Comparison of brain tissue oxygen tension to microdialysis-based measures of cerebral ischemia in fatally head-injured humans

Dimethyl fumarate ameliorates oxidative stress-induced acute kidney injury after traumatic brain injury by activating Keap1-Nrf2/HO-1 signaling pathway

Acute kidney injury (AKI) frequently emerges as a consequential non-neurological sequel to traumatic brain injury (TBI), significantly contributing to heightened mortality risks. The intricate interplay of oxidative stress in the pathophysiology of TBI underscores the centrality of the Keap1-Nrf2/HO-1 signaling pathway as a pivotal regulator in this context. This study endeavors to elucidate the involvement of the Keap1-Nrf2/HO-1 pathway in modulating oxidative stress in AKI subsequent to TBI and concurrently explore the therapeutic efficacy of dimethyl fumarate (DMF). A rat model of TBI was established via the Feeney free-fall method, incorporating interventions with varying concentrations of DMF. Assessment of renal function ensued through measurements of serum creatinine and neutrophil gelatinase-associated lipocalin. Morphological evaluation of renal pathology was conducted employing quantitative hematoxylin and eosin staining. The inflammatory response was scrutinized by quantifying interleukin (IL)-6, IL-1β, and tumor necrosis factor-α levels. Oxidative stress levels were discerned through quantification of malondialdehyde and superoxide dismutase. The apoptotic cascade was examined via the terminal deoxynucleotidyl transferase dUTP deletion labeling assay. Western blotting provided insights into the expression dynamics of proteins affiliated with the Keap1-Nrf2/HO-1 pathway and apoptosis. The findings revealed severe kidney injury, heightened oxidative stress, inflammation, and apoptosis in the traumatic brain injury model. Treatment with DMF effectively reversed these changes, alleviating oxidative stress by activating the Keap1-Nrf2/HO-1 signaling pathway, ultimately conferring protection against AKI. Activating Keap1-Nrf2/HO-1 signaling pathway may be a potential therapeutic strategy for attenuating oxidative stress-induced AKI after TBI.

The Impact of Inotropes and Vasopressors on Cerebral Oxygenation in Patients with Traumatic Brain Injury and Subarachnoid Hemorrhage: A Narrative Review

Traumatic brain injury (TBI) and subarachnoid hemorrhage (SAH) are critical neurological conditions that necessitate specialized care in the Intensive Care Unit (ICU). Managing cerebral perfusion pressure (CPP) and mean arterial pressure (MAP) is of primary importance in these patients. To maintain targeted MAP and CPP, vasopressors and/or inotropes are commonly used. However, their effects on cerebral oxygenation are not fully understood. The aim of this review is to provide an up-to date review regarding the current uses and pathophysiological issues related to the use of vasopressors and inotropes in TBI and SAH patients. According to our findings, despite achieving similar hemodynamic parameters and CPP, the effects of various vasopressors and inotropes on cerebral oxygenation, local CBF and metabolism are heterogeneous. Therefore, a more accurate understanding of the cerebral activity of these medications is crucial for optimizing patient management in the ICU setting.

The Role of Brain Tissue Oxygenation Monitoring in the Management of Subarachnoid Hemorrhage: A Scoping Review

Monitoring of brain tissue oxygenation (PbtO2) is an important component of multimodal monitoring in traumatic brain injury. Over recent years, use of PbtO2 monitoring has also increased in patients with poor-grade subarachnoid hemorrhage (SAH), particularly in those with delayed cerebral ischemia. The aim of this scoping review was to summarize the current state of the art regarding the use of this invasive neuromonitoring tool in patients with SAH. Our results showed that PbtO2 monitoring is a safe and reliable method to assess regional cerebral tissue oxygenation and that PbtO2 represents the oxygen available in the brain interstitial space for aerobic energy production (i.e., the product of cerebral blood flow and the arterio-venous oxygen tension difference). The PbtO2 probe should be placed in the area at risk of ischemia (i.e., in the vascular territory in which cerebral vasospasm is expected to occur). The most widely used PbtO2 threshold to define brain tissue hypoxia and initiate specific treatment is between 15 and 20 mm Hg. PbtO2 values can help identify the need for or the effects of various therapies, such as hyperventilation, hyperoxia, induced hypothermia, induced hypertension, red blood cell transfusion, osmotic therapy, and decompressive craniectomy. Finally, a low PbtO2 value is associated with a worse prognosis, and an increase of the PbtO2 value in response to treatment is a marker of good outcome.

Multimodal Neuromonitoring and Neurocritical Care in Swine to Enhance Translational Relevance in Brain Trauma Research

Neurocritical care significantly impacts outcomes after moderate-to-severe acquired brain injury, but it is rarely applied in preclinical studies. We created a comprehensive neurointensive care unit (neuroICU) for use in swine to account for the influence of neurocritical care, collect clinically relevant monitoring data, and create a paradigm that is capable of validating therapeutics/diagnostics in the unique neurocritical care space. Our multidisciplinary team of neuroscientists, neurointensivists, and veterinarians adapted/optimized the clinical neuroICU (e.g., multimodal neuromonitoring) and critical care pathways (e.g., managing cerebral perfusion pressure with sedation, ventilation, and hypertonic saline) for use in swine. Moreover, this neurocritical care paradigm enabled the first demonstration of an extended preclinical study period for moderate-to-severe traumatic brain injury with coma beyond 8 h. There are many similarities with humans that make swine an ideal model species for brain injury studies, including a large brain mass, gyrencephalic cortex, high white matter volume, and topography of basal cisterns, amongst other critical factors. Here we describe the neurocritical care techniques we developed and the medical management of swine following subarachnoid hemorrhage and traumatic brain injury with coma. Incorporating neurocritical care in swine studies will reduce the translational gap for therapeutics and diagnostics specifically tailored for moderate-to-severe acquired brain injury.

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.

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.

Big data and predictive analytics in neurocritical care

PURPOSE OF REVIEW

To describe predictive data and workflow in the intensive care unit when managing neurologically ill patients.

RECENT FINDINGS

In the era of Big Data in medicine, intensive critical care units are data-rich environments. Neurocritical care adds another layer of data with advanced multimodal monitoring to prevent secondary brain injury from ischemia, tissue hypoxia, and a cascade of ongoing metabolic events. A step closer toward personalized medicine is the application of multimodal monitoring of cerebral hemodynamics, bran oxygenation, brain metabolism, and electrophysiologic indices, all of which have complex and dynamic interactions. These data are acquired and visualized using different tools and monitors facing multiple challenges toward the goal of the optimal decision support system. In this review, we highlight some of the predictive data used to diagnose, treat, and prognosticate the neurologically ill patients. We describe information management in neurocritical care units including data acquisition, wrangling, analysis, and visualization.

Cerebral Oxygenation in Traumatic Brain Injury: Can a Non-Invasive Frequency Domain Near-Infrared Spectroscopy Device Detect Changes in Brain Tissue Oxygen Tension as Well as the Established Invasive Monitor?

The cost and highly invasive nature of brain monitoring modality in traumatic brain injury patients currently restrict its utility to specialist neurological intensive care settings. We aim to test the abilities of a frequency domain near-infrared spectroscopy (FD-NIRS) device in predicting changes in invasively measured brain tissue oxygen tension. Individuals admitted to a United Kingdom specialist major trauma center were contemporaneously monitored with an FD-NIRS device and invasively measured brain tissue oxygen tension probe. Area under the curve receiver operating characteristic (AUROC) statistical analysis was utilized to assess the predictive power of FD-NIRS in detecting both moderate and severe hypoxia (20 and 10 mm Hg, respectively) as measured invasively. Sixteen individuals were prospectively recruited to the investigation. Severe hypoxic episodes were detected in nine of these individuals, with the NIRS demonstrating a broad range of predictive abilities (AUROC 0.68-0.88) from relatively poor to good. Moderate hypoxic episodes were detected in seven individuals with similar predictive performance (AUROC 0.576-0.905). A variable performance in the predictive powers of this FD-NIRS device to detect changes in brain tissue oxygen was demonstrated. Consequently, this enhanced NIRS technology has not demonstrated sufficient ability to replace the established invasive measurement.

Effects of Hypertonic Saline and Sodium Lactate on Cortical Cerebral Microcirculation and Brain Tissue Oxygenation

BACKGROUND

Hyperosmolar solutions have been used in neurosurgery to modify brain bulk. The aim of this animal study was to compare the short-term effects of equivolemic, equiosmolar solutions of hypertonic saline (HTS) and sodium lactate (HTL) on cerebral cortical microcirculation and brain tissue oxygenation in a rabbit craniotomy model.

METHODS

Rabbits (weight, 1.5 to 2.0 kg) were anesthetized, ventilated mechanically, and subjected to a craniotomy. The animals were allocated randomly to receive a 3.75 mL/kg intravenous infusion of either 3.2% HTS (group HTS, n=9), half-molar sodium lactate (group HTL, n=10), or normal saline (group C, n=9). Brain tissue partial pressure of oxygen (PbtO2) and microcirculation in the cerebral cortex using sidestream dark-field imaging were evaluated before, 20 and 40 minutes after 15 minutes of hyperosmolar solution infusion. Global hemodynamic data were recorded, and blood samples for laboratory analysis were obtained at the time of sidestream dark-field image recording.

RESULTS

No differences in the microcirculatory parameters were observed between the groups before and after the use of osmotherapy. Brain tissue oxygen deteriorated over time in groups C and HTL, this deterioration was not significant in the group HTS.

CONCLUSIONS

Our findings suggest that equivolemic, equiosmolar HTS and HTL solutions equally preserve perfusion of cortical brain microcirculation in a rabbit craniotomy model. The use of HTS was better in preventing the worsening of brain tissue oxygen tension.

Pathophysiology and Management of Intracranial Hypertension and Tissular Brain Hypoxia After Severe Traumatic Brain Injury: An Integrative Approach

Monitoring intracranial pressure in comatose patients with severe traumatic brain injury (TBI) is considered necessary by most experts. Acute intracranial hypertension (IHT), when severe and sustained, is a life-threatening complication that demands emergency treatment. Yet, secondary anoxic-ischemic injury after brain trauma can occur in the absence of IHT. In such cases, adding other monitoring modalities can alert clinicians when the patient is in a state of energy failure. This article reviews the mechanisms, diagnosis, and treatment of IHT and brain hypoxia after TBI, emphasizing the need to develop a physiologically integrative approach to the management of these complex situations.

A systematic review of cerebral microdialysis and outcomes in TBI: relationships to patient functional outcome, neurophysiologic measures, and tissue outcome

OBJECTIVE

To perform a systematic review on commonly measured cerebral microdialysis (CMD) analytes and their association to: (A) patient functional outcome, (B) neurophysiologic measures, and (C) tissue outcome; after moderate/severe TBI. The aim was to provide a foundation for next-generation CMD studies and build on existing pragmatic expert guidelines for CMD.

METHODS

We searched MEDLINE, BIOSIS, EMBASE, Global Health, Scopus, Cochrane Library (inception to October 2016). Strength of evidence was adjudicated using GRADE.

RESULTS

(A) Functional Outcome: 55 articles were included, assessing outcome as mortality or Glasgow Outcome Scale (GOS) at 3-6 months post-injury. Overall, there is GRADE C evidence to support an association between CMD glucose, glutamate, glycerol, lactate, and LPR to patient outcome at 3-6 months. (B) Neurophysiologic Measures: 59 articles were included. Overall, there currently exists GRADE C level of evidence supporting an association between elevated CMD measured mean LPR, glutamate and glycerol with elevated ICP and/or decreased CPP. In addition, there currently exists GRADE C evidence to support an association between elevated mean lactate:pyruvate ratio (LPR) and low PbtO2. Remaining CMD measures and physiologic outcomes displayed GRADE D or no evidence to support a relationship. (C) Tissue Outcome: four studies were included. Given the conflicting literature, the only conclusion that can be drawn is acute/subacute phase elevation of CMD measured LPR is associated with frontal lobe atrophy at 6 months.

CONCLUSIONS

This systematic review replicates previously documented relationships between CMD and various outcome, which have driven clinical application of the technique. Evidence assessments do not address the application of CMD for exploring pathophysiology or titrating therapy in individual patients, and do not account for the modulatory effect of therapy on outcome, triggered at different CMD thresholds in individual centers. Our findings support clinical application of CMD and refinement of existing guidelines.

Brain Oxygen Optimization in Severe Traumatic Brain Injury Phase-II: A Phase II Randomized Trial

OBJECTIVES

A relationship between reduced brain tissue oxygenation and poor outcome following severe traumatic brain injury has been reported in observational studies. We designed a Phase II trial to assess whether a neurocritical care management protocol could improve brain tissue oxygenation levels in patients with severe traumatic brain injury and the feasibility of a Phase III efficacy study.

DESIGN

Randomized prospective clinical trial.

SETTING

Ten ICUs in the United States.

PATIENTS

One hundred nineteen severe traumatic brain injury patients.

INTERVENTIONS

Patients were randomized to treatment protocol based on intracranial pressure plus brain tissue oxygenation monitoring versus intracranial pressure monitoring alone. Brain tissue oxygenation data were recorded in the intracranial pressure -only group in blinded fashion. Tiered interventions in each arm were specified and impact on intracranial pressure and brain tissue oxygenation measured. Monitors were removed if values were normal for 48 hours consecutively, or after 5 days. Outcome was measured at 6 months using the Glasgow Outcome Scale-Extended.

MEASUREMENTS AND MAIN RESULTS

A management protocol based on brain tissue oxygenation and intracranial pressure monitoring reduced the proportion of time with brain tissue hypoxia after severe traumatic brain injury (0.45 in intracranial pressure-only group and 0.16 in intracranial pressure plus brain tissue oxygenation group; p < 0.0001). Intracranial pressure control was similar in both groups. Safety and feasibility of the tiered treatment protocol were confirmed. There were no procedure-related complications. Treatment of secondary injury after severe traumatic brain injury based on brain tissue oxygenation and intracranial pressure values was consistent with reduced mortality and increased proportions of patients with good recovery compared with intracranial pressure-only management; however, the study was not powered for clinical efficacy.

CONCLUSIONS

Management of severe traumatic brain injury informed by multimodal intracranial pressure and brain tissue oxygenation monitoring reduced brain tissue hypoxia with a trend toward lower mortality and more favorable outcomes than intracranial pressure-only treatment. A Phase III randomized trial to assess impact on neurologic outcome of intracranial pressure plus brain tissue oxygenation-directed treatment of severe traumatic brain injury is warranted.

