Changes in cerebral hemodynamics assessed by transcranial Doppler ultrasonography in children after head injury

Cerebral Infarction Due to Post-traumatic Cerebral Vasospasm in a 12-Year-Old Female

Cerebral infarction due to post-traumatic cerebral vasospasm is rare. Although some modalities are recommended to detect post-traumatic cerebral vasospasm, its diagnosis remains controversial and challenging. Therefore, in this report, we will use a case report to highlight challenges and to delineate the characteristics of post-traumatic cerebral vasospasm in pediatric patients, including the diagnostic and treatment options. A 12-year-old female was admitted to our hospital following a motor vehicle collision. Her consciousness was severely impaired. Initial computed tomography (CT) revealed an acute subdural hematoma along the tentorium, and a focal subarachnoid hemorrhage was observed in the Sylvian fissure. The patient underwent the insertion of an intracranial pressure sensor and received therapy for increased intracranial pressure (ICP) control under sedation. On the second day, CT angiography (CTA) revealed no signs of arterial abnormality. A patient who is comatose or under sedation has masked neurological symptoms. Thus, new neurological events could only be detected via an intracranial pressure sensor. Her ICP increased on the seventh day, and a CT scan showed a new cerebral infarction in the right middle cerebral artery (MCA) region. We performed decompressive craniectomy to reduce ICP. Postoperative CTA confirmed severe vasospasm in the right MCA. The severe cerebral vasospasm induced the cerebral infarction. Our review suggests that physicians in trauma departments should frequently perform vascular evaluations by CTA, magnetic resonance angiography (MRA), transcranial Doppler ultrasound, or digital subtraction angiography (DSA), especially within two weeks from onset, to detect post-traumatic cerebral vasospasm.

Multispectral Optoacoustic Tomography (MSOT): Monitoring Neurovascular Changes in a Mouse Repetitive Traumatic Brain Injury Model

BACKGROUND

Evidence suggests that mild TBI injuries, which comprise >75% of all TBIs, can cause chronic post-concussive symptoms, especially when experienced repetitively (rTBI). rTBI is a major cause of cognitive deficit in athletes and military personnel and is associated with neurovascular changes. Current methods to monitor neurovascular changes in detail are prohibitively expensive and invasive for patients with mild injuries.

NEW METHOD

We evaluated the potential of multispectral optoacoustic tomography (MSOT) to monitor neurovascular changes and assess therapeutic strategies in a mouse model of rTBI. Mice were subjected to rTBI or sham via controlled cortical impact and administered pioglitazone (PG) or vehicle. Oxygenated and deoxygenated hemoglobin were monitored using MSOT. Indocyanine green clearance was imaged via MSOT to evaluate blood-brain barrier (BBB) integrity.

RESULTS

Mice subjected to rTBI show a transient increase in oxygenated/total hemoglobin ratio which can be mitigated by PG administration. rTBI mice also show BBB disruption shortly after injury and reduction of oxygenated/total hemoglobin in the chronic stage, neither of which were affected by PG intervention.

COMPARISON WITH EXISTING METHODS

MSOT imaging has the potential as a noninvasive in vivo imaging method to monitor neurovascular changes and assess therapeutics in mouse models of rTBI. In comparison to standard methods of tracking inflammation and BBB disruption, MSOT can be used multiple times throughout the course of injury without the need for surgery. Thus, MSOT is especially useful in research of rTBI models for screening therapeutics, and with further technological improvements may be extended for use in rTBI patients.

Microglia dynamics in adolescent traumatic brain injury

Repetitive, mild traumatic brain injuries (RmTBIs) are increasingly common in adolescents and encompass one of the largest neurological health concerns in the world. Adolescence is a critical period for brain development where RmTBIs can substantially impact neurodevelopmental trajectories and life-long neurological health. Our current understanding of RmTBI pathophysiology suggests key roles for neuroinflammation in negatively regulating neural health and function. Microglia, the brain’s resident immune population, play important roles in brain development by regulating neuronal number, and synapse formation and elimination. In response to injury, microglia activate to inflammatory phenotypes that may detract from these normal homeostatic, physiological, and developmental roles. To date, however, little is known regarding the impact of RmTBIs on microglia function during adolescent brain development. This review details key concepts surrounding RmTBI pathophysiology, adolescent brain development, and microglia dynamics in the developing brain and in response to injury, in an effort to formulate a hypothesis on how the intersection of these processes may modify long-term trajectories.

Isolated Infarction of the Splenium: A Rare Presentation of Mild Head Injury

Posttraumatic cerebral infarction (PTCI) is a devastating complication of traumatic brain injury. It is usually seen in patients with moderate-to-severe head injury with a reported incidence of 1.9%–10.4%. Brain shift associated with the traumatic intracranial space-occupying lesions with or without severe cerebral edema is the most common mechanism underlying the PTCI. Without associated direct vascular injury, isolated PTCI is very rare after mild head injury. Such cases of PTCI following mild head injury have been reported in children in whom they usually affect the gangliocapsular region supplied by the lenticulostriate arteries. Such infarcts in adults are extremely rare. Although the exact pathogenesis is not clear, vasospasm or shearing-associated intimal tear is proposed to be the cause for this infarct. Other common causes of cerebral infarction should be ruled out before making such a diagnosis. Unlike PTCI associated with a severe head injury, cerebral infarction following mild head injury is expected to have a better neurological outcome.

Approaches to Multimodality Monitoring in Pediatric Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality in children. Improved methods of monitoring real-time cerebral physiology are needed to better understand when secondary brain injury develops and what treatment strategies may alleviate or prevent such injury. In this review, we discuss emerging technologies that exist to better understand intracranial pressure (ICP), cerebral blood flow, metabolism, oxygenation and electrical activity. We also discuss approaches to integrating these data as part of a multimodality monitoring strategy to improve patient care.

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.

Improving Understanding and Outcomes of Traumatic Brain Injury Using Bidirectional Translational Research

Recent clinical trials in traumatic brain injury (TBI) have failed to demonstrate therapeutic effects even when there appears to be good evidence for efficacy in one or more appropriate pre-clinical models. While existing animal models mimic the injury, difficulties in translating promising therapeutics are exacerbated by the lack of alignment of discrete measures of the underlying injury pathology between the animal models and human subjects. To address this mismatch, we have incorporated reverse translation of bedside experience to inform pre-clinical studies in a large animal (pig) model of TBI that mirror practical clinical assessments. Cerebral autoregulation is impaired after TBI, contributing to poor outcome. 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. Vasoactive agents clinically used to elevate MAP to increase CPP after TBI, such as phenylephrine (Phe), dopamine (DA), norepinephrine (NE), and epinephrine (EPI), however, have not been compared sufficiently regarding effect on CPP, autoregulation, and survival after TBI, and clinically, current vasoactive agent use is variable. The cerebral effects of these clinically commonly used vasoactive agents are not known. This review will emphasize pediatric work and will describe bidirectional translational studies using a more human-like animal model of TBI to identify better therapeutic strategies to improve outcome post-injury. These studies in addition investigated the mechanism(s) involved in improvement of outcome in the setting of TBI.

A model of longitudinal hemodynamic alterations after mild traumatic brain injury in adolescents

There is an unquestionable need for quantitative biomarkers of mild traumatic brain injuries. Something that is particularly true for adolescents – where the recovery from these injuries is still poorly understood. However, within this population, it is clear that the vasculature is distinctly affected by a mild traumatic brain injury. In addition, our group recently demonstrated how that effect appears to show a progression of alterations similar but in contrast to that found in severe traumatic injuries. Through measuring an adolescent population with transcranial Doppler ultrasound during a hypercapnia challenge, multiple phases of hemodynamic dysfunction were suggested. Here, we create a generalized model of the hemodynamic responses by fitting a set of inverse models to the dominant features from that work. The resulting model helps define the multiple phases of hemodynamic recovery after a mild traumatic brain injury. This can eventually be generalized, potentially providing a diagnostic tool for clinicians tracking patient’s recovery, and ultimately, resulting in more informed decisions and better outcomes.

Cerebral Blood Flow Velocities and Functional Outcomes in Pediatric Mild Traumatic Brain Injury

Outcomes can be challenging to predict in children with mild traumatic brain injury (TBI). Transcranial Doppler (TCD) ultrasound has become an increasingly useful modality in adult and pediatric TBI by measuring blood flow velocities within the circle of Willis. In children with moderate-to-severe TBI, multiple studies have correlated abnormal TCD measurements and poor outcomes. Additionally, TCD has shown value in assessing adults with mild brain injury. To date, there are no studies that correlate TCD findings and outcomes in children with mild TBI. We hypothesize that altered cerebral blood flow after mild TBI is associated with poor functional outcome using the Glasgow Outcome Scale-Extended, Pediatrics (GOS-E Peds). TCD was performed within 24 h of admission on 60 patients at a tertiary Level 1 children's hospital. A secondary analysis was performed on the subgroup of 28 mild TBI patients. GOS-E Peds was measured at the time of hospital discharge and 4-6 weeks post-discharge. Cerebral blood flow velocities did not show correlation with outcome. At discharge, the right-sided Spearman's correlation coefficient was 0.19 (p value = 0.33) and the left-sided was 0.36 (p = 0.06). At follow up the right-sided coefficient was -0.04 (p = 0.84), the left-sided was -0.25 (p = 0.24). Pulsatility index likewise showed no correlation. Right and left-sided correlation at discharge were -0.25 (p = 0.19) and 0.01 (p = 0.96), respectively. At follow up the right side showed 0.004 (p = 0.99), and the left showed 0.18 (p = 0.41). Although our data did not show correlation, it showed that the investigation could feasibly be done in pediatric patients with mild TBI. The study was limited by small sample size and infrequent outcome of interest. Future studies may help define the role of TCD in the large population of mild pediatric TBI patients.

A Cross-Sectional Study on Cerebral Hemodynamics After Mild Traumatic Brain Injury in a Pediatric Population

The microvasculature is prominently affected by traumatic brain injury (TBI), including mild TBI (concussion). Assessment of cerebral hemodynamics shows promise as biomarkers of TBI, and may help inform development of therapies aimed at promoting neurologic recovery. The objective of this study was to assess the evolution in cerebral hemodynamics observable with transcranial Doppler (TCD) ultrasound in subjects suffering from a concussion at different intervals during recovery. Pediatric subjects between the ages of 14 and 19 years clinically diagnosed with a concussion were observed at different points post-injury. Blood flow velocity in the middle cerebral artery was measured with TCD. After a baseline period, subjects participated in four breath holding challenges. Pulsatility index (PI), resistivity index (RI), the ratio of the first two pulse peaks (P2R), and the mean velocity (MV) were computed from the baseline section. The breath hold index (BHI) was computed from the challenge sections. TCD detected two phases of hemodynamic changes after concussion. Within the first 48 h, PI, RI, and P2R show a significant difference from the controls (U = −3.10; P < 0.01, U = −2.86; P < 0.01, and U = 2.62; P < 0.01, respectively). In addition, PI and P2R were not correlated (r_p = −0.36; P = 0.23). After 48 h, differences in pulsatile features were no longer observable. However, BHI was significantly increased when grouped as 2–3, 4–5, and 6–7 days post-injury (U = 2.72; P < 0.01, U = 2.46; P = 0.014, and U = 2.38; P = 0.018, respectively). To our knowledge, this is the first longitudinal study of concussions using TCD. In addition, these results are the first to suggest the multiple hemodynamic changes after a concussion are observable with TCD and could ultimately lead to a better understanding of the underlying pathophysiology. In addition, the different hemodynamic responses to a concussion as compared to severe traumatic brain injuries highlight the need for specific diagnostic and therapeutic treatments of mild head injuries in adolescents.

Sport-Related Concussion Alters Indices of Dynamic Cerebral Autoregulation

Sport-related concussion is known to affect a variety of brain functions. However, the impact of this brain injury on cerebral autoregulation (CA) is poorly understood. Thus, the goal of the current study was to determine the acute and cumulative effects of sport-related concussion on indices of dynamic CA. Toward this end, 179 elite, junior-level (age 19.6 ± 1.5 years) contact sport (ice hockey, American football) athletes were recruited for preseason testing, 42 with zero prior concussions and 31 with three or more previous concussions. Eighteen athletes sustained a concussion during that competitive season and completed follow-up testing at 72 h, 2 weeks, and 1 month post injury. Beat-by-beat arterial blood pressure (BP) and middle cerebral artery blood velocity (MCAv) were recorded using finger photoplethysmography and transcranial Doppler ultrasound, respectively. Five minutes of repetitive squat-stand maneuvers induced BP oscillations at 0.05 and 0.10 Hz (20- and 10-s cycles, respectively). The BP-MCAv relationship was quantified using transfer function analysis to estimate Coherence (correlation), Gain (amplitude ratio), and Phase (timing offset). At a group level, repeated-measures ANOVA indicated that 0.10 Hz Phase was significantly reduced following an acute concussion, compared to preseason, by 23% (-0.136 ± 0.033 rads) at 72 h and by 18% (-0.105 ± 0.029 rads) at 2 weeks post injury, indicating impaired autoregulatory functioning; recovery to preseason values occurred by 1 month. Athletes were cleared to return to competition after a median of 14 days (range 7-35), implying that physiologic dysfunction persisted beyond clinical recovery in many cases. When comparing dynamic pressure buffering between athletes with zero prior concussions and those with three or more, no differences were observed. Sustaining an acute sport-related concussion induces transient impairments in the capabilities of the cerebrovascular pressure-buffering system that may persist beyond 2 weeks and may be due to a period of autonomic dysregulation. Athletes with a history of three or more concussions did not exhibit impairments relative to those with zero prior concussions, suggesting recovery of function over time. Findings from this study support the potential need to consider physiological recovery in deciding when patients should return to play following a concussion.

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.

Exposure to Surgery and Anesthesia After Concussion Due to Mild Traumatic Brain Injury

OBJECTIVE

To describe the epidemiology of surgical and anesthetic procedures in patients recently diagnosed as having a concussion due to mild traumatic brain injury.

PATIENTS AND METHODS

Study patients presented to a tertiary care center after a concussion due to mild traumatic brain injury from July 1, 2005, through June 30, 2015, and underwent a surgical procedure and anesthesia support under the direct or indirect care of a physician anesthesiologist.

RESULTS

During the study period, 1038 patients met all the study inclusion criteria and subsequently received 1820 anesthetics. In this population of anesthetized patients, rates of diagnosed concussions due to sports injuries, falls, and assaults, but not motor vehicle accidents, increased during 2010-2011. Concussions were diagnosed in 965 patients (93%) within 1 week after injury. In the 552 patients who had surgery within 1 week after concussive injury, 29 (5%) had anesthesia and surgical procedures unrelated to their concussion-producing traumatic injury. The highest use of surgery occurred early after injury and most frequently required general anesthesia. Orthopedic and general surgical procedures accounted for 57% of procedures. Nine patients received 29 anesthetics before a concussion diagnosis, and all of these patients had been involved in motor vehicle accidents and received at least 1 anesthetic within 1 week of injury.

CONCLUSION

Surgical and anesthesia use are common in patients after concussion. Clinicians should have increased awareness for concussion in patients who sustain a trauma and may need to take measures to avoid potentially injury-augmenting cerebral physiology in these patients.

Cerebral Blood Flow Autoregulation and Dysautoregulation

This article provides a review of cerebral autoregulation, particularly as it relates to the clinician scientist experienced in neuroscience in anesthesia and critical care. Topics covered are biological mechanisms; methods used for assessment of autoregulation; effects of anesthetics; role in control of cerebral hemodynamics in health and disease; and emerging areas, such as role of age and sex in contribution to dysautoregulation. Emphasis is placed on bidirectional translational research wherein the clinical informs the study design of basic science studies, which, in turn, informs the clinical to result in development of improved therapies for treatment of central nervous system conditions.

Pathophysiology and Treatment of Severe Traumatic Brain Injuries in Children

Traumatic brain injuries (TBIs) in children are a major cause of morbidity and mortality worldwide. Severe TBIs account for 15,000 admissions annually and a mortality rate of 24% in children in the United States. The purpose of this article is to explore pathophysiologic events, examine monitoring techniques, and explain current treatment modalities and nursing care related to caring for children with severe TBI. The primary injury of a TBI is because of direct trauma from an external force, a penetrating object, blast waves, or a jolt to the head. Secondary injury occurs because of alterations in cerebral blood flow, and the development of cerebral edema leads to necrotic and apoptotic cellular death after TBI. Monitoring focuses on intracranial pressure, cerebral oxygenation, cerebral edema, and cerebrovascular injuries. If abnormalities are identified, treatments are available to manage the negative effects caused to the cerebral tissue. The mainstay treatments are hyperosmolar therapy; temperature control; cerebrospinal fluid drainage; barbiturate therapy; decompressive craniectomy; analgesia, sedation, and neuromuscular blockade; and antiseizure prophylaxis.

The role of the cervical spine in post-concussion syndrome

While much is known regarding the pathophysiology surrounding concussion injuries in the acute phase, there is little evidence to support many of the theorized etiologies to post-concussion syndrome (PCS); the chronic phase of concussion occurring in ∼ 10-15% of concussed patients. This paper reviews the existing literature surrounding the numerous proposed theories of PCS and introduces another potential, and very treatable, cause of this chronic condition; cervical spine dysfunction due to concomitant whiplash-type injury. We also discuss a short case-series of five patients with diagnosed PCS having very favorable outcomes following various treatment and rehabilitative techniques aimed at restoring cervical spine function.

