Hemispheric differences in cerebral autoregulation in children with moderate and severe traumatic brain injury

Cerebral autoregulation in paediatric and neonatal intensive care: A scoping review

Deranged cerebral autoregulation (CA) is associated with worse outcome in adult brain injury. Strategies for monitoring CA and maintaining the brain at its 'best CA status' have been implemented, however, this approach has not yet developed for the paediatric population. This scoping review aims to find up-to-date evidence on CA assessment in children and neonates with a view to identify patient categories in which CA has been measured so far, CA monitoring methods and its relationship with clinical outcome if any. A literature search was conducted for studies published within 31st December 2022 in 3 bibliographic databases. Out of 494 papers screened, this review includes 135 studies. Our literature search reveals evidence for CA measurement in the paediatric population across different diagnostic categories and age groups. The techniques adopted, indices and thresholds used to assess and define CA are heterogeneous. We discuss the relevance of available evidence for CA assessment in the paediatric population. However, due to small number of studies and heterogeneity of methods used, there is no conclusive evidence to support universal adoption of CA monitoring, technique, and methodology. This calls for further work to understand the clinical impact of CA monitoring in paediatric and neonatal intensive care.

Update in Pediatric Neurocritical Care: What a Neurologist Caring for Critically Ill Children Needs to Know

Currently nearly one-quarter of admissions to pediatric intensive care units (PICUs) worldwide are for neurocritical care diagnoses that are associated with significant morbidity and mortality. Pediatric neurocritical care is a rapidly evolving field with unique challenges due to not only age-related responses to primary neurologic insults and their treatments but also the rarity of pediatric neurocritical care conditions at any given institution. The structure of pediatric neurocritical care services therefore is most commonly a collaborative model where critical care medicine physicians coordinate care and are supported by a multidisciplinary team of pediatric subspecialists, including neurologists. While pediatric neurocritical care lies at the intersection between critical care and the neurosciences, this narrative review focuses on the most common clinical scenarios encountered by pediatric neurologists as consultants in the PICU and synthesizes the recent evidence, best practices, and ongoing research in these cases. We provide an in-depth review of (1) the evaluation and management of abnormal movements (seizures/status epilepticus and status dystonicus); (2) acute weakness and paralysis (focusing on pediatric stroke and select pediatric neuroimmune conditions); (3) neuromonitoring modalities using a pathophysiology-driven approach; (4) neuroprotective strategies for which there is evidence (e.g., pediatric severe traumatic brain injury, post-cardiac arrest care, and ischemic stroke and hemorrhagic stroke); and (5) best practices for neuroprognostication in pediatric traumatic brain injury, cardiac arrest, and disorders of consciousness, with highlights of the 2023 updates on Brain Death/Death by Neurological Criteria. Our review of the current state of pediatric neurocritical care from the viewpoint of what a pediatric neurologist in the PICU needs to know is intended to improve knowledge for providers at the bedside with the goal of better patient care and outcomes.

Near-Infrared Spectroscopy Regional Oxygen Saturation Based Cerebrovascular Reactivity Assessments in Chronic Traumatic Neural Injury versus in Health: A Prospective Cohort Study

Near-infrared spectroscopy (NIRS) regional cerebral oxygen saturation (rSO2)-based cerebrovascular reactivity (CVR) monitoring has enabled entirely non-invasive, continuous monitoring during both acute and long-term phases of care. To date, long-term post-injury CVR has not been properly characterized after acute traumatic neural injury, also known as traumatic brain injury (TBI). This study aims to compare CVR in those recovering from moderate-to-severe TBI with a healthy control group. A total of 101 heathy subjects were recruited for this study, along with 29 TBI patients. In the healthy cohort, the arterial blood pressure variant of the cerebral oxygen index (COx_a) was not statistically different between males and females or in the dominant and non-dominant hemispheres. In the TBI cohort, COx_a was not statistically different between the first and last available follow-up or by the side of cranial surgery. Surprisingly, CVR, as measured by COx_a, was statistically better in those recovering from TBI than those in the healthy cohort. In this prospective cohort study, CVR, as measured by NIRS-based methods, was found to be more active in those recovering from TBI than in the healthy cohort. This study may indicate that in individuals that survive TBI, CVR may be enhanced as a neuroprotective measure.

Cerebral Autoregulation-guided Management of Adult and Pediatric Traumatic Brain Injury

Cerebral autoregulation (CA) plays a vital role in maintaining cerebral blood flow in response to changes in systemic blood pressure. Impairment of CA following traumatic brain injury (TBI) may exacerbate the injury, potentially impacting patient outcomes. This focused review addresses 4 key questions regarding the measurement, natural history of CA after TBI, and potential clinical implications of CA status and CA-guided management in adults and children with TBI. We examine the feasibility and safety of CA assessment, its association with clinical outcomes, and the potential for reversing deranged CA following TBI. Finally, we discuss how the knowledge of CA status may affect TBI management and outcomes.

A multicentre retrospective cohort study on health-related quality of life after traumatic acute subdural haematoma: does cranial laterality affect long-term recovery?

Background

Traumatic acute subdural haematoma is a debilitating condition. Laterality intuitively influences management and outcome. However, in contrast to stroke, this research area is rarely studied. The aim is to investigate whether the hemisphere location of the ASDH influences patient outcome.

Methods

For this multicentre observational retrospective cohort study, patients were considered eligible when they were treated by a neurosurgeon for traumatic brain injury between 2008 and 2012, were > 16 years of age, had sustained brain injury with direct presentation to the emergency room and showed a hyperdense, crescent shaped lesion on the computed tomography scan. Patients were followed for a duration of 3-9 months post-trauma for functional outcome and 2-6 years for health-related quality of life. Main outcomes and measures included mortality, Glasgow Outcome Scale and the Quality of Life after Brain Injury score. The hypothesis was formulated after data collection.

Results

Of the 187 patients included, 90 had a left-sided ASDH and 97 had a right-sided haematoma. Both groups were comparable at baseline and with respect to the executed treatment. Furthermore, both groups showed no significant difference in mortality and Glasgow Outcome Scale score. Health-related quality of life, assessed 59 months (IQR 43-66) post-injury, was higher for patients with a right-sided haematoma (Quality of Life after Brain Injury score: 80 vs 61, P = 0.07).

