Post-traumatic multimodal brain monitoring: response to hypertonic saline

Leveraging Function Intersectionality and Multi-Modal Cerebrovascular Reactivity Measures for the Derivation of Individualized Intracranial Pressure Thresholds in Acute Traumatic Neural Injury

It has been proposed that subject-specific intracranial pressure (ICP) thresholds can be feasibly derived using the relationship between cerebrovascular reactivity and ICP. Such individualized intracranial pressure (iICP) thresholds have been suggested to have more robust associations with long-term outcomes of post-traumatic brain injury (TBI) than current guideline-based thresholds. However, both existing works have derived iICP using solely the pressure reactivity index (PRx) and a threshold of +0.20. Therefore, the goal of this study was to validate prior works and compare various cerebrovascular reactivity indices for their utility in deriving iICP. A custom iICP derivation algorithm was developed. Then, using existing archived human datasets from the Winnipeg Acute TBI Database, iICP thresholds were derived using three cerebrovascular reactivity indices: PRx, the pulse amplitude index (PAx), and the RAC (correlation (R) between the pulse amplitude of ICP (A) and cerebral perfusion pressure (C)). The yield of iICP derivation was found to vary significantly, depending on the cerebrovascular reactivity index and threshold used. A logistic regression analysis was then used to evaluate and compare the abilities of each index-derived iICP to predict the 6-month outcome. Among all index-threshold combinations tested, only PRx > 0 was able to produce an iICP that was able to outperform guideline-based ICP thresholds. PRx-based iICP seems to be superior to both PAx- and RAC-based iICP for predicting long-term outcomes. However, further work is needed to identify the ideal cerebrovascular reactivity thresholds for iICP derivation.

Characterization of RAP Signal Patterns, Temporal Relationships, and Artifact Profiles Derived from Intracranial Pressure Sensors in Acute Traumatic Neural Injury

GOAL

Current methodologies for assessing cerebral compliance using pressure sensor technologies are prone to errors and issues with inter- and intra-observer consistency. RAP, a metric for measuring intracranial compensatory reserve (and therefore compliance), holds promise. It is derived using the moving correlation between intracranial pressure (ICP) and the pulse amplitude of ICP (AMP). RAP remains largely unexplored in cases of moderate to severe acute traumatic neural injury (also known as traumatic brain injury (TBI)). The goal of this work is to explore the general description of (a) RAP signal patterns and behaviors derived from ICP pressure transducers, (b) temporal statistical relationships, and (c) the characterization of the artifact profile.

METHODS

Different summary and statistical measurements were used to describe RAP's pattern and behaviors, along with performing sub-group analyses. The autoregressive integrated moving average (ARIMA) model was employed to outline the time-series structure of RAP across different temporal resolutions using the autoregressive (p-order) and moving average orders (q-order). After leveraging the time-series structure of RAP, similar methods were applied to ICP and AMP for comparison with RAP. Finally, key features were identified to distinguish artifacts in RAP. This might involve leveraging ICP/AMP signals and statistical structures.

RESULTS

The mean and time spent within the RAP threshold ranges ([0.4, 1], (0, 0.4), and [-1, 0]) indicate that RAP exhibited high positive values, suggesting an impaired compensatory reserve in TBI patients. The median optimal ARIMA model for each resolution and each signal was determined. Autocorrelative function (ACF) and partial ACF (PACF) plots of residuals verified the adequacy of these median optimal ARIMA models. The median of residuals indicates that ARIMA performed better with the higher-resolution data. To identify artifacts, (a) ICP q-order, AMP p-order, and RAP p-order and q-order, (b) residuals of ICP, AMP, and RAP, and (c) cross-correlation between residuals of RAP and AMP proved to be useful at the minute-by-minute resolution, whereas, for the 10-min-by-10-min data resolution, only the q-order of the optimal ARIMA model of ICP and AMP served as a distinguishing factor.

CONCLUSIONS

RAP signals derived from ICP pressure sensor technology displayed reproducible behaviors across this population of TBI patients. ARIMA modeling at the higher resolution provided comparatively strong accuracy, and key features were identified leveraging these models that could identify RAP artifacts. Further research is needed to enhance artifact management and broaden applicability across varied datasets.

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.

The impact of sedative and vasopressor agents on cerebrovascular reactivity in severe traumatic brain injury

BACKGROUND

The aim of this study is to evaluate the impact of commonly administered sedatives (Propofol, Alfentanil, Fentanyl, and Midazolam) and vasopressor (Dobutamine, Ephedrine, Noradrenaline and Vasopressin) agents on cerebrovascular reactivity in moderate/severe TBI patients. Cerebrovascular reactivity, as a surrogate for cerebral autoregulation was assessed using the long pressure reactivity index (LPRx). We evaluated the data in two phases, first we assessed the minute-by-minute data relationships between different dosing amounts of continuous infusion agents and physiological variables using boxplots, multiple linear regression and ANOVA. Next, we assessed the relationship between continuous/bolus infusion agents and physiological variables, assessing pre-/post- dose of medication change in physiology using a Wilcoxon signed-ranked test. Finally, we evaluated sub-groups of data for each individual dose change per medication, focusing on key physiological thresholds and demographics.

RESULTS

Of the 475 patients with an average stay of 10 days resulting in over 3000 days of recorded information 367 (77.3%) were male with a median Glasgow coma score of 7 (4-9). The results of this retrospective observational study confirmed that the infusion of most administered agents do not impact cerebrovascular reactivity, which is confirmed by the multiple linear regression components having p value > 0.05. Incremental dose changes or bolus doses in these medications in general do not lead to significant changes in cerebrovascular reactivity (confirm by Wilcoxon signed-ranked p value > 0.05 for nearly all assessed relationships). Within the sub-group analysis that separated the data based on LPRx pre-dose, a significance between pre-/post-drug change in LPRx was seen, however this may be more of a result from patient state than drug impact.

CONCLUSIONS

Overall, this study indicates that commonly administered agents with incremental dosing changes have no clinically significant influence on cerebrovascular reactivity in TBI (nor do they impair cerebrovascular reactivity). Though further investigation in a larger and more diverse TBI patient population is required.

A Brief Review of Bolus Osmotherapy Use for Managing Severe Traumatic Brain Injuries in the Pre-Hospital and Emergency Department Settings

Background: Severe traumatic brain injury (TBI) management begins in the pre-hospital setting, but clinicians are left with limited options for stabilisation during retrieval due to time and space constraints, as well as a lack of access to monitoring equipment. Bolus osmotherapy with hypertonic substances is commonly utilised as a temporising measure for life-threatening brain herniation, but much contention persists around its use, largely stemming from a limited evidence base. Method: The authors conducted a brief review of hypertonic substance use in patients with TBI, with a particular focus on studies involving the pre-hospital and emergency department (ED) settings. We aimed to report pragmatic information useful for clinicians involved in the early management of this patient group. Results: We reviewed the literature around the pharmacology of bolus osmotherapy, commercially available agents, potential pitfalls, supporting evidence and guideline recommendations. We further reviewed what the ideal agent is, when it should be administered, dosing and treatment endpoints and/or whether it confers meaningful long-term outcome benefits. Conclusions: There is a limited evidence-based argument in support of the implementation of bolus osmotherapy in the pre-hospital or ED settings for patients who sustain a TBI. However, decades’ worth of positive clinician experiences with osmotherapy for TBI will likely continue to drive its on-going use. Choices regarding osmotherapy will likely continue to be led by local policies, individual patient characteristics and clinician preferences.

Cerebral Autoregulation Monitoring in Traumatic Brain Injury: An Overview of Recent Advances in Personalized Medicine

Impaired cerebral autoregulation (CA) in moderate/severe traumatic brain injury (TBI) has been identified as a strong associate with poor long-term outcomes, with recent data highlighting its dominance over cerebral physiologic dysfunction seen in the acute phase post injury. With advances in bedside continuous cerebral physiologic signal processing, continuously derived metrics of CA capacity have been described over the past two decades, leading to improvements in cerebral physiologic insult detection and development of novel personalized approaches to TBI care in the intensive care unit (ICU). This narrative review focuses on highlighting the concept of continuous CA monitoring and consequences of impairment in moderate/severe TBI. Further, we provide a comprehensive description and overview of the main personalized cerebral physiologic targets, based on CA monitoring, that are emerging as strong associates with patient outcomes. CA-based personalized targets, such as optimal cerebral perfusion pressure (CPPopt), lower/upper limit of regulation (LLR/ULR), and individualized intra-cranial pressure (iICP) are positioned to change the way we care for TBI patients in the ICU, moving away from the "one treatment fits all" paradigm of current guideline-based therapeutic approaches, towards a true personalized medicine approach tailored to the individual patient. Future perspectives regarding research needs in this field are also discussed.

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.

Cerebrovascular Autoregulation Monitoring in the Management of Adult Severe Traumatic Brain Injury: A Delphi Consensus of Clinicians

BACKGROUND

Several methods have been proposed to measure cerebrovascular autoregulation (CA) in traumatic brain injury (TBI), but the lack of a gold standard and the absence of prospective clinical data on risks, impact on care and outcomes of implementation of CA-guided management lead to uncertainty.

AIM

To formulate statements using a Delphi consensus approach employing a group of expert clinicians, that reflect current knowledge of CA, aspects that can be implemented in TBI management and CA research priorities.

METHODS

A group of 25 international academic experts with clinical expertise in the management of adult severe TBI patients participated in this consensus process. Seventy-seven statements and multiple-choice questions were submitted to the group in two online surveys, followed by a face-to-face meeting and a third online survey. Participants received feedback on average scores and the rationale for resubmission or rephrasing of statements. Consensus on a statement was defined as agreement of more than 75% of participants.

RESULTS

Consensus amongst participants was achieved on the importance of CA status in adult severe TBI pathophysiology, the dynamic non-binary nature of CA impairment, its association with outcome and the inadvisability of employing universal and absolute cerebral perfusion pressure targets. Consensus could not be reached on the accuracy, reliability and validation of any current CA assessment method. There was also no consensus on how to implement CA information in clinical management protocols, reflecting insufficient clinical evidence.

CONCLUSION

The Delphi process resulted in 25 consensus statements addressing the pathophysiology of impaired CA, and its impact on cerebral perfusion pressure targets and outcome. A research agenda was proposed emphasizing the need for better validated CA assessment methods as well as the focused investigation of the application of CA-guided management in clinical care using prospective safety, feasibility and efficacy studies.

Secondary Cerebral Ischemia at Traumatic Brain Injury Is More Closely Related to Cerebrovascular Reactivity Impairment than to Intracranial Hypertension

The purpose of this study was to investigate the relationship between the development of secondary cerebral ischemia (SCI), intracranial pressure (ICP) and cerebrovascular reactivity (CVR) after traumatic brain injury (TBI).

METHODS

89 patients with severe TBI with ICP monitoring were studied retrospectively. The mean age was 36.3 ± 4.8 years, 53 men, 36 women. The median Glasgow Coma Score (GCS) was 6.2 ± 0.7. The median Injury Severity Score was 38.2 ± 12.5. To specify the degree of impact of changes in ICP and CVR on the SCI progression in TBI patients, logistic regression was performed. Significant p-values were <0.05.

RESULTS

The deterioration of CVR in combination with the severity of ICP has a significant impact on the increase in the prevalence rate of SCI. A logistic regression analysis for a model of SCI dependence on intracranial hypertension and CVR was performed. The results of the analysis showed that CVR was the most significant factor affecting SCI development in TBI.

CONCLUSIONS

The development of SCI in severe TBI depends largely on CVR impairment and to a lesser extent on ICP level. Treatment for severe TBI patients with SCI progression should not be aimed solely at intracranial hypertension correction but also at CVR recovery.

Escalate and De-Escalate Therapies for Intracranial Pressure Control in Traumatic Brain Injury

Severe traumatic brain injury (TBI) is frequently associated with an elevation of intracranial pressure (ICP), followed by cerebral perfusion pressure (CPP) reduction. Invasive monitoring of ICP is recommended to guide a step-by-step “staircase approach” which aims to normalize ICP values and reduce the risks of secondary damage. However, if such monitoring is not available clinical examination and radiological criteria should be used. A major concern is how to taper the therapies employed for ICP control. The aim of this manuscript is to review the criteria for escalating and withdrawing therapies in TBI patients. Each step of the staircase approach carries a risk of adverse effects related to the duration of treatment. Tapering of barbiturates should start once ICP control has been achieved for at least 24 h, although a period of 2–12 days is often required. Administration of hyperosmolar fluids should be avoided if ICP is normal. Sedation should be reduced after at least 24 h of controlled ICP to allow neurological examination. Removal of invasive ICP monitoring is suggested after 72 h of normal ICP. For patients who have undergone surgical decompression, cranioplasty represents the final step, and an earlier cranioplasty (15–90 days after decompression) seems to reduce the rate of infection, seizures, and hydrocephalus.

Hypertonic Saline for Moderate Traumatic Brain Injury: A Scoping Review of Impact on Neurological Deterioration

Hypertonic saline (HTS) is a commonly administered agent for intracranial pressure (ICP) control in traumatic brain injury (TBI). The literature on its use is mainly in moderate/severe TBI where invasive ICP monitoring is present. The role of HTS in patients with moderate TBI (mTBI) outside of the intensive care unit (ICU) setting remains unclear. The goal of this scoping review was to provide an overview of the available literature on HTS administration in patients with mTBI without ICP monitoring, assessing its impact on outcome and transitions in care. We performed a scoping systematic review of the literature of MEDLINE, Embase, Scopus, BIOSIS, and the Cochrane Databases from inception to July 31, 2020. We searched for those published articles documenting the administration of HTS in patients with mTBI with recorded functional outcome or transitions in hospital care. A two-step review process was conducted in accordance with methodology outlined in the Cochrane Handbook for Systematic Reviews of Interventions. There were many studies with combined moderate/severe TBI populations. However, most failed to document subgroup analysis for patients with mTBI. Our search strategy identified only one study that documented the administration of HTS in mTBI in which subgroup analysis for mTBI and outcomes were provided. This retrospective cohort study assessed patients with mTBI who did/did not receive prophylactic HTS, finding that those not receiving HTS demonstrated a deterioration in Glasgow Coma Scale (GCS) score in the first 48 h. However, the HTS group did demonstrate a trend to longer hospital stay and pneumonia. Our scoping review identified a significant gap in knowledge surrounding the use of HTS for patients with mTBI without invasive ICP monitoring. The limited identified literature suggests prophylactic administration prevents clinical deterioration, although this is based on a single study with data available for mTBI sub-analysis. Further studies on HTS in non-monitored patients with mTBI are required.

Immunomodulatory Effect of Hypertonic Saline Solution in Traumatic Brain-Injured Patients and Intracranial Hypertension

Traumatic brain injury (TBI) is often associated with an increase in the intracranial pressure (ICP). This increase in ICP can cross the physiological range and lead to a reduction in cerebral perfusion pressure (CPP) and the resultant cerebral blood flow (CBF). It is this reduction in the CBF that leads to the secondary damage to the neural parenchyma along with the physical axonal and neuronal damage caused by the mass effect. In certain cases, a surgical intervention may be required to either remove the mass lesion (hematoma of contusion evacuation) or provide more space to the insulted brain to expand (decompressive craniectomy). Whether or not a surgical intervention is performed, all these patients require some form of pharmaceutical antiedema agents to bring down the raised ICP. These agents have been broadly classified as colloids (e.g., mannitol, glycerol, urea) and crystalloids (e.g., hypertonic saline), and have been used since decades. Even though mannitol has been the workhorse for ICP reduction owing to its unique properties, crystalloids have been found to be the preferred agents, especially when long-term use is warranted. The safest and most widely used agent is hypertonic saline in various concentrations. Whatever be the concentration, hypertonic saline has created special interest among physicians owing to its additional property of immunomodulation and neuroprotection. In this review, we summarize and understand the various mechanism by which hypertonic saline exerts its immunomodulatory effects that helps in neuroprotection after TBI.

Paths to Successful Translation of New Therapies for Severe Traumatic Brain Injury in the Golden Age of Traumatic Brain Injury Research: A Pittsburgh Vision

New neuroprotective therapies for severe traumatic brain injury (TBI) have not translated from pre-clinical to clinical success. Numerous explanations have been suggested in both the pre-clinical and clinical arenas. Coverage of TBI in the lay press has reinvigorated interest, creating a golden age of TBI research with innovative strategies to circumvent roadblocks. We discuss the need for more robust therapies. We present concepts for traditional and novel approaches to defining therapeutic targets. We review lessons learned from the ongoing work of the pre-clinical drug and biomarker screening consortium Operation Brain Trauma Therapy and suggest ways to further enhance pre-clinical consortia. Biomarkers have emerged that empower choice and assessment of target engagement by candidate therapies. Drug combinations may be needed, and it may require moving beyond conventional drug therapies. Precision medicine may also link the right therapy to the right patient, including new approaches to TBI classification beyond the Glasgow Coma Scale or anatomical phenotyping-incorporating new genetic and physiologic approaches. Therapeutic breakthroughs may also come from alternative approaches in clinical investigation (comparative effectiveness, adaptive trial design, use of the electronic medical record, and big data). The full continuum of care must also be represented in translational studies, given the important clinical role of pre-hospital events, extracerebral insults in the intensive care unit, and rehabilitation. TBI research from concussion to coma can cross-pollinate and further advancement of new therapies. Misconceptions can stifle/misdirect TBI research and deserve special attention. Finally, we synthesize an approach to deliver therapeutic breakthroughs in this golden age of TBI research.

Impaired Dynamic Cerebral Autoregulation in Cerebral Venous Thrombosis

Background: Cerebral autoregulation is crucial in traumatic brain injury, which might be used for determining the optimal intracranial pressure. Cerebral venous thrombosis (CVT) is a cerebral vascular disease with features of high intracranial pressure. However, the autoregulatory mechanism of CVT remains unknown. We aimed to investigate the capacity of cerebral autoregulation in patients with CVT. Methods: This study consecutively enrolled 23 patients with CVT and 16 controls from December 2018 to May 2019. Cerebral autoregulation was assessed by transfer function analysis (rate of recovery/phase/gain) using the spontaneous oscillations of the cerebral blood flow velocity and arterial blood pressure. Results: In total, 76 middle cerebral arteries (MCAs) were investigated, including 44 MCAs in patients with CVT and 32 normal ones. The phase shift estimated in patients with CVT was significantly different from that of the controls (37.37 ± 36.53 vs. 54.00 ± 26.78, p = 0.03). The rate of recovery and gain in patients with CVT were lower than those in controls but without statistical significance. Conclusion: To our knowledge, this is the first time that a study has indicated that patients with CVT were more likely to have impaired cerebral autoregulation. Hence, cautious blood pressure control is required in such patients to prevent hyper- or hypoperfusion.

The impact of hypertonic saline on cerebrovascular reactivity and compensatory reserve in traumatic brain injury: an exploratory analysis

Background

Intravenous hypertonic saline is utilized commonly in critical care for treatment of acute or refractory elevations of intracranial pressure (ICP) in traumatic brain injury (TBI) patients. Though there is a clear understanding of the general physiological effects of a hypertonic saline solution over long periods of time, smaller epoch effects of hypertonic saline (HTS) have not been thoroughly analyzed. The aim of this study was to perform a direct evaluation of the high-frequency response of HTS on the cerebrovascular physiological responses in TBI.

Methods

We retrospectively reviewed our prospectively maintained adult TBI database for those with archived high-frequency cerebral physiology and available HTS treatment information. We evaluated different epochs of physiology around HTS bolus dosing, comparing pre- with post-HTS. We assessed for changes in slow fluctuations in ICP, pulse amplitude of ICP (AMP), cerebral perfusion pressure (CPP), mean arterial pressure (MAP), cerebrovascular reactivity (as measured through pressure reactivity index (PRx)), and cerebral compensatory reserve (correlation (R) between AMP (A) and ICP (P)). Comparisons of mean measures and percentage time above clinically relevant thresholds for the physiological parameters were compared pre- and post-HTS using descriptive statistics and Mann-Whitney U testing. We assessed for subgroups of physiological responses using latent profile analysis (LPA).

Results

Fifteen patients underwent 69 distinct bolus infusions of hypertonic saline. Apart from the well-documented decrease in ICP, there was also a reduction in AMP. The analysis of cerebrovascular reactivity response to HTS solution had two main effects. For patients with grossly impaired cerebrovascular reactivity pre-HTS (PRx > + 0.30), HTS bolus led to improved reactivity. However, for those with intact cerebrovascular reactivity pre-HTS (PRx < 0), HTS bolus demonstrated a trend towards more impaired reactivity. This indicates that HTS has different impacts, dependent on pre-bolus cerebrovascular status. There was no significant change in metrics of cerebral compensatory reserve. LPA failed to demonstrate any subgroups of physiological responses to HTS administration.

Conclusions

The direct decrease in ICP and AMP confirms that a bolus dose of a HTS solution is an effective therapeutic agent for intracranial hypertension. However, in patients with intact autoregulation, hypertonic saline may impair cerebral hemodynamics. These findings regarding cerebrovascular reactivity remain preliminary and require further investigation.

Electronic supplementary material

The online version of this article (10.1007/s00701-020-04579-0) contains supplementary material, which is available to authorized users.

The Limited Impact of Current Therapeutic Interventions on Cerebrovascular Reactivity in Traumatic Brain Injury: A Narrative Overview

Current intensive care unit (ICU) treatment strategies for traumatic brain injury (TBI) care focus on intracranial pressure (ICP)- and cerebral perfusion pressure (CPP)-directed therapeutics, dictated by guidelines. Impaired cerebrovascular reactivity in moderate/severe TBI is emerging as a major associate with poor outcome and appears to dominate the landscape of physiologic derangement over the course of a patient's ICU stay. Within this article, we review the literature on the known drivers of impaired cerebrovascular reactivity in adult TBI, highlight the current knowledge surrounding the impact of guideline treatment strategies on continuously monitored cerebrovascular reactivity, and discuss current treatment paradigms for impaired reactivity. Finally, we touch on the areas of future research, as we strive to develop specific therapeutics for impaired cerebrovascular reactivity in TBI. There exists limited literature to suggest advanced age, intracranial injury patterns of diffuse injury, and sustained ICP elevations may drive impaired cerebrovascular reactivity. To date, the literature suggests there is a limited impact of such ICP/CPP guideline-based therapies on cerebrovascular reactivity, with large portions of a given patients ICU period spent with impaired cerebrovascular reactivity. Emerging treatment paradigms focus on the targeting individualized CPP and ICP thresholds based on cerebrovascular reactivity, without directly targeting the pathways involved in its dysfunction. Further work involved in uncovering the molecular pathways involved in impaired cerebrovascular reactivity is required, so that we can develop therapeutics directed at its prevention and treatment.

Continuous cerebrovascular reactivity monitoring in moderate/severe traumatic brain injury: a narrative review of advances in neurocritical care

Impaired cerebrovascular reactivity in adult moderate and severe traumatic brain injury (TBI) is known to be associated with worse global outcome at 6-12 months. As technology has improved over the past decades, monitoring of cerebrovascular reactivity has shifted from intermittent measures, to experimentally validated continuously updating indices at the bedside. Such advances have led to the exploration of individualised physiologic targets in adult TBI management, such as optimal cerebral perfusion pressure (CPP) values, or CPP limits in which vascular reactivity is relatively intact. These targets have been shown to have a stronger association with outcome compared with existing consensus-based guideline thresholds in severe TBI care. This has sparked ongoing prospective trials of such personalised medicine approaches in adult TBI. In this narrative review paper, we focus on the concept of cerebral autoregulation, proposed mechanisms of control and methods of continuous monitoring used in TBI. We highlight multimodal cranial monitoring approaches for continuous cerebrovascular reactivity assessment, physiologic and neuroimaging correlates, and associations with outcome. Finally, we explore the recent 'state-of-the-art' advances in personalised physiologic targets based on continuous cerebrovascular reactivity monitoring, their benefits, and implications for future avenues of research in TBI.

Venous sinus stenting improves cerebral autoregulation in a patient with venous sinus stenosis: a case report

BACKGROUND

Venous sinus stenosis (VSS) is a type of cerebral venous vascular disease. Cerebral autoregulation is an indicator of cerebral arterial function. The cerebral circulatory system is composed of the venous system and arterial system. Impaired venous function may affect arterial function. Thus, cerebral venous stenosis may influence cerebral autoregulation.

CASE PRESENTATION

In this case, a 50-year-old woman with transient blindness and headache was admitted to the hospital. The patient was diagnosed with VSS. A stent was placed at the stenosis. The stent released the intravenous pressure and remitted the patient's symptoms. Measurements of dynamic cerebral autoregulation (dCA) were performed at 3 time points: before stenting, after stenting, and 3 months later. The dCA gradually improved after stenting.

CONCLUSION

VSS may have an influence on cerebral autoregulation, and effective treatment improves cerebral autoregulation in patients with VSS.

Higher Concentration of Hypertonic Saline Shows Better Recovery Effects on Rabbits with Uncontrolled Hemorrhagic Shock

Background

Our previous study found a novel fluid combination with better resuscitation effects under hypotensive condition at the early stage of uncontrolled hemorrhagic shock (UHS). However, the optimal recovery concentration of hypertonic saline in this fluid combination remains unknown. This experiment aimed to explore the optimal concentration.

Material/Methods

New Zealand white rabbits (n=40) were randomly divided into 5 groups, including a sham-operated group (SO), a shock non-treated group (SNT), a normal saline group (NS), and hypertonic saline groups (4.5% and 7.5%). We established an UHS model and administered various fluid combinations (dose-related sodium chloride solution+crystal-colloidal solution) to the groups followed by monitoring indexes of hemodynamic and renal function, measuring infusion volume and blood loss, and analyzing pathological morphology by hematoxylin and eosin staining.

Results

The hypertonic saline groups showed more stable hemodynamic indexes, reduced blood loss, fewer required infusions, and milder decreases in renal function than those of control groups (SNT and NS groups), and exhibited fewer pathological changes in the heart, lung, kidney, and liver. All indexes in the 4.5% and 7.5% groups were better than those of the NS group, and the hemodynamic indexes in the 7.5% group were more stable than those of the 4.5% group (P<0.05), with reduced blood loss and infusion volume and a milder decrease in renal function.

Conclusions

The novel fluid combination with 7.5% hypertonic saline group had a better recovery effect at the early stage of UHS before hemostasis compared to that of the 4.5% hypertonic saline group. This result may provide guidance for clinical fluid resuscitation.

Continuous Thermal Diffusion-Based Cerebral Blood Flow Monitoring in Adult Traumatic Brain Injury: A Scoping Systematic Review

Thermal diffusion flowmetry (TDF) is an appealing candidate for monitoring of cerebral blood flow (CBF) in neurocritical-care patients as it provides absolute measurements with a high temporal resolution, potentially allowing for bedside intervention that could mitigate secondary injury. We performed a systematic review of TDF-regional(r)CBF measurements and their association with (1) patient functional outcome, (2) other neurophysiological parameters, and (3) imaging-based tissue outcomes. We searched MEDLINE, EMBASE, SCOPUS, BIOSIS, GlobalHealth, and the Cochrane Databases from inception to October 2018 and relevant conference proceedings published over the last 5 years. Nine articles that explored the relationship between TDF-rCBF, mortality, and Glasgow Outcome Scale (GOS) or GOS-Extended (GOS-E) at various intervals were included. Despite being based on an overall weak body of evidence, our analysis suggests a link between sustained low or high CBF and poor functional outcome. Twenty-five studies reporting associations with neurophysiological parameters were included. The available data also point to an association between low or high TDF-rCBF and intracranial hypertension. TDF-rCBF appears to correlate well with regional brain tissue oxygenation measurements. We found no studies reporting on imaging-based tissue outcome in relation to TDF. In conclusion, despite being based on a relatively weak body of evidence, the available literature suggests a link between consistently abnormal TDF-rCBF values, intracranial hypertension, and poor functional outcome. TDF-rCBF also appears to correlate well with regional measurements of brain tissue oxygenation. Currently, such monitoring should be considered experimental, requiring much further evaluation prior to widespread adoption.

The Effects of Induction and Treatment of Intracranial Hypertension on Cerebral Autoregulation: An Experimental Study

Background

This study aimed to analyse cerebral autoregulation (CA) during induction and treatment of intracranial hypertension (ICH) in an experimental model.

Materials and Methods

Landrace and Duroc piglets were divided into mild and severe ICH groups. Four or seven millilitres of saline solution was infused into paediatric bladder catheter inserted in the parietal lobe (balloon inflation). After 1.5 h, a 3% saline solution was infused via venous catheter, and 30 min later, the bladder catheter balloon was deflated (surgery). The cerebral static autoregulation (sCA) index was evaluated using cerebral blood flow velocities (CBFV) obtained with Doppler ultrasound.

Results

Balloon inflation increased ICP in both groups. The severe ICH group showed significantly lower sCA index values (p=0.001, ANOVA) after balloon inflation (ICH induction) and a higher sCA index after saline injection (p=0.02) and after surgery (p=0.04). ICP and the sCA index were inversely correlated (r=-0.68 and p<0.05). CPP and the sCA index were directly correlated (r=0.74 and p<0.05).

Conclusion

ICH was associated with local balloon expansion, which triggered CA impairment, particularly in the severe ICH group. Moreover, ICP-reducing treatments were associated with improved CA in subjects with severe ICH.

Different resuscitation strategies and novel pharmacologic treatment with valproic acid in traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of death in young adults, and effective treatment strategies have the potential to save many lives. TBI results in coagulopathy, endothelial dysfunction, inflammation, cell death, and impaired epigenetic homeostasis, ultimately leading to morbidity and/or mortality. Commonly used resuscitation fluids such as crystalloids or colloids have several disadvantages and might even be harmful when administered in large quantities. There is a need for next-generation treatment strategies (especially in the prehospital setting) that minimize cellular damage, improve survival, and enhance neurological recovery. Pharmacologic treatment with histone deacetylase inhibitors, such as valproic acid, has shown promising results in animal studies of TBI and may therefore be an excellent example of next-generation therapy. This review briefly describes traditional resuscitation strategies for TBI combined with hemorrhagic shock and describes preclinical studies on valproic acid as a new pharmacologic agent in the treatment of TBI. It finally discusses limitations and future directions on the use of histone deacetylase inhibitors for the treatment of TBI.

Intracranial Hypertension and Cerebral Autoregulation: A Systematic Review and Meta-Analysis

OBJECTIVE

To present a systematic review and meta-analysis to establish the relation between cerebral autoregulation (CA) and intracranial hypertension.

METHODS

An electronic search using the term "Cerebral autoregulation and intracranial hypertension" was designed to identify studies that analyzed cerebral blood flow autoregulation in patients undergoing intracranial pressure (ICP) monitoring. The data were used in meta-analyses and sensitivity analyses.

RESULTS

A static CA technique was applied in 10 studies (26.3%), a dynamic technique was applied in 25 studies (65.8%), and both techniques were used in 3 studies (7.9%). Static CA studies using the cerebral blood flow technique revealed impaired CA in patients with an ICP ≥20 (standardized mean difference [SMD] 5.44%, 95% confidence interval [CI] 0.25-10.65, P = 0.04); static CA studies with transcranial Doppler revealed a tendency toward impaired CA in patients with ICP ≥20 (SMD -7.83%, 95% CI -17.52 to 1.85, P = 0.11). Moving correlation studies reported impaired CA in patients with ICP ≥20 (SMD 0.06, 95% CI 0.07-0.14, P < 0.00001). A comparison of CA values and mean ICP revealed a correlation between greater ICP and impaired CA (SMD 5.47, 95% CI 1.39-10.1, P = 0.01). Patients with ICP ≥20 had an elevated risk of impaired CA (OR 2.27, 95% CI 1.20-4.31, P = 0.01).

CONCLUSIONS

A clear tendency toward CA impairment was observed in patients with increased ICP.

A narrative review of the clinical application of pressure reactiviy indices in the neurocritical care unit

Pressure reactivity indices are used in clinical research as a surrogate marker of the ability of the cerebrovasculature to maintain cerebral autoregulation. The use of pressure reactivity indices in patients with neurological injury represents a potential to move away from population-based physiological targets used in guidelines to individualized physiological targets. The aim of this review is to describe the underlying principles and development of pressure reactivity indices, alongside a critique of how they have been used in clinical research, including their limitations. The primary source literature was identified from a database search of PUBMed and OVID online using the search terms "pressure reactivity index" and "pressure reactivity indices". The evidence base regarding pressure reactivity indices currently remains Level III. Pressure reactivity indices rely on the correlation (-1 to +1) between the arterial blood pressure and intracranial pressure, with negative values indicating intact cerebral autoregulation and positive values indicating dysfunctional cerebral autoregulation. Meaningful data is taken from summary measures and trends. The traumatic brain injury population feature most prominently in the literature. There is limited description of the potential confounding factors that may affect pressure reactivity indices, including physiological parameters and therapeutic interventions. Plotting a pressure reactivity index against a cerebral perfusion pressure can indicate an optimal cerebral perfusion pressure to individualise patient care. There is potential to over interpret optimal cerebral perfusion pressure targets when the values of pressure reactivity indices are close to zero. There is an association between pressure reactivity indices and neurological outcomes, however the use of pressure reactivity indices as a prognostication tool is to be challenged. Average values of cerebral perfusion pressure that are not close to averaged values of optimal cerebral perfusion pressure are also associated with poor outcome. Further research is required to ascertain whether targeting an optimal cerebral perfusion pressure may alter outcome.

Pressure Autoregulation Measurement Techniques in Adult Traumatic Brain Injury, Part II: A Scoping Review of Continuous Methods

A scoping review of the literature was performed systematically on commonly described continuous autoregulation measurement techniques in adult traumatic brain injury (TBI) to provide an overview of methodology and comprehensive reference library of the available literature for each technique. Five separate small systematic reviews were conducted for each of the continuous techniques: pressure reactivity index (PRx), laser Doppler flowmetry (LDF), near infrared spectroscopy (NIRS) techniques, brain tissue oxygen tension (PbtO2), and thermal diffusion (TD) techniques. Articles from MEDLINE, BIOSIS, EMBASE, Global Health, Scopus, Cochrane Library (inception to December 2016), and reference lists of relevant articles were searched. A two-tier filter of references was conducted. The literature base identified from the individual searches was limited, except for PRx. The total number of articles using each of the five searched techniques for continuous autoregulation in adult TBI were: PRx (28), LDF (4), NIRS (9), PbtO2 (10), and TD (8). All continuous techniques described in adult TBI are based on moving correlation coefficients. The premise behind the calculation of these moving correlation coefficients focuses on the impact of slow fluctuations in either mean arterial pressure (MAP) or cerebral perfusion pressure (CPP) on some indirect measure of cerebral blood flow (CBF), such as: intracranial pressure (ICP), LDF, NIRS signals, PbtO2, or TD CBF. The thought is the correlation between a hemodynamic driving factor, such as MAP or CPP, and a surrogate for CBF or cerebral perfusion sheds insight on the state of cerebral autoregulation. Both PRx and NIRS indices were validated experimentally against the "gold standard" static autoregulatory curve (Lassen curve) at least around the lower threshold of autoregulation. The PRx has the largest literature base supporting the association with patient outcome. Various methods of continuous autoregulation assessment are described within the adult TBI literature. Many studies exist on these various indices, suggesting an association between their values and patient morbidity/death.

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.

A Comparison of Pharmacologic Therapeutic Agents Used for the Reduction of Intracranial Pressure After Traumatic Brain Injury

OBJECTIVE

In neurotrauma care, a better understanding of treatments after traumatic brain injury (TBI) has led to a significant decrease in morbidity and mortality in this population. TBI represents a significant medical problem, and complications after TBI are associated with the initial injury and postevent intracranial processes such as increased intracranial pressure and brain edema. Consequently, appropriate therapeutic interventions are required to reduce brain tissue damage and improve cerebral perfusion. We present a contemporary review of literature on the use of pharmacologic therapies to reduce intracranial pressure after TBI and a comparison of their efficacy.

METHODS

This review was conducted by PubMed query. Only studies discussing pharmacologic management of patients after TBI were included. This review includes prospective and retrospective studies and includes randomized controlled trials as well as cohort, case-control, observational, and database studies. Systematic literature reviews, meta-analyses, and studies that considered conditions other than TBI or pediatric populations were not included.

RESULTS

Review of the literature describing the current pharmacologic treatment for intracranial hypertension after TBI most often discussed the use of hyperosmolar agents such as hypertonic saline and mannitol, sedatives such as fentanyl and propofol, benzodiazepines, and barbiturates. Hypertonic saline is associated with faster resolution of intracranial hypertension and restoration of optimal cerebral hemodynamics, although these advantages did not translate into long-term benefits in morbidity or mortality. In patients refractory to treatment with hyperosmolar therapy, induction of a barbiturate coma can reduce intracranial pressure, although requires close monitoring to prevent adverse events.

CONCLUSIONS

Current research suggests that the use of hypertonic saline after TBI is the best option for immediate decrease in intracranial pressure. A better understanding of the efficacy of each treatment option can help to direct treatment algorithms during the critical early hours of trauma care and continue to improve morbidity and mortality after TBI.

Chronic Histopathological and Behavioral Outcomes of Experimental Traumatic Brain Injury in Adult Male Animals

The purpose of this review is to survey the use of experimental animal models for studying the chronic histopathological and behavioral consequences of traumatic brain injury (TBI). The strategies employed to study the long-term consequences of TBI are described, along with a summary of the evidence available to date from common experimental TBI models: fluid percussion injury; controlled cortical impact; blast TBI; and closed-head injury. For each model, evidence is organized according to outcome. Histopathological outcomes included are gross changes in morphology/histology, ventricular enlargement, gray/white matter shrinkage, axonal injury, cerebrovascular histopathology, inflammation, and neurogenesis. Behavioral outcomes included are overall neurological function, motor function, cognitive function, frontal lobe function, and stress-related outcomes. A brief discussion is provided comparing the most common experimental models of TBI and highlighting the utility of each model in understanding specific aspects of TBI pathology. The majority of experimental TBI studies collect data in the acute postinjury period, but few continue into the chronic period. Available evidence from long-term studies suggests that many of the experimental TBI models can lead to progressive changes in histopathology and behavior. The studies described in this review contribute to our understanding of chronic TBI pathology.

Trending autoregulatory indices during treatment for traumatic brain injury

Our goal is to use automatic data monitoring for reliable prediction of episodes of intracranial hypertension in patients with traumatic brain injury. Here we test the validity of our method on retrospective patient data. We developed the Continuous Hemodynamic Autoregulatory Monitor (CHARM), that siphons and stores signals from existing monitors in the surgical intensive care unit (SICU), efficiently compresses them, and standardizes the search for statistical relationships between any proposed index and adverse events. CHARM uses an automated event detector to reliably locate episodes of elevated intracranial pressure (ICP), while eliminating artifacts within retrospective patient data. A graphical user interface allowed data scanning, selection of criteria for events, and calculating indices. The pressure reactivity index (PRx), defined as the least square linear regression slope of intracranial pressure versus arterial BP, was calculated for a single case that spanned 259 h. CHARM collected continuous records of ABP, ICP, ECG, SpO2, and ventilation from 29 patients with TBI over an 18-month period. Analysis of a single patient showed that PRx data distribution in the single hours immediately prior to all 16 intracranial hypertensive events, significantly differed from that in the 243 h that did not precede such events (p < 0.0001). The PRx index, however, lacked sufficient resolution as a real-time predictor of IH in this patient. CHARM streamlines the search for reliable predictors of intracranial hypertension. We report statistical evidence supporting the predictive potential of the pressure reactivity index.

Clinical evidence of inflammation driving secondary brain injury: a systematic review

BACKGROUND

Despite advances in both prevention and treatment, traumatic brain injury (TBI) remains one of the most burdensome diseases; 2% of the US population currently lives with disabilities resulting from TBI. Recent advances in the understanding of inflammation and its impact on the pathophysiology of trauma have increased the interest in inflammation as a possible mediator in TBI outcome.

OBJECTIVES

The goal of this systematic review is to address the question: "What is the evidence in humans that inflammation is linked to secondary brain injury?" As the experimental evidence has been well described elsewhere, this review will focus on the clinical evidence for inflammation as a mechanism of secondary brain injury.

DATA SOURCES

Medline database (1996-Week 1 June 2014), Pubmed and Google Scholar databases were queried for relevant studies.

STUDY ELIGIBILITY CRITERIA

Studies were eligible if participants were adults and/or children who sustained moderate or severe TBI in the acute phase of injury, published in English. Studies published in the last decade (since 2004) were preferentially included. Trials could be observational or interventional in nature.

APPRAISAL AND SYNTHESIS METHODS

To address the quality of the studies retrieved, we applied the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) criteria to assess the limitations of the included studies.

RESULTS

Trauma initiates local central nervous system as well as systemic immune activation. Numerous observational studies describe elevation of pro-inflammatory cytokines that are associated with important clinical variables including neurologic outcome and mortality. A small number of clinical trials have included immunomodulating strategies, but no intervention to date has proven effective in improving outcomes after TBI.

LIMITATIONS

Inclusion of studies not initially retrieved by the search terms may have biased our results. Additionally, some reports may have been inadvertently excluded due to use of non-search term key words. Conclusions and Implications of Key Findings Clinical evidence of inflammation causing secondary brain injury in humans is gaining momentum. While inflammation is certainly present, it is not clear from the literature at what juncture inflammation becomes maladaptive, promoting secondary injury rather than facilitating repairand identifying patients with maladaptive inflammation (neuro-inflammation, systemic, or both) after TBI remains elusive. Direct agonism/antagonism represents an exciting target for future study.

LEVEL OF EVIDENCE

Systematic review, level III.

Hypertonic saline for the management of raised intracranial pressure after severe traumatic brain injury

Hyperosmolar agents are commonly used as an initial treatment for the management of raised intracranial pressure (ICP) after severe traumatic brain injury (TBI). They have an excellent adverse-effect profile compared to other therapies, such as hyperventilation and barbiturates, which carry the risk of reducing cerebral perfusion. The hyperosmolar agent mannitol has been used for several decades to reduce raised ICP, and there is accumulating evidence from pilot studies suggesting beneficial effects of hypertonic saline (HTS) for similar purposes. An ideal therapeutic agent for ICP reduction should reduce ICP while maintaining cerebral perfusion (pressure). While mannitol can cause dehydration over time, HTS helps maintain normovolemia and cerebral perfusion, a finding that has led to a large amount of pilot data being published on the benefits of HTS, albeit in small cohorts. Prophylactic therapy is not recommended with mannitol, although it may be beneficial with HTS. To date, no large clinical trial has been performed to directly compare the two agents. The best current evidence suggests that mannitol is effective in reducing ICP in the management of traumatic intracranial hypertension and carries mortality benefit compared to barbiturates. Current evidence regarding the use of HTS in severe TBI is limited to smaller studies, which illustrate a benefit in ICP reduction and perhaps mortality.