Rethinking Neuroprotection in Severe Traumatic Brain Injury: Toward Bedside Neuroprotection

Neuroprotection after traumatic brain injury (TBI) is an important goal pursued strenuously in the last 30 years. The acute cerebral injury triggers a cascade of biochemical events that may worsen the integrity, function, and connectivity of the brain cells and decrease the chance of functional recovery. A number of molecules acting against this deleterious cascade have been tested in the experimental setting, often with preliminary encouraging results. Unfortunately, clinical trials using those candidate neuroprotectants molecules have consistently produced disappointing results, highlighting the necessity of improving the research standards. Despite repeated failures in pharmacological neuroprotection, TBI treatment in neurointensive care units has achieved outcome improvement. It is likely that intensive treatment has contributed to this progress offering a different kind of neuroprotection, based on a careful prevention and limitations of intracranial and systemic threats. The natural course of acute brain damage, in fact, is often complicated by additional adverse events, like the development of intracranial hypertension, brain hypoxia, or hypoperfusion. All these events may lead to additional brain damage and worsen outcome. An approach designed for early identification and prompt correction of insults may, therefore, limit brain damage and improve results.

Brain microdialysis as a tool to explore the ionic profile of the brain extracellular space in neurocritical patients: a methodological approach and feasibility study

Our aim is to determine whether the ionic concentration in brain microdialysate enables calculations of the actual Na(+), K(+), and Cl(-) concentrations in vitro and whether this method can be applied to determine the ionic concentrations in the brain extracellular fluid. We designed an experiment using CMA-71 probes (M Dialysis, Stockholm, Sweden) and the standard conditions used in a clinical setting. Nine CMA-71 probes were inserted in different matrices and perfused with mock cerebrospinal fluid containing 3% albumin at the standard infusion rate used in the clinical setting (0.3 μL/min). Microvials were replaced every 12 h, and the ionic concentrations, both in the dialysate and the matrix, were analyzed. For each ion, scatter plots were built, with [Na(+)], [K(+)], and [Cl(-)] in the dialysate as the predictor variables and the matrix concentrations as the outcome variables. A linear regression model allowed us to calculate the true ionic concentrations in the matrix. To demonstrate the feasibility of the method, we present the calculated ionic profile of one patient with a malignant infarction and a second with a severe traumatic brain injury. Our results confirm that the ionic concentration in microdialysate can be used to calculate the true concentrations of ions in a matrix and the actual concentrations in the extracellular fluid. Microdialysis offers the unique possibility of monitoring the dynamic changes of ions in the brain over time and opens a new avenue to explore the brain's ionic profile, its changes in brain edema, and how this profile can be modified with different therapies.

A Prospective Randomized Study of Brain Tissue Oxygen Pressure-Guided Management in Moderate and Severe Traumatic Brain Injury Patients

The purpose of this study was to compare the effect of PbtO₂-guided therapy with traditional intracranial pressure- (ICP-) guided treatment on the management of cerebral variables, therapeutic interventions, survival rates, and neurological outcomes of moderate and severe traumatic brain injury (TBI) patients. From 2009 to 2010, TBI patients with a Glasgow coma scale <12 were recruited from 6 collaborative hospitals in northern Taiwan, excluding patients with severe systemic injuries, fixed and dilated pupils, and other major diseases. In total, 23 patients were treated with PbtO₂-guided management (PbtO₂ > 20 mmHg), and 27 patients were treated with ICP-guided therapy (ICP < 20 mmHg and CPP > 60 mmHg) in the neurosurgical intensive care unit (NICU); demographic characteristics were similar across groups. The survival rate in the PbtO₂-guided group was also significantly increased at 3 and 6 months after injury. Moreover, there was a significant correlation between the PbtO₂ signal and Glasgow outcome scale-extended in patients from 1 to 6 months after injury. This finding demonstrates that therapy directed by PbtO₂ monitoring is valuable for the treatment of patients with moderate and severe TBI and that increasing PaO₂ to 150 mmHg may be efficacious for preventing cerebral hypoxic events after brain trauma.

Lactate storm marks cerebral metabolism following brain trauma

Brain metabolism is thought to be maintained by neuronal-glial metabolic coupling. Glia take up glutamate from the synaptic cleft for conversion into glutamine, triggering glial glycolysis and lactate production. This lactate is shuttled into neurons and further metabolized. The origin and role of lactate in severe traumatic brain injury (TBI) remains controversial. Using a modified weight drop model of severe TBI and magnetic resonance (MR) spectroscopy with infusion of (13)C-labeled glucose, lactate, and acetate, the present study investigated the possibility that neuronal-glial metabolism is uncoupled following severe TBI. Histopathology of the model showed severe brain injury with subarachnoid and hemorrhage together with glial cell activation and positive staining for Tau at 90 min post-trauma. High resolution MR spectroscopy of brain metabolites revealed significant labeling of lactate at C-3 and C-2 irrespective of the infused substrates. Increased (13)C-labeled lactate in all study groups in the absence of ischemia implied activated astrocytic glycolysis and production of lactate with failure of neuronal uptake (i.e. a loss of glial sensing for glutamate). The early increase in extracellular lactate in severe TBI with the injured neurons rendered unable to pick it up probably contributes to a rapid progression toward irreversible injury and pan-necrosis. Hence, a method to detect and scavenge the excess extracellular lactate on site or early following severe TBI may be a potential primary therapeutic measure.

Brain Tissue Oxygen Monitoring in Neurocritical Care

Brain injury results from ischemia, tissue hypoxia, and a cascade of secondary events. The cornerstone of neurocritical care management is optimization and maintenance of cerebral blood flow (CBF) and oxygen and substrate delivery to prevent or attenuate this secondary damage. New techniques for monitoring brain tissue oxygen tension (PtiO2) are now available. Brain PtiO2 reflects both oxygen delivery and consumption. Brain hypoxia (low brain PtiO2) has been associated with poor outcomes in patients with brain injury. Strategies to improve brain PtiO2 have focused mainly on increasing oxygen delivery either by increasing CBF or by increasing arterial oxygen content. The results of nonrandomized studies comparing brain PtiO2-guided therapy with intracranial pressure/cerebral perfusion pressure-guided therapy, while promising, have been mixed. More studies are needed including prospective, randomized controlled trials to assess the true value of this approach. The following is a review of the physiology of brain tissue oxygenation, the effect of brain hypoxia on outcome, strategies to increase oxygen delivery, and outcome studies of brain PtiO2-guided therapy in neurocritical care.

Mechanisms underlying cell death in ischemia-like damage to the rat spinal cord in vitro

New spinal cord injury (SCI) cases are frequently due to non-traumatic causes, including vascular disorders. To develop mechanism-based neuroprotective strategies for acute SCI requires full understanding of the early pathophysiological changes to prevent disability and paralysis. The aim of our study was to identify the molecular and cellular mechanisms of cell death triggered by a pathological medium (PM) mimicking ischemia in the rat spinal cord in vitro. We previously showed that extracellular Mg²⁺ (1 mM) worsened PM-induced damage and inhibited locomotor function. The present study indicated that 1 h of PM+Mg²⁺ application induced delayed pyknosis chiefly in the spinal white matter via overactivation of poly (ADP-ribose) polymerase 1 (PARP1), suggesting cell death mediated by the process of parthanatos that was largely suppressed by pharmacological block of PARP-1. Gray matter damage was less intense and concentrated in dorsal horn neurons and motoneurons that became immunoreactive for the mitochondrial apoptosis-inducing factor (the intracellular effector of parthanatos) translocated into the nucleus to induce chromatin condensation and DNA fragmentation. Immunoreactivity to TRPM ion channels believed to be involved in ischemic brain damage was also investigated. TRPM2 channel expression was enhanced 24 h later in dorsal horn and motoneurons, whereas TRPM7 channel expression concomitantly decreased. Conversely, TRPM7 expression was found earlier (3 h) in white matter cells, whereas TRPM2 remained undetectable. Simulating acute ischemic-like damage in vitro in the presence of Mg²⁺ showed how, during the first 24 h, this divalent cation unveiled differential vulnerability of white matter cells and motoneurons, with distinct changes in their TRPM expression.

A prospective, randomized Phase II clinical trial to evaluate the effect of combined hyperbaric and normobaric hyperoxia on cerebral metabolism, intracranial pressure, oxygen toxicity, and clinical outcome in severe traumatic brain injury

OBJECT

Preclinical and clinical investigations indicate that the positive effect of hyperbaric oxygen (HBO2) for severe traumatic brain injury (TBI) occurs after rather than during treatment. The brain appears better able to use baseline O2 levels following HBO2 treatments. In this study, the authors evaluate the combination of HBO2 and normobaric hyperoxia (NBH) as a single treatment.

METHODS

Forty-two patients who sustained severe TBI (mean Glasgow Coma Scale [GCS] score 5.7) were prospectively randomized within 24 hours of injury to either: 1) combined HBO2/NBH (60 minutes of HBO2 at 1.5 atmospheres absolute [ATA] followed by NBH, 3 hours of 100% fraction of inspired oxygen [FiO2] at 1.0 ATA) or 2) control, standard care. Treatments occurred once every 24 hours for 3 consecutive days. Intracranial pressure, surrogate markers for cerebral metabolism, and O2 toxicity were monitored. Clinical outcome was assessed at 6 months using the sliding dichotomized Glasgow Outcome Scale (GOS) score. Mixed-effects linear modeling was used to statistically test differences between the treatment and control groups. Functional outcome and mortality rates were compared using chi-square tests.

RESULTS

There were no significant differences in demographic characteristics between the 2 groups. In comparison with values in the control group, brain tissue partial pressure of O2 (PO2) levels were significantly increased during and following combined HBO2/NBH treatments in both the noninjured and pericontusional brain (p < 0.0001). Microdialysate lactate/pyruvate ratios were significantly decreased in the noninjured brain in the combined HBO2/NBH group as compared with controls (p < 0.0078). The combined HBO2/NBH group's intracranial pressure values were significantly lower than those of the control group during treatment, and the improvement continued until the next treatment session (p < 0.0006). The combined HBO2/NBH group's levels of microdialysate glycerol were significantly lower than those of the control group in both noninjured and pericontusional brain (p < 0.001). The combined HBO2/NBH group's level of CSF F2-isoprostane was decreased at 6 hours after treatment as compared with that of controls, but the difference did not quite reach statistical significance (p = 0.0692). There was an absolute 26% reduction in mortality for the combined HBO2/NBH group (p = 0.048) and an absolute 36% improvement in favorable outcome using the sliding dichotomized GOS (p = 0.024) as compared with the control group.

CONCLUSIONS

In this Phase II clinical trial, in comparison with standard care (control treatment) combined HBO2/NBH treatments significantly improved markers of oxidative metabolism in relatively uninjured brain as well as pericontusional tissue, reduced intracranial hypertension, and demonstrated improvement in markers of cerebral toxicity. There was significant reduction in mortality and improved favorable outcome as measured by GOS. The combination of HBO2 and NBH therapy appears to have potential therapeutic efficacy as compared with the 2 treatments in isolation. CLINICAL TRIAL REGISTRATION NO.: NCT00170352 (ClinicalTrials.gov).

The frequency of cerebral ischemia/hypoxia in pediatric severe traumatic brain injury

INTRODUCTION

The frequency of adverse events, such as cerebral ischemia, following traumatic brain injury (TBI) is often debated. Point-in-time monitoring modalities provide important information, but have limited temporal resolution.

PURPOSE

This study examines the frequency of an adverse event as a point prevalence at 24 and 72 h post-injury, compared with the cumulative burden measured as a frequency of the event over the full duration of monitoring.

METHODS

Reduced brain tissue oxygenation (PbtO(2) < 10 mmHg) was the adverse event chosen for examination. Data from 100 consecutive children with severe TBI who received PbtO(2) monitoring were retrospectively examined, with data from 87 children found suitable for analysis. Hourly recordings were used to identify episodes of PbtO(2) less than 10 mmHg, at 24 and 72 h post-injury, and for the full duration of monitoring.

RESULTS

Reduced PbtO(2) was more common early than late after injury. The point prevalence of reduced PbtO(2) at the selected time points was relatively low (10 % of patients at 24 h and no patients at the 72-h mark post-injury). The cumulative burden of these events over the full duration of monitoring was relatively high: 50 % of patients had episodes of PbtO(2) less than 10 mmHg and 88 % had PbtO(2) less than 20 mmHg.

CONCLUSION

Point-in-time monitoring in a dynamic condition like TBI may underestimate the overall frequency of adverse events, like reduced PbtO(2), particularly when compared with continuous monitoring, which also has limitations, but provides a dynamic assessment over a longer time period.

Are initial radiographic and clinical scales associated with subsequent intracranial pressure and brain oxygen levels after severe traumatic brain injury?

BACKGROUND

Prediction of clinical course and outcome after severe traumatic brain injury (TBI) is important.

OBJECTIVE

To examine whether clinical scales (Glasgow Coma Scale [GCS], Injury Severity Score [ISS], and Acute Physiology and Chronic Health Evaluation II [APACHE II]) or radiographic scales based on admission computed tomography (Marshall and Rotterdam) were associated with intensive care unit (ICU) physiology (intracranial pressure [ICP], brain tissue oxygen tension [PbtO2]), and clinical outcome after severe TBI.

METHODS

One hundred one patients (median age, 41.0 years; interquartile range [26-55]) with severe TBI who had ICP and PbtO2 monitoring were identified. The relationship between admission GCS, ISS, APACHE II, Marshall and Rotterdam scores and ICP, PbtO2, and outcome was examined by using mixed-effects models and logistic regression.

RESULTS

Median (25%-75% interquartile range) admission GCS and APACHE II without GCS scores were 3.0 (3-7) and 11.0 (8-13), respectively. Marshall and Rotterdam scores were 3.0 (3-5) and 4.0 (4-5). Mean ICP and PbtO2 during the patients' ICU course were 15.5 ± 10.7 mm Hg and 29.9 ± 10.8 mm Hg, respectively. Three-month mortality was 37.6%. Admission GCS was not associated with mortality. APACHE II (P = .003), APACHE-non-GCS (P = .004), Marshall (P < .001), and Rotterdam scores (P < .001) were associated with mortality. No relationship between GCS, ISS, Marshall, or Rotterdam scores and subsequent ICP or PbtO2 was observed. The APACHE II score was inversely associated with median PbtO2 (P = .03) and minimum PbtO2 (P = .008) and had a stronger correlation with amount of time of reduced PbtO2.

CONCLUSION

Following severe TBI, factors associated with outcome may not always predict a patient's ICU course and, in particular, intracranial physiology.

Interaction between brain chemistry and physiology after traumatic brain injury: impact of autoregulation and microdialysis catheter location

Bedside monitoring of cerebral metabolism in traumatic brain injury (TBI) with microdialysis is gaining wider clinical acceptance. The objective of this study was to examine the relationship between the fundamental physiological neuromonitoring modalities intracranial pressure (ICP), cerebral perfusion pressure (CPP), brain tissue oxygen (P(bt)O(2)), and cerebrovascular pressure reactivity index (PRx), and cerebral chemistry assessed with microdialysis, with particular focus on the lactate/pyruvate (LP) ratio as a marker of energy metabolism. Prospectively collected observational neuromonitoring data from 97 patients with TBI, requiring neurointensive care management and invasive cerebral monitoring, were analyzed. A linear mixed model analysis was used to account for individual patient differences. Perilesional tissue chemistry exhibited a significant independent relationship with ICP, P(bt)O(2) and CPP thresholds, with increasing LP ratio in response to decrease in P(bt)O(2) and CPP, and increase in ICP. The relationship between CPP and chemistry depended upon the state of PRx. Within the studied physiological range, tissue chemistry only changed in response to increasing ICP or drop in P(bt)O(2)<1.33 kPa (10 mmHg). In agreement with previous studies, significantly higher levels of cerebral lactate (p<0.001), glycerol (p=0.013), LP ratio (p<0.001) and lactate/glucose (LG) ratio (p=0.003) were found in perilesional tissue, compared to "normal" brain tissue (Mann-Whitney test). These differences remained significant following adjustment for the influences of other important physiological parameters (ICP, CPP, P(bt)O(2), P(bt)CO(2), PRx, and brain temperature; mixed linear model), suggesting that they may reflect inherent tissue properties related to the initial injury. Despite inherent biochemical differences between less-injured brain and "perilesional" cerebral tissue, both tissue types exhibited relationships between established physiological variables and biochemistry. Decreases in perfusion and oxygenation were associated with deteriorating neurochemistry and these effects were more pronounced in perilesional tissue and when cerebrovascular reactivity was impaired.

A prospective, randomized clinical trial to compare the effect of hyperbaric to normobaric hyperoxia on cerebral metabolism, intracranial pressure, and oxygen toxicity in severe traumatic brain injury

Object

Oxygen delivered in supraphysiological amounts is currently under investigation as a therapy for severe traumatic brain injury (TBI). Hyperoxia can be delivered to the brain under normobaric as well as hyperbaric conditions. In this study the authors directly compare hyperbaric oxygen (HBO2) and normobaric hyperoxia (NBH) treatment effects.

Methods

Sixty-nine patients who had sustained severe TBIs (mean Glasgow Coma Scale Score 5.8) were prospectively randomized to 1 of 3 groups within 24 hours of injury: 1) HBO2, 60 minutes of HBO2 at 1.5 ATA; 2) NBH, 3 hours of 100% fraction of inspired oxygen at 1 ATA; and 3) control, standard care. Treatments occurred once every 24 hours for 3 consecutive days. Brain tissue PO2, microdialysis, and intracranial pressure were continuously monitored. Cerebral blood flow (CBF), arteriovenous differences in oxygen, cerebral metabolic rate of oxygen (CMRO2), CSF lactate and F2-isoprostane concentrations, and bronchial alveolar lavage (BAL) fluid interleukin (IL)–8 and IL-6 assays were obtained pretreatment and 1 and 6 hours posttreatment. Mixed-effects linear modeling was used to statistically test differences among the treatment arms as well as changes from pretreatment to posttreatment.

Results

In comparison with values in the control group, the brain tissue PO2 levels were significantly increased during treatment in both the HBO2 (mean ± SEM, 223 ± 29 mm Hg) and NBH (86 ± 12 mm Hg) groups (p < 0.0001) and following HBO2 until the next treatment session (p = 0.003). Hyperbaric O2 significantly increased CBF and CMRO2 for 6 hours (p ≤ 0.01). Cerebrospinal fluid lactate concentrations decreased posttreatment in both the HBO2 and NBH groups (p < 0.05). The dialysate lactate levels in patients who had received HBO2 decreased for 5 hours posttreatment (p = 0.017). Microdialysis lactate/pyruvate (L/P) ratios were significantly decreased posttreatment in both HBO2 and NBH groups (p < 0.05). Cerebral blood flow, CMRO2, microdialysate lactate, and the L/P ratio had significantly greater improvement when a brain tissue PO2 ≥ 200 mm Hg was achieved during treatment (p < 0.01). Intracranial pressure was significantly lower after HBO2 until the next treatment session (p < 0.001) in comparison with levels in the control group. The treatment effect persisted over all 3 days. No increase was seen in the CSF F2-isoprostane levels, microdialysate glycerol, and BAL inflammatory markers, which were used to monitor potential O2 toxicity.

Conclusions

Hyperbaric O2 has a more robust posttreatment effect than NBH on oxidative cerebral metabolism related to its ability to produce a brain tissue PO2 ≥ 200 mm Hg. However, it appears that O2 treatment for severe TBI is not an all or nothing phenomenon but represents a graduated effect. No signs of pulmonary or cerebral O2 toxicity were present.

The physiology behind direct brain oxygen monitors and practical aspects of their use

INTRODUCTION

Secondary neuronal injury is implicated in poor outcome after acute neurological insults. Outcome can be improved with protocol-driven therapy. These therapies have largely been based on monitoring and control of intracranial pressure and the maintenance of an adequate cerebral perfusion pressure.

DISCUSSION

In recent years, brain tissue oxygen partial pressure (PbtO2) monitoring has emerged as a clinically useful modality and a complement to intracranial pressure monitors. This review examines the physiology of PbtO2 monitors and practical aspects of their use.

Intracranial pressure pulse morphological features improved detection of decreased cerebral blood flow

We investigated whether intracranial pressure (ICP) pulse morphological metrics could be used to realize continuous detection of low cerebral blood flow. Sixty-three acutely brain injured patients with ICP monitoring, daily (133)Xenon cerebral blood flow (CBF) and daily transcranial Doppler (TCD) assessments were studied. Their ICP recordings were time-aligned with the CBF and TCD measurements so that a 1 h ICP segment near the CBF and TCD measurements was obtained. Each of these recordings was processed by the Morphological Cluster and Analysis of Intracranial Pressure (MOCAIP) algorithm to extract pulse morphological metrics. Then the differential evolution algorithm was used to find the optimal combination of the metrics that provided, using the regularized linear discriminant analysis, the largest combined positive predictivity and sensitivity. At a CBF threshold of 20 ml/min/100 g, a sensitivity of 81.8 +/- 0.9% and a specificity of 50.1 +/- 0.2% were obtained using the optimal combination of conventional TCD and blood analysis metrics as input to a regularized linear classifier. However, using the optimal combination of the MOCAIP metrics alone we were able to achieve a sensitivity of 92.5 +/- 0.7% and a specificity of 84.8 +/- 0.8%. Searching the optimal combination of all available metrics, we achieved the best result that was marginally better than those from using MOCAIP alone. This study demonstrated that the potential role of ICP monitoring may be extended to provide an indicator of low global cerebral blood perfusion.