A pediatric perspective on concussion pathophysiology

PURPOSE OF REVIEW

According to recent Centers for Disease Control (CDC) data, the annual incidence of traumatic brain injury (TBI) in the United States is 1.6-3.2 million, of which the majority is classified as mild. Over half of these injuries occur in the pediatric population, and can often be attributed to a sports-related mechanism. Although postconcussion symptoms are usually short-lived, more lasting deficits can occur, which can be particularly disruptive to the developing brain. Recent literature detailing the pathophysiology of mild TBI (mTBI), with attention to pediatric studies, is presented.

RECENT FINDINGS

Although concussion generally does not produce any structural damage on conventional computed tomography (CT) or MRI, advanced neuroimaging modalities reveal microstructural and functional neurobiological changes. Diffuse axonal injury, metabolic impairment, alterations in neural activation and cerebral blood flow perturbations can occur and may contribute to acute symptomatology. Although these physiological changes usually recover to baseline in 7-10 days, sustaining recurrent injury before full recovery may increase the potential for persistent deficits.

SUMMARY

Understanding the pathophysiology of concussion in the pediatric population can potentially open therapeutic avenues to decrease symptom persistence and prevent further injury. Future studies in the pediatric population are necessary given the pathophysiologic differences between the developing and adult brains.

Posterior cerebral artery dissection on a serial magnetic resonance angiography

Posterior cerebral artery (PCA) dissection in children seldom is reported in the literature. This is the second report of acute PCA dissection with infarct occurring in a young child. A serial magnetic resonance angiography demonstrated a delayed and transient narrowing of the arterial caliber, which was consistent with a focal PCA dissection with delayed vascular recanalization. PCA dissection should be included in the causes of infarct in children and a thorough and serial neurovascular imaging should be considered if no cause of stroke is found.

The pathophysiology of concussions in youth

Mild traumatic brain injury, especially sport-related concussion, is common among young persons. Consequences of transient pathophysiologic dysfunction must be considered in the context of a developing or immature brain, as must the potential for an accumulation of damage with repeated exposure. This review summarizes the underlying neurometabolic cascade of concussion, with emphasis on the young brain in terms of acute pathophysiology, vulnerability, alterations in plasticity and activation, axonal injury, and cumulative risk from chronic, repetitive damage, and discusses their implications in the context of clinical care for the concussed youth, highlighting areas for future investigation.

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.

Cerebrovascular pathophysiology following mild traumatic brain injury

Mild traumatic brain injury (mTBI) or sport-induced concussion has recently become a prominent concern not only in the athletic setting (i.e. sports venue) but also in the general population. The majority of research to date has aimed at understanding the neurological and neuropsychological outcomes of injury as well as return-to-play guidelines. Remaining relatively unexamined has been the pathophysiological aspect of mTBI. Recent technological advances including transcranial Doppler ultrasound and near infrared spectroscopy have allowed researchers to examine the systemic effects of mTBI from rest to exercise, and during both asymptomatic and symptomatic conditions. In this review, we focus on the current research available from both human and experimental (animal) studies surrounding the pathophysiology of mTBI. First, the quest for a unified definition of mTBI, its historical development and implications for future research is discussed. Finally, the impact of mTBI on the control and regulation of cerebral blood flow, cerebrovascular reactivity, cerebral oxygenation and neuroautonomic cardiovascular regulation, all of which may be compromised with mTBI, is discussed.

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.

Vasospasm in children with traumatic brain injury

Objective

To determine the incidence of vasospasm in children who have suffered moderate to severe traumatic brain injury.

Methods

A prospective observational pilot study in a 24-bed pediatric intensive care unit was performed. Twenty-two children aged 7 months to 14 years with moderate to severe traumatic brain injury as indicated by Glasgow Coma Score ≤12 and abnormal head imaging were enrolled. Transcranial Doppler ultrasound was performed to identify and follow vasospasm. Patients with a flow velocity in the middle cerebral artery (MCA) >120 cm/s were considered to have vasospasm by criterion A. If flow velocity in the MCA was >120 cm/s and the Lindegaard ratio was >3, vasospasm was considered to be present by criterion B. Patients with basilar artery (BA) flow velocity >90 cm/s met criteria for vasospasm in the posterior circulation (criterion C).

Results

In the MCA, 45.5% of patients developed vasospasm based on criterion A and 36.3% developed vasospasm based on criterion B. A total of 18.2% of patients developed vasospasm in the BA by criterion C. Typical day of onset of vasospasm was hospital day 2–3. Duration of vasospasm in the anterior circulation was 4 ± 2 days based on criteria A and 3 ± 1 days based on criteria B. Vasospasm in the posterior circulation persisted for 2 ± 1 days.