Conclusions

This study suggests patients with a right-sided acute subdural haematoma have a better long-term health-related quality of life compared to patients with a left-sided acute subdural haematoma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02790-3.

Optimal bispectral index level of sedation and cerebral oximetry in traumatic brain injury: a non-invasive individualized approach in critical care?

Background

Impaired cerebral autoregulation has been linked with worse outcomes, with literature suggesting that current therapy guidelines fail to significantly impact cerebrovascular reactivity. The cerebral oximetry index (COx_a) is a surrogate measure of cerebrovascular reactivity which can in theory be obtained non-invasively using regional brain tissue oxygen saturation and arterial blood pressure. The goal of this study was to assess the relationship between objectively measured depth of sedation through BIS and autoregulatory capacity measured through COx_a.

Methods

In a prospectively maintained observational study, we collected continuous regional brain tissue oxygen saturation, intracranial pressure, arterial blood pressure and BIS in traumatic brain injury patients. COx_a was obtained using the Pearson’s correlation between regional brain tissue oxygen saturation and arterial blood pressure and ranges from − 1 to 1 with higher values indicating impairment of cerebrovascular reactivity. Using BIS values and COx_a, a curve-fitting method was applied to determine the minimum value for the COx_a. The associated BIS value with the minimum COx_a is called BISopt. This BISopt was both visually and algorithmically determined, which were compared and assessed over the whole dataset.

Results

Of the 42 patients, we observed that most had a parabolic relationship between BIS and COx_a. This suggests a potential “optimal” depth of sedation where COx_a is the most intact. Furthermore, when comparing the BISopt algorithm with visual inspection of BISopt, we obtained similar results. Finally, BISopt % yield (determined algorithmically) appeared to be independent from any individual sedative or vasopressor agent, and there was agreement between BISopt found with COx_a and the pressure reactivity index (another surrogate for cerebrovascular reactivity).

Conclusions

This study suggests that COx_a is capable of detecting disruption in cerebrovascular reactivity which occurs with over-/under-sedation, utilizing a non-invasive measure of determination and assessment. This technique may carry implications for tailoring sedation in patients, focusing on individualized neuroprotection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40635-022-00460-9.

Pediatric Traumatic Brain Injury: An Update on Preclinical Models, Clinical Biomarkers, and the Implications of Cerebrovascular Dysfunction

Traumatic brain injury (TBI) is a leading cause of pediatric morbidity and mortality. Recent studies suggest that children and adolescents have worse post-TBI outcomes and take longer to recover than adults. However, the pathophysiology and progression of TBI in the pediatric population are studied to a far lesser extent compared to the adult population. Common causes of TBI in children are falls, sports/recreation-related injuries, non-accidental trauma, and motor vehicle-related injuries. A fundamental understanding of TBI pathophysiology is crucial in preventing long-term brain injury sequelae. Animal models of TBI have played an essential role in addressing the knowledge gaps relating to pTBI pathophysiology. Moreover, a better understanding of clinical biomarkers is crucial to diagnose pTBI and accurately predict long-term outcomes. This review examines the current preclinical models of pTBI, the implications of pTBI on the brain’s vasculature, and clinical pTBI biomarkers. Finally, we conclude the review by speculating on the emerging role of the gut-brain axis in pTBI pathophysiology.

Multiorgan Dysfunction After Severe Traumatic Brain Injury: Epidemiology, Mechanisms, and Clinical Management

Traumatic brain injury (TBI) is a major global health problem and a major contributor to morbidity and mortality following multisystem trauma. Extracranial organ dysfunction is common after severe TBI and significantly impacts clinical care and outcomes following injury. Despite this, extracranial organ dysfunction remains an understudied topic compared with organ dysfunction in other critical care paradigms. In this review, we will: 1) summarize the epidemiology of extracranial multiorgan dysfunction following severe TBI; 2) examine relevant mechanisms that may be involved in the development of multi-organ dysfunction following severe TBI; and 3) discuss clinical management strategies to care for these complex patients.

Incidence and Clinical Impact of Myocardial Injury Following Traumatic Brain Injury: A Pilot TRACK-TBI Study

BACKGROUND

Traumatic brain injury (TBI) is a major global health problem. Little research has addressed extracranial organ dysfunction following TBI, particularly myocardial injury. Using a sensitive marker of myocardial injury-high sensitivity troponin (hsTn)-we examined the incidence of early myocardial injury following TBI and explored its association with neurological outcomes following moderate-severe TBI.

METHODS

We conducted a pilot cohort study of 133 adult (age above 17 y) subjects enrolled in the TRACK-TBI 18-center prospective cohort study. Descriptive statistics were used to examine the incidence of myocardial injury (defined as hsTn >99th percentile for a standardized reference population) across TBI severities, and to explore the association of myocardial injury with a 6-month extended Glasgow Outcome Score among patients with moderate-severe TBI.

RESULTS

The mean (SD) age of the participants was 44 (17) years, and 87 (65%) were male. Twenty-six patients (20%) developed myocardial injury following TBI; myocardial injury was present in 15% of mild TBI patients and 29% of moderate-severe TBI patients (P=0.13). Median (interquartile range) hsTn values were 3.8 ng/L (2.1, 9.0), 5.8 ng/L (4.5, 34.6), and 10.2 ng/L (3.0, 34.0) in mild, moderate, and severe TBI participants, respectively (P=0.04). Overall, 11% of participants with moderate-severe TBI and myocardial injury experienced a good outcome (6-mo extended Glasgow Outcome Score≥5) at 6 months, compared with 65% in the group that did not experience myocardial injury (P=0.01).

CONCLUSIONS

Myocardial injury is common following TBI, with a likely dose-response relationship with TBI severity. Early myocardial injury was associated with poor 6-month clinical outcomes following moderate-severe TBI.

