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

Commercial NIRS May Not Detect Hemispheric Regional Disparity in Continuously Measured COx/COx-a: An Exploratory Healthy and Cranial Trauma Time-Series Analysis

Continuous metrics of cerebral autoregulation (CA) assessment have been developed using various multimodal cerebral physiological monitoring devices. However, CA regional disparity remains unclear in states of health and disease. Leveraging existing archived data sources, we preliminarily evaluated regional hemispheric disparity in CA using the near infrared spectroscopy (NIRS)-derived cerebral oximetry index (COx/COx-a). Along with bilateral NIRS, regional cerebral oxygen saturation, arterial blood pressure, cerebral perfusion pressure, and bilateral COx/COx-a were derived using three different temporal resolutions-10 s, 1 min, and 5 min-based on non-overlapping mean values. The regional disparity between hemispheres was evaluated based on median and median absolute deviation. Further, patient-level autoregressive integrative moving average models were calculated for each signal stream and used to generate personalized vector autoregressive models. Multi-variate cerebral physiologic relationships between hemispheres were assessed via impulse response functions and Granger causality analyses. Data from 102 healthy control volunteers, 27 spinal surgery patients, and 95 TBI patients (varying in frontal lobe pathology impacting the optode path; 64 without bifrontal lobe pathology, 15 without left frontal lobe pathology, 11 without right frontal lobe pathology, and 5 with bifrontal lobe pathology) were retrospectively analyzed. For subjects with or without cranial pathology, no difference in COx/COx-a was found between hemispheres regardless of the analytic method. In TBI patients without pathology underneath the NIRS sensor, distant parenchymal injury does not seem to have an effect on the CA of uninjured frontal lobes. Further work is required to characterize regional disparities with multi-channel CA measurements in healthy and disease states.

Autoregulatory-guided management in traumatic brain injury: does age matter?

BACKGROUND

Although older traumatic brain injury (TBI) patients often exhibit cerebral autoregulatory impairment with high pressure reactivity index (PRx), the role of autoregulatory-guided management in these patients remains elusive. In this study, we aimed to explore if age affected the prognostic role of the autoregulatory variables, PRx and the PRx-derived optimal cerebral perfusion pressure (CPPopt), in a large TBI cohort.

METHODS

In this observational study, 550 TBI patients who had been treated in the neurocritical care unit, Addenbrooke's Hospital, Cambridge, UK, between 2002 and 2022 with available data on age, intracranial pressure monitoring, and outcome (Glasgow Outcome Scale [GOS]) were included. The patients were classified into three age groups; youth and early adulthood (16-39 years), middle adulthood (40-59 years), and senior adulthood (60 years and above). Autoregulatory variables were studied in relation to outcome using heatmaps. Multivariate logistic regressions of mortality and favourable outcome (GOS 4 to 5) were performed with PRx and ΔCPPopt (CPP-CPPopt) in addition to baseline variables.

RESULTS

TBI patients in the senior adulthood group exhibited higher PRx and lower ICP than younger patients. There was a transition towards worse outcome with higher PRx in heatmaps for all age groups. The combination of high PRx together with low CPP or negative ΔCPPopt was particularly associated with lower GOS. In multivariate logistic regressions, higher PRx remained independently associated with higher mortality and lower rate of favourable outcome in the senior adulthood cohort. There was a transition towards worse outcome for negative ΔCPPopt for all age groups, but it did not reach statistical significance for the senior adulthood group.

CONCLUSIONS

PRx was found to be an independent outcome predictor and influenced the safe and dangerous CPP and ΔCPPopt interval for all age groups. Thus, TBI patients older than 60 years may also benefit from autoregulatory-guided management and should not necessarily be excluded from future trials on such therapeutic strategies.

High-Frequency Analysis of the Cerebral Physiological Impact of Ketamine in Acute Traumatic Neural Injury

Acute traumatic neural injury, also known as traumatic brain injury (TBI), is a leading cause of death. TBI treatment focuses on the use of sedatives, vasopressors, and invasive intracranial pressure (ICP) monitoring to mitigate ICP elevations and maintain cerebral perfusion pressure (CPP). While common sedatives such as propofol and fentanyl have significant side effects, ketamine is an attractive alternative due to its rapid onset and cardiovascular stability. Despite these benefits, ketamine's use remains controversial due to historical concerns about increasing ICP. Using high-frequency monitoring, this retrospective study compared cerebral pressure-flow dynamics in patients with moderate/severe TBI who received ketamine with those who did not. Statistical analysis included descriptive statistics, comparisons within and between patients receiving ketamine, and evaluation of physiological response around incremental dose changes in ketamine. Various cerebral physiological indices were analyzed, including ICP, CPP, regional cerebral oxygen delivery, intracranial compliance, and cardiovascular reactivity metrics. A total of 122 patients were studied, with 17 receiving ketamine (median age: 37 years) and 105 not receiving ketamine (median age: 42 years). Results indicated higher median ICP in the ketamine group compared with the no ketamine group (9.05 mmHg and 14.00 mmHg, respectively, p = 0.00017); however, this is likely due to differences in patient characteristics and injury severity between the groups. No significant differences were observed in any other index of cerebral pressure-flow dynamics or between any incremental dose change condition. These findings suggest that ketamine does not significantly impact cerebral pressure-flow dynamics, challenging historical concerns about its use in patients with TBI.

Revisiting the oxygen reactivity index in traumatic brain injury: the complementary value of combined focal and global autoregulation monitoring

BACKGROUND

The oxygen reactivity index (ORx) reflects the correlation between focal brain tissue oxygen (pbtO2) and the cerebral perfusion pressure (CPP). Previous, small cohort studies were conflicting on whether ORx conveys cerebral autoregulatory information and if it is related to outcome in traumatic brain injury (TBI). Thus, we aimed to investigate these issues in a larger TBI cohort.

METHODS

425 TBI patients with intracranial pressure (ICP)- and pbtO2-monitoring for at least 12 h, who had been treated at Addenbrooke's Hospital, Cambridge, UK, were included. Association between ORx and ICP, pressure reactivity index (PRx), CPP, ΔCPPopt (actual CPP-CPPopt [PRx based optimal CPP]), and pbtO2 were evaluated with generalized additive models (GAMs). Association between ORx and outcome (Glasgow Outcome Scale [GOS]) was investigated with logistic regressions and heatmaps for those 239 patients with GOS data.

RESULTS

GAMs showed that ORx increased with higher ICP, PRx above + 0.30, CPP below 60-70 mmHg, and negative ΔCPPopt. In contrast to PRx, ORx did not increase at higher CPP. In outcome heatmaps, there was a transition towards unfavourable outcome when ORx exceeded + 0.50, particularly for longer durations, and in combination with high ICP, high PRx, low CPP, negative ΔCPPopt, and low pbtO2. In multivariable logistic regressions, higher ORx was associated with increased mortality.

CONCLUSIONS

ORx seemed to be sensitive to the lower, but not the upper, limit of autoregulation, in contrast to PRx which was sensitive to both. The combination of high values for both ORx and PRx was particularly associated with worse outcome and, thus, ORx may provide a complementary value to the global index PRx. ORx could also be useful to determine the safe and dangerous perfusion target intervals.

Managing Intracranial Pressure Crisis

PURPOSE OF REVIEW

The objective of this review is to provide a comprehensive management protocol for the treatment of intracranial pressure (ICP) crises based on the latest evidence.

RECENT FINDINGS

The review discusses updated information on various aspects of critical care management in patients experiencing ICP crises, including mechanical ventilation, fluid therapy, hemoglobin targets, and hypertonic saline infusion, the advantages of ICP monitoring, the critical ICP threshold, and bedside neuromonitoring. All aspects of critical care treatment, including hemodynamic and respiratory support and adjustment of ICP reduction therapy, may impact patient outcomes. ICP monitoring allows ICP values, trends, waveforms, and CPP calculation, which are helpful to guide patient care. Advanced neuromonitoring devices are available at the bedside to diagnose impaired intracranial compliance and intracranial hypertension, assess brain function, and optimize cerebral perfusion. Future research should focus on developing appropriate intervention protocols for both invasive and noninvasive neuromonitoring in managing ICP crisis patients.

How to Define and Meet Blood Pressure Targets After Traumatic Brain Injury: A Narrative Review

BACKGROUND

Traumatic brain injury (TBI) poses a significant challenge to healthcare providers, necessitating meticulous management of hemodynamic parameters to optimize patient outcomes. This article delves into the critical task of defining and meeting continuous arterial blood pressure (ABP) and cerebral perfusion pressure (CPP) targets in the context of severe TBI in neurocritical care settings.

METHODS

We narratively reviewed existing literature, clinical guidelines, and emerging technologies to propose a comprehensive approach that integrates real-time monitoring, individualized cerebral perfusion target setting, and dynamic interventions.

RESULTS

Our findings emphasize the need for personalized hemodynamic management, considering the heterogeneity of patients with TBI and the evolving nature of their condition. We describe the latest advancements in monitoring technologies, such as autoregulation-guided ABP/CPP treatment, which enable a more nuanced understanding of cerebral perfusion dynamics. By incorporating these tools into a proactive monitoring strategy, clinicians can tailor interventions to optimize ABP/CPP and mitigate secondary brain injury.

DISCUSSION

Challenges in this field include the lack of standardized protocols for interpreting multimodal neuromonitoring data, potential variability in clinical decision-making, understanding the role of cardiac output, and the need for specialized expertise and customized software to have individualized ABP/CPP targets regularly available. The patient outcome benefit of monitoring-guided ABP/CPP target definitions still needs to be proven in patients with TBI.

CONCLUSIONS

We recommend that the TBI community take proactive steps to translate the potential benefits of personalized ABP/CPP targets, which have been implemented in certain centers, into a standardized and clinically validated reality through randomized controlled trials.

Should Patients with Traumatic Brain Injury with Significant Contusions be Treated with Different Neurointensive Care Targets?

BACKGROUND

Patients with traumatic brain injury (TBI) with large contusions make up a specific TBI subtype. Because of the risk of brain edema worsening, elevated cerebral perfusion pressure (CPP) may be particularly dangerous. The pressure reactivity index (PRx) and optimal cerebral perfusion pressure (CPPopt) are new promising perfusion targets based on cerebral autoregulation, but they reflect the global brain state and may be less valid in patients with predominant focal lesions. In this study, we aimed to investigate if patients with TBI with significant contusions exhibited a different association between PRx, CPP, and CPPopt in relation to functional outcome compared to those with small/no contusions.

METHODS

This observational study included 385 patients with moderate to severe TBI treated at a neurointensive care unit in Uppsala, Sweden. The patients were classified into two groups: (1) significant contusions (> 10 mL) and (2) small/no contusions (but with extra-axial or diffuse injuries). The percentage of good monitoring time (%GMT) with intracranial pressure > 20 mm Hg; PRx > 0.30; CPP < 60 mm Hg, within 60-70 mm Hg, or > 70 mm Hg; and ΔCPPopt less than - 5 mm Hg, ± 5 mm Hg, or > 5 mm Hg was calculated. Outcome (Glasgow Outcome Scale-Extended) was assessed after 6 months.

RESULTS

Among the 120 (31%) patients with significant contusions, a lower %GMT with CPP between 60 and 70 mm Hg was independently associated with unfavorable outcome. The %GMTs with PRx and ΔCPPopt ± 5 mm Hg were not independently associated with outcome. Among the 265 (69%) patients with small/no contusions, a higher %GMT of PRx > 0.30 and a lower %GMT of ΔCPPopt ± 5 mm Hg were independently associated with unfavorable outcome.

CONCLUSIONS

In patients with TBI with significant contusions, CPP within 60-70 mm Hg may improve outcome. PRx and CPPopt, which reflect global cerebral pressure autoregulation, may be useful in patients with TBI without significant focal brain lesions but seem less valid for those with large contusions. However, this was an observational, hypothesis-generating study; our findings need to be validated in prospective studies before translating them into clinical practice.

The Optimal pressure reactivity index range is disease-specific: A comparison between aneurysmal subarachnoid hemorrhage and traumatic brain injury

PURPOSE

Impaired cerebral pressure autoregulation is common and detrimental after acute brain injuries. Based on the prevalence of delayed cerebral ischemia in aneurysmal subarachnoid hemorrhage (aSAH) patients compared to traumatic brain injury (TBI), we hypothesized that the type of autoregulatory disturbance and the optimal PRx range may differ between these two conditions. The aim of this study was to determine the optimal PRx ranges in relation to functional outcome following aSAH and TBI, respectively.

METHODS

In this observational study, 487 aSAH patients and 413 TBI patients, treated in the neurointensive care, Uppsala, Sweden, between 2008 and 2018, were included. The percentage of good monitoring time (%GMT) of PRx was calculated within 8 intervals covering the range from -1.0 to + 1.0, and analyzed in relation to favorable outcome (GOS-E 5 to 8).

RESULTS

In multiple logistic regressions, a higher %GMTs of PRx in the intervals -1.0 to -0.5 and + 0.75 to + 1.0 were independently associated with a lower rate of favorable outcome in the aSAH cohort. In a similar analysis in the TBI cohort, only positive PRx in the interval + 0.75 to + 1.0 was independently associated with a lower rate of favorable outcome.

CONCLUSION

Extreme PRx values in both directions were unfavorable in aSAH, possibly as high PRx could indicate proximal vasospasm with exhausted distal vasodilatory reserve, while very negative PRx could reflect myogenic hyperreactivity with suppressed cerebral blood flow. Only elevated PRx was unfavorable in TBI, possibly as pressure passive vessels may be a more predominant pathomechanism in this disease.

Neurovascular coupling methods in healthy individuals using transcranial doppler ultrasonography: A systematic review and consensus agreement

Neurovascular coupling (NVC) is the perturbation of cerebral blood flow (CBF) to meet varying metabolic demands induced by various levels of neural activity. NVC may be assessed by Transcranial Doppler ultrasonography (TCD), using task activation protocols, but with significant methodological heterogeneity between studies, hindering cross-study comparisons. Therefore, this review aimed to summarise and compare available methods for TCD-based healthy NVC assessments. Medline (Ovid), Scopus, Web of Science, EMBASE (Ovid) and CINAHL were searched using a predefined search strategy (PROSPERO: CRD42019153228), generating 6006 articles. Included studies contained TCD-based assessments of NVC in healthy adults. Study quality was assessed using a checklist, and findings were synthesised narratively. 76 studies (2697 participants) met the review criteria. There was significant heterogeneity in the participant position used (e.g., seated vs supine), in TCD equipment, and vessel insonated (e.g. middle, posterior, and anterior cerebral arteries). Larger, more significant, TCD-based NVC responses typically included a seated position, baseline durations >one-minute, extraneous light control, and implementation of previously validated protocols. In addition, complementary, combined position, vessel insonated and stimulation type protocols were associated with more significant NVC results. Recommendations are detailed here, but further investigation is required in patient populations, for further optimisation of TCD-based NVC assessments.

Critical thresholds of long-pressure reactivity index and impact of intracranial pressure monitoring methods in traumatic brain injury

BACKGROUND

Moderate-to-severe traumatic brain injury (TBI) has a global mortality rate of about 30%, resulting in acquired life-long disabilities in many survivors. To potentially improve outcomes in this TBI population, the management of secondary injuries, particularly the failure of cerebrovascular reactivity (assessed via the pressure reactivity index; PRx, a correlation between intracranial pressure (ICP) and mean arterial blood pressure (MAP)), has gained interest in the field. However, derivation of PRx requires high-resolution data and expensive technological solutions, as calculations use a short time-window, which has resulted in it being used in only a handful of centers worldwide. As a solution to this, low resolution (longer time-windows) PRx has been suggested, known as Long-PRx or LPRx. Though LPRx has been proposed little is known about the best methodology to derive this measure, with different thresholds and time-windows proposed. Furthermore, the impact of ICP monitoring on cerebrovascular reactivity measures is poorly understood. Hence, this observational study establishes critical thresholds of LPRx associated with long-term functional outcome, comparing different time-windows for calculating LPRx as well as evaluating LPRx determined through external ventricular drains (EVD) vs intraparenchymal pressure device (IPD) ICP monitoring.

METHODS

The study included a total of n = 435 TBI patients from the Karolinska University Hospital. Patients were dichotomized into alive vs. dead and favorable vs. unfavorable outcomes based on 1-year Glasgow Outcome Scale (GOS). Pearson's chi-square values were computed for incrementally increasing LPRx or ICP thresholds against outcome. The thresholds that generated the greatest chi-squared value for each LPRx or ICP parameter had the highest outcome discriminatory capacity. This methodology was also completed for the segmentation of the population based on EVD, IPD, and time of data recorded in hospital stay.

RESULTS

LPRx calculated with 10-120-min windows behaved similarly, with maximal chi-square values ranging at around a LPRx of 0.25-0.35, for both survival and favorable outcome. When investigating the temporal relations of LPRx derived thresholds, the first 4 days appeared to be the most associated with outcomes. The segmentation of the data based on intracranial monitoring found limited differences between EVD and IPD, with similar LPRx values around 0.3.

CONCLUSION

Our work suggests that the underlying prognostic factors causing impairment in cerebrovascular reactivity can, to some degree, be detected using lower resolution PRx metrics (similar found thresholding values) with LPRx found clinically using as low as 10 min-by-minute samples of MAP and ICP. Furthermore, EVD derived LPRx with intermittent cerebrospinal fluid draining, seems to present similar outcome capacity as IPD. This low-resolution low sample LPRx method appears to be an adequate substitute for the clinical prognostic value of PRx and may be implemented independent of ICP monitoring method when PRx is not feasible, though further research is warranted.

Thiamine use is associated with better outcomes for traumatic brain injury patients

Background

Traumatic brain injury (TBI) is a global health concern that often leads to poor prognosis. We designed this study to explore whether thiamine use is associated with a better prognosis of TBI.

Methods

TBI patients selected from the Medical Information Mart for Intensive Care-III database were included in the study. Univariate and multivariate Cox regression analyses were performed to examine the relationship between thiamine use and mortality in TBI patients. Propensity score matching (PSM) was utilized to generate balanced cohorts of the non-thiamine use group and the thiamine use group. Subgroup analysis was performed in the cohort after PSM to verify the association between thiamine use and mortality in TBI patients across different stratifications.

Results

The incidence of thiamine use in TBI was 18.3%. The thiamine use group had a lower 30-day mortality rate (p < 0.001), a longer length of ICU stay (p < 0.001), and a longer length of hospital stay (p < 0.001) than the non-thiamine use group, both in the primary cohort before PSM and the cohort after PSM. A multivariate Cox regression analysis confirmed that thiamine use was independently associated with mortality (OR = 0.454, p < 0.001) after adjusting for confounding effects. In the cohort after PSM, the subgroup analysis showed that thiamine use is associated with lower mortality in TBI patients with a Glasgow Coma Scale (GCS) score of < 13, but it is not associated with mortality in TBI patients whose GCS score is ≥13.

Conclusion

Thiamine supplementation is effective in improving the outcome of TBI, except in cases of mild TBI. The optimal thiamine supplementation strategy for TBI is worthwhile to be explored in future studies.

Autoregulatory Cerebral Perfusion Pressure Insults in Traumatic Brain Injury and Aneurysmal Subarachnoid Hemorrhage: The Role of Insult Intensity and Duration on Clinical Outcome

BACKGROUND

This single-center, retrospective study investigated the outcome effect of the combined intensity and duration of differences between actual cerebral perfusion pressure (CPP) and optimal cerebral perfusion pressure (CPPopt), and also for absolute CPP, in patients with traumatic brain injury (TBI) and aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

A total of 378 TBI and 432 aSAH patients treated in a neurointensive care unit between 2008 and 2018 with at least 24 hours of CPPopt data during the first 10 days following injury, and with 6-month (TBI) or 12-month (aSAH) extended Glasgow Outcome Scale (GOS-E) scores, were included in the study. ∆CPPopt-insults (∆CPPopt=actual CPP-CPPopt) and CPP-insults were visualized as 2-dimensional plots to highlight the combined effect of insult intensity (mm Hg) and duration (min) on patient outcome.

RESULTS

In TBI patients, a zone of ∆CPPopt ± 10 mm Hg was associated with more favorable outcome, with transitions towards unfavorable outcome above and below this zone. CPP in the range of 60 to 80 mm Hg was associated with higher GOS-E, whereas CPP outside this range was associated with lower GOS-E. In aSAH patients, there was no clear transition from higher to lower GOS-E for ∆CPPopt-insults; however, there was a transition from favorable to unfavorable outcome when CPP was <80 mm Hg.

CONCLUSIONS

TBI patients with CPP close to CPPopt exhibited better clinical outcomes, and absolute CPP within the 60 to 80 mm Hg range was also associated with favorable outcome. In aSAH patients, there was no clear transition for ∆CPPopt-insults in relation to outcome, whereas generally high absolute CPP values were associated overall with favorable recovery.

Cerebral autoregulation in traumatic brain injury: ultra-low-frequency pressure reactivity index and intracranial pressure across age groups

BACKGROUND

The ultra-low-frequency pressure reactivity index (UL-PRx) has been established as a surrogate method for bedside estimation of cerebral autoregulation (CA). Although this index has been shown to be a predictor of outcome in adult and pediatric patients with traumatic brain injury (TBI), a comprehensive evaluation of low sampling rate data collection (0.0033 Hz averaged over 5 min) on cerebrovascular reactivity has never been performed.

OBJECTIVE

To evaluate the performance and predictive power of the UL-PRx for 12-month outcome measures, alongside all International Mission for Prognosis and Analysis of Clinical Trials (IMPACT) models and in different age groups. To investigate the potential for optimal cerebral perfusion pressure (CPPopt).

METHODS

Demographic data, IMPACT variables, in-hospital mortality, and Glasgow Outcome Scale Extended (GOSE) at 12 months were extracted. Filtering and processing of the time series and creation of the indices (cerebral intracranial pressure (ICP), cerebral perfusion pressure (CPP), UL-PRx, and deltaCPPopt (ΔCPPopt and CPPopt-CPP)) were performed using an in-house algorithm. Physiological parameters were assessed as follows: mean index value, % time above threshold, and mean hourly dose above threshold.

RESULTS

A total of 263 TBI patients were included: pediatric (17.5% aged ≤ 16 y) and adult (60.5% aged > 16 and < 70 y and 22.0% ≥ 70 y, respectively) patients. In-hospital and 12-month mortality were 25.9% and 32.7%, respectively, and 60.0% of patients had an unfavorable outcome at 12 months (GOSE). On univariate analysis, ICP, CPP, UL-PRx, and ΔCPPopt were associated with 12-month outcomes. The cutoff of ~ 20-22 for mean ICP and of ~ 0.30 for mean UL-PRx were confirmed in all age groups, except in patients older than 70 years. Mean UL-PRx remained significantly associated with 12-month outcomes even after adjustment for IMPACT models. This association was confirmed in all age groups. UL-PRx resulted associate with CPPopt.

CONCLUSIONS

The study highlights UL-PRx as a tool for assessing CA and valuable outcome predictor for TBI patients. The results emphasize the potential clinical utility of the UL-PRx and its adaptability across different age groups, even after adjustment for IMPACT models. Furthermore, the correlation between UL-PRx and CPPopt suggests the potential for more targeted treatment strategies.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT05043545, principal investigator Paolo Gritti, date of registration 2021.08.21.

Evaluation of Morlet Wavelet Analysis for Artifact Detection in Low-Frequency Commercial Near-Infrared Spectroscopy Systems

Regional cerebral oxygen saturation (rSO2), a method of cerebral tissue oxygenation measurement, is recorded using non-invasive near-infrared Spectroscopy (NIRS) devices. A major limitation is that recorded signals often contain artifacts. Manually removing these artifacts is both resource and time consuming. The objective was to evaluate the applicability of using wavelet analysis as an automated method for simple signal loss artifact clearance of rSO2 signals obtained from commercially available devices. A retrospective observational study using existing populations (healthy control (HC), elective spinal surgery patients (SP), and traumatic brain injury patients (TBI)) was conducted. Arterial blood pressure (ABP) and rSO2 data were collected in all patients. Wavelet analysis was determined to be successful in removing simple signal loss artifacts using wavelet coefficients and coherence to detect signal loss artifacts in rSO2 signals. The removal success rates in HC, SP, and TBI populations were 100%, 99.8%, and 99.7%, respectively (though it had limited precision in determining the exact point in time). Thus, wavelet analysis may prove to be useful in a layered approach NIRS signal artifact tool utilizing higher-frequency data; however, future work is needed.

The pressure reactivity index as a measure of cerebral autoregulation and its application in traumatic brain injury management

Severe traumatic brain injury (TBI) is a major cause of morbidity and mortality globally. The Brain Trauma Foundation guidelines advocate for the maintenance of a cerebral perfusion pressure (CPP) between 60 and 70 mmHg following severe TBI. However, such a uniform goal does not account for changes in cerebral autoregulation (CA). CA refers to the complex homeostatic mechanisms by which cerebral blood flow is maintained, despite variations in mean arterial pressure and intracranial pressure. Disruption to CA has become increasingly recognised as a key mediator of secondary brain injury following severe TBI. The pressure reactivity index is calculated as the degree of statistical correlation between the slow wave components of mean arterial pressure and intracranial pressure signals and is a validated dynamic marker of CA status following brain injury. The widespread acceptance of pressure reactivity index has precipitated the consideration of individualised CPP targets or an optimal cerebral perfusion pressure (CPPopt). CPPopt represents an alternative target for cerebral haemodynamic optimisation following severe TBI, and early observational data suggest improved neurological outcomes in patients whose CPP is more proximate to CPPopt. The recent publication of a prospective randomised feasibility study of CPPopt guided therapy in TBI, suggests clinicians caring for such patients should be increasingly familiar with these concepts. In this paper, we present a narrative review of the key landmarks in the development of CPPopt and offer a summary of the evidence for CPPopt-based therapy in comparison to current standards of care.

Brain tissue oxygen monitoring in traumatic brain injury-part II: isolated and combined insults in relation to outcome

BACKGROUND

The primary aim was to explore the concept of isolated and combined threshold-insults for brain tissue oxygenation (pbtO2) in relation to outcome in traumatic brain injury (TBI).

METHODS

A total of 239 TBI patients with data on clinical outcome (GOS) and intracranial pressure (ICP) and pbtO2 monitoring for at least 12 h, who had been treated at the neurocritical care unit, Addenbrooke's Hospital, Cambridge, UK, between 2002 and 2022 were included. Outcome was dichotomised into favourable/unfavourable (GOS 4-5/1-3) and survival/mortality (GOS 2-5/1). PbtO2 was studied over the entire monitoring period. Thresholds were analysed in relation to outcome based on median and mean values, percentage of time and dose per hour below critical values and visualised as the combined insult intensity and duration.

RESULTS

Median pbtO2 was slightly, but not significantly, associated with outcome. A pbtO2 threshold at 25 and 20 mmHg, respectively, yielded the highest x2 when dichotomised for favourable/unfavourable outcome and mortality/survival in chi-square analyses. A higher dose and higher percentage of time spent with pbtO2 below 25 mmHg as well as lower thresholds were associated with unfavourable outcome, but not mortality. In a combined insult intensity and duration analysis, there was a transition from favourable towards unfavourable outcome when pbtO2 went below 25-30 mmHg for 30 min and similar transitions occurred for shorter durations when the intensity was higher. Although these insults were rare, pbtO2 under 15 mmHg was more strongly associated with unfavourable outcome if, concurrently, ICP was above 20 mmHg, cerebral perfusion pressure below 60 mmHg, or pressure reactivity index above 0.30 than if these variables were not deranged. In a multiple logistic regression, a higher percentage of monitoring time with pbtO2 < 15 mmHg was associated with a higher rate of unfavourable outcome.

CONCLUSIONS

Low pbtO2, under 25 mmHg and particularly below 15 mmHg, for longer durations and in combination with disturbances in global cerebral physiological variables were associated with poor outcome and may indicate detrimental ischaemic hypoxia. Prospective trials are needed to determine if pbtO2-directed therapy is beneficial, at what individualised pbtO2 threshold therapies are warranted, and how this may depend on the presence/absence of concurrent cerebral physiological disturbances.

Brain tissue oxygen monitoring in traumatic brain injury: part I-To what extent does PbtO2 reflect global cerebral physiology?

BACKGROUND

The primary aim was to explore the association of global cerebral physiological variables including intracranial pressure (ICP), cerebrovascular reactivity (PRx), cerebral perfusion pressure (CPP), and deviation from the PRx-based optimal CPP value (∆CPPopt; actual CPP-CPPopt) in relation to brain tissue oxygenation (pbtO2) in traumatic brain injury (TBI).

METHODS

A total of 425 TBI patients with ICP- and pbtO2 monitoring for at least 12 h, who had been treated at the neurocritical care unit, Addenbrooke's Hospital, Cambridge, UK, between 2002 and 2022 were included. Generalized additive models (GAMs) and linear mixed effect models were used to explore the association of ICP, PRx, CPP, and CPPopt in relation to pbtO2. PbtO2 < 20 mmHg, ICP > 20 mmHg, PRx > 0.30, CPP < 60 mmHg, and ∆CPPopt < - 5 mmHg were considered as cerebral insults.

RESULTS

PbtO2 < 20 mmHg occurred in median during 17% of the monitoring time and in less than 5% in combination with ICP > 20 mmHg, PRx > 0.30, CPP < 60 mmHg, or ∆CPPopt < - 5 mmHg. In GAM analyses, pbtO2 remained around 25 mmHg over a large range of ICP ([0;50] mmHg) and PRx [- 1;1], but deteriorated below 20 mmHg for extremely low CPP below 30 mmHg and ∆CPPopt below - 30 mmHg. In linear mixed effect models, ICP, CPP, PRx, and ∆CPPopt were significantly associated with pbtO2, but the fixed effects could only explain a very small extent of the pbtO2 variation.

CONCLUSIONS

PbtO2 below 20 mmHg was relatively frequent and often occurred in the absence of disturbances in ICP, PRx, CPP, and ∆CPPopt. There were significant, but weak associations between the global cerebral physiological variables and pbtO2, suggesting that hypoxic pbtO2 is often a complex and independent pathophysiological event. Thus, other variables may be more crucial to explain pbtO2 and, likewise, pbtO2 may not be a suitable outcome measure to determine whether global cerebral blood flow optimization such as CPPopt therapy is successful.

Statistical properties of cerebral near infrared and intracranial pressure-based cerebrovascular reactivity metrics in moderate and severe neural injury: a machine learning and time-series analysis

BACKGROUND

Cerebrovascular reactivity has been identified as a key contributor to secondary injury following traumatic brain injury (TBI). Prevalent intracranial pressure (ICP) based indices of cerebrovascular reactivity are limited by their invasive nature and poor spatial resolution. Fortunately, interest has been building around near infrared spectroscopy (NIRS) based measures of cerebrovascular reactivity that utilize regional cerebral oxygen saturation (rSO2) as a surrogate for pulsatile cerebral blood volume (CBV). In this study, the relationship between ICP- and rSO2-based indices of cerebrovascular reactivity, in a cohort of critically ill TBI patients, is explored using classical machine learning clustering techniques and multivariate time-series analysis.

METHODS

High-resolution physiologic data were collected in a cohort of adult moderate to severe TBI patients at a single quaternary care site. From this data both ICP- and rSO2-based indices of cerebrovascular reactivity were derived. Utilizing agglomerative hierarchical clustering and principal component analysis, the relationship between these indices in higher dimensional physiologic space was examined. Additionally, using vector autoregressive modeling, the response of change in ICP and rSO2 (ΔICP and ΔrSO2, respectively) to an impulse in change in arterial blood pressure (ΔABP) was also examined for similarities.

RESULTS

A total of 83 patients with 428,775 min of unique and complete physiologic data were obtained. Through agglomerative hierarchical clustering and principal component analysis, there was higher order clustering between rSO2- and ICP-based indices, separate from other physiologic parameters. Additionally, modeled responses of ΔICP and ΔrSO2 to impulses in ΔABP were similar, indicating that ΔrSO2 may be a valid surrogate for pulsatile CBV.

CONCLUSIONS

rSO2- and ICP-based indices of cerebrovascular reactivity relate to one another in higher dimensional physiologic space. ΔICP and ΔrSO2 behave similar in modeled responses to impulses in ΔABP. This work strengthens the body of evidence supporting the similarities between ICP-based and rSO2-based indices of cerebrovascular reactivity and opens the door to cerebrovascular reactivity monitoring in settings where invasive ICP monitoring is not feasible.

Ursolic acid ameliorates traumatic brain injury in mice by regulating microRNA-141-mediated PDCD4/PI3K/AKT signaling pathway

BACKGROUND

Neuronal apoptosis and inflammation are the key pathogenic features of secondary brain injury, which results in the neurological impairment that traumatic brain injury (TBI) patients experience. Ursolic Acid (UA) has been shown to have neuroprotective properties against brain damage, however, detailed mechanisms have not been fully disclosed. Research on brain-related microRNAs (miRNAs) has opened up new possibilities for the neuroprotective treatment of UA by manipulating miRNAs. The present study was designed to investigate the impact of UA on neuronal apoptosis and the inflammatory response in TBI mice.

METHODS

The mice's neurologic condition was assessed using the modified neurological severity score (mNSS) and the learning and memory abilities were assessed using the Morris water maze (MWM). Cell apoptosis, oxidative stress, and inflammation were utilized to examine the impact of UA on neuronal pathological damage. miR-141-3p was selected to evaluate whether UA influences miRNAs in a way that has neuroprotective benefits.

RESULTS

The results showed that UA markedly decreased brain edema and neuronal mortality through oxidative stress and neuroinflammation in TBI mice. Using data from the GEO database, we found that miR-141-3p was considerably downregulated in TBI mice and that this downregulation was reversed by UA treatment. Further studies have shown that UA regulates miR-141-3p expression to exhibit its neuroprotective effect in mouse models and cell injury models. Then, miR-141-3p was discovered to directly target PDCD4 in TBI mice and neurons, a well-known PI3K/AKT pathway regulator in the neurons. Most importantly, the upregulation of phosphorylated (p)-AKT and p-PI3K provided the most compelling evidence that UA reactivated the PI3K/AKT pathway in the TBI mouse model, which was through regulating miR-141-3p.

CONCLUSION

Our findings support the notion that UA can improve TBI by modulating miR-141 mediated PDCD4/PI3K/AKT signaling pathway.

Multimodal and autoregulation monitoring in the neurointensive care unit

Given the complexity of cerebral pathology in patients with acute brain injury, various neuromonitoring strategies have been developed to better appreciate physiologic relationships and potentially harmful derangements. There is ample evidence that bundling several neuromonitoring devices, termed "multimodal monitoring," is more beneficial compared to monitoring individual parameters as each may capture different and complementary aspects of cerebral physiology to provide a comprehensive picture that can help guide management. Furthermore, each modality has specific strengths and limitations that depend largely on spatiotemporal characteristics and complexity of the signal acquired. In this review we focus on the common clinical neuromonitoring techniques including intracranial pressure, brain tissue oxygenation, transcranial doppler and near-infrared spectroscopy with a focus on how each modality can also provide useful information about cerebral autoregