Hyperemia following traumatic brain injury: relationship to intracranial hypertension and outcome

Effect of Increasing Blood Pressure on Brain Tissue Oxygenation in Adults After Severe Traumatic Brain Injury

OBJECTIVES

To examine if increasing blood pressure improves brain tissue oxygenation (PbtO 2 ) in adults with severe traumatic brain injury (TBI).

DESIGN

Retrospective review of prospectively collected data.

SETTING

Level-I trauma center teaching hospital.

PATIENTS

Included patients greater than or equal to 18 years of age and with severe (admission Glasgow Coma Scale [GCS] score < 9) TBI who had advanced neuromonitoring (intracranial blood pressure [ICP], PbtO 2 , and cerebral autoregulation testing).

INTERVENTIONS

The exposure was mean arterial pressure (MAP) augmentation with a vasopressor, and the primary outcome was a PbtO 2 response. Cerebral hypoxia was defined as PbtO 2 less than 20 mm Hg (low).

MAIN RESULTS

MAP challenge test results conducted between ICU admission days 1-3 from 93 patients (median age 31; interquartile range [IQR], 24-44 yr), 69.9% male, White ( n = 69, 74.2%), median head abbreviated injury score 5 (IQR 4-5), and median admission GCS 3 (IQR 3-5) were examined. Across all 93 tests, a MAP increase of 25.7% resulted in a 34.2% cerebral perfusion pressure (CPP) increase and 16.3% PbtO 2 increase (no MAP or CPP correlation with PbtO 2 [both R2 = 0.00]). MAP augmentation increased ICP when cerebral autoregulation was impaired (8.9% vs. 3.8%, p = 0.06). MAP augmentation resulted in four PbtO 2 responses (normal and maintained [group 1: 58.5%], normal and deteriorated [group 2: 2.2%; average 45.2% PbtO 2 decrease], low and improved [group 3: 12.8%; average 44% PbtO 2 increase], and low and not improved [group 4: 25.8%]). The average end-tidal carbon dioxide (ETCO 2 ) increase of 5.9% was associated with group 2 when cerebral autoregulation was impaired ( p = 0.02).

CONCLUSIONS

MAP augmentation after severe TBI resulted in four distinct PbtO 2 response patterns, including PbtO 2 improvement and cerebral hypoxia. Traditionally considered clinical factors were not significant, but cerebral autoregulation status and ICP responses may have moderated MAP and ETCO 2 effects on PbtO 2 response. Further study is needed to examine the role of MAP augmentation as a strategy to improve PbtO 2 in some patients.

Cerebral autoregulation, spreading depolarization, and implications for targeted therapy in brain injury and ischemia

Cerebral autoregulation is an intrinsic myogenic response of cerebral vasculature that allows for preservation of stable cerebral blood flow levels in response to changing systemic blood pressure. It is effective across a broad range of blood pressure levels through precapillary vasoconstriction and dilation. Autoregulation is difficult to directly measure and methods to indirectly ascertain cerebral autoregulation status inherently require certain assumptions. Patients with impaired cerebral autoregulation may be at risk of brain ischemia. One of the central mechanisms of ischemia in patients with metabolically compromised states is likely the triggering of spreading depolarization (SD) events and ultimately, terminal (or anoxic) depolarization. Cerebral autoregulation and SD are therefore linked when considering the risk of ischemia. In this scoping review, we will discuss the range of methods to measure cerebral autoregulation, their theoretical strengths and weaknesses, and the available clinical evidence to support their utility. We will then discuss the emerging link between impaired cerebral autoregulation and the occurrence of SD events. Such an approach offers the opportunity to better understand an individual patient's physiology and provide targeted treatments.

Quantifying injury expansion in the cervical spinal cord with intravital ultrafast contrast-enhanced ultrasound imaging

Spinal cord injury is characterized by hemodynamic disruption at the injury epicenter and hypoperfusion in the penumbra, resulting in progressive ischemia and cell death. This degenerative secondary injury process has been well-described, though mostly using ex vivo or depth-limited optical imaging techniques. Intravital contrast-enhanced ultrasound enables longitudinal, quantitative evaluation of anatomical and hemodynamic changes in vivo through the entire spinal parenchyma. Here, we used ultrasound imaging to visualize and quantify subacute injury expansion (through 72 h post-injury) in a rodent cervical contusion model. Significant intraparenchymal hematoma expansion was observed through 72 h post-injury (1.86 ± 0.17-fold change from acute, p < 0.05), while the volume of the ischemic deficit largely increased within 24 h post-injury (2.24 ± 0.27-fold, p < 0.05). Histology corroborated these findings; increased apoptosis, tissue and vessel loss, and sustained tissue hypoxia were observed at 72 h post-injury. Vascular resistance was significantly elevated in the remaining perfused tissue, likely due in part to deformation of the central sulcal artery nearest to the lesion site. In conjunction, substantial hyperemia was observed in all perilesional areas examined except the ipsilesional gray matter. This study demonstrates the utility of longitudinal ultrasound imaging as a quantitative tool for tracking injury progression in vivo.

Hyperemia in head injury: can transcranial doppler help to personalize therapies for intracranial hypertension?

Introduction

An increase in cerebral blood flow is frequent after traumatic brain injury (TBI) and can lead to brain swelling and refractory intracranial hypertension. We hypothesized that Transcranial EcoDoppler (TCD) monitoring could be useful to detect the cause of intracranial hypertension in these patients. Our main objective was to investigate if the increase of velocity in the middle cerebral artery (MCA) on TCD could be associated with intracranial hypertension.

Methods

We retrospectively studied TBI patients consecutively monitored with TCD. Hyperemia was defined as MCA mean velocity higher than 80 cm/s. Intracranial hypertension was considered when hyperosmolar therapy, hyperventilation, or deep sedation was used.

Results

We found hyperemia in 40 patients out of 118 (33.9%). On average, it started at day 2.1 ± 0.9 from admission and significantly increased (MCA velocity at day 1: 74 ± 25 cm/s vs. 109 ± 36 cm/s at day 4; p < 0.001). Intracranial hypertension was significantly associated with hyperemia, occurring in 92.5% of hyperemic and 51.3% of non-hyperemic patients (p < 0.001). Moreover, we found that hyperemia preceded severe intracranial hypertension (p < 0.0001). In a logistic regression model, hyperemia was the only variable significantly correlated with intracranial hypertension (OR 10.64; p < 0.001).

Discussion

Hyperemia was frequent in our population of TBI patients and preceded intracranial hypertension. TCD monitoring, if performed on a daily regular basis, can be a useful method to detect this phenomenon and to guide the therapy. It could be a tool for a cause-oriented therapy of intracranial hypertension.

Electrical stimulation methods and protocols for the treatment of traumatic brain injury: a critical review of preclinical research

BACKGROUND

Traumatic brain injury (TBI) is a leading cause of disabilities resulting from cognitive and neurological deficits, as well as psychological disorders. Only recently, preclinical research on electrical stimulation methods as a potential treatment of TBI sequelae has gained more traction. However, the underlying mechanisms of the anticipated improvements induced by these methods are still not fully understood. It remains unclear in which stage after TBI they are best applied to optimize the therapeutic outcome, preferably with persisting effects. Studies with animal models address these questions and investigate beneficial long- and short-term changes mediated by these novel modalities.

METHODS

In this review, we present the state-of-the-art in preclinical research on electrical stimulation methods used to treat TBI sequelae. We analyze publications on the most commonly used electrical stimulation methods, namely transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), deep brain stimulation (DBS) and vagus nerve stimulation (VNS), that aim to treat disabilities caused by TBI. We discuss applied stimulation parameters, such as the amplitude, frequency, and length of stimulation, as well as stimulation time frames, specifically the onset of stimulation, how often stimulation sessions were repeated and the total length of the treatment. These parameters are then analyzed in the context of injury severity, the disability under investigation and the stimulated location, and the resulting therapeutic effects are compared. We provide a comprehensive and critical review and discuss directions for future research. RESULTS AND CONCLUSION: We find that the parameters used in studies on each of these stimulation methods vary widely, making it difficult to draw direct comparisons between stimulation protocols and therapeutic outcome. Persisting beneficial effects and adverse consequences of electrical simulation are rarely investigated, leaving many questions about their suitability for clinical applications. Nevertheless, we conclude that the stimulation methods discussed here show promising results that could be further supported by additional research in this field.

Avoiding brain hypoxia in severe traumatic brain injury in settings with limited resources - A pathophysiological guide

Cerebral oxygenation represents the balance between oxygen delivery, consumption and utilization by the brain, and therefore reflects the adequacy of cerebral perfusion. Different factors can influence the amount of oxygen to the brain including arterial blood pressure, hemoglobin levels, systemic oxygenation, and transfer of oxygen from blood to the cerebral microcirculation. A mismatch between cerebral oxygen supply and demand results in cerebral hypoxia/ischemia, and is associated with secondary brain damage and worsened outcome after acute brain injury. Therefore, monitoring and prompt treatment of cerebral oxygenation compromise is warranted in both neuro and general intensive care unit populations. Several tools have been proposed for the assessment of cerebral oxygenation, including non-invasive/invasive or indirect/direct methods, including Jugular Venous Oxygen Saturation (SjO2), Partial Brain Tissue Oxygen Tension (PtiO2), Near infrared spectroscopy (NIRS), Transcranial Doppler, electroencephalography and Computed Tomography. In this manuscript, we aim to review the pathophysiology of cerebral oxygenation, describe monitoring technics, and generate recommendations for avoiding brain hypoxia in settings with low availability of resources for direct brain oxygen monitoring.

Prediction of Increased Intracranial Pressure in Traumatic Brain Injury Using Quantitative Electroencephalogram in a Porcine Experimental Model

Continuous and non-invasive measurement of intracranial pressure (ICP) in traumatic brain injury (TBI) is important to recognize increased ICP (IICP), which can reduce treatment delays. The purpose of this study was to develop an electroencephalogram (EEG)-based prediction model for IICP in a porcine TBI model. Thirty swine were anaesthetized and underwent IICP by inflating a Foley catheter in the intracranial space. Single-channel EEG data were collected every 6 min in 10 mmHg increments in the ICP from baseline to 50 mmHg. We developed EEG-based models to predict the IICP (equal or over 25 mmHg) using four algorithms: logistic regression (LR), naive Bayes (NB), support vector machine (SVM), and random forest (RF). We assessed the performance of each model based on the accuracy, sensitivity, specificity, and AUC values. The accuracy of each prediction model for IICP was 0.773 for SVM, 0.749 for NB, 0.746 for RF, and 0.706 for LR. The AUC of each model was 0.860 for SVM, 0.824 for NB, 0.802 for RF, and 0.748 for LR. We developed a machine learning prediction model for IICP using single-channel EEG signals in a swine TBI experimental model. The SVM model showed good predictive power with the highest AUC value.

Autoregulation of Cerebral Blood Flow During 3-h Continuous Cardiopulmonary Resuscitation at 27°C

Introduction: Victims of accidental hypothermia in hypothermic cardiac arrest (HCA) may survive with favorable neurologic outcome if early and continuous prehospital cardiopulmonary resuscitation (CPR) is started and continued during evacuation and transport. The efficacy of cerebral autoregulation during hypothermic CPR is largely unknown and is aim of the present experiment. Methods: Anesthetized pigs (n = 8) were surface cooled to HCA at 27°C before 3 h continuous CPR. Central hemodynamics, cerebral O₂ delivery (DO₂) and uptake (VO₂), cerebral blood flow (CBF), and cerebral perfusion pressure (CPP) were determined before cooling, at 32°C and at 27°C, then at 15 min after the start of CPR, and hourly thereafter. To estimate cerebral autoregulation, the static autoregulatory index (sARI), and the CBF/VO₂ ratio were determined. Results: After the initial 15-min period of CPR at 27°C, cardiac output (CO) and mean arterial pressure (MAP) were reduced significantly when compared to corresponding values during spontaneous circulation at 27°C (-66.7% and -44.4%, respectively), and remained reduced during the subsequent 3-h period of CPR. During the first 2-h period of CPR at 27°C, blood flow in five different brain areas remained unchanged when compared to the level during spontaneous circulation at 27°C, but after 3 h of CPR blood flow in 2 of the 5 areas was significantly reduced. Cooling to 27°C reduced cerebral DO₂ by 67.3% and VO₂ by 84.4%. Cerebral VO₂ was significantly reduced first after 3 h of CPR. Cerebral DO₂ remained unaltered compared to corresponding levels measured during spontaneous circulation at 27°C. Cerebral autoregulation was preserved (sARI > 0.4), at least during the first 2 h of CPR. Interestingly, the CBF/VO₂ ratio during spontaneous circulation at 27°C indicated the presence of an affluent cerebral DO₂, whereas after CPR, the CBF/VO₂ ratio returned to the level of spontaneous circulation at 38°C. Conclusion: Despite a reduced CO, continuous CPR for 3 h at 27°C provided sufficient cerebral DO₂ to maintain aerobic metabolism and to preserve cerebral autoregulation during the first 2-h period of CPR. This new information supports early start and continued CPR in accidental hypothermia patients during rescue and transportation for in hospital rewarming.

Densitometric analysis of brain computed tomography as a new prognostic factor in patients with acute subdural hematoma

OBJECTIVE

Acute subdural hematoma (ASDH) is a major cause of mortality and morbidity after traumatic brain injury (TBI). Surgical evacuation is the mainstay of treatment in patients with altered neurological status or significant mass effect. Nevertheless, concerns regarding surgical indication still persist. Given that clinicians often make therapeutic decisions on the basis of their prognosis assessment, to accurately evaluate the prognosis is of great significance. Unfortunately, there is a lack of specific and reliable prognostic models. In addition, the interdependence of certain well-known predictive variables usually employed to guide surgical decision-making in ASDH has been proven. Because gray matter and white matter are highly susceptible to secondary insults during the early phase after TBI, the authors aimed to assess the extent of these secondary insults with a brain parenchyma densitometric quantitative CT analysis and to evaluate its prognostic capacity.

METHODS

The authors performed a retrospective analysis among their prospectively collected cohort of patients with moderate to severe TBI. Patients with surgically evacuated, isolated, unilateral ASDH admitted between 2010 and 2017 were selected. Thirty-nine patients were included. For each patient, brain parenchyma density in Hounsfield units (HUs) was measured in 10 selected slices from the supratentorial region. In each slice, different regions of interest (ROIs), including and excluding the cortical parenchyma, were defined. The injured hemisphere, the contralateral hemisphere, and the absolute differences between them were analyzed. The outcome was evaluated using the Glasgow Outcome Scale–Extended at 1 year after TBI.

RESULTS

Fifteen patients (38.5%) had a favorable outcome. Collected demographic, clinical, and radiographic data did not show significant differences between favorable and unfavorable outcomes. In contrast, the densitometric analysis demonstrated that greater absolute differences between both hemispheres were associated with poor outcome. These differences were detected along the supratentorial region, but were greater at the high convexity level. Moreover, these HU differences were far more marked at the cortical parenchyma. It was also detected that these differences were more prone to ischemic and/or edematous insults than to hyperemic changes. Age was significantly correlated with the side-to-side HU differences in patients with unfavorable outcome.

CONCLUSIONS

The densitometric analysis is a promising prognostic tool in patients diagnosed with ASDH. The supplementary prognostic information provided by the densitometric analysis should be evaluated in future studies.

Artifact removal from neurophysiological signals: impact on intracranial and arterial pressure monitoring in traumatic brain injury

OBJECTIVE

Monitoring intracranial and arterial blood pressure (ICP and ABP, respectively) provides crucial information regarding the neurological status of patients with traumatic brain injury (TBI). However, these signals are often heavily affected by artifacts, which may significantly reduce the reliability of the clinical determinations derived from the signals. The goal of this work was to eliminate signal artifacts from continuous ICP and ABP monitoring via deep learning techniques and to assess the changes in the prognostic capacities of clinical parameters after artifact elimination.

METHODS

The first 24 hours of monitoring ICP and ABP in a total of 309 patients with TBI was retrospectively analyzed. An artifact elimination model for ICP and ABP was constructed via a stacked convolutional autoencoder (SCAE) and convolutional neural network (CNN) with 10-fold cross-validation tests. The prevalence and prognostic capacity of ICP- and ABP-related clinical events were compared before and after artifact elimination.

RESULTS

The proposed SCAE-CNN model exhibited reliable accuracy in eliminating ABP and ICP artifacts (net prediction rates of 97% and 94%, respectively). The prevalence of ICP- and ABP-related clinical events (i.e., systemic hypotension, intracranial hypertension, cerebral hypoperfusion, and poor cerebrovascular reactivity) all decreased significantly after artifact removal.

CONCLUSIONS

The SCAE-CNN model can be reliably used to eliminate artifacts, which significantly improves the reliability and efficacy of ICP- and ABP-derived clinical parameters for prognostic determinations after TBI.

Pioglitazone Therapy and Fractures: Systematic Review and Meta- Analysis

INTRODUCTION

Thiazolidinediones are a group of synthetic medications used in type 2 diabetes treatment. Among available thiazolidinediones, pioglitazone is gaining increased attention due to its lower cardiovascular risk in type 2 diabetes mellitus sufferers and seems a promising future therapy. Accumulating evidence suggests that diabetic patients may exert bone fractures due to such treatments. Simultaneously, the female population is thought to be at greater risk. Still, the safety outcomes of pioglitazone treatment especially in terms of fractures are questionable and need to be clarified.

METHODS

We searched MEDLINE, Scopus, PsyInfo, eLIBRARY.ru electronic databases and clinical trial registries for studies reporting an association between pioglitazone and bone fractures in type 2 diabetes mellitus patients published before Feb 15, 2016. Among 1536 sources that were initially identified, six studies including 3172 patients proved relevant for further analysis.

RESULT

Pooled analysis of the included studies demonstrated that after treatment with pioglitazone patients with type 2 diabetes mellitus had no significant increase in fracture risk [odds ratio (OR): 1.18, 95% confidence interval (CI): 0.82 to 1.71, p=0.38] compared to other antidiabetic drugs or placebo. Additionally, no association was found between the risk of fractures and pioglitazone therapy duration. The gender of the patients involved was not relevant to the risk of fractures, too.

CONCLUSION

Pioglitazone treatment in diabetic patients does not increase the incidence of bone fractures. Moreover, there is no significant association between patients' fractures, their gender and the period of exposure to pioglitazone. Additional longitudinal studies need to be undertaken to obtain more detailed information on bone fragility and pioglitazone therapy.

High Oxygen Exchange to Music Indicates Auditory Distractibility in Acquired Brain Injury: An fNIRS Study with a Vector-Based Phase Analysis

Attention deficits due to auditory distractibility are pervasive among patients with acquired brain injury (ABI). It remains unclear, however, whether attention deficits following ABI specific to auditory modality are associated with altered haemodynamic responses. Here, we examined cerebral haemodynamic changes using functional near-infrared spectroscopy combined with a topological vector-based analysis method. A total of thirty-seven participants (22 healthy adults, 15 patients with ABI) performed a melodic contour identification task (CIT) that simulates auditory distractibility. Findings demonstrated that the melodic CIT was able to detect auditory distractibility in patients with ABI. The rate-corrected score showed that the ABI group performed significantly worse than the non-ABI group in both CIT1 (target contour identification against environmental sounds) and CIT2 (target contour identification against target-like distraction). Phase-associated response intensity during the CITs was greater in the ABI group than in the non-ABI group. Moreover, there existed a significant interaction effect in the left dorsolateral prefrontal cortex (DLPFC) during CIT1 and CIT2. These findings indicated that stronger hemodynamic responses involving oxygen exchange in the left DLPFC can serve as a biomarker for evaluating and monitoring auditory distractibility, which could potentially lead to the discovery of the underlying mechanism that causes auditory attention deficits in patients with ABI.

Sulfonylurea Receptor 1, Transient Receptor Potential Cation Channel Subfamily M Member 4, and KIR6.2:Role in Hemorrhagic Progression of Contusion

In severe traumatic brain injury (TBI), contusions often are worsened by contusion expansion or hemorrhagic progression of contusion (HPC), which may double the original contusion volume and worsen outcome. In humans and rodents with contusion-TBI, sulfonylurea receptor 1 (SUR1) is upregulated in microvessels and astrocytes, and in rodent models, blockade of SUR1 with glibenclamide reduces HPC. SUR1 does not function by itself, but must co-assemble with either KIR6.2 or transient receptor potential cation channel subfamily M member 4 (TRPM4) to form K_ATP (SUR1-KIR6.2) or SUR1-TRPM4 channels, with the two having opposite effects on membrane potential. Both KIR6.2 and TRPM4 are reportedly upregulated in TBI, especially in astrocytes, but the identity and function of SUR1-regulated channels post-TBI is unknown. Here, we analyzed human and rat brain tissues after contusion-TBI to characterize SUR1, TRPM4, and KIR6.2 expression, and in the rat model, to examine the effects on HPC of inhibiting expression of the three subunits using intravenous antisense oligodeoxynucleotides (AS-ODN). Glial fibrillary acidic protein (GFAP) immunoreactivity was used to operationally define core versus penumbral tissues. In humans and rats, GFAP-negative core tissues contained microvessels that expressed SUR1 and TRPM4, whereas GFAP-positive penumbral tissues contained astrocytes that expressed all three subunits. Förster resonance energy transfer imaging demonstrated SUR1-TRPM4 heteromers in endothelium, and SUR1-TRPM4 and SUR1-KIR6.2 heteromers in astrocytes. In rats, glibenclamide as well as AS-ODN targeting SUR1 and TRPM4, but not KIR6.2, reduced HPC at 24 h post-TBI. Our findings demonstrate upregulation of SUR1-TRPM4 and K_ATP after contusion-TBI, identify SUR1-TRPM4 as the primary molecular mechanism that accounts for HPC, and indicate that SUR1-TRPM4 is a crucial target of glibenclamide.

Neutrophils in traumatic brain injury (TBI): friend or foe?

Our knowledge of the pathophysiology about traumatic brain injury (TBI) is still limited. Neutrophils, as the most abundant leukocytes in circulation and the first-line transmigrated immune cells at the sites of injury, are highly involved in the initiation, development, and recovery of TBI. Nonetheless, our understanding about neutrophils in TBI is obsolete, and mounting evidences from recent studies have challenged the conventional views. This review summarizes what is known about the relationships between neutrophils and pathophysiology of TBI. In addition, discussions are made on the complex roles as well as the controversial views of neutrophils in TBI.

Cerebral Microcirculation and Histological Mapping After Severe Head Injury: A Contusion and Acceleration Experimental Model

Background

Cerebral microcirculation after severe head injury is heterogeneous and temporally variable. Microcirculation is dependent upon the severity of injury, and it is unclear how histology relates to cerebral regional blood flow.

Objective

This study assesses the changes of cerebral microcirculation blood flow over time after an experimental brain injury model in sheep and contrasts these findings with the histological analysis of the same regions with the aim of mapping cerebral flow and tissue changes after injury.

Methods

Microcirculation was quantified using flow cytometry of color microspheres injected under intracardiac ultrasound to ensure systemic and homogeneous distribution. Histological analysis used amyloid precursor protein staining as a marker of axonal injury. A mapping of microcirculation and axonal staining was performed using adjacent layers of tissue from the same anatomical area, allowing flow and tissue data to be available from the same anatomical region. A mixed effect regression model assessed microcirculation during 4 h after injury, and those results were then contrasted to the amyloid staining qualitative score.

Results

Microcirculation values for each subject and tissue region over time, including baseline, ranged between 20 and 80 ml/100 g/min with means that did not differ statistically from baseline flows. However, microcirculation values for each subject and tissue region were reduced from baseline, although their confidence intervals crossing the horizontal ratio of 1 indicated that such reduction was not statistically significant. Histological analysis demonstrated the presence of moderate and severe score on the amyloid staining throughout both hemispheres.

Conclusion

Microcirculation at the ipsilateral and contralateral site of a contusion and the ipsilateral thalamus and medulla showed a consistent decline over time. Our data suggest that after severe head injury, microcirculation in predefined areas of the brain is reduced from baseline with amyloid staining in those areas reflecting the early establishment of axonal injury.

Impact of extended monitoring-guided intensive care on outcome after severe traumatic brain injury: A prospective multicentre cohort study (PariS-TBI study)

OBJECTIVE

We evaluated whether an integrated monitoring with systemic and specific monitoring affect mortality and disability in adults with severe traumatic brain injury (sTBI).

METHODS

Adults with severeTBI (Glasgow Coma Scale [GCS] ≤ 8) admitted alive in intensive care units (ICUs) were prospectively included. Primary endpoints were in-hospital 30-day mortality and extended Glasgow outcome score (GOSE) at 3 years. Association with the intensity of monitoring and outcome was studied by comparing a high level of monitoring (HLM) (systemic and ≥3 specific monitoring) and low level of monitoring (LLM) (systemic and 0-2 specific monitoring) and using inverse probability weighting procedure.

RESULTS

476 patients were included and IPW was used to improve the balance between the two groups of treatments (HLM/LMM). Overall hospital mortality (at 30 days) was 43%, being significantly lower in HLM than LLM group (27% vs. 53%: RR, 1.63: 95% CI: 1.23-2.15). The 14-day hospital mortality was also lower in the HLM group than expected, based upon the CRASH prediction model (35%). At 3 years, disability was not significantly different between the monitoring groups.

CONCLUSIONS

After adjustment, HLM group improved short-term mortality but did not show any improvement in the 3-year outcome compared with LLM.

Hyperventilation Therapy for Control of Posttraumatic Intracranial Hypertension

During traumatic brain injury, intracranial hypertension (ICH) can become a life-threatening condition if it is not managed quickly and adequately. Physicians use therapeutic hyperventilation to reduce elevated intracranial pressure (ICP) by manipulating autoregulatory functions connected to cerebrovascular CO₂ reactivity. Inducing hypocapnia via hyperventilation reduces the partial pressure of arterial carbon dioxide (PaCO₂), which incites vasoconstriction in the cerebral resistance arterioles. This constriction decrease cerebral blood flow, which reduces cerebral blood volume and, ultimately, decreases the patient’s ICP. The effects of therapeutic hyperventilation (HV) are transient, but the risks accompanying these changes in cerebral and systemic physiology must be carefully considered before the treatment can be deemed advisable. The most prominent criticism of this approach is the cited possibility of developing cerebral ischemia and tissue hypoxia. While it is true that certain measures, such as cerebral oxygenation monitoring, are needed to mitigate these dangerous conditions, using available evidence of potential poor outcomes associated with HV as justification to dismiss the implementation of therapeutic HV is debatable and remains a controversial subject among physicians. This review highlights various issues surrounding the use of HV as a means of controlling posttraumatic ICH, including indications for treatment, potential risks, and benefits, and a discussion of what techniques can be implemented to avoid adverse complications.

Hyperemia causing delayed recovery in traumatic brain injury

Subarachnoid hemorrhage is a common manifestation of traumatic brain injury. A clinical deterioration in Glasgow Coma Scale score without an accompanying radiological worsening is suggestive of vasospasm. However, hyperemia could be another possibility which can easily be considered with corroborating transcranial Doppler (TCD) features. This case report reiterates the value of TCD in such instances.

Cerebral microcirculation during mild head injury after a contusion and acceleration experimental model in sheep

BACKGROUND

Cerebral microcirculation after head injury is heterogeneous and temporally variable. Regions at risk of infarction such as peri-contusional areas are vulnerable to anaemia. However, direct quantification of the cerebral microcirculation is clinically not feasible. This study describes a novel experimental head injury model correlating cerebral microcirculation with histopathology analysis.

OBJECTIVE

To test the hypothesis that cerebral microcirculation at the ischaemic penumbrae is reduced over time when compared with non-injured regions.

METHODS

Merino sheep were instrumented using a transeptal catheter to inject coded microspheres into the left cardiac atrium, ensuring systemic distribution. After a blunt impact over the left parietal region, cytometric analyses quantified cerebral microcirculation and amyloid precursor protein staining identified axonal injury in pre-defined anatomical regions. A mixed effect regression model assessed the hourly blood flow results during 4 hours after injury.

RESULTS

Cerebral microcirculation showed temporal reductions with minimal amyloid staining except for the ipsilateral thalamus and medulla.

CONCLUSION

The spatial heterogeneity and temporal reduction of cerebral microcirculation in ovine models occur early, even after mild head injury, independent of the intracranial pressure and the level of haemoglobin. Alternate approaches to ensure recovery of regions with reversible injury require a targeted assessment of cerebral microcirculation.

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

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

Traumatic brain injury: pathophysiology for neurocritical care

Severe cases of traumatic brain injury (TBI) require neurocritical care, the goal being to stabilize hemodynamics and systemic oxygenation to prevent secondary brain injury. It is reported that approximately 45 % of dysoxygenation episodes during critical care have both extracranial and intracranial causes, such as intracranial hypertension and brain edema. For this reason, neurocritical care is incomplete if it only focuses on prevention of increased intracranial pressure (ICP) or decreased cerebral perfusion pressure (CPP). Arterial hypotension is a major risk factor for secondary brain injury, but hypertension with a loss of autoregulation response or excess hyperventilation to reduce ICP can also result in a critical condition in the brain and is associated with a poor outcome after TBI. Moreover, brain injury itself stimulates systemic inflammation, leading to increased permeability of the blood–brain barrier, exacerbated by secondary brain injury and resulting in increased ICP. Indeed, systemic inflammatory response syndrome after TBI reflects the extent of tissue damage at onset and predicts further tissue disruption, producing a worsening clinical condition and ultimately a poor outcome.