Early cerebrovascular and long-term neurological modifications ensue following juvenile mild traumatic brain injury in male mice

Clinical evidence suggests that a mild traumatic brain injury occurring at a juvenile age (jmTBI) may be sufficient to elicit pathophysiological modifications. However, clinical reports are not adequately integrated with experimental studies examining brain changes occurring post-jmTBI. We monitored the cerebrovascular modifications and assessed the long-term behavioral and electrographic changes resulting from experimental jmTBI. In vivo photoacoustic imaging demonstrated a decrease of cerebrovascular oxygen saturation levels in the impacted area hours post-jmTBI. Three days post-jmTBI oxygenation returned to pre-jmTBI levels, stabilizing at 7 and 30 days after the injury. At the functional level, cortical arterioles displayed no NMDA vasodilation response, while vasoconstriction induced by thromboxane receptor agonist was enhanced at 1 day post-jmTBI. Arterioles showed abnormal NMDA vasodilation at 3 days post-jmTBI, returning to normality at 7 days post injury. Histology showed changes in vessel diameters from 1 to 30 days post-jmTBI. Neurological evaluation indicated signs of anxiety-like behavior up to 30 days post-jmTBI. EEG recordings performed at the cortical site of impact 30 days post-jmTBI did not indicate seizures activity, although it revealed a reduction of gamma waves as compared to age matched sham. Histology showed decrease of neuronal filament staining. In conclusion, experimental jmTBI triggers an early cerebrovascular hypo‑oxygenation in vivo and faulty vascular reactivity. The exact topographical coherence and the direct casualty between early cerebrovascular changes and the observed long-term neurological modifications remain to be investigated. A potential translational value for cerebro-vascular oxygen monitoring in jmTBI is discussed.

Cerebral Perfusion Pressure Directed-Therapy Modulates Cardiac Dysfunction After Traumatic Brain Injury to Influence Cerebral Autoregulation in Pigs

BACKGROUND

Traumatic brain injury (TBI) is an important contributor to morbidity and mortality. Low cerebral perfusion pressure (CPP, mean arterial pressure [MAP] minus intracranial pressure) after TBI is associated with cerebral ischemia, impaired cerebral autoregulation, and poor outcomes. Normalization of CPP and limitation of cerebral autoregulation impairment is a key therapeutic goal. However, some vasoactive agents used to elevate MAP such as phenylephrine (Phe) improve outcome in females but not male piglets after TBI while dopamine (DA) does so in both sexes. Clinical evidence has implicated neurological injuries as a cause of cardiac dysfunction, and we recently described cardiac dysfunction after TBI. Cardiac dysfunction may, in turn, influence brain health. One mechanism of myocyte injury may involve catecholamine excess. We therefore tested the hypothesis that TBI caused cardiac dysfunction and catecholamine excess which may reciprocally be modulated by vasoactive agent choice to normalize CPP and prevent impairment of cerebral autoregulation after injury.

METHODS

TBI was produced in anesthetized pigs equipped with a closed cranial window, and Phe or DA administered to normalize CPP.

RESULTS

Plasma cardiac enzymes troponin and creatine kinase and catecholamines epinephrine and norepinephrine were elevated by TBI, such release potentiated by Phe in males but blocked in female piglets and blocked in both sexes after DA. Cerebral autoregulation was impaired after TBI, worsened by Phe in males but protected in females and males treated with DA. Papaverine-induced dilation was unchanged by fluid percussion brain injury, DA, and Phe.

CONCLUSIONS

These data indicate that pressor choice in elevation of CPP is important in limiting cardiac dysfunction and suggest that DA protects cerebral autoregulation in both sexes via reduction of cardiac biomarkers of injury and catecholamines released after TBI.

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

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

Prevalence, Evolution, and Extent of Impaired Cerebral Autoregulation in Children Hospitalized With Complex Mild Traumatic Brain Injury

OBJECTIVES

To examine cerebral autoregulation in children with complex mild traumatic brain injury.

DESIGN

Prospective observational convenience sample.

SETTING

PICU at a level I trauma center.

PATIENTS

Children with complex mild traumatic brain injury (trauma, admission Glasgow Coma Scale score 13-15 with either abnormal head CT, or history of loss of consciousness).

INTERVENTIONS

Cerebral autoregulation was tested using transcranial Doppler ultrasound between admission day 1 and 8.

MEASUREMENTS AND MAIN RESULTS

The primary outcome was prevalence of impaired cerebral autoregulation (autoregulation index < 0.4),determined using transcranial Doppler ultrasonography and tilt testing. Secondary outcomes examined factors associated with and evolution and extent of impairment. Cerebral autoregulation testing occurred in 31 children 10 years (SD, 5.2 yr), mostly male (59%) with isolated traumatic brain injury (91%), median admission Glasgow Coma Scale 15, Injury Severity Scores 14.2 (SD, 7.7), traumatic brain injury due to fall (50%), preadmission loss of consciousness (48%), and abnormal head CT scan (97%). Thirty-one children underwent 56 autoregulation tests. Impaired cerebral autoregulation occurred in 15 children (48.4%) who underwent 19 tests; 68% and 32% of tests demonstrated unilateral and bilateral impairment, respectively. Compared with children on median day 6 of admission after traumatic brain injury, impaired autoregulation was most common in the first 5 days after traumatic brain injury (day 1: relative risk, 3.7; 95% CI, 1.9-7.3 vs day 2: relative risk, 2.7; 95% CI, 1.1-6.5 vs day 5: relative risk, 1.33; 95% CI, 0.7-2.3). Children with impaired autoregulation were older (12.3 yr [SD, 1.3 yr] vs 8.7 yr [SD, 1.1 yr]; p = 0.04) and tended to have subdural hematoma (64% vs 44%), epidural hematoma (29% vs 17%), and subarachnoid hemorrhage (36% vs 28%). Eight children (53%) were discharged home with ongoing impaired cerebral autoregulation.

CONCLUSIONS

Impaired cerebral autoregulation is common in children with complex mild traumatic brain injury, despite reassuring admission Glasgow Coma Scale 13-15. Children with complex mild traumatic brain injury have abnormal cerebrovascular hemodynamics, mostly during the first 5 days. Impairment commonly extends to the contralateral hemisphere and discharge of children with ongoing impaired cerebral autoregulation is common.