Intracerebral microdialysis in children

INTRODUCTION

Cerebral microdialysis is a relatively new, minimally invasive technique that permits sampling and analyzing the chemical constituents of the extracellular fluid. Although mainly used as a research tool, it is also used in the neurointensive care, in combination with other monitoring methods, in patients with severe traumatic brain injury and subarachnoid hemorrhage. Its main clinical utility is the identification of markers of ischemia and cell damage with the ultimate goal of preventing any secondary insults to the brain by instituting early appropriate treatment measures. With few exceptions, all the available data on intracerebral microdialysis in humans comes from studies performed in adults.

OBJECTIVE

The purpose of this report is to provide a brief review of the intracerebral microdialysis studies performed in children.

CONCLUSION

Differences in trends of concentrations of structural and excitatory amino acids have been identified in children, in comparison to those observed in adults, the significance of which remains unknown at present.

Hypertonic saline in patients with poor-grade subarachnoid hemorrhage improves cerebral blood flow, brain tissue oxygen, and pH

BACKGROUND AND PURPOSE

Delayed cerebral ischemia and infarction due to reduced CBF remains the leading cause of poor outcome after aneurysmal subarachnoid hemorrhage. Hypertonic saline (HS) is associated with an increase in CBF. This study explores whether CBF enhancement with HS in patients with poor-grade subarachnoid hemorrhage is associated with improved cerebral tissue oxygenation.

METHODS

Continuous monitoring of arterial blood pressure, intracranial pressure, cerebral perfusion pressure, brain tissue oxygen, carbon dioxide, pH, and middle cerebral artery flow velocity was performed in 44 patients. Patients were given an infusion (2 mL/kg) of 23.5% HS. In 16 patients, xenon CT scanning was also performed. CBF in a region surrounding the tissue oxygen sensor was calculated. Data are mean+/-SD.

RESULTS

Thirty minutes postinfusion, a significant increase in arterial blood pressure, cerebral perfusion pressure, flow velocity, brain tissue pH, and brain tissue oxygen was seen together with a decrease in intracranial pressure (P<0.05). Intracranial pressure remained reduced for >300 minutes and flow velocity elevated for >240 minutes. A significant increase in brain tissue oxygen persisted for 240 minutes. Average baseline regional CBF was 33.9+/-13.5 mL/100 g/min, rising by 20.3%+/-37.4% (P<0.05) after HS. Patients with favorable outcome responded better to HS in terms of increased CBF, brain tissue oxygen, and pH and reduced intracranial pressure compared with those with an unfavorable outcome. A sustained increase in brain tissue oxygen (beyond 210 minutes) was associated with favorable outcome (P<0.023).

CONCLUSIONS

HS augments CBF in patients with poor-grade subarachnoid hemorrhage and significantly improves cerebral oxygenation for 4 hours postinfusion. Favorable outcome is associated with an improvement in brain tissue oxygen beyond 210 minutes.

Microdialysis: is it ready for prime time?

PURPOSE OF REVIEW

This review highlights recent advances in cerebral microdialysis for investigational and clinical neurochemical monitoring in patients with critical neurological conditions.

RECENT FINDINGS

Use of microdialysis with other methods, including PET, electrophysiological monitoring and brain tissue oximetry in traumatic brain injury, subarachnoid hemorrhage with vasospasm, and infarction with refractory increased intracranial pressure have been reported. Potentially adverse neurochemical effects of nonconvulsive status epilepticus and cortical slow depolarization waves, both of which are increasingly recognized in traumatic brain injury and stroke patients, have been reported. The explosive growth in the use of cerebral oximetry with targeted management of brain tissue oxygen levels is leading to greater understanding of derangements of cerebral bioenergetics in the critically ill brain, but there remain unresolved basic issues. Understanding of the analytes that are measurable at the bedside - glucose, lactate, pyruvate, glutamate and glycerol - continues to evolve with glucose, lactate, pyruvate and the lactate-pyruvate ratio taking center stage. Analytes including inflammatory biomarkers such as cytokines and metabolites of nitric oxide are presently investigational, but hold promise for future application in advancing our understanding of basic pathophysiology, therapeutic target selection and prognostication. Growing consensus on indications for use of clinical microdialysis and advances in commercially available equipment continue to make microdialysis increasingly 'ready for prime time.'

SUMMARY

Cerebral microdialysis is an established tool for neurochemical research in the ICU. This technique cannot be fruitfully used in isolation, but when combined with other monitoring methods provides unique insights into the biochemical and physiological derangements in the injured brain.

Brain tissue oxygen tension monitoring in pediatric severe traumatic brain injury. Part 1: Relationship with outcome

INTRODUCTION

Intracranial pressure (ICP) monitoring and cerebral perfusion pressure (CPP) management are the current standards to guide care of severe traumatic brain injury (TBI). However, brain hypoxia and secondary brain injury can occur despite optimal ICP and CPP. In this study, we used brain tissue oxygen tension (PbtO(2)) monitoring to examine the association between multiple patient factors, including PbtO(2), and outcome in pediatric severe TBI.

MATERIALS AND METHODS

In this prospective observational study, 52 children (less than 15 years) with severe TBI were managed with continuous PbtO(2) and ICP monitoring. The relationships between outcome [Glasgow Outcome Score (GOS) and Pediatric Cerebral Performance Category Scale] and clinical, radiologic, treatment, and physiological variables, including PbtO(2), were examined using multiple logistic regression analysis.

RESULTS

Outcome was favorable in 40 patients (77%) and unfavorable (mortality, 9.6%; n = 5) in 12 (23%). In univariate analysis, the following variables had a significant association with unfavorable outcome: initial GCS, computed tomography classification, ICP(peak), mICP(24), mICP, CPP(low), CPP(<40), pupil reactivity, PbtO(2)(low), PbtO(2) < 5 mmHg, PbtO(2) < 10 mmHg, mPbtO(2)(24), and time-severity product. PbtO(2) parameters had the strongest independent association with poor outcome in multiple regression analysis. In particular, when PbtO(2) was <5 mmHg for >1 h, the adjusted OR for poor outcome was 27.4 (95% confidence interval, 1.9-391). No variables apart from PbtO(2) were independently associated with mortality when controlled for PbtO(2).

CONCLUSION

Reduced PbtO(2) is shown to be an independent factor associated with poor outcome in pediatric severe TBI in the largest study to date. It appears to have a stronger association with outcome than conventionally evaluated measures.

Physiologic and functional outcome correlates of brain tissue hypoxia in traumatic brain injury

OBJECTIVE

Assess the prevalence of brain tissue hypoxia in patients with severe traumatic brain injuries (TBI), and to characterize the relationship between brain tissue hypoxia and functional outcome.

DESIGN

Retrospective review of severe TBI patients.

SETTING

Intensive care unit of a level I trauma center.

PATIENTS

Twenty-seven patients with severe TBI requiring intracranial pressure (ICP) monitoring. Median age was 22 yrs, and a majority (63%) had traumatic subarachnoid hemorrhage.