Elevation of blood catecholamine levels after severe brain damage has been reported to contribute to the regulation of the cytokine network, but this phenomenon is a systemic protective response against systemic insults. Catecholamines are directly involved in the regulation of cytokines, and elevated levels appear to influence the immune system during stress. Medical complications are the leading cause of late morbidity and mortality in many types of brain damage. Neurocritical care after severe TBI has therefore been refined to focus not only on secondary brain injury but also on systemic organ damage after excitation of sympathetic nerves following a stress reaction.

Brain tissue oxygen evaluation by wireless near-infrared spectroscopy

BACKGROUND

Monitoring the partial pressure of oxygen in brain tissue (PbtO2) is an important tool for traumatic brain injury (TBI) but is invasive and inconvenient for real time monitoring. Near-infrared spectroscopy (NIRS), which can monitor hemoglobin parameters in the brain tissue, has been used widely as a noninvasive tool for assessing cerebral ischemia and hypoxia. Therefore, it may have the potential as a noninvasive tool for estimating the change of PbtO2. In this study, a novel wireless NIRS system was designed to monitor hemoglobin parameters of rat brains under different impact strengths and was used to estimate the change of PbtO2 noninvasively in TBI.

MATERIALS AND METHODS

The proposed wireless NIRS system and a PbtO2 monitoring system were used to monitor the oxygenation of rat brains under different impact strengths. Rats were randomly assigned to four different impact strength groups (sham, 1.6 atm, 2.0 atm, and 2.4 atm; n = 6 per group), and the relationships of concentration changes in oxyhemoglobin (HbO2), deoxyhemoglobin (HbR), and total hemoglobin (HbT), and PbtO2 during and after TBI with different impact strengths were investigated. Triphenyltetrazolium chloride (TTC) staining was also used to evaluate infarction volume.

RESULTS

Concentration changes in HbO2, HbR, and HbT dropped immediately after the impact, increased gradually, and then became stable. Changes in PbtO2 had a similar tendency with the hemoglobin parameters. There was significant correlation between changes in PbtO2 and HbO2 (correlation = 0.76) but not with changes in HbR (correlation = 0.06). In triphenyltetrazolium chloride staining, the infarction volume was highly but negatively associated with oxygen-related parameters like PbtO2 and HbO2.

CONCLUSIONS

Changes in HbO2 under TBI was highly and positively correlated with changes in PbtO2. By using the relative changes in HbO2 as a reference parameter, the proposed wireless NIRS system may be developed as a noninvasive tool for estimating the change of PbtO2 in brain tissue after TBI.

Should the neurointensive care management of traumatic brain injury patients be individualized according to autoregulation status and injury subtype?

INTRODUCTION

The status of autoregulation is an important prognostic factor in traumatic brain injury (TBI), and is important to consider in the management of TBI patients. Pressure reactivity index (PRx) is a measure of autoregulation that has been thoroughly studied, but little is known about its variation in different subtypes of TBI. In this study, we examined the impact of PRx and cerebral perfusion pressure (CPP) on outcome in different TBI subtypes.

METHODS

107 patients were retrospectively studied. Data on PRx, CPP, and outcome were collected from our database. The first CT scan was classified according to the Marshall classification system. Patients were assigned to "diffuse" (Marshall class: diffuse-1, diffuse-2, and diffuse-3) or "focal" (Marshall class: diffuse-4, evacuated mass lesion, and non-evacuated mass lesion) groups. 2 × 2 tables were constructed calculating the proportions of favorable/unfavorable outcome at different combinations of PRx and CPP.

RESULTS

Low PRx was significantly associated with favorable outcome in the combined group (p = 0.002) and the diffuse group (p = 0.04), but not in the focal group (p = 0.06). In the focal group higher CPP values were associated with worse outcome (p = 0.02). In diffuse injury patients with disturbed autoregulation (PRx >0.1), CPP >70 mmHg was associated with better outcome (p = 0.03).

CONCLUSION

TBI patients with diffuse injury may differ from those with mass lesions. In the latter higher levels of CPP may be harmful, possibly due to BBB disruption. In TBI patients with diffuse injury and disturbed autoregulation higher levels of CPP may be beneficial.

Cerebral hemodynamic changes of mild traumatic brain injury at the acute stage

Mild traumatic brain injury (mTBI) is a significant public health care burden in the United States. However, we lack a detailed understanding of the pathophysiology following mTBI and its relation to symptoms and recovery. With advanced magnetic resonance imaging (MRI), we can investigate brain perfusion and oxygenation in regions known to be implicated in symptoms, including cortical gray matter and subcortical structures. In this study, we assessed 14 mTBI patients and 18 controls with susceptibility weighted imaging and mapping (SWIM) for blood oxygenation quantification. In addition to SWIM, 7 patients and 12 controls had cerebral perfusion measured with arterial spin labeling (ASL). We found increases in regional cerebral blood flow (CBF) in the left striatum, and in frontal and occipital lobes in patients as compared to controls (p = 0.01, 0.03, 0.03 respectively). We also found decreases in venous susceptibility, indicating increases in venous oxygenation, in the left thalamostriate vein and right basal vein of Rosenthal (p = 0.04 in both). mTBI patients had significantly lower delayed recall scores on the standardized assessment of concussion, but neither susceptibility nor CBF measures were found to correlate with symptoms as assessed by neuropsychological testing. The increased CBF combined with increased venous oxygenation suggests an increase in cerebral blood flow that exceeds the oxygen demand of the tissue, in contrast to the regional hypoxia seen in more severe TBI. This may represent a neuroprotective response following mTBI, which warrants further investigation.

My paper 20 years later: cerebral venous oxygen saturation studied with bilateral samples in the internal jugular veins

INTRODUCTION

Jugular oxygen saturation monitoring was introduced in neurointensive care after severe traumatic brain injury (TBI) to explore the adequacy of brain perfusion and guide therapeutic interventions. The brain was considered homogeneous, and oxygen saturation was taken as representative of the whole organ. We investigated whether venous outflow from the brain was homogeneous by measuring oxygen saturation simultaneously from the two jugular veins.

METHODS

In 32 comatose TBI patients both internal jugular veins (IJs) were simultaneously explored using intermittent samples; hemoglobin saturation was also recorded continuously by fiber-optic catheters in five patients. In five cases long catheters were inserted bilaterally upstream, up to the sigmoid sinuses.

MAIN FINDINGS

On average, measurements from the two sides were in agreement (mean and standard deviation of the differences between the saturation of the two IJs were respectively 5.32 and 5.15). However, 15 patients showed differences of more than 15 % in hemoglobin saturation at some point; three others showed differences larger than 10 %. No relationship was found between the computed tomographic scan data and the hemoglobin saturation pattern.

DISCUSSION/CONCLUSION

Several groups have confirmed differences between oxygen saturation in the two jugular veins. After years of enthusiasm, interest for jugular saturation has decreased and more modern methods, such as tissue oxygenation monitoring, are now available. Jugular saturation monitoring has low sensitivity, with the risk of missing low saturation, but high specificity; moreover it is cheap, when used with intermittent sampling. Monitoring the adequacy of brain perfusion after severe TBI is essential. However the choice of a specific monitor depends on local resources and expertise.