Association of Early Myocardial Workload and Mortality Following Severe Traumatic Brain Injury

OBJECTIVES

To examine the impact of early myocardial workload on in-hospital mortality following isolated severe traumatic brain injury.

DESIGN

Retrospective cohort study.

SETTING

Data from the National Trauma Databank, a multicenter trauma registry operated by the American College of Surgeons, from 2007 to 2014.

PATIENTS

Adult patients with isolated severe traumatic brain injury (defined as admission Glasgow Coma Scale < 8 and head Abbreviated Injury Score ≥ 4).

INTERVENTIONS

Admission rate-pressure product, categorized into five levels based on published low, normal, and submaximal human thresholds: less than 5,000; 5,000-9,999; 10,000-14,999; 15,000-19,999; and greater than 20,000.

MEASUREMENTS AND MAIN RESULTS

Data from 26,412 patients were analyzed. Most patients had a normal rate-pressure product (43%), 35% had elevated rate-pressure product, and 22% had depressed rate-pressure product at hospital admission. Compared with the normal rate-pressure product group, in-hospital mortality was 22 percentage points higher in the lowest rate-pressure product group (cumulative mortality, 50.2%; 95% CI, 43.6-56.9%) and 11 percentage points higher in the highest rate-pressure product group (cumulative mortality, 39.2%; 95% CI, 37.4-40.9%). The lowest rate-pressure product group was associated with a 50% increased risk of mortality, compared with the normal rate-pressure product group (adjusted relative risk, 1.50; 95% CI, 1.31-1.76%; p < 0.0001), and the highest rate-pressure product group was associated with a 25% increased risk of mortality, compared with the normal rate-pressure product group (adjusted relative risk, 1.25; 95% CI, 1.18-1.92%; p < 0.0001). This relationship was blunted with increasing age. Among patients with normotension, those with depressed and elevated rate-pressure products experienced increased mortality.

CONCLUSIONS

Adults with severe traumatic brain injury experience heterogeneous myocardial workload profiles that have a "U-shaped" relationship with mortality, even in the presence of a normal blood pressure. Our findings are novel and suggest that cardiac performance is important following severe traumatic brain injury.

Anatomical and Physiological Differences between Children and Adults Relevant to Traumatic Brain Injury and the Implications for Clinical Assessment and Care

General and central nervous system anatomy and physiology in children is different to that of adults and this is relevant to traumatic brain injury (TBI) and spinal cord injury. The controversies and uncertainties in adult neurotrauma are magnified by these differences, the lack of normative data for children, the scarcity of pediatric studies, and inappropriate generalization from adult studies. Cerebral metabolism develops rapidly in the early years, driven by cortical development, synaptogenesis, and rapid myelination, followed by equally dramatic changes in baseline and stimulated cerebral blood flow. Therefore, adult values for cerebral hemodynamics do not apply to children, and children cannot be easily approached as a homogenous group, especially given the marked changes between birth and age 8. Their cranial and spinal anatomy undergoes many changes, from the presence and disappearance of the fontanels, the presence and closure of cranial sutures, the thickness and pliability of the cranium, anatomy of the vertebra, and the maturity of the cervical ligaments and muscles. Moreover, their systemic anatomy changes over time. The head is relatively large in young children, the airway is easily compromised, the chest is poorly protected, the abdominal organs are large. Physiology changes—blood volume is small by comparison, hypothermia develops easily, intracranial pressure (ICP) is lower, and blood pressure normograms are considerably different at different ages, with potentially important implications for cerebral perfusion pressure (CPP) thresholds. Mechanisms and pathologies also differ—diffuse injuries are common in accidental injury, and growing fractures, non-accidental injury and spinal cord injury without radiographic abnormality are unique to the pediatric population. Despite these clear differences and the vulnerability of children, the amount of pediatric-specific data in TBI is surprisingly weak. There are no robust guidelines for even basics aspects of care in children, such as ICP and CPP management. This is particularly alarming given that TBI is a leading cause of death in children. To address this, there is an urgent need for pediatric-specific clinical research. If this goal is to be achieved, any clinician or researcher interested in pediatric neurotrauma must be familiar with its unique pathophysiological characteristics.

Early changes in cerebral autoregulation among youth hospitalized after sports-related traumatic brain injury

OBJECTIVE

To examine early cerebral haemodynamic changes among youth hospitalized with sports-related traumatic brain injury (TBI).

STUDY DESIGN

Youth 0-18 years admitted to a level one trauma centre with sports-related TBI were enrolled. Daily measures included clinical symptoms and Glasgow Coma Scale (GCS) score. Using Transcranial Doppler (TCD) ultrasonography and tilt testing, we measured middle cerebral artery flow velocity (Vmca) and cerebral autoregulation index (ARI).

RESULTS

Six previously healthy males age 14 (IQR 12-16) years with headache and abnormal head CT were admitted with median admission GCS 15. Six patients underwent 12 TCD examinations between hospital days 0-9. Low Vmca occurred in 3/6 patients and on the side of TBI, whereas high Vmca occurred in 2/6 patients. Five patients had at least one measurement of impaired and five patients had absent cerebral autoregulation of at least one hemisphere; all these five patients had GCS 15 and headache during TCD examinations. Three patients were discharged with absent cerebral autoregulation. Five (83%) patients were discharged to home and one patient was discharged to a rehabilitation facility.

CONCLUSION

Headache, abnormal Vmca and impaired cerebral autoregulation occur after sports-related TBI, despite normal GCS. Headache may signal underlying neurovascular abnormality in sports-related TBI.

Hypertension After Severe Traumatic Brain Injury: Friend or Foe?