Conclusions

Using the adult criteria outlined above to diagnose vasospasm, a significant proportion of pediatric patients who have suffered moderate to severe traumatic brain injury develop vasospasm during the course of their treatment.

New transcranial Doppler index in infants with hydrocephalus: transsystolic time in clinical practice

Raised intracranial pressure (ICP) in infants with hydrocephalus may cause (ir)reversible damage to the brain parenchyma but can be present without clinical signs and/or symptoms. Therefore, new, favorably noninvasive, detection methods are needed to distinguish between compensated hydrocephalus with normal intracranial pressure and slowly progressive hydrocephalus with increased intracranial pressure. Because early ischemic changes in the brain parenchyma are associated with increased intracranial pressure, transcranial Doppler (TCD) indices may be useful to detect increased intracranial pressure in infants with hydrocephalus. Twenty-four infants with hydrocephalus underwent noninvasive ICP measurement, magnetic resonance imaging and TCD before and after cerebrospinal fluid (CSF) diversion. The TCD indices were paired to the anterior fontanelle pressure findings and compared for correlation. After CSF diversion, ICP decreased significantly from 21.8 cm H(2)O to 7.7 cm H(2)O (p<0.005). The transsystolic time (TST) as measured with TCD increased significantly from 176 to 221 ms (p<0.005), whereas the pulsatility index (PI) decreased significantly from 1.3 to 1.0 (p<0.05). The resistance index (RI) decreased significantly from 0.73 to 0.63 (p<0.05). Mean bloodflow velocity through the middle cerebral artery increased significantly from 55.5 to 75.8 cm/s (p<0.005). TST has a strong correlation with the ICP (p<0.005). Measuring TST with TCD can be helpful in the decision-making process about whether to perform CSF diversion in infants with hydrocephalus. Because TST is related solely to the relative changes in the flow velocity caused by intracranial physical properties, it has a closer relation to ICP than the PI and the RI.

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.

Intracranial vasospasm with subsequent stroke after traumatic subarachnoid hemorrhage in a 22-month-old child

Clinical and radiographic evidence of subarachnoid hemorrhage (SAH)-related vasospasm is rare in children and has not been reported in infants. In this report the authors present the case of a 22-month-old child who developed clinically symptomatic, radiographically identifiable vasospasm after traumatic SAH. To the authors' knowledge, this is the first report of vasospasm associated with SAH in a child this young. This 22-month-old boy fell and had a dense SAH. He had a history of surgically corrected craniosynostosis and nonsymptomatic ventriculomegaly. The boy was evaluated for occult vascular lesions using imaging; none were found and normal vessel caliber was noted. Ten days later, the child developed left-sided weakness and a right middle cerebral artery infarct was identified. Evaluation disclosed significant intracranial vasospasm. This diagnosis was supported by findings on CT angiography, transcranial Doppler ultrasonography, MR imaging, and conventional angiography. The child was treated using intraarterial verapamil with a good result, as well as with conventional intensive care measures to reduce vasospasm. This report documents the first known case of intracranial vasospasm with stroke after SAH in a patient under the age of 2 years. This finding is important because it demonstrates that the entity of SAH-associated vasospasm can affect the very young, widening the spectrum of ages susceptible to this condition. This case is also important because it demonstrates that even very young children can respond to conventional therapeutic interventions such as intraarterial verapamil. Thus, clinicians need to be alert to the possibility of vasospasm as a potential diagnosis when evaluating young children with SAH.

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

INTRODUCTION

To examine hemispheric differences in cerebral autoregulation in children with traumatic brain injury (TBI). After IRB approval and consent, subjects underwent static cerebral autoregulation testing during the first 9 days after PICU admission. Cerebral autoregulation was quantified using the autoregulatory index (ARI).

RESULTS

Forty-two (27 M:15 F) children (10 +/- 5 years) with TBI and admission Glasgow coma scale score (5 +/- 2) were enrolled. Seven (54%) of the 13 children with focal TBI and 8 (28%) of 29 children with diffuse TBI had impairment or absence of cerebral autoregulation of at least one hemisphere. In patients with isolated focal TBI, ARI was lower (0.40 +/- 0.40 vs. 0.67 +/- 0.40; P = 0.03) in the side of TBI than in the unaffected hemisphere, but cerebral autoregulation was often impaired on the side without TBI or shift (5/13) on head CT. There was no difference in ARI between hemispheres in children with diffuse TBI, with or without superimposed focal lesions (P = 0.17). Patients with bilateral intact cerebral autoregulation tended to have higher 6 month Glasgow Outcome Score (GOS) than patients with either unilateral or bilateral cerebral autoregulation impairment (GOS 4.0 +/- 0.60 vs. 3.6 +/- 0.80; P = 0.08).