Critical cerebral perfusion pressure at high intracranial pressure measured by induced cerebrovascular and intracranial pressure reactivity

OBJECTIVES

The lower limit of cerebral blood flow autoregulation is the critical cerebral perfusion pressure at which cerebral blood flow begins to fall. It is important that cerebral perfusion pressure be maintained above this level to ensure adequate cerebral blood flow, especially in patients with high intracranial pressure. However, the critical cerebral perfusion pressure of 50 mm Hg, obtained by decreasing mean arterial pressure, differs from the value of 30 mm Hg, obtained by increasing intracranial pressure, which we previously showed was due to microvascular shunt flow maintenance of a falsely high cerebral blood flow. The present study shows that the critical cerebral perfusion pressure, measured by increasing intracranial pressure to decrease cerebral perfusion pressure, is inaccurate but accurately determined by dopamine-induced dynamic intracranial pressure reactivity and cerebrovascular reactivity.

DESIGN

Cerebral perfusion pressure was decreased either by increasing intracranial pressure or decreasing mean arterial pressure and the critical cerebral perfusion pressure by both methods compared. Cortical Doppler flux, intracranial pressure, and mean arterial pressure were monitored throughout the study. At each cerebral perfusion pressure, we measured microvascular RBC flow velocity, blood-brain barrier integrity (transcapillary dye extravasation), and tissue oxygenation (reduced nicotinamide adenine dinucleotide) in the cerebral cortex of rats using in vivo two-photon laser scanning microscopy.

SETTING

University laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

At each cerebral perfusion pressure, dopamine-induced arterial pressure transients (~10 mm Hg, ~45 s duration) were used to measure induced intracranial pressure reactivity (Δ intracranial pressure/Δ mean arterial pressure) and induced cerebrovascular reactivity (Δ cerebral blood flow/Δ mean arterial pressure).

MEASUREMENTS AND MAIN RESULTS

At a normal cerebral perfusion pressure of 70 mm Hg, 10 mm Hg mean arterial pressure pulses had no effect on intracranial pressure or cerebral blood flow (induced intracranial pressure reactivity = -0.03 ± 0.07 and induced cerebrovascular reactivity = -0.02 ± 0.09), reflecting intact autoregulation. Decreasing cerebral perfusion pressure to 50 mm Hg by increasing intracranial pressure increased induced intracranial pressure reactivity and induced cerebrovascular reactivity to 0.24 ± 0.09 and 0.31 ± 0.13, respectively, reflecting impaired autoregulation (p < 0.05). By static cerebral blood flow, the first significant decrease in cerebral blood flow occurred at a cerebral perfusion pressure of 30 mm Hg (0.71 ± 0.08, p < 0.05).

CONCLUSIONS

Critical cerebral perfusion pressure of 50 mm Hg was accurately determined by induced intracranial pressure reactivity and induced cerebrovascular reactivity, whereas the static method failed.

Capillary transit time heterogeneity and flow-metabolism coupling after traumatic brain injury

Most patients who die after traumatic brain injury (TBI) show evidence of ischemic brain damage. Nevertheless, it has proven difficult to demonstrate cerebral ischemia in TBI patients. After TBI, both global and localized changes in cerebral blood flow (CBF) are observed, depending on the extent of diffuse brain swelling and the size and location of contusions and hematoma. These changes vary considerably over time, with most TBI patients showing reduced CBF during the first 12 hours after injury, then hyperperfusion, and in some patients vasospasms before CBF eventually normalizes. This apparent neurovascular uncoupling has been ascribed to mitochondrial dysfunction, hindered oxygen diffusion into tissue, or microthrombosis. Capillary compression by astrocytic endfeet swelling is observed in biopsies acquired from TBI patients. In animal models, elevated intracranial pressure compresses capillaries, causing redistribution of capillary flows into patterns argued to cause functional shunting of oxygenated blood through the capillary bed. We used a biophysical model of oxygen transport in tissue to examine how capillary flow disturbances may contribute to the profound changes in CBF after TBI. The analysis suggests that elevated capillary transit time heterogeneity can cause critical reductions in oxygen availability in the absence of 'classic' ischemia. We discuss diagnostic and therapeutic consequences of these predictions.

Posttraumatic refractory intracranial hypertension and brain herniation syndrome: cerebral hemodynamic assessment before decompressive craniectomy

Background. The pathophysiology of traumatic brain swelling remains little understood. An improved understanding of intracranial circulatory process related to brain herniation may have treatment implications. Objective. To investigate the cerebral hemodynamic changes associated with brain herniation syndrome due to traumatic brain swelling. Methods. Nineteen head-injured patients with evidence of refractory intracranial hypertension and transtentorial herniation were prospectively studied. Cerebral hemodynamic assessment by transcranial Doppler (TCD) ultrasonography was performed prior to decompressive craniectomy. Patients and their cerebral hemispheres were classified according to TCD-hemodynamic patterns, and the data correlated with neurological status, midline shift on CT scan, and Glasgow outcome scale scores at 6 months after injury. Results. A wide variety of cerebral hemodynamic findings were observed. Ten patients (52.7%) presented with cerebral oligoemia, 3 patients (15.8%) with cerebral hyperemia, and 6 patients with nonspecific circulatory pattern. Circulatory disturbances were more frequently found in the side of maximal cerebral swelling than in the opposite side. Pulsatility index (PI) values suggested that ICP varied from acceptable to considerably high; patients with increased PI, indicating higher microvascular resistance. No correlation was found between cerebral hemodynamic findings and outcome. Conclusions. There is a marked heterogeneity of cerebral hemodynamic disturbances among patients with brain herniation syndrome.

Functional imaging of cerebral perfusion

The functional imaging of perfusion enables the study of its properties such as the vasoreactivity to circulating gases, the autoregulation and the neurovascular coupling. Downstream from arterial stenosis, this imaging can estimate the vascular reserve and the risk of ischemia in order to adapt the therapeutic strategy. This method reveals the hemodynamic disorders in patients suffering from Alzheimer's disease or with arteriovenous malformations revealed by epilepsy. Functional MRI of the vasoreactivity also helps to better interpret the functional MRI activation in practice and in clinical research.

Decompressive craniectomy and cerebral blood flow regulation in head injured patients: a case studied by perfusion CT

Previous studies have reported increased cerebral blood flow (CBF) velocity after decompressive craniectomy in traumatic brain injury (TBI) patients. A 27-year-old man presented with clinical and tomographic signs of cerebral herniation secondary to TBI. Prior to decompressive craniectomy, hemodynamic study by perfusion computed tomography (CT) indicated diffuse cerebral hyperperfusion. Following surgical decompression, the patient recovered neurologically and perfusion CT disclosed a decrease in the intensity of cerebral perfusion. The patient's blood pressure levels were similar at both pre- and postoperative perfusion CT examinations. This finding provides indirect evidence that decompressive craniectomy may improve mechanisms of CBF regulation in TBI, providing pathophysiological insights in the cerebral hemodynamics of TBI patients. This is the first report analyzing the hemodynamic changes through perfusion CT (PCT) in a patient with decompressive craniotomy due to TBI.