Traumatic brain injury (TBI) is a major public health problem, with severe TBI contributing to a large number of deaths and disability worldwide. Early hypotension has been linked with poor outcomes following severe TBI, and guidelines suggest early and aggressive management of hypotension after TBI. Despite these recommendations, no guidelines exist for the management of hypertension after severe TBI, although observational data suggests that early hypertension is also associated with an increased risk of mortality after severe TBI. The purpose of this review is to discuss the underlying pathophysiology of hypertension after TBI, provide an overview of the current clinical data on early hypertension after TBI, and discuss future research that should test the benefits and harms of treating high blood pressure in TBI patients.

Predictors of Outcome With Cerebral Autoregulation Monitoring: A Systematic Review and Meta-Analysis

OBJECTIVE

To compare cerebral autoregulation indices as predictors of patient outcome and their dependence on duration of monitoring.

DATA SOURCES

Systematic literature search and meta-analysis using PubMed, EMBASE, and the Cochrane Library from January 1990 to October 2015.

STUDY SELECTION

We chose articles that assessed the association between cerebral autoregulation indices and dichotomized or continuous outcomes reported as standardized mean differences or correlation coefficients (R), respectively. Animal and validation studies were excluded.

DATA EXTRACTION

Two authors collected and assessed the data independently. The studies were grouped into two sets according to the type of analysis used to assess the relationship between cerebral autoregulation indices and predictors of outcome (standardized mean differences or R).

DATA SYNTHESIS

Thirty-three studies compared cerebral autoregulation indices and patient outcomes using standardized mean differences, and 20 used Rs. The only data available for meta-analysis were from patients with traumatic brain injury or subarachnoid hemorrhage. Based on z score analysis, the best three cerebral autoregulation index predictors of mortality or Glasgow Outcome Scale for patients with traumatic brain injury were the pressure reactivity index, transcranial Doppler-derived mean velocity index based on cerebral perfusion pressure, and autoregulation reactivity index (z scores: 8.97, 6.01, 3.94, respectively). Mean velocity index based on arterial blood pressure did not reach statistical significance for predicting outcome measured as a continuous variable (p = 0.07) for patients with traumatic brain injury. For patients with subarachnoid hemorrhage, autoregulation reactivity index was the only cerebral autoregulation index that predicted patient outcome measured with the Glasgow Outcome Scale as a continuous outcome (R = 0.82; p = 0.001; z score, 3.39). We found a significant correlation between the duration of monitoring and predictive value for mortality (R = 0.78; p < 0.001).

CONCLUSIONS

Three cerebral autoregulation indices, pressure reactivity index, mean velocity index based on cerebral perfusion pressure, and autoregulation reactivity index were the best outcome predictors for patients with traumatic brain injury. For patients with subarachnoid hemorrhage, autoregulation reactivity index was the only cerebral autoregulation index predictor of Glasgow Outcome Scale. Continuous assessment of cerebral autoregulation predicted outcome better than intermittent monitoring.

Vascular impairment as a pathological mechanism underlying long-lasting cognitive dysfunction after pediatric traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of death and disability in children. Indeed, the acute mechanical injury often evolves to a chronic brain disorder with long-term cognitive, emotional and social dysfunction even in the case of mild TBI. Contrary to the commonly held idea that children show better recovery from injuries than adults, pediatric TBI patients actually have worse outcome than adults for the same injury severity. Acute trauma to the young brain likely interferes with the fine-tuned developmental processes and may give rise to long-lasting consequences on brain's function. This review will focus on cerebrovascular dysfunction as an important early event that may lead to long-term phenotypic changes in the brain after pediatric TBI. These, in turn may be associated with accelerated brain aging and cognitive dysfunction. Finally, since no effective treatments are currently available, understanding the unique pathophysiological mechanisms of pediatric TBI is crucial for the development of new therapeutic options.

Traumatic brain injury-induced autoregulatory dysfunction and spreading depression-related neurovascular uncoupling: Pathomechanisms, perspectives, and therapeutic implications

Traumatic brain injury (TBI) is a major health problem worldwide. In addition to its high mortality (35-40%), survivors are left with cognitive, behavioral, and communicative disabilities. While little can be done to reverse initial primary brain damage caused by trauma, the secondary injury of cerebral tissue due to cerebromicrovascular alterations and dysregulation of cerebral blood flow (CBF) is potentially preventable. This review focuses on functional, cellular, and molecular changes of autoregulatory function of CBF (with special focus on cerebrovascular myogenic response) that occur in cerebral circulation after TBI and explores the links between autoregulatory dysfunction, impaired myogenic response, microvascular impairment, and the development of secondary brain damage. We further provide a synthesized translational view of molecular and cellular mechanisms involved in cortical spreading depolarization-related neurovascular dysfunction, which could be targeted for the prevention or amelioration of TBI-induced secondary brain damage.

Pathophysiology and Management of Moderate and Severe Traumatic Brain Injury in Children

Traumatic brain injury remains a leading cause of morbidity and mortality in children. Key pathophysiologic processes of traumatic brain injury are initiated by mechanical forces at the time of trauma, followed by complex excitotoxic cascades associated with compromised cerebral autoregulation and progressive edema. Acute care focuses on avoiding secondary insults, including hypoxia, hypotension, and hyperthermia. Children with moderate or severe traumatic brain injury often require intensive monitoring and treatment of multiple parameters, including intracranial pressure, blood pressure, metabolism, and seizures, to minimize secondary brain injury. Child neurologists can play an important role in acute and long-term care. Acutely, as members of a multidisciplinary team in the intensive care unit, child neurologists monitor for early signs of neurological change, guide neuroprotective therapies, and transition patients to long-term recovery. In the longer term, neurologists are uniquely positioned to treat complications of moderate and severe traumatic brain injury, including epilepsy and cognitive and behavioral issues.

Cardiac Dysfunction After Neurologic Injury: What Do We Know and Where Are We Going?

Recent literature has implicated severe neurologic injuries, such as aneurysmal subarachnoid hemorrhage, as a cause of cardiac dysfunction, impaired hemodynamic function, and poor outcomes. Mechanistic links between the brain and the heart have been explored in detail over the past several decades, and catecholamine excess, neuroendocrine dysfunction, and unchecked inflammation all likely contribute to the pathophysiologic process. Although cardiac dysfunction has also been described in other disease paradigms, including septic shock and thermal injury, there is likely a common underlying pathophysiology. In this review, we will examine the pathophysiology of cardiac dysfunction after neurologic injury, discuss the evidence surrounding cardiac dysfunction after different neurologic injuries, and suggest future research goals to gain knowledge and improve outcomes in this patient population.

