60 min at baseline and 240 min after LPS/NaCl injection.

RESULTS

After LPS injection, a significant increase in cerebral lactate/pyruvate ratio (LPR) compared to control group was registered (p = 0.01). This increase was due to a significant increased lactate with stable and normal values of pyruvate. No significant change in PbtO₂ or ICP was registered. No changes in physiological variables were observed.

CONCLUSIONS

The metabolic changes after intracisternal LPS injection is compatible with disturbance in the oxidative metabolism and partly due to mitochondrial dysfunction with increasing cerebral LPR due to increased lactate and normal pyruvate, PbtO₂, and ICP. The metabolic pattern resembles the one observed in patients with bacterial meningitis. Metabolic monitoring in these patients is feasible to monitor for cerebral metabolic derangements otherwise missed by conventional intensive care monitoring.

In Vivo Microdialysis of Endogenous and 13C-labeled TCA Metabolites in Rat Brain: Reversible and Persistent Effects of Mitochondrial Inhibition and Transient Cerebral Ischemia

Cerebral micro-dialysis allows continuous sampling of extracellular metabolites, including glucose, lactate and pyruvate. Transient ischemic events cause a rapid drop in glucose and a rise in lactate levels. Following such events, the lactate/pyruvate (L/P) ratio may remain elevated for a prolonged period of time. In neurointensive care clinics, this ratio is considered a metabolic marker of ischemia and/or mitochondrial dysfunction. Here we propose a novel, sensitive microdialysis liquid chromatography-mass spectrometry (LC-MS) approach to monitor mitochondrial dysfunction in living brain using perfusion with ¹³C-labeled succinate and analysis of ¹³C-labeled tricarboxylic acid cycle (TCA) intermediates. This approach was evaluated in rat brain using malonate-perfusion (10-50 mM) and endothelin-1 (ET-1)-induced transient cerebral ischemia. In the malonate model, the expected changes upon inhibition of succinate dehydrogenase (SDH) were observed, i.e., an increase in endogenous succinate and decreases in fumaric acid and malic acid. The inhibition was further elaborated by incorporation of ¹³C into specific TCA intermediates from ¹³C-labeled succinate. In the ET-1 model, increases in non-labeled TCA metabolites (reflecting release of intracellular compounds) and decreases in ¹³C-labeled TCA metabolites (reflecting inhibition of de novo synthesis) were observed. The analysis of ¹³C incorporation provides further layers of information to identify metabolic disturbances in experimental models and neuro-intensive care patients.

Ammonia-induced mitochondrial impairment is intensified by manganese co-exposure: relevance to the management of subclinical hepatic encephalopathy and cirrhosis-associated brain injury

Aim of the study

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome ensuing from liver failure. The liver is the major site of ammonia detoxification in the human body. Hence, acute and chronic liver dysfunction can lead to hyperammonemia. Manganese (Mn) is a trace element incorporated in several physiological processes in the human body. Mn is excreted through bile. It has been found that cirrhosis is associated with hyperammonemia as well as body Mn accumulation. The brain is the primary target organ for both ammonia and Mn toxicity. On the other hand, brain mitochondria impairment is involved in the mechanism of Mn and ammonia neurotoxicity.

Material and methods

The current study was designed to evaluate the effect of Mn and ammonia and their combination on mitochondrial indices of functionality in isolated brain mitochondria. Isolated brain mitochondria were exposed to increasing concentrations of ammonia and Mn alone and/or in combination and several mitochondrial indices were assessed.

Results

The collapse of mitochondrial membrane potential, increased mitochondrial permeabilization, reactive oxygen species formation, and a significant decrease in mitochondrial dehydrogenase activity and ATP content were evident in Mn-exposed (0.005-1 mM) brain mitochondria. On the other hand, ammonia (0.005-0.5 mM) caused no significant changes in brain mitochondrial function. It was found that co-exposure of the brain mitochondria to Mn and ammonia causes more evident mitochondrial impairment in comparison with Mn and/or ammonia alone.

Conclusions

These data indicate additive toxicity of ammonia and Mn in isolated brain mitochondria exposed to these neurotoxins.

TAT-mGluR1 Attenuation of Neuronal Apoptosis through Prevention of MGluR1α Truncation after Experimental Subarachnoid Hemorrhage

Excessive glutamate-mediated overactivation of metabotropic glutamate receptor 1 (mGluR1) plays a leading role in neuronal apoptosis following subarachnoid hemorrhage (SAH). TAT-mGluR1, a fusion peptide consisting of a peptide spanning the calpain cleavage site of mGluR1α and the trans-activating regulatory protein (TAT) of HIV, effectively blocks mGluR1α truncation and protects neurons against excitotoxic damage. This study investigated the effects of TAT-mGluR1 on neuronal apoptosis in the rat SAH model. Here, we report that SAH caused activation of calpain and truncation of mGluR1α; intraperitoneally administered TAT-mGluR1 did not affect calpain activity, while it blocked truncation of mGluR1α after SAH. Intraperitoneally administered FITC-labeled TAT-mGluR1 was colocalized with mGluR1α in thecortex after SAH. Furthermore, TAT-mGluR1 significantly improved the neurological deficit, increased p-PI3K, p-Akt, and p-GSK3β, downregulated Bax, upregulated Bcl-2, and reduced cortical apoptosis in the basal cortex at 24 h after SAH. These findings indicated that TAT-mGluR1 acted against SAH-induced cell apoptosis through preventing mGluR1α truncation.

Non-Ischemic Cerebral Energy Dysfunction at the Early Brain Injury Phase following Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

The pathophysiology of early brain injury following aneurysmal subarachnoid hemorrhage (SAH) is still not completely understood.

OBJECTIVE

Using brain perfusion CT (PCT) and cerebral microdialysis (CMD), we examined whether non-ischemic cerebral energy dysfunction may be a pathogenic determinant of EBI.

METHODS

A total of 21 PCTs were performed (a median of 41 h from ictus onset) among a cohort of 18 comatose mechanically ventilated SAH patients (mean age 58 years, median admission WFNS score 4) who underwent CMD and brain tissue PO₂ (PbtO₂) monitoring. Cerebral energy dysfunction was defined as CMD episodes with lactate/pyruvate ratio (LPR) >40 and/or lactate >4 mmol/L. PCT-derived global CBF was categorized as oligemic (CBF < 28 mL/100 g/min), normal (CBF 28-65 mL/100 g/min), or hyperemic (CBF 69-85 mL/100 g/min), and was matched to CMD/PbtO₂ data.

RESULTS

Global CBF (57 ± 14 mL/100 g/min) and PbtO₂ (25 ± 9 mm Hg) were within normal ranges. Episodes with cerebral energy dysfunction (n = 103 h of CMD samples, average duration 7.4 h) were frequent (66% of CMD samples) and were associated with normal or hyperemic CBF. CMD abnormalities were more pronounced in conditions of hyperemic vs. normal CBF (LPR 54 ± 12 vs. 42 ± 7, glycerol 157 ± 76 vs. 95 ± 41 µmol/L; both p < 0.01). Elevated brain LPR correlated with higher CBF (r = 0.47, p < 0.0001).

CONCLUSION

Cerebral energy dysfunction is frequent at the early phase following poor-grade SAH and is associated with normal or hyperemic brain perfusion. Our data support the notion that mechanisms alternative to ischemia/hypoxia are implicated in the pathogenesis of early brain injury after SAH.

Ammonia-induced mitochondrial dysfunction and energy metabolism disturbances in isolated brain and liver mitochondria, and the effect of taurine administration: relevance to hepatic encephalopathy treatment

INTRODUCTION

Ammonia-induced oxidative stress, mitochondrial dysfunction, and energy crisis are known as some the major mechanisms of brain injury in hepatic encephalopathy (HE). Hyperammonemia also affects the liver and hepatocytes. Therefore, targeting mitochondria seems to be a therapeutic point of intervention in the treatment of HE. Taurine is an abundant amino acid in the human body. Several biological functions including the mitochondrial protective properties are attributed to this amino acid. The aim of this study is to evaluate the effect of taurine administration on ammonia-induced mitochondrial dysfunction.

MATERIAL AND METHODS

Isolated mice liver and brain mitochondria were exposed to different concentrations of ammonia (1, 5, 10, and 20 mM) and taurine (1, 5, and 10 mM), and several mitochondrial indices were assessed.

RESULTS

It was found that ammonia inhibited mitochondrial dehydrogenases activity caused collapse of mitochondrial membrane potential (MMP), induced mitochondrial swelling (MPP), and increased reactive oxygen species (ROS) in isolated liver and brain mitochondria. Furthermore, a significant amount of lipid peroxidation (LPO), along with glutathione (GSH) and ATP depletion, was detected in ammonia exposed mitochondria. Taurine administration (5 and 10 mM) mitigated ammonia-induced mitochondrial dysfunction.

CONCLUSIONS

The current investigation demonstrates that taurine is instrumental in preserving brain and liver mitochondrial function in a hyperammonemic environment. The data suggest taurine as a potential protective agent with a therapeutic capability against hepatic encephalopathy and hyperammonemia.

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.

Taurine treatment preserves brain and liver mitochondrial function in a rat model of fulminant hepatic failure and hyperammonemia

Ammonia-induced mitochondrial dysfunction and energy crisis is known as a critical consequence of hepatic encephalopathy (HE). Hence, mitochondria are potential targets of therapy in HE. The current investigation was designed to evaluate the role of taurine treatment on the brain and liver mitochondrial function in a rat model of hepatic encephalopathy and hyperammonemia. The animals received thioacetamide (400mg/kg, i.p, for three consecutive days at 24-h intervals) as a model of acute liver failure and hyperammonemia. Several biochemical parameters were investigated in the serum, while the animals' cognitive function and locomotor activity were monitored. Mitochondria was isolated from the rats' brain and liver and several indices were assessed in isolated mitochondria. Liver failure led to cognitive dysfunction and impairment in locomotor activity in the rats. Plasma and brain ammonia was high and serum markers of liver injury were drastically elevated in the thioacetamide-treated group. An assessment of brain and liver mitochondrial function in the thioacetamide-treated animals revealed an inhibition of succinate dehydrogenase activity (SDA), collapsed mitochondrial membrane potential, mitochondrial swelling, and increased reactive oxygen species (ROS). Furthermore, a significant decrease in mitochondrial ATP was detected in the brain and liver mitochondria isolated from thioacetamide-treated animals. Taurine treatment (250, 500, and 1000mg/kg) decreased mitochondrial swelling, ROS, and LPO. Moreover, the administration of this amino acid restored brain and liver mitochondrial ATP. These data suggest taurine to be a potential protective agent with therapeutic capability against hepatic encephalopathy and hyperammonemia-induced mitochondrial dysfunction and energy crisis.

Biochemical indications of cerebral ischaemia and mitochondrial dysfunction in severe brain trauma analysed with regard to type of lesion

BACKGROUND

The study focuses on three questions related to the clinical usefulness of microdialysis in severe brain trauma: (1) How frequently is disturbed cerebral energy metabolism observed in various types of lesions? (2) How often does the biochemical pattern indicate cerebral ischaemia and mitochondrial dysfunction? (3) How do these patterns relate to mortality?

METHOD

The study includes 213 consecutive patients with severe brain trauma (342 intracerebral microdialysis catheters). The patients were classified into four groups according to the type of lesion: extradural haematoma (EDH), acute subdural haematoma (SDH), cerebral haemorrhagic contusion (CHC) and no mass lesion (NML). Altogether about 150,000 biochemical analyses were performed during the initial 96 h after trauma.

RESULTS

Compromised aerobic metabolism occurred during 38 % of the study period. The biochemical pattern indicating mitochondrial dysfunction was more common than that of ischaemia. In EDH and NML aerobic metabolism was generally close to normal. In SDH or CHC it was often severely compromised. Mortality was increased in SDH with impaired aerobic metabolism, while CHC did not exhibit a similar relation.

CONCLUSIONS

Compromised energy metabolism is most frequent in patients with SDH and CHC (32 % and 49 % of the study period, respectively). The biochemical pattern of mitochondrial dysfunction is more common than that of ischaemia (32 % and 6 % of the study period, respectively). A correlation between mortality and biochemical data is obtained provided the microdialysis catheter is placed in an area where energy metabolism reflects tissue outcome in a large part of the brain.

A technique for continuous bedside monitoring of global cerebral energy state

Background

Cerebral cytoplasmatic redox state is a sensitive indicator of cerebral oxidative metabolism and is conventionally evaluated from the extracellular lactate/pyruvate (LP) ratio. In the present experimental study of global cerebral ischemia induced by hemorrhagic shock, we investigate whether the LP ratio obtained from microdialysis of cerebral venous blood may be used as a surrogate marker of global cerebral energy state.

Methods

Six female pigs were anesthetized and vital parameters were recorded. Microdialysis catheters were placed in the left parietal lobe, the superior sagittal sinus, and the femoral artery. Hemorrhagic shock was achieved by bleeding the animals to a mean arterial pressure (MAP) of approximately 40 mmHg and kept at a MAP of about 30–40 mmHg for 90 min. The animals were resuscitated with autologous whole blood followed by 3 h of observation.

Results

The LP ratio obtained from the intracerebral and intravenous catheters immediately increased during the period of hemorrhagic shock while the LP ratio in the arterial blood remained close to normal levels. At the end of the experiment, median LP ratio (interquartile range) obtained from the intracerebral, intravenous, and intra-arterial microdialysis catheters were 846 (243–1990), 309 (103–488), and 27 (21–31), respectively. There was a significant difference in the LP ratio obtained from the intravenous location and the intra-arterial location (P < 0.001).

Conclusions

During cerebral ischemia induced by severe hemorrhagic shock, intravascular microdialysis of the draining venous blood will exhibit changes of the LP ratio revealing the deterioration of global cerebral oxidative energy metabolism. In neurocritical care, this technique might be used to give information regarding global cerebral energy metabolism in addition to the regional information obtained from intracerebral microdialysis catheters. The technique might also be used to evaluate cerebral energy state in various critical care conditions when insertion of an intracerebral microdialysis catheter may be contraindicated, e.g., resuscitation after cardiac standstill, open-heart surgery, and multi-trauma.

Bedside evaluation of cerebral energy metabolism in severe community-acquired bacterial meningitis

BACKGROUND

Mortality and morbidity have remained high in bacterial meningitis. Impairment of cerebral energy metabolism probably contributes to unfavorable outcome. Intracerebral microdialysis is routinely used to monitor cerebral energy metabolism, and recent experimental studies indicate that this technique may separate ischemia and non-ischemic mitochondrial dysfunction. The present study is a retrospective interpretation of biochemical data obtained in a series of patients with severe community-acquired meningitis.

METHODS

Cerebral energy metabolism was monitored in 15 patients with severe community-acquired meningitis utilizing intracerebral microdialysis and bedside biochemical analysis. According to previous studies, cerebral ischemia was defined as lactate/pyruvate (LP) ratio > 30 with intracerebral pyruvate level < 70 µmol L(-1). Non-ischemic mitochondrial dysfunction was defined as LP-ratio > 30 at a normal or increased interstitial concentration of pyruvate (≥ 70 μmol L(-1)). Patients with LP-ratios < 30 were classified as no mitochondrial dysfunction.

RESULTS

The biochemical pattern was in 8 patients (10 microdialysis catheters) classified as no mitochondrial dysfunction, in 5 patients classified as non-ischemic mitochondrial dysfunction, and in 2 patients (3 catheters) classified as ischemia.

CONCLUSIONS

In patients with severe community-acquired meningitis, compromised cerebral energy metabolism occurs frequently and was diagnosed in 7 out of 15 cases. A biochemical pattern of non-ischemic mitochondrial dysfunction appears to be a more common underlying condition than cerebral ischemia.

Detection and quantification of microRNA in cerebral microdialysate

Background

Secondary brain injury accounts for a major part of the morbidity and mortality in patients with spontaneous aneurysmal subarachnoid hemorrhage (SAH), but the pathogenesis and pathophysiology remain controversial. MicroRNAs (miRNAs) are important posttranscriptional regulators of complementary mRNA targets and have been implicated in the pathophysiology of other types of acute brain injury. Cerebral microdialysis is a promising tool to investigate these mechanisms. We hypothesized that miRNAs would be present in human cerebral microdialysate.

Methods

RNA was extracted and miRNA profiles were established using high throughput real-time quantification PCR on the following material: 1) Microdialysate sampled in vitro from A) a solution of total RNA extracted from human brain, B) cerebrospinal fluid (CSF) from a neurologically healthy patient, and C) a patient with SAH; and 2) cerebral microdialysate and CSF sampled in vivo from two patients with SAH. MiRNAs were categorized according to their relative recovery (RR) and a pathway analysis was performed for miRNAs exhibiting a high RR in vivo.

Results

Seventy-one of the 160 miRNAs detected in CSF were also found in in vivo microdialysate from SAH patients. Furthermore specific miRNAs consistently exhibited either a high or low RR in both in vitro and in vivo microdialysate. Analysis of repeatability showed lower analytical variation in microdialysate than in CSF.

Conclusions

MiRNAs are detectable in cerebral microdialysate; a large group of miRNAs consistently showed a high RR in cerebral microdialysate. Measurement of cerebral interstitial miRNA concentrations may aid in the investigation of secondary brain injury in neurocritical conditions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0505-1) contains supplementary material, which is available to authorized users.

Biochemical neuromonitoring of poor-grade aneurysmal subarachnoid hemorrhage: comparative analysis of metabolic events detected by cerebral microdialysis and by retrograde jugular vein catheterization

OBJECTIVES

In severe aneurysmal subarachnoid hemorrhage (aSAH), pathological changes in cerebral energy metabolism can be detected either by local measurements using cerebral microdialysis (cMD) together with brain tissue oxygen probe or by global measurements of arterio-jugular difference performed with retrograde jugular vein catheter. Our main objective was to compare the two methods of detection and assess whether combining biomarkers from both procedures could improve outcome prediction, which has never been studied before.

METHODS

This study included 400 sets of paired arterial and jugular venous samples and 3138 brain microdialyzates obtained from 18 poor-grade aSAH patients. Using Glasgow outcome scale (GOS), neurochemical data from unfavorable (GOS 1-3) and favorable (GOS 4-5) outcome groups were compared.

RESULTS

The lactate/pyruvate ratio was found as the most sensitive marker for predicting unfavorable outcome (90%), although not specific. In contrast, hypoxic lactate events and those of metabolic ratio (MR) < 3.44, most frequently observed in the unfavorable outcome group than in the favorable one (13.9 vs 0.9% and 33.3 vs 3.75% respectively), were shown to be more specific biomarkers (86%) to predict unfavorable outcome, but less sensitive ( < 70%). The combination of these three biomarkers improved the accuracy of outcome prediction (sensitivity 90% and specificity 71%).

DISCUSSION

Both retrograde jugular venous catheterization (RJVC) and cMD contribute to monitor poor-grade aSAH patients. In this preliminary study, we show that these two techniques are complementary and their combination increases the accuracy of outcome prediction.

The radical scavenger edaravone improves neurologic function and perihematomal glucose metabolism after acute intracerebral hemorrhage

Oxidative injury caused by reactive oxygen species plays an important role in the progression of intracerebral hemorrhage (ICH)-induced secondary brain injury. Previous studies have demonstrated that the free radical scavenger edaravone may prevent neuronal injury and brain edema after ICH. However, the influence of edaravone on cerebral metabolism in the early stages after ICH and the underlying mechanism have not been fully investigated. In the present study, we investigated the effect of edaravone on perihematomal glucose metabolism using (18)F-fluorordeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT). Additionally, the neurologic deficits, brain edemas, and cell death that followed ICH were quantitatively analyzed. After blood infusion, the rats treated with edaravone showed significant improvement in both forelimb placing and corner turn tests compared with those treated with vehicle. Moreover, the brain water content of the edaravone-treated group was significantly decreased compared with that of the vehicle group on day 3 after ICH. PET/CT images of ICH rats exhibited obvious decreases in FDG standardized uptake values in perihematomal region on day 3, and the lesion-to-normal ratio of the edaravone-treated ICH rats was significantly increased compared with that of the control rats. Calculation of the brain injury volumes from the PET/CT images revealed that the volumes of the blood-induced injuries were significantly smaller in the edaravone group compared with the vehicle group. Terminal Deoxynucleotidyl Transferase-mediated dUTP Nick End Labeling assays performed 3 days after ICH revealed that the numbers of apoptotic cells in perihematomal region of edaravone-treated ICH rats were decreased relative to the vehicle group. Thus, the present study demonstrates that edaravone has scavenging properties that attenuate neurologic behavioral deficits and brain edema in the early period of ICH. Additionally, edaravone may improve cerebral metabolism around the hematoma by attenuating apoptotic cell death after ICH.

Higher brain extracellular potassium is associated with brain metabolic distress and poor outcome after aneurysmal subarachnoid hemorrhage

Introduction

Elevated brain potassium levels ([K⁺]) are associated with neuronal damage in experimental models. The role of brain extracellular [K⁺] in patients with poor-grade aneurysmal subarachnoid hemorrhage (aSAH) and its association with hemorrhage load, metabolic dysfunction and outcome has not been studied so far.

Methods

Cerebral microdialysis (CMD) samples from 28 poor grade aSAH patients were analyzed for CMD [K⁺] for 12 consecutive days after ictus, and time-matched to brain metabolic and hemodynamic parameters as well as corresponding plasma [K⁺]. Statistical analysis was performed using a generalized estimating equation with an autoregressive function to handle repeated observations of an individual patient.

Results

CMD [K⁺] did not correlate with plasma [K⁺] (Spearman’s ρ = 0.114, P = 0.109). Higher CMD [K⁺] was associated with the presence of intracerebral hematoma on admission head computed tomography, CMD lactate/pyruvate ratio >40 and CMD lactate >4 mmol/L (P < 0.05). In vitro retrodialysis data suggest that high CMD [K⁺] was of brain cellular origin. Higher CMD [K⁺] was significantly associated with poor 3-month outcome, even after adjusting for age and disease severity (P < 0.01).

Conclusions

The results of this pilot study suggest that brain extracellular [K⁺] may serve as a biomarker for brain tissue injury in poor-grade aSAH patients. Further studies are needed to elucidate the relevance of brain interstitial K⁺ levels in the pathophysiology of secondary brain injury after aSAH.

Brain tissue oxygenation and cerebral metabolic patterns in focal and diffuse traumatic brain injury

INTRODUCTION

Neurointensive care of traumatic brain injury (TBI) patients is currently based on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) targeted protocols. There are reasons to believe that knowledge of brain tissue oxygenation (BtipO2) would add information with the potential of improving patient outcome. The aim of this study was to examine BtipO2 and cerebral metabolism using the Neurovent-PTO probe and cerebral microdialysis (MD) in TBI patients.

METHODS

Twenty-three severe TBI patients with monitoring of physiological parameters, ICP, CPP, BtipO2, and MD for biomarkers of energy metabolism (glucose, lactate, and pyruvate) and cellular distress (glutamate, glycerol) were included. Patients were grouped according to injury type (focal/diffuse) and placement of the Neurovent-PTO probe and MD catheter (injured/non-injured hemisphere).

RESULTS

We observed different patterns in BtipO2 and MD biomarkers in diffuse and focal injury where placement of the probe also influenced the results (ipsilateral/contralateral). In all groups, despite fairly normal levels of ICP and CPP, increased MD levels of glutamate, glycerol, or the L/P ratio were observed at BtipO2 <5 mmHg, indicating increased vulnerability of the brain at this level.

CONCLUSION

Monitoring of BtipO2 adds important information in addition to traditional ICP and CPP surveillance. Because of the different metabolic responses to very low BtipO2 in the individual patient groups we submit that brain tissue oximetry is a complementary tool rather than an alternative to MD monitoring.

Cerebral extracellular lactate increase is predominantly nonischemic in patients with severe traumatic brain injury

Growing evidence suggests that endogenous lactate is an important substrate for neurons. This study aimed to examine cerebral lactate metabolism and its relationship with brain perfusion in patients with severe traumatic brain injury (TBI). A prospective cohort of 24 patients with severe TBI monitored with cerebral microdialysis (CMD) and brain tissue oxygen tension (PbtO2) was studied. Brain lactate metabolism was assessed by quantification of elevated CMD lactate samples (>4 mmol/L); these were matched to CMD pyruvate and PbtO2 values and dichotomized as glycolytic (CMD pyruvate >119 μmol/L vs. low pyruvate) and hypoxic (PbtO2 <20 mm Hg vs. nonhypoxic). Using perfusion computed tomography (CT), brain perfusion was categorized as oligemic, normal, or hyperemic, and was compared with CMD and PbtO2 data. Samples with elevated CMD lactate were frequently observed (41±8%), and we found that brain lactate elevations were predominantly associated with glycolysis and normal PbtO2 (73±8%) rather than brain hypoxia (14±6%). Furthermore, glycolytic lactate was always associated with normal or hyperemic brain perfusion, whereas all episodes with hypoxic lactate were associated with diffuse oligemia. Our findings suggest predominant nonischemic cerebral extracellular lactate release after TBI and support the concept that lactate may be used as an energy substrate by the injured human brain.

Metabolic crisis in severely head-injured patients: is ischemia just the tip of the iceberg?

Ischemia and metabolic crisis are frequent post-traumatic secondary brain insults that negatively influence outcome. Clinicians commonly mix up these two types of insults, mainly because high lactate/pyruvate ratio (LPR) is the common marker for both ischemia and metabolic crisis. However, LPR elevations during ischemia and metabolic crisis reflect two different energetic imbalances: ischemia (Type 1 LPR elevations with low oxygenation) is characterized by a drastic deprivation of energetic substrates, whereas metabolic crisis (Type 2 LPR elevations with normal or high oxygenation) is associated with profound mitochondrial dysfunction but normal supply of energetic substrates. The discrimination between ischemia and metabolic crisis is crucial because conventional recommendations against ischemia may be detrimental for patients with metabolic crisis. Multimodal monitoring, including microdialysis and brain tissue oxygen monitoring, allows such discrimination, but these techniques are not easily accessible to all head-injured patients. Thus, a new “gold standard” and adapted medical education are required to optimize the management of patients with metabolic crisis.

Cerebral energy metabolism during mitochondrial dysfunction induced by cyanide in piglets

BACKGROUND

Mitochondrial dysfunction is an important factor contributing to tissue damage in both severe traumatic brain injury and ischemic stroke. This experimental study explores the possibility to diagnose the condition bedside by utilising intracerebral microdialysis and analysis of chemical variables related to energy metabolism.

METHODS

Mitochondrial dysfunction was induced in piglets and evaluated by monitoring brain tissue oxygen tension (PbtO2 ) and cerebral levels of glucose, lactate, pyruvate, glutamate, and glycerol bilaterally. The biochemical variables were obtained by microdialysis and immediate enzymatic analysis. Mitochondrial function was blocked by unilateral infusion of NaCN/KCN (0.5 mol/L) through the microdialysis catheter (N = 5). As a reference, NaCl (0.5 mol/L) was infused by intracerebral microdialysis in one group of animals (N = 3).

RESULTS

PbtO2 increased during cyanide infusion and returned to baseline afterwards. The lactate/pyruvate (LP) ratio increased significantly following cyanide infusion because of a marked increase in lactate level while pyruvate remained within normal limits. Glutamate and glycerol increased after cyanide infusion indicating insufficient energy metabolism and degradation of cellular membranes, respectively.

CONCLUSION

Mitochondrial dysfunction is characterised by an increased LP ratio signifying a shift in cytoplasmatic redox state at normal or elevated PbtO2 . The condition is biochemically characterised by a marked increase in cerebral lactate with a normal or elevated pyruvate level. The metabolic pattern is different from cerebral ischemia, which is characterised by simultaneous decreases in intracerebral pyruvate and PbtO2 . The study supports the hypothesis that cerebral ischemia and mitochondrial dysfunction may be identified and separated at the bedside by utilising intracerebral microdialysis.

Comparison between cerebral tissue oxygen tension and energy metabolism in experimental subdural hematoma

BACKGROUND

An experimental swine model (n = 7) simulating an acute subdural hematoma (ASDH) was employed (1) to explore the relation between the brain tissue oxygenation (PbtO(2)) and the regional cerebral energy metabolism as obtained by microdialysis, and (2) to define the lowest level of PbtO(2) compatible with intact energy metabolism.

METHODS

ASDH was produced by infusion of 7 ml of autologous blood (infusion rate 0.5 ml/min) by a catheter placed subdurally. PbtO(2) and microdialysis probes were placed symmetrically in the injured ("bad-side") and non-injured ("good-side") hemispheres. Intracranial pressure (ICP) was monitored in the "good-side."

RESULTS

ICP, cerebral perfusion pressure (CPP), PbtO(2), glucose, lactate, pyruvate, lactate-pyruvate ratio (LP ratio), glutamate, and glycerol were recorded at baseline (60 min) and post trauma (360 min). After the creation of the ASDH, PbtO(2) decreased significantly in both the hemispheres (P < 0.001). No significant difference was found between the sides post trauma. The LP ratio, glutamate, and glycerol in the "bad-side" increased significantly over the "good-side" where the values remained within the normal limits. A PbtO(2) value below approximately 25 mmHg was found to be associated with disturbed energy metabolism in the "bad-side" but not in the "good-side." No correlation was found between the LP ratio and PbtO(2) in either hemisphere.

CONCLUSIONS

PbtO(2) monitoring accurately describes tissue oxygenation but does not disclose whether the oxygen delivery is sufficient for maintaining cerebral energy metabolism. Accordingly, it may not be possible to define a threshold level for PbtO(2) below which energy failure and permanent tissue damage occurs.

Brain Lactate Metabolism in Humans With Subarachnoid Hemorrhage

Background and Purpose—

Lactate is central for the regulation of brain metabolism and is an alternative substrate to glucose after injury. Brain lactate metabolism in patients with subarachnoid hemorrhage has not been fully elucidated.

Methods—

Thirty-one subarachnoid hemorrhage patients monitored with cerebral microdialysis (CMD) and brain oxygen (PbtO 2 ) were studied. Samples with elevated CMD lactate (>4 mmol/L) were matched to PbtO 2 and CMD pyruvate and categorized as hypoxic (PbtO 2 <20 mm Hg) versus nonhypoxic and hyperglycolytic (CMD pyruvate >119 μmol/L) versus nonhyperglycolytic.

Results—

Median per patient samples with elevated CMD lactate was 54% (interquartile range, 11%–80%). Lactate elevations were more often attributable to cerebral hyperglycolysis (78%; interquartile range, 5%–98%) than brain hypoxia (11%; interquartile range, 4%–75%). Mortality was associated with increased percentage of samples with elevated lactate and brain hypoxia (28% [interquartile range 9%–95%] in nonsurvivors versus 9% [interquartile range 3%–17%] in survivors; P =0.02) and lower percentage of elevated lactate and cerebral hyperglycolysis (13% [interquartile range, 1%–87%] versus 88% [interquartile range, 27%–99%]; P =0.07). Cerebral hyperglycolytic lactate production predicted good 6-month outcome (odds ratio for modified Rankin Scale score, 0–3 1.49; CI, 1.08–2.05; P =0.016), whereas increased lactate with brain hypoxia was associated with a reduced likelihood of good outcome (OR, 0.78; CI, 0.59–1.03; P =0.08).

Conclusions—

Brain lactate is frequently elevated in subarachnoid hemorrhage patients, predominantly because of hyperglycolysis rather than hypoxia. A pattern of increased cerebral hyperglycolytic lactate was associated with good long-term recovery. Our data suggest that lactate may be used as an aerobic substrate by the injured human brain.

The importance of early brain injury after subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a medical emergency that accounts for 5% of all stroke cases. Individuals affected are typically in the prime of their lives (mean age 50 years). Approximately 12% of patients die before receiving medical attention, 33% within 48 h and 50% within 30 days of aSAH. Of the survivors 50% suffer from permanent disability with an estimated lifetime cost more than double that of an ischemic stroke. Traditionally, spasm that develops in large cerebral arteries 3-7 days after aneurysm rupture is considered the most important determinant of brain injury and outcome after aSAH. However, recent studies show that prevention of delayed vasospasm does not improve outcome in aSAH patients. This finding has finally brought in focus the influence of early brain injury on outcome of aSAH. A substantial amount of evidence indicates that brain injury begins at the aneurysm rupture, evolves with time and plays an important role in patients' outcome. In this manuscript we review early brain injury after aSAH. Due to the early nature, most of the information on this injury comes from animals and few only from autopsy of patients who died within days after aSAH. Consequently, we began with a review of animal models of early brain injury, next we review the mechanisms of brain injury according to the sequence of their temporal appearance and finally we discuss the failure of clinical translation of therapies successful in animal models of aSAH.

Measuring multiple neurochemicals and related metabolites in blood and brain of the rhesus monkey by using dual microdialysis sampling and capillary hydrophilic interaction chromatography-mass spectrometry

In vivo measurement of multiple functionally related neurochemicals and metabolites (NMs) is highly interesting but remains challenging in the field of basic neuroscience and clinical research. We present here an analytical method for determining five functionally and metabolically related polar substances, including acetylcholine (quaternary ammonium), lactate and pyruvate (organic acids), as well as glutamine and glutamate (amino acids). These NMs are acquired from samples of the brain and the blood of non-human primates in parallel by dual microdialysis, and subsequently analyzed by a direct capillary hydrophilic interaction chromatography (HILIC)-mass spectrometry (MS) based method. To obtain high sensitivity in electrospray ionization (ESI)-MS, lactate and pyruvate were detected in negative ionization mode whereas the other NMs were detected in positive ionization mode during each HILIC-MS run. The method was validated for linearity, the limits of detection and quantification, precision, accuracy, stability and matrix effect. The detection limit of acetylcholine, lactate, pyruvate, glutamine, and glutamate was 150 pM, 3 μM, 2 μM, 5 nM, and 50 nM, respectively. This allowed us to quantitatively and simultaneously measure the concentrations of all the substances from the acquired dialysates. The concentration ratios of both lactate/pyruvate and glutamine/glutamate were found to be higher in the brain compared to blood (p < 0.05). The reliable and simultaneous quantification of these five NMs from brain and blood samples allows us to investigate their relative distribution in the brain and blood, and most importantly paves the way for future non-invasive studies of the functional and metabolic relation of these substances to each other.

Relation between brain interstitial and systemic glucose concentrations after subarachnoid hemorrhage

OBJECT

The aim in the present investigation was to study the relation between brain interstitial and systemic blood glucose concentrations during the acute phase after subarachnoid hemorrhage (SAH). The authors also evaluated the effects of insulin administration on local brain energy metabolism.

METHODS

Nineteen patients with spontaneous SAH were prospectively monitored with intracerebral microdialysis (MD). The relation between plasma glucose and MD-measured interstitial brain glucose concentrations as well as the temporal pattern of MD glucose, lactate, pyruvate, glutamate, and glycerol was studied for 7 days after SAH. Using a target plasma glucose concentration of 5-10 mmol/L, the effect of insulin injection was also evaluated.

RESULTS

The mean (± SD) correlation coefficient between plasma glucose and MD glucose was 0.27 ± 0.27 (p = 0.0005), with a high degree of individual variation. Microdialysis glucose, the MD/plasma glucose ratio, and MD glutamate concentrations decreased in parallel with a gradual increase in MD pyruvate and MD lactate concentrations. There were no significant changes in the MD L/P ratio or MD glycerol levels. Insulin administration induced a decrease in MD glucose and MD pyruvate.

CONCLUSIONS

After SAH, there was a positive correlation between plasma and MD glucose concentrations with a high degree of individual variation. A gradual decline in MD glucose and the MD/plasma glucose ratio and an increase in MD pyruvate and MD lactate concentrations during the 1st week after SAH suggest a transition to a hyperglycolytic state with increased cerebral glucose consumption. The administration of insulin was related to a lowering of MD glucose and MD pyruvate, often to low levels even though plasma glucose values remained above 6 mmol/L. After SAH, the administration of insulin could impede the glucose supply of the brain.

Detection of Cerebral Compromise With Multimodality Monitoring in Patients With Subarachnoid Hemorrhage

BACKGROUND:

Studies in traumatic brain injury suggest that monitoring techniques such as brain tissue oxygen (Pbto2) and cerebral microdialysis may complement conventional intracranial pressure (ICP) and cerebral perfusion pressure (CPP) measurements.

OBJECTIVE:

In this study of poor-grade (Hunt and Hess grade IV and V) subarachnoid hemorrhage (SAH) patients, we examined the prevalence of brain hypoxia and brain energy dysfunction in the presence of normal and abnormal ICP and CPP.

METHODS:

SAH patients who underwent multimodal neuromonitoring and cerebral microdialysis were studied. We examined the frequency of brain hypoxia and energy dysfunction in different ICP and CPP ranges and the relationship between Pbto2 and the lactate/pyruvate ratio (LPR).

RESULTS:

A total of 2394 samples from 19 patients were analyzed. There were 149 samples with severe brain hypoxia (Pbto2 ≤10 mm Hg) and 347 samples with brain energy dysfunction (LPR &gt;40). The sensitivities of abnormal ICP or CPP for elevated LPR and reduced Pbto2 were poor (21.2% at best), and the LPR or Pbto2 was abnormal in many instances when ICP or CPP was normal. Severe brain hypoxia was often associated with an LPR greater than 40 (86% of samples). In contrast, mild brain hypoxia (≤20 mm Hg) and severe brain hypoxia were observed in only 53% and 36% of samples with brain energy dysfunction, respectively.

CONCLUSION:

Our data demonstrate that ICP and CPP monitoring may not always detect episodes of cerebral compromise in SAH patients. Our data suggest that several complementary monitors may be needed to optimize the care of poor-grade SAH patients.

Brain energy metabolism in patients with spontaneous subarachnoid hemorrhage and global cerebral edema

BACKGROUND

Previous studies of spontaneous subarachnoid hemorrhage (SAH) have shown that global cerebral edema on the first computed tomography scan is associated with a more severe initial injury and is an independent predictor of poor outcome. Effects of secondary ischemic events also influence outcome after SAH.

OBJECTIVE

This study demonstrates that early global edema is related to markers of an increased cerebral energy metabolism as measured with intracerebral microdialysis, which could increase vulnerability to adverse events.

METHODS

Fifty-two patients with microdialysis monitoring after spontaneous SAH were stratified according to the occurrence of global cerebral edema on the first computed tomography scan taken a median of 2 hours after the initial bleed. Microdialysis levels of glucose, lactate, and pyruvate were compared between the global edema (n = 31) and no global edema (n = 21) groups. Clinical outcome was assessed with the Glasgow Outcome Scale score at >/= 6 months.

RESULTS

Patients with global edema showed significantly elevated lactate and pyruvate levels 70 to 79 hours after SAH and marginally significantly higher levels of lactate 60 to 69 hours and 80 to 89 hours after SAH. There was a trend toward worse outcome in the edema group.

CONCLUSION

Patients with global cerebral edema have higher interstitial levels of lactate and pyruvate. The edema group may have developed a cerebral hypermetabolism to meet the increased energy demand in the recovery phase after SAH. This stress would make the brain more vulnerable to secondary insults, increasing the likelihood of energy failure.

Anemia is associated with metabolic distress and brain tissue hypoxia after subarachnoid hemorrhage

BACKGROUND

Anemia is frequently encountered in critically ill patients and adversely affects cerebral oxygen delivery and brain tissue oxygen (PbtO2). The objective of this study is to assess whether there is an association between anemia and metabolic distress or brain tissue hypoxia in patients with subarachnoid hemorrhage.

METHODS

Retrospective study was conducted in a neurological intensive care unit in a university hospital. Patients with subarachnoid hemorrhage that underwent multimodality monitoring with intracranial pressure, PbtO2 and microdialysis were analyzed. The relationships between hemoglobin (Hb) concentrations and brain tissue hypoxia (PbtO2 < or = 15 mmHg) and metabolic distress (lactate/pyruvate ratio > or =40) were analyzed with general linear models of logistic function for dichotomized outcomes utilizing generalized estimating equations.

RESULTS

A total of 359 matched neuromonitoring hours and Hb measurements were analyzed from 34 consecutive patients. The median hemoglobin was 9.7 g/dl (interquartile range 8.8-10.5). After adjusting for significant covariates, reduced hemoglobin concentration was associated with a progressively increased risk of brain tissue hypoxia (adjusted OR 1.7 [1.1-2.4]; P = 0.01 for every unit decrease). Also after adjusting for significant covariates, hemoglobin concentrations below 9 g/dl and between 9.1 and 10 g/dl were associated with an increased risk of metabolic distress as compared to concentrations between 10.1 and 11 g/dl (adjusted OR 3.7 [1.5-9.4]; P = 0.004 for Hb < or = 9 g/dl and adjusted OR 1.9 [1.1-3.3]; P = 0.03 for Hb 9.1-10 g/dl).

CONCLUSIONS

Anemia is associated with a progressively increased risk of cerebral metabolic distress and brain tissue hypoxia after subarachnoid hemorrhage.

Relationship between intracranial hemodynamics and microdialysis markers of energy metabolism and glutamate-glutamine turnover in patients with subarachnoid hemorrhage. Clinical article

OBJECT

The aim of this study was to explore the relationship between hemodynamics (intracranial and systemic) and brain tissue energy metabolism, and between hemodynamics and glutamate (Glt)-glutamine (Gln) cycle activity.

METHODS

Brain interstitial levels of lactate, pyruvate, Glt, and Gln were prospectively monitored in the neurointensive care unit for more than 3600 hours using intracerebral microdialysis in 33 patients with subarachnoid hemorrhage (SAH). Intracranial pressure (ICP), mean arterial blood pressure, and cerebral perfusion pressure (CPP) were recorded using a digitalized system.

RESULTS

Interstitial Gln and pyruvate correlated with CPP (r = 0.25 and 0.24, respectively). Intracranial pressure negatively correlated with Gln (r = -0.29) and the Gln/Glt ratio (r = -0.40). Levels of Gln and pyruvate and the Gln/Glt ratio were higher and levels of Glt and lactate and the lactate/pyruvate ratio were lower during periods of decreased ICP (<or= 10 mm Hg) as compared with values in periods of elevated ICP (> 10 mm Hg). In 3 patients, a poor clinical condition was attributed to high ICP levels (range 15-25 mm Hg). When CSF drainage was increased and the ICP was lowered to 10 mm Hg, there was an instantaneous sharp increase in interstitial Glt and pyruvate in these 3 patients.

CONCLUSIONS

Increasing interstitial Gln and pyruvate levels appear to be favorable signs associated with improved CPP and low ICP. The authors suggest that this pattern indicates an energy metabolic situation allowing augmented astrocytic energy metabolism with accelerated Glt uptake and Gln synthesis. Moreover, their data raised the question of whether patients with SAH and moderately elevated ICP (15-20 mm Hg) would benefit from CSF drainage at lower pressure levels than what is usually indicated in current clinical protocols.