Cerebral blood volume alterations in the perilesional areas in the rat brain after traumatic brain injury--comparison with behavioral outcome

In the traumatic brain injury (TBI) the initial impact causes both primary injury, and launches secondary injury cascades. One consequence, and a factor that may contribute to these secondary changes and functional outcome, is altered hemodynamics. The relative cerebral blood volume (CBV) changes in rat brain after severe controlled cortical impact injury were characterized to assess their interrelations with motor function impairment. Magnetic resonance imaging (MRI) was performed 1, 2, 4 h, and 1, 2, 3, 4, 7, and 14 days after TBI to quantify CBV and water diffusion. Neuroscore test was conducted before, and 2, 7, and 14 days after the TBI. We found distinct temporal profile of CBV in the perilesional area, hippocampus, and in the primary lesion. In all regions, the first response was drop of CBV. Perifocal CBV was reduced for over 4 days thereafter gradually recovering. After the initial drop, the hippocampal CBV was increased for 2 weeks. Neuroscore demonstrated severely impaired motor functions 2 days after injury (33% decrease), which then slowly recovered in 2 weeks. This recovery parallelled the recovery of perifocal CBV. CBV MRI can detect cerebrovascular pathophysiology after TBI in the vulnerable perilesional area, which seems to potentially associate with time course of sensory-motor deficit.

Transient changes in brain tissue oxygen in response to modifications of cerebral perfusion pressure: an observational study

BACKGROUND

The relative merits of the mechanisms for the maintenance of brain tissue oxygenation (PbtO(2)) have been much debated. There is a wealth of studies regarding various factors that may determine the absolute value and changes in PbtO(2). However, only a few of them analyzed fast (few minutes) and transient behavior of PbtO(2) in response to variations (waves) of intracranial pressure (ICP) and cerebral perfusion pressure (CPP).

METHODS

This was a retrospective analysis and observational study. PbtO(2), arterial blood pressure (ABP), and ICP waveforms were digitally monitored in 23 head-injured patients, admitted to the Neuroscience Critical Care Unit, who were sedated, paralyzed, and ventilated. Computer recordings were retrospectively reviewed. The dynamic changes in PbtO(2) in response to transient changes in ABP and ICP were investigated.

RESULTS

Several patterns of response to short-lasting arterial hypotension and hypertension, intracranial hypertension, cerebral vasocycling, and cerebral hyperemia were observed and characterized. During the majority of the transient events, PbtO(2) generally followed the direction of changes in CPP. Only during episodes of hyperemia, CPP and PbtO(2) changed in the opposite direction. Changes in PbtO(2) were delayed after dynamic changes in ABP, CPP, and ICP. The CPP-PbtO(2) delay during changes provoked by variations in ABP was 35.0 s (range: maximum 827.0 s; minimum 0.0 s) compared with changes induced by variations in ICP of 0.0 s (range: maximum 265.0 s; minimum 0.0 s); the difference was significant at P < 0.0001.

CONCLUSIONS

PbtO(2) is more than a number; it is rather a waveform following rapid changes in ICP and ABP. We show that PbtO(2) generally tracks the direction of CPP irrespective of the state of cerebral autoregulation.

Hyperemia beneath evacuated acute subdural hematoma is frequent and prolonged in patients with an unfavorable outcome: a xe-computed tomographic study

OBJECTIVE

To verify the values and the time course of regional cerebral blood flow (rCBF) in the cortex located beneath an evacuated acute subdural hematoma (SDH) and their relationship with neurological outcome.

METHODS

rCBF levels were measured in multiple regions of interest, by means of a Xe-computed tomographic technique, in the cortex underlying an evacuated SDH and contralaterally in 20 patients with moderate or severe traumatic brain injury and an evacuated acute SDH. Twenty-three patients with moderate or severe traumatic brain injury and an evacuated extradural hematoma or diffuse injury served as the control group. Outcome was evaluated by means of the Glasgow Outcome Scale at 12 months.

RESULTS

Values for the maximum (rCBFmax) and the mean of all rCBF levels in the cortex beneath the evacuated SDH were more frequently consistent with hyperemia. The side-to-side differences in the mean of all rCBF and rCBFmax levels between lesioned and nonlesioned hemispheres were greater in patients with evacuated SDH than in controls (P = 0.0013 and P = 0.0018, respectively). The side-to-side difference in the maximum rCBF value was higher in SDH patients with unfavorable outcomes than in controls at 24 to 96 hours and at 4 to 7 days and higher than in patients with favorable outcomes at 4 to 7 days. The widest side-to-side difference in rCBFmax value was more elevated in patients with an evacuated SDH with unfavorable outcome than in patients with a favorable outcome (P = 0.047), whereas no differences were found in controls. The SDH thickness and the associated midline shift were greater in patients with unfavorable outcomes than in those with favorable outcomes.

CONCLUSION

On average, hyperemic long-lasting rCBF values frequently occur in the cortex located beneath an evacuated SDH and seem to be associated with unfavorable outcome.

Assessment of intra-cranial pressure after severe traumatic brain injury by transcranial Doppler ultrasonography

PRIMARY OBJECTIVE

To investigate the potential of transcranial Doppler ultrasonography in estimating post-traumatic intra-cranial pressure early after severe traumatic brain injury.

RESEARCH DESIGN

The group of 24 patients was analysed for the observation of an early post-traumatic cerebral haemodynamic by middle cerebral artery blood velocity measuring.

METHODS AND PROCEDURES

The standard method of measuring the mean blood middle cerebral artery velocity by transcranial Doppler ultrasonic device was performed.

MAIN OUTCOMES AND RESULTS

The increased duration of intra-cranial hypertension correlated to the middle cerebral artery low blood velocity (p = 0.042; r = -0.498) (n = 17) and to elevated pulsatility indices (p = 0.007; r = 0.753) (n = 11) significantly. The increased duration of lowered cerebral perfusion pressure correlated to the middle cerebral artery low blood velocity significantly (p = 0.001; r = -0.619) (n = 24).

CONCLUSIONS

The significance of transcranial Doppler ultrasonography as a method to estimate an early post-traumatic intra-cranial pressure after severe brain injury was confirmed. This simple and non-invasive technique could be easily used in daily clinical practice and precede intra-cranial pressure monitoring in selected patients.

Pathophysiology of traumatic brain injury

The knowledge of the pathophysiology after traumatic head injury is necessary for adequate and patient-oriented treatment. As the primary insult, which represents the direct mechanical damage, cannot be therapeutically influenced, target of the treatment is the limitation of the secondary damage (delayed non-mechanical damage). It is influenced by changes in cerebral blood flow (hypo- and hyperperfusion), impairment of cerebrovascular autoregulation, cerebral metabolic dysfunction and inadequate cerebral oxygenation. Furthermore, excitotoxic cell damage and inflammation may lead to apoptotic and necrotic cell death. Understanding the multidimensional cascade of secondary brain injury offers differentiated therapeutic options.

Time Course of Early Metabolic Changes following Diffuse Traumatic Brain Injury in Rats as Detected by1H NMR Spectroscopy

Experimental models of traumatic brain injury (TBI) provide a useful tool for understanding the cerebral metabolic changes induced by this pathological condition. Here, we report on the time course of changes in cerebral metabolites after TBI and its correlation with early brain morphological changes using a combination of high-resolution proton magnetic resonance spectroscopy ((1)H MRS) and magnetic resonance imaging (MRI). Adult male Sprague-Dawley rats were subjected to closed head impact and examined by MRI at 1, 9, 24, 48, and and 72 h after the injury. Extracts from funnel frozen rat brains were then obtained and analyzed quantitatively by high-resolution (1)H MRS. Finally, statistical multivariate analysis was carried out to identify the combination of cerebral metabolites that best described the time evolution of diffuse TBI. The temporal changes observed in the concentration of cerebral metabolites followed three different patterns. The first pattern included taurine, threonine, and glycine, with concentrations peaking 24 h after the injury. The second pattern included glutamate, GABA, and alanine, with concentrations remaining elevated between 24 and 48 h post-injury. The third one involved creatine-phosphocreatine, N-acetylaspartate, and myo-inositol, with concentrations peaking 48 h after the injury. A multivariate stepwise discriminant analysis revealed that the combination of the organic osmolytes taurine and myo-inositol allowed optimal discrimination among the different time groups. Our findings suggest that the profile of some specific brain molecules that play a role as organic osmolytes can be used to follow-up the progression of the early diffuse brain edema response induced by TBI.