Intraoperative blood pressure and cerebral perfusion: strategies to clarify hemodynamic goals

Blood pressure can vary considerably during anesthesia. If blood pressure falls outside the limits of cerebrovascular autoregulation, children can become at risk of cerebral ischemic or hyperemic injury. However, the blood pressure limits of autoregulation are unclear in infants and children, and these limits can shift after brain injury. This article will review autoregulation, considerations for the hemodynamic management of children with brain injuries, and research on autoregulation monitoring techniques.

Hemispheric differences in the surgical outcomes of patients with traumatic acute subdural hematoma

Background

Our assumption that prognosis of patients with traumatic acute subdural hematoma (ASDH) does not differ significantly according to the hemispheric laterality has never been verified.

Methods

A review of the charts/radiographic images of 61 adult traumatic ASDH patients (33 left/28 right) was conducted. Intergroup comparison was made on the demographics, autonomic/laboratory data, and outcomes (90-day mortality rate). Based on the presence of concomitant brain contusion, patients were further quadrichotomized as: left ASDH with contusion (n = 14), right ASDH with contusion (n = 16), left ASDH without contusion (n = 19), and right ASDH without contusion (n = 12). Comparisons were made on demographic and outcome variables between the left ASDH with contusion and right ASDH with contusion, and between the left ASDH without contusion and right ASDH without contusion. Multivariate regression analysis was conducted to identify clinical variables correlated with fatality.

Results

There were no significant differences in the demographic, autonomic, and laboratory data between the left and right ASDH patients. However, 90-day mortality rate was significantly higher in the left ASDH patients when concomitant contusion was present (79% vs. 25%, p = 0.009). However, there were no significant hemispheric differences in the mortality rate among those without contusion (32% vs. 33%, p = 0.77). Multivariate regression analysis showed that left ASDH was correlated with fatality among those with contusion (OR: 6.620; 95% CI: 1.219-46.249).

Conclusions

This study is probably the first to report that the left ASDH patients fared substantially worse than the right-sided counterparts. Future trials on traumatic ASDHs may benefit from considering hemispheric differences in the outcomes.

Cerebrovascular autoregulation and neurologic injury in neonatal hypoxic-ischemic encephalopathy

BACKGROUND

Neonates with hypoxic-ischemic encephalopathy (HIE) are at risk of cerebral blood flow dysregulation. Our objective was to describe the relationship between autoregulation and neurologic injury in HIE.

METHODS

Neonates with HIE had autoregulation monitoring with the hemoglobin volume index (HVx) during therapeutic hypothermia, rewarming, and the first 6 h of normothermia. The 5-mm Hg range of mean arterial blood pressure (MAP) with best vasoreactivity (MAPOPT) was identified. The percentage of time spent with MAP below MAPOPT and deviation in MAP from MAPOPT were measured. Neonates received brain magnetic resonance imaging (MRI) 3-7 d after treatment. MRIs were coded as no, mild, or moderate/severe injury in five regions.

RESULTS

HVx identified MAPOPT in 79% (19/24), 77% (17/22), and 86% (18/21) of the neonates during hypothermia, rewarming, and normothermia, respectively. Neonates with moderate/severe injury in paracentral gyri, white matter, basal ganglia, and thalamus spent a greater proportion of time with MAP below MAPOPT during rewarming than neonates with no or mild injury. Neonates with moderate/severe injury in paracentral gyri, basal ganglia, and thalamus had greater MAP deviation below MAPOPT during rewarming than neonates without injury.

CONCLUSION

Maintaining MAP within or above MAPOPT may reduce the risk of neurologic injuries in neonatal HIE.

Cerebrovascular autoregulation in pediatric moyamoya disease

BACKGROUND

Moyamoya syndrome carries a high risk of cerebral ischemia, and impaired cerebrovascular autoregulation may play a critical role. Autoregulation indices derived from near-infrared spectroscopy (NIRS) may clarify hemodynamic goals that conform to the limits of autoregulation.

OBJECTIVES

The aims of this pilot study were to determine whether the NIRS-derived indices could identify blood pressure ranges that optimize autoregulation and whether autoregulatory function differs between anatomic sides in patients with unilateral vasculopathy.

METHODS

Pediatric patients undergoing indirect surgical revascularization for moyamoya were enrolled sequentially. NIRS-derived autoregulation indices, the cerebral oximetry index (COx) and the hemoglobin volume index (HVx), were calculated intraoperatively and postoperatively to measure autoregulatory function. The 5-mmHg ranges of optimal mean arterial blood pressure (MAPOPT ) with best autoregulation and the lower limit of autoregulation (LLA) were identified.

RESULTS

Of seven enrolled patients (aged 2-16 years), six had intraoperative and postoperative autoregulation monitoring and one had only intraoperative monitoring. Intraoperative MAPOPT was identified in six (86%) of seven patients with median values of 60-80 mmHg. Intraoperative LLA was identified in three (43%) patients with median values of 55-65 mmHg. Postoperative MAPOPT was identified in six (100%) of six patients with median values of 70-90 mmHg. Patients with unilateral disease had higher intraoperative HVx (P = 0.012) on side vasculopathy.

CONCLUSIONS

NIRS-derived indices may identify hemodynamic goals that optimize autoregulation in pediatric moyamoya.