CONCLUSIONS

Hemispheric differences in cerebral autoregulation were common in children with isolated focal TBI. Absence of TBI on CT was not always associated with intact cerebral autoregulation. Patients with bilaterally intact cerebral autoregulation tended to have better outcomes.

Cerebral blood flow and autoregulation after pediatric traumatic brain injury

Traumatic brain injury is a global health concern and is the leading cause of traumatic morbidity and mortality in children. Despite a lower overall mortality than in adult traumatic brain injury, the cost to society from the sequelae of pediatric traumatic brain injury is very high. Predictors of poor outcome after traumatic brain injury include altered systemic and cerebral physiology, including altered cerebral hemodynamics. Cerebral autoregulation is often impaired after traumatic brain injury and may adversely impact the outcome. Although altered cerebrovascular hemodynamics early after traumatic brain injury may contribute to disability in children, there is little information regarding changes in cerebral blood flow and cerebral autoregulation after pediatric traumatic brain injury. This review addresses normal pediatric cerebral physiology and cerebrovascular pathophysiology after pediatric traumatic brain injury.

Change in cerebral autoregulation as a function of time in children after severe traumatic brain injury: a case series

OBJECTIVE

The objective of this study was to describe changes in cerebral autoregulation after severe pediatric traumatic brain injury (TBI).

MATERIALS AND METHODS

Two cerebral autoregulation tests were performed during the first 10 days after severe TBI in children <16 years. Cerebral autoregulation was quantified using the mean autoregulatory index (mARI).

RESULTS

Nine (five males/four females) children (10 +/- 5 years) with severe (admission Glasgow Coma Scale (GCS), 5 +/- 2) TBI were enrolled. Thirty (3/9) percent of initial exams revealed impaired cerebral autoregulation; all three had returned to intact cerebral autoregulation on second exam. However, in three of nine (33%) patients, cerebral autoregulation worsened on second exam. Of the factors examined, worsening mARI on second exam was associated with worsening head computed tomography (CT) lesion.

CONCLUSIONS

Cerebral autoregulation often changed and worsened during the first 9 days after severe pediatric TBI. Worsening cerebral autoregulation may mirror worsening TBI.

Early childhood gender differences in anterior and posterior cerebral blood flow velocity and autoregulation

OBJECTIVE

We aimed to describe gender differences in blood flow velocity and autoregulation of the anterior and posterior cerebral circulations in prepubertal children.

METHODS

A prospective observational cohort study was performed at Harborview Medical Center's Cerebrovascular Laboratory after institutional review board approval, consent, and assent procedures. Children underwent measurement of middle cerebral and basilar artery flow velocities and cerebral autoregulation testing of the middle cerebral and basilar arteries. Cerebral autoregulation was quantified using the autoregulatory index, and estimated cerebrovascular resistance was calculated. Autoregulatory index <0.4 reflects impaired cerebral autoregulation. Data are presented as mean +/- SD. Patients were healthy 4- to 8-year-old children.

RESULTS

Forty-eight children (24 boys and 24 girls) 4 to 8 years of age (mean: 6 +/- 2 years) were enrolled. Middle cerebral artery flow velocity was higher than basilar artery flow velocity (96 +/- 13 vs 65 +/- 11 cm/s). Girls had higher middle cerebral artery flow velocity (99 +/- 11 vs 91 +/- 13 cm/s) and basilar artery flow velocity (70 +/- 10 vs 61 +/- 9 cm/s) than boys. Cerebral autoregulation was intact in all children. There was no gender difference in autoregulation between the middle cerebral artery (boys: 0.97 +/- 0.07; girls: 0.94 +/- 0.11) or basilar artery (boys: 0.94 +/- 0.13; girls: 0.94 +/- 0.11).

CONCLUSIONS

Similar to older children and adults, girls between 4 and 8 years of age had higher middle cerebral and basilar artery flow velocity than age-matched boys. This difference may reflect inherent differences in cerebral metabolic rate and/or estimated cerebrovascular resistance between the genders.

Cerebral hyperemia and impaired cerebral autoregulation associated with diabetic ketoacidosis in critically ill children*

OBJECTIVE

Cerebral edema associated with diabetic ketoacidosis is an uncommon but severe complication of insulin-dependent diabetes mellitus with unclear pathophysiology. We sought to determine whether cerebral edema in patients with diabetic ketoacidosis was related to changes in cerebral blood flow, autoregulation, regional cerebral saturation, or S100B.

DESIGN

Prospective case series.

SETTING

Pediatric intensive care unit of a tertiary children's hospital.

PATIENTS

Six patients with diabetic ketoacidosis and altered mental status, requiring computed tomographic scan of the head.

INTERVENTIONS

Study evaluations included: 1) transcranial Doppler evaluations to determine middle cerebral artery flow velocities and cerebral autoregulation, defined by the autoregulatory index, at 6 and 36 hrs; 2) continuous monitoring of regional cerebral oxygenation on the left lateral forehead using near-infrared spectroscopy for the first 24 hrs of admission; 3) serial measurement of S100B as a marker of central nervous system injury; and 4) follow-up head computed tomographic scan.

RESULTS

Serial computed tomographic scans showed that four of six patients had changes in brain volume without overt cerebral edema. Initial scans showed narrowing of the third and lateral ventricles when compared with follow-up. There was no difference in middle cerebral artery flow velocities between admission and recovery at 36 hrs, despite Paco2 increasing during treatment. Cerebral flow was normal to increased, despite hypocapnia. Cerebral autoregulation was impaired in five of six patients at 6 hrs and normalized by 36 hrs. Mean regional cerebral oxygenation was measured in five of six patients and decreased linearly with time. Two patients showed maximal regional cerebral oxygenation before returning to baseline. There were no periods of low regional cerebral oxygenation in any patient at any time. No elevation in S100B was found.

CONCLUSIONS

We found normal to increased cerebral blood flow, elevated regional cerebral oxygenation, impaired autoregulation, and changes in brain volume in clinically ill pediatric patients with diabetic ketoacidosis. We found no evidence of cerebral ischemia. These findings suggest that the pathophysiology of cerebral edema in diabetic ketoacidosis may involve a transient loss of cerebral autoregulation, allowing a paradoxic increase in cerebral blood flow and the development of vasogenic cerebral edema.

Cerebral autoregulation in pediatric traumatic brain injury

OBJECTIVE

The aims of this study were to document the incidence of impaired cerebral autoregulation in children with traumatic brain injury using transcranial Doppler ultrasonography and to examine the relationship between autoregulatory capacity and outcome in children following traumatic brain injury.

DESIGN

Prospective cohort study.

SETTING

Harborview Medical Center (level I pediatric trauma center) in Washington state.

PATIENTS

Thirty-six children <15 yrs old with traumatic brain injury: Glasgow Coma Scale score <9 (n = 12, group 1), Glasgow Coma Scale score 9-12 (n = 12, group 2), and Glasgow Coma Scale score 13-15 (n = 12, group 3).

INTERVENTIONS

Cerebral autoregulation testing was conducted during extracranial surgery. Mean middle cerebral artery flow velocities were measured using transcranial Doppler as mean arterial pressure was increased to whichever variable was greater: 20% above baseline or a set value (80 mm Hg for <9 yrs and 90 mm Hg for 9-14 yrs). Autoregulatory capacity was quantified by the Autoregulatory Index. Autoregulatory Index <0.4 was considered impaired cerebral autoregulation. Discharge outcome using the Glasgow Outcome Scale score was considered good if the Glasgow Outcome Scale score was > or =4.

MEASUREMENTS AND MAIN RESULTS

Twenty-four (67%) of 36 children had an Autoregulatory Index > or =0.4. The incidence of impaired cerebral autoregulation was 42% (five of 12) in group 1, 42% (five of 12) in group 2, and 17% (two of 12) in group 3. Ten (42%) of the 24 children with intact cerebral autoregulation had a good outcome compared with only one of 12 (8%) children with impaired cerebral autoregulation (p =.04). Six of 12 (50%) children with impaired cerebral autoregulation had hyperemia compared with one of 24 (4%) children with intact cerebral autoregulation (p <.01). Hyperemia was associated with poor outcome (p =.01).

CONCLUSIONS

The incidence of impaired cerebral autoregulation was greatest following moderate to severe traumatic brain injury. Impaired cerebral autoregulation was associated with poor outcome. Hyperemia was associated with impaired cerebral autoregulation and poor outcome.