Hemodynamic manipulation in the neuro-intensive care unit: cerebral perfusion pressure therapy in head injury and hemodynamic augmentation for cerebral vasospasm

PURPOSE OF REVIEW

The intent of this manuscript is to summarize the pathophysiologic basis for hemodynamic manipulation in subarachnoid hemorrhage and traumatic brain injury, highlight the most recent literature and present expert opinion on indications and use.

RECENT FINDINGS

Hemodynamic augmentation with vasopressors and inotropes along with hypervolemia are the mainstay of treatment of vasospasm due to subarachnoid hemorrhage. Considerable variation continues to exist regarding fluid management and the use of vasopressors and inotropes. Blood pressure augmentation, volume expansion and cardiac contractility enhancement improve cerebral blood flow in ischemic areas, ameliorate vasospasm and improve clinical condition. In patients suffering from severe traumatic brain injury, while every attempt is made to control intracranial hypertension, cerebral perfusion-directed therapy with fluids and vasopressors is also used to keep cerebral perfusion pressure above 60-70 mmHg. Yet, recent observations suggest that posttraumatic mitochondrial dysfunction has been proposed as an alternative explanation for lower cerebral blood flow after acute trauma.

SUMMARY

Hemodynamic manipulation is routinely used in the management of patients with acute vasospasm following subarachnoid hemorrhage and severe head injury. The rationale is to improve blood flow to the injured brain and prevent secondary ischemia.

How to get 133Xe into solution for blood flow studies: a technical note with an emphasis on neurosurgical patients

OBJECTIVE

133Xe has been widely used for measuring blood flow in various organs. Because an injectable solution of 133Xe is not commercially available, a technique is presented that allows both the production of the radiopharmaceutical and the drawing of individualized patient doses.

METHOD

A system was designed to crush ampoules of 133Xe gas inside a sealed cylinder containing sodium chloride injection 0.9%.

RESULTS

133Xe ampoules of different sizes and filled with different activities were crushed within the system. The steel cylinder shielded 98% of the radiation. With 34 GBq 133Xe a total of 20 studies of cerebral blood flow were performed. No bacteriological contamination of the drawn doses was detected.

CONCLUSION

The crusher system allows the efficient and safe production of an injectable solution of 133Xe with sodium chloride 0.9%.

Métabolisme énergétique et agression cérébrale

Brain energy metabolism and signal transduction are intimely intricated. At the cellular level this is reflected by the interdependent metabolism of glutamate and glucose and the energetic compartmentalization between astrocytic glycolysis and neuronal metabolism. Astrocytes appear to have a particular importance in brain metabolism by regulating microcirculation and the repartition of energetic substrates in function of synaptic activity. The high level of O(2) consumption compared to the mass of tissue confers a particular vulnerability of brain to oxidative stress. The synthesis of glutathione, the main anti-oxidant of brain, appears to be dependent of the regulation of synaptic glutamate concentration by astrocytes. Deficiencies of astrocytes functions appear to play a key role in the physiopathology of brain injury.

Xenon-CT and transcranial Doppler in poor-grade or complicated aneurysmatic subarachnoid hemorrhage patients undergoing aggressive management of intracranial hypertension

OBJECTIVE

To evaluate whether elevated flow velocimetry values are associated with critically reduced cerebral blood flow values in deeply sedated patients with acute aneurysmatic subarachnoid hemorrhage and in whom the detection of clinical vasospasm is not feasible.

DESIGN

Retrospective analysis of prospectively collected data.

SETTING

Neurosurgical and trauma patients in an intensive care unit in a regional hospital.

PATIENTS AND PARTICIPANTS

Twenty-nine patients in the acute phase following subarachnoid hemorrhage who were sedated and ventilated for elevated intracranial pressure, transcranial Doppler vasospasm, or respiratory failure and were studied with at least a coupled xenon-CT/transcranial Doppler study.

MEASUREMENTS AND RESULTS

Combined measurement and comparison of cerebral blood flow by means of xenon-CT and of mean velocity by means of transcranial Doppler in middle cerebral artery territories. The case mix studied was consistent with patients' predominantly poor grade and with a complicated course. The results suggest that in sedated patients flow velocity and measured cortical mixed cerebral blood flow are not correlated, and, more specifically, that flow velocities values above 120 or 160 cm/s and Lindegaard index above 3 are not associated with an ischemic regional cerebral blood flow. Conversely, as many as 55% of the xenon-CT studies were associated with hyperemia.

CONCLUSIONS

In patients with elevated intracranial pressure, mean middle cerebral artery flow velocity or Lindegaard Index does not help to detect critical cerebral blood flow nor elevated cerebral blood flow.

Posttraumatic vasospasm: the epidemiology, severity, and time course of an underestimated phenomenon: a prospective study performed in 299 patients

OBJECT

The purpose of this prospective study was to evaluate the cumulative incidence, duration, and time course of cerebral vasospasm after traumatic brain injury (TBI) in a cohort of 299 patients.

METHODS

Transcranial Doppler (TCD) ultrasonography studies of blood flow velocity in the middle cerebral and basilar arteries (VMCA and VBA, respectively) were performed at regular intervals during the first 2 weeks posttrauma in association with 133Xe cerebral blood flow (CBF) measurements. According to current definitions of vasospasm, five different criteria were used to classify the patients: A (VMCA > 120 cm/second); B (VMCA > 120 cm/second and a Lindegaard ratio [LR] > 3); C (spasm index [SI] in the anterior circulation > 3.4); D (VBA > 90 cm/second); and E (SI in the posterior circulation > 2.5). Criteria C and E were considered to represent hemodynamically significant vasospasm. Mixed-effects spline models were used to analyze the data of multiple measurements with an inconsistent sampling rate. Overall 45.2% of the patients demonstrated at least one criterion for vasospasm. The patients in whom vasospasm developed were significantly younger and had lower Glasgow Coma Scale scores on admission. The normalized cumulative incidences were 36.9 and 36.2% for patients with Criteria A and B, respectively. Hemodynamically significant vasospasm in the anterior circulation (Criterion C) was found in 44.6% of the patients, whereas vasospasm in the BA-Criterion D or E-was found in only 19 and 22.5% of the patients, respectively. The most common day of onset for Criteria A, B, D, and E was postinjury Day 2. The highest risk of developing hemodynamically significant vasospasm in the anterior circulation was found on Day 3. The daily prevalence of vasospasm in patients in the intensive care unit was 30% from postinjury Day 2 to Day 13. Vasospasm resolved after a duration of 5 days in 50% of the patients with Criterion A or B and after a period of 3.5 days in 50% of those patients with Criterion D or E. Hemodynamically significant vasospasm in the anterior circulation resolved after 2.5 days in 50% of the patients. The time course of that vasospasm was primarily determined by a decrease in CBF.

CONCLUSIONS

The incidence of vasospasm after TBI is similar to that following aneurysmal subarachnoid hemorrhage. Because vasospasm is a significant event in a high proportion of patients after severe head injury, close TCD and CBF monitoring is recommended for the treatment of such patients.