The relationship of resting cerebral blood flow and brain activation during a social cognition task in adolescents with chronic moderate to severe traumatic brain injury: a preliminary investigation

Alterations in cerebrovascular function are evident acutely in moderate to severe traumatic brain injury (TBI), although less is known about their chronic effects. Adolescent and adult patients with moderate to severe TBI have been reported to demonstrate diffuse activation throughout the brain during functional magnetic resonance imaging (fMRI). Because fMRI is a measure related to blood flow, it is possible that any deficits in blood flow may alter activation. An arterial spin labeling (ASL) perfusion sequence was performed on seven adolescents with chronic moderate to severe TBI and seven typically developing (TD) adolescents during the same session in which they had performed a social cognition task during fMRI. In the TD group, prefrontal CBF was positively related to prefrontal activation and negatively related to non-prefrontal, posterior, brain activation. This relationship was not seen in the TBI group, who demonstrated a greater positive relationship between prefrontal CBF and non-prefrontal activation than the TD group. An analysis of CBF data independent of fMRI showed reduced CBF in the right non-prefrontal region (p<.055) in the TBI group. To understand any role reduced CBF may play in diffuse extra-activation, we then related the right non-prefrontal CBF to activation. CBF in the right non-prefrontal region in the TD group was positively associated with prefrontal activation, suggesting an interactive role of non-prefrontal and prefrontal blood flow throughout the right hemisphere in healthy brains. However, the TBI group demonstrated a positive association with activation constrained to the right non-prefrontal region. These data suggest a relationship between impaired non-prefrontal CBF and the presence of non-prefrontal extra-activation, where the region with more limited blood flow is associated with activation limited to that region. In a secondary analysis, pathology associated with hyperintensities on T2-weighted FLAIR imaging over the whole brain was related to whole brain activation, revealing a negative relationship between lesion volume and frontal activation, and a positive relationship between lesion volume and posterior activation. These preliminary data, albeit collected with small sample sizes, suggest that reduced non-prefrontal CBF, and possibly pathological tissue associated with T2-hyperintensities, may provide contributions to the diffuse, primarily posterior extra-activation observed in adolescents following moderate to severe TBI.

Cerebral blood flow and cerebrovascular autoregulation in a swine model of pediatric cardiac arrest and hypothermia

OBJECTIVE

Knowledge remains limited regarding cerebral blood flow autoregulation after cardiac arrest and during postresuscitation hypothermia. We determined the relationship of cerebral blood flow to cerebral perfusion pressure in a swine model of pediatric hypoxic-asphyxic cardiac arrest during normothermia and hypothermia and tested novel measures of autoregulation derived from near-infrared spectroscopy.

DESIGN

Prospective, balanced animal study.

SETTING

Basic physiology laboratory at an academic institution.

SUBJECTS

Eighty-four neonatal swine.

INTERVENTIONS

Piglets underwent hypoxic-asphyxic cardiac arrest or sham surgery and recovered for 2 hrs with normothermia followed by 4 hrs of either moderate hypothermia or normothermia. In half of the groups, blood pressure was slowly decreased through inflation of a balloon catheter in the inferior vena cava to identify the lower limit of cerebral autoregulation at 6 hrs postresuscitation. In the remaining groups, blood pressure was gradually increased by inflation of a balloon catheter in the aorta to determine the autoregulatory response to hypertension. Measures of autoregulation obtained from standard laser-Doppler flowmetry and indices derived from near-infrared spectroscopy were compared.

MEASUREMENTS AND MAIN RESULTS

Laser-Doppler flux was lower in postarrest animals compared to sham-operated controls during the 2-hr normothermic period after resuscitation. During the subsequent 4-hr recovery, hypothermia decreased laser-Doppler flux in both the sham surgery and postarrest groups. Autoregulation was intact during hypertension in all groups. With arterial hypotension, postarrest, hypothermic piglets had a significant decrease in the perfusion pressure lower limit of autoregulation compared to postarrest, normothermic piglets. The near-infrared spectroscopy-derived measures of autoregulation accurately detected loss of autoregulation during hypotension.

CONCLUSIONS

In a pediatric model of cardiac arrest and resuscitation, delayed induction of hypothermia decreased cerebral perfusion and decreased the lower limit of autoregulation. Metrics derived from noninvasive near-infrared spectroscopy accurately identified the lower limit of autoregulation during normothermia and hypothermia in piglets resuscitated from arrest.

Transcranial Doppler in children

Transcranial Doppler US, a non-invasive tool for evaluating the cerebral arteries, has evolved significantly during the last two decades. This review describes the practical procedure, and summarises and illustrates its established and "work-in-progress" indications in children. Indications for a transcranial Doppler US examination include, but are not limited to: (1) evaluation of cerebral blood flow velocities in the circle of Willis in patients with sickle cell anaemia to guide transfusion therapy; (2) diagnosis and follow-up of vasculopathy, such as moyamoya disease; (3) diagnosis and monitoring of acute cerebrovascular disorders in intensive care patients, in particular following traumatic brain injury, and during cardiovascular surgery; and (4) confirmation of a clinical diagnosis of brain death by documentation of cerebral circulatory arrest.

Endothelin-1 is increased in cerebrospinal fluid and associated with unfavorable outcomes in children after severe traumatic brain injury

Severe pediatric traumatic brain injury (TBI) is associated with unfavorable outcomes secondary to injury from activation of the inflammatory cascade, the release of excitotoxic neurotransmitters, and changes in the reactivity of cerebral vessels, causing ischemia. Hypoperfusion of injured brain tissues after TBI is also associated with unfavorable outcomes. Therapeutic hypothermia is an investigational treatment strategy for use in patients with severe TBI that has shown differential effects on various cerebrospinal fluid (CSF) mediators in pediatric patients. Endothelin-1 (ET-1) is a powerful vasoconstrictor that exerts its effects on the cerebrovascular endothelium for sustained periods after TBI. The purpose of this study was to determine if CSF concentrations of ET-1 are increased after severe TBI in children, and if they are associated with demographics and outcomes that are affected by therapeutic hypothermia. This was an ancillary study to a prospective, randomized-controlled trial of early hypothermia in a tertiary care pediatric intensive care unit. Children (n = 34, age 3 months-15 years) suffering from severe TBI were randomized to hypothermia (n = 19) and normothermia (n = 15) as part of the efficacy study. Children undergoing diagnostic lumbar puncture (n = 11) to rule out infection were used as controls. Patients received either mild to moderate hypothermia (32-33°C) or normothermia as part of their treatment protocol. CSF was serially collected during the first 5 days after TBI. ET-1 concentrations were quantitated in patient and control CSF samples by a validated ELISA in duplicate with a limit of quantification of 0.195 pg/mL. CSF ET-1 concentrations were increased by two- to threefold in children after TBI compared to controls, and the increase was sustained for up to 5 days post-TBI. This relationship was not affected by hypothermia, and there were no differences in ET-1 response between children with inflicted and accidental TBI. Group-based trajectory analysis revealed two distinct groups with similar ET-1 levels over time. Univariate analysis showed a significant association between ET-1 levels and Glasgow Outcome Scale (GOS) scores, for which higher ET-1 levels over time were associated with unfavorable outcomes. ET-1 is increased in children with severe TBI and is associated with unfavorable outcomes. This increase in ET-1 may mediate the hypoperfusion or cerebrovascular dysfunction accompanying severe TBI in children. Importantly, hypothermia does not affect the brain's ET-1 response as measured in the CSF.

Practical aspects of bedside cerebral hemodynamics monitoring in pediatric TBI

INTRODUCTION

Disturbances in cerebral hemodynamics may have a profound influence on secondary injury after traumatic brain injury (TBI), and many therapies in the neurocritical care unit may adversely affect cerebral blood flow. However, the clinician is often unaware of this when it occurs because practical methods for monitoring cerebral hemodynamics by the bedside have been lacking. Current imaging studies only provide a snapshot of the brain at one point in time, giving limited information about a dynamic condition.

DISCUSSION

This review will focus on key pathophysiological concepts required to understand changes in cerebral hemodynamics after TBI and the principles, potential benefits, and limitations of currently available bedside monitoring techniques, including transcranial Doppler, autoregulation, and local/regional cerebral blood flow.

Clinical management and functional neuromonitoring in traumatic brain injury in children

PURPOSE OF REVIEW

Traumatic brain injury is the main cause of childhood disability and death. In this review, we highlight recent original findings and emerging themes from published literature on children with serious traumatic brain injury.

RECENT FINDINGS

We focus this review on lessons learned from our recent randomized clinical trial of hypothermia therapy in severe traumatic brain injury in children and on bedside neuromonitoring. We propose that integrating the measurement of biomarkers into clinical care as surrogate endpoints and as potential prognostic markers would allow us to evaluate earlier the effect of injury and clinical care in children after traumatic brain injury. Several methods are now more readily available to monitor cerebral physiology in children. These methods include indices evaluating the integrity of cerebral autoregulation, such as the pressure reactivity index derived from values obtained from intracranial pressure measurements, flow velocity measurements from transcranial Doppler ultrasonography or from cerebral oximetry. Other methods allow the evaluation of coma with the nonlinear analysis of electroencephalography or the evaluation of cerebral metabolism and cell death pathways with biomarkers from serum, cerebral spinal fluid, and cerebral microdialysis.

SUMMARY

We suggest expanding clinical functional neuromonitoring to help clinicians understand the burden of exposure to physiological variables and response to therapies during intensive care in order to enhance the management of critically ill children with traumatic brain injury.

Cerebrovascular pathophysiology in pediatric traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is the leading cause of traumatic morbidity and mortality in children. Although there is increasing information concerning TBI in adults and experimental animal models, relatively little is known regarding cerebrovascular pathophysiology specific to children.

MATERIALS

A review of the pertinent medical literature.

RESULTS

Systemic and cerebral hemodynamic factors such as hypotension, hypoxia, hyperglycemia, and fever are associated with poor outcome in pediatric TBI. Similarly, cerebral autoregulation is often impaired after TBI and may adversely affect outcome, especially if systemic hemodynamics are altered. Furthermore, CO2 vasoreactivity may be altered after pediatric TBI and lead to either cerebral ischemia or hyperemia.

CONCLUSIONS

Understanding the effect of pediatric TBI on the cerebral circulation is needed to potentially develop protocols to improve outcome in this vulnerable population. Specifically, changes in pediatric cerebrovascular physiology and pathophysiology, including CO2 vasoreactivity and pressure autoregulation, must be understood and their mechanism elucidated.

Cerebral hemodynamic predictors of poor 6-month Glasgow Outcome Score in severe pediatric traumatic brain injury

Little is known regarding the cerebral autoregulation in pediatric traumatic brain injury (TBI). We examined the relationship between cerebral hemodynamic predictors, including cerebral autoregulation, and long-term outcome after severe pediatric TBI. After Institutional Review Board (IRB) approval, a retrospective analysis of prospectively collected data (May 2002 to October 2007) for children age < or =16 years with severe TBI (admission Glasgow Coma Scale [GCS] score <9) was performed. Cerebral autoregulation was assessed within 72 h after TBI. Cerebral hemodynamic predictors (intracranial pressure [ICP], systolic blood pressure [SBP], and cerebral perfusion pressure [CPP]) through the first 72 h after TBI were abstracted. Univariate and multivariate analyses examined the relationship between impaired cerebral autoregulation (autoregulatory index <0.4), intracranial hypertension (ICP >20 mm Hg), and hypotension (SBP <5th percentile and CPP <40 mm Hg). Six-month Glasgow Outcome Scale (GOS) score of <4 defined poor outcome. Ten (28%) of the 36 children examined (9.1 +/- 5.3 [0.8-16] years; 74% male) had poor outcome. Univariate factors associated with poor outcome were impaired cerebral autoregulation (p = 0.005), SBP <5(th) percentile for age and gender (p = 0.02), and low middle cerebral artery flow velocity (<2 SD for age and gender; p = 0.04). Independent risk factors for poor 6-month GOS were impaired cerebral autoregulation (adjusted odds ratio [aOR] 12.0; 95% confidence interval [CI] 1.4-99.4) and hypotension (SBP <5th percentile; aOR 8.8; 95% CI 1.1-70.5), respectively. Previous studies of TBI describing poor outcome with hemodynamics did not consider the status of cerebral autoregulation. In this study, both impaired cerebral autoregulation and SBP <5th percentile were independent risk factors for poor 6-month GOS.