INTERVENTIONS

Hourly assessments of ICP, brain tissue oxygen, mean arterial pressure, fraction of inspired oxygen (FiO2), partial pressure of arterial carbon dioxide (PaCO2), and hemoglobin concentration (hemoglobin) were recorded. Outcome was assessed 6-9 months postinjury.

MEASUREMENTS AND MAIN RESULTS

Mean (SD) ICP and BTpO2 were 13.7 (6.6) cm H2O and 30.8 (13.6) mm Hg. A total of 13.5% (379) of the BTpO2 values recorded were < 20 mm Hg, only 86 of which were associated with ICP > or = 20 cm H2O. This prevalence was comparable with episodes of ICP elevations above 20 cm H2O (14.1%, 397). Hypoxic episodes were more common when cerebral perfusion pressure was below 60 mm Hg (relative risk = 3.0, p < 0.0001). We did not find an association in hypoxic risk and hemoglobin in the range of 7-12 g/dL or PaCO2 in the range of 25-40 mm Hg. Subjects with hourly episodes (epochs) of hypoxia > 20% of the time had poorer scores on outcome measures compared with those with fewer hypoxic epochs.

CONCLUSIONS

Hypoxic episodes are common after severe TBI, and most are independent of ICP elevations. Most episodes of hypoxia occur while cerebral perfusion pressure and mean arterial pressure are within the accepted target range. There is no clear association between PaCO2 and hemoglobin with BTpO2. The young age and high prevalence of traumatic subarachnoid hemorrhage in this cohort may limit its generalizability. Increased frequency of hypoxic episodes is associated with poor functional outcome.

The significance of altered temperature after traumatic brain injury: an analysis of investigations in experimental and human studies: part 2

Raised body temperature is a common occurrence after severe traumatic brain injury (TBI). It is widely accepted that experimental evidence points to a harmful effect of raised temperature both during and after TBI. Consequently, the policy of many neurocritical care units is to implement therapies for body temperature control. This article reviews the evidence that links spontaneous temperature changes with worsened outcome after experimentally-induced and human brain trauma. The current evidence-base and rationale for treatment of raised temperature after TBI is presented with discussion positing areas for further work to explore the notion that raised temperature may not be deleterious in all neurosurgical patients.

Brain metabolic and hemodynamic effects of cyclosporin A after human severe traumatic brain injury: a microdialysis study

BACKGROUND

Mitochondrial dysfunction is a major limiting factor in neuronal recovery following traumatic brain injury. Cyclosporin A (CsA) has been recently proposed for use in the early phase after severe head injury, for its ability to preserve mitochondrial bioenergetic state, potentially exerting a neuroprotective effect. The aim of this study was, therefore, to evaluate the effect of CsA on brain energy metabolism, as measured by cerebral microdialysis, and on cerebral hemodynamics, in a group of severely head injured patients.

METHODS

Fifty adult patients with a severe head injury were enrolled in this randomized, double-blind, placebo-controlled study. Patients received 5 mg/kg of CsA over 24 h, or placebo, within 12 h of the injury. A microdialysis probe was placed in all patients, who were managed according to standard protocols for the treatment of severe head injury.

FINDINGS

The most robust result of this study was that, over most of the monitoring period, brain dialysate glucose was significantly higher in the CsA treated patients than in placebo. Both lactate and pyruvate were also significantly higher in the CsA group. Glutamate concentration and lactate/pyruvate ratio were significantly higher in the placebo group than in CsA treated patients, respectively 1 to 2 days, and 2 to 3 days after the end of the 24-h drug infusion. The administration of CsA was also associated with a significant increase in mean arterial pressure (MAP) and cerebral perfusion pressure (CPP).

CONCLUSIONS

The administration of CsA in the early phase after head injury resulted in significantly higher extracellular fluid glucose and pyruvate, which may be evidence of a beneficial effect. The early administration of CsA was also associated with a significant increase in MAP and CPP and such a potentially beneficial hemodynamic effect might contribute to a neuroprotective effect.

Simultaneous transdermal extraction of glucose and lactate from human subjects by reverse iontophoresis

This study investigated the possibility of simultaneously extracting glucose and lactate from human subjects, at the same skin location, using transdermal reverse iontophoresis. Transdermal monitoring using iontophoresis is made possible by the skin’s permeability to small molecules and the nanoporous and microporous nature of the structure of skin. The study was intended to provide information which could be used to develop a full, biosensor-based, monitoring system for multiple parameters from transdermal extraction. As a precursor to the human study, in vitro reverse iontophoresis experiments were performed in an artificial skin system to establish the optimum current waveforms to be applied during iontophoresis. In the human study, a bipolar DC current waveform (with reversal of the electrode current direction every 15 minutes) was applied to ten healthy volunteers via skin electrodes and utilized for simultaneous glucose and lactate transdermal extraction at an applied current density of 300 μA/cm². Glucose and lactate were successfully extracted through each subject’s skin into the conducting gel that formed part of each iontophoresis electrode. The results suggest that it will be possible to noninvasively and simultaneously monitor glucose and lactate levels in patients using this approach and this could have future applications in diagnostic monitoring for a variety of medical conditions.

Brain tissue oxygen tension in clinical brain death: a case series

OBJECTIVES

Brain death is a clinical diagnosis often confirmed with supplementary tests. In this study, we examined the relationship between brain death and the partial pressure of brain tissue oxygen (PbtO(2)). We hypothesized that a sustained PbtO(2) of 0 is associated with brain death.

METHODS

One hundred and twenty-six patients (Glasgow coma scale < or = 8, median age: 50 years) who underwent PbtO(2) monitoring were studied prospectively during a 2 year period in the neurointensive care unit at a university-based level I trauma center. PbtO(2), intracranial pressure (ICP), mean arterial pressure (MAP), cerebral perfusion pressure (CPP) and brain temperature (BT) were compared before and after the diagnosis of brain death.

RESULTS

Six patients (median age: 52 years) experienced brain death. In these patients, PbtO(2) decreased toward 0 mmHg as ICP increased and CPP decreased. PbtO(2) reached 0 only when there was clinical evidence for brain death. During the subsequent 12 hours until the second brain death examination, PbtO(2) remained 0 mmHg and did not respond to oxygen challenge. In addition, TCD examination demonstrated a 'to and fro' pattern consistent with brain death and cerebral circulatory arrest. PbtO(2) of 0 mmHg was observed in five non-brain dead patients. These episodes were transient (>30 minutes) and responded to an oxygen challenge, directed treatment or catheter replacement.

DISCUSSION

A sustained (>30 minutes) brain PbtO(2) of 0 is consistent with brain death. We suggest that a sustained 'zero' PbtO(2) may be used to determine when a brain death examination is appropriate in the pharmacologically suppressed patient.

Multimodality monitoring in neurocritical care

Multimodality monitoring of cerebral physiology encompasses the application of different monitoring techniques and integration of several measured physiologic and biochemical variables into assessment of brain metabolism, structure, perfusion, and oxygenation status. Novel monitoring techniques include transcranial Doppler ultrasonography, neuroimaging, intracranial pressure, cerebral perfusion, and cerebral blood flow monitors, brain tissue oxygen tension monitoring, microdialysis, evoked potentials, and continuous electroencephalogram. Multimodality monitoring enables immediate detection and prevention of acute neurologic injury as well as appropriate intervention based on patients' individual disease states in the neurocritical care unit. Real-time analysis of cerebral physiologic, metabolic, and cardiovascular parameters simultaneously has broadened knowledge about complex brain pathophysiology and cerebral hemodynamics. Integration of this information allows for more precise diagnosis and optimization of management of patients with brain injury.

Hyperbaric oxygen in traumatic brain injury

OBJECTIVES

This critical literature review examines historical and current investigations on the efficacy and mechanisms of hyperbaric oxygen (HBO) treatment in traumatic brain injury (TBI). Potential safety risks and oxygen toxicity, as well as HBO's future potential, are also discussed.

METHODS

Directed literature review.

RESULTS

Historically, cerebral vasoconstriction and increased oxygen availability were seen as the primary mechanisms of HBO in TBI. HBO now appears to be improving cerebral aerobic metabolism at a cellular level, namely, by enhancing damaged mitochondrial recovery. HBO given at the ideal treatment paradigm, 1.5 ATA for 60 minutes, does not appear to produce oxygen toxicity and is relatively safe.

DISCUSSION

The use of HBO in TBI remains controversial. Growing evidence, however, shows that HBO may be a potential treatment for patients with severe brain injury. Further investigations, including a multicenter prospective randomized clinical trial, will be required to definitively define the role of HBO in severe TBI.

New developments in cerebral monitoring

In past years, cerebral monitoring was mostly focused around global cerebral perfusion and metabolism monitoring, with the use of transcranial Doppler recordings, jugular bulb oximetry and near-infrared spectroscopy. Most of the recently introduced cerebral monitoring modalities, such as brain tissue partial oxygen tension monitoring and cerebral microdialysis, offer new opportunities by providing regional information on the specific brain area in which the probe is inserted. Ideally, these probes should be inserted in that area of the brain that is most vulnerable to ischaemia, but that may be salvageable with appropriate therapy. In this case, the combination of global and regional cerebral monitoring might offer the best information on which to base patient management. Also, the introduction of more clinically useful, functional neuroimaging techniques may be a valuable adjunct to future neurological critical care management.

Decompressive hemicraniectomy for the treatment of intractable intracranial hypertension after aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Decompressive hemicraniectomy and duroplasty (DHCD) can improve survival in patients with severe cerebral edema. We present our clinical experience with DHCD for the treatment of refractory elevated intracranial pressure (ICP) in patients with aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

DHCD was performed in 16 patients (11 female; median age, 49.5 years) with aSAH (11 Hunt-Hess grade 4 to 5) for sustained ICP >250 mm H(2)O refractory to maximal medical treatment and cerebrospinal fluid drainage at a median of 2 days from admission. Half of the patients were treated with endovascular coiling and the other half with surgical clipping.

RESULTS

DHCD (mean flap size, 8536 mm(2)) reduced ICP from 350+/-157 to 147+/-124 mm H(2)O. Eleven patients survived (69%), and at latest follow-up (median, 450 days), 7 (64%) had a modified Rankin score of 0 to 3 and 4 (36%) a score of 4 to 5. Peak herniated brain volume was inversely associated with good outcome (P<0.005). Early craniectomy performed within 48 hours after the aSAH was associated with better outcome: 6 of 8 patients had good outcomes (75%) compared with 1 of 8 patients in whom late decompression was performed (P<0.01). Midline shift, Hunt-Hess grade, presence of hemorrhage, hematoma volume, craniectomy area, peak ICP, and relative ICP reduction were not associated with outcome in this patient population.

CONCLUSIONS

DHCD is a useful adjunct modality for management of refractory intracranial hypertension in patients with high-grade aSAH, even in the absence of large intraparenchymal hemorrhage. In our series, long-term outcome was better in patients who underwent early intervention.

Quantitation of ischemic events after severe traumatic brain injury in humans: a simple scoring system

BACKGROUND

Cerebral ischemia is recognized as one of the most important mechanisms responsible for secondary brain damage following severe traumatic brain injury (TBI), contributing to an increased mortality and a worse neurologic outcome.

METHOD

A simple 5-item scoring system, taking into account the occurrence of specific potentially brain-damaging events (hypoxemia, hypotension, low cerebral blood flow, herniation, and low cerebral perfusion pressure) has been tested in a large population of severe TBI patients. Aims of this retrospective study were to validate the ability of the proposed ischemic score to predict neurologic outcome and to correlate the ischemic score with the results of microdialysis-based neurochemical monitoring and brain tissue oxygen monitoring.

FINDINGS

In a population of 172 severe TBI patients, a significant correlation was found between ischemic score and neurologic outcome, both at 3 months (r = -0.32; P < 0.01) and at 6 months (r = -0.31; P < 0.01). Significant correlations were also found with the most important neurochemical analytes.

CONCLUSIONS

The ischemic score proposed here, may be determined during the acute intensive care unit period, and correlates closely with outcome, which can only be determined 3 to 6 months, after injury. It also shows a correlation with neurochemical analytes.

[Monitoring of cerebral oxygenation with SvjO(2) or PtiO(2)]

Jugular venous oxygen saturation (SvjO(2)) monitoring has been developed in order to detect cerebral ischaemia. The interpretation of SvjO(2) values remains nevertheless complex, and should be associated with cerebral haemodynamic multimonitoring with ICP and transcranial Doppler. With the hypothesis of a constant cerebral oxygen consummation, and also with a constant haematocrit, SvjO(2) variations correlates with cerebral blood flow variations. After a brain trauma, an SvjO(2)<50% or>75% is associated with a bad prognosis. To maintain SvjO(2)>50% constitutes a reasonable therapeutic objective, but the benefice associated with such a strategy has not been validated. Oxygen partial pressure (PtiO(2)) in the brain parenchyma may be monitored in the non-lesioned area (usually frontal) in order to detect a global cerebral ischaemia, or in the penumbra of a cerebral lesion in order to detect a local ischaemia. The values associated with an ischemic risk are not fully defined and may be under 10-15 mmHg. A concomitant metabolic monitoring by cerebral microdialysis is of importance to fully address the real cerebral local ischaemic burden. Scientific studies are mainly focused on patients with a brain traumatism. Nor SvjO(2), nor PtiO(2) monitoring have at present been demonstrated to be associated with a clinical benefit, and their use should be restricted to scientific research.

Future of brain support: multimodality monitoring

Multimodality monitoring of cerebral physiology encompasses the application of different monitoring techniques and integration of several measured physiological and biochemical variables into the assessment of brain metabolism, structure, perfusion and oxygenation status, in addition to clinical evaluation. Novel monitoring techniques include transcranial Doppler ultrasonography, neuroimaging, intracranial pressure, cerebral perfusion and cerebral blood flow monitors, brain tissue oxygen tension monitoring, microdialysis, evoked potentials and continuous electroencephalography. Multimodality monitoring enables the immediate detection and prevention of acute neurological events, as well as appropriate intervention based on a patient’s individual disease state in the neurocritical care unit. Simultaneous real-time analysis of cerebral physiological, metabolic and cardiovascular parameters has broadened knowledge regarding complex brain pathophysiology and cerebral hemodynamics. Integration of this information allows for a more precise diagnosis and optimization of management of patients with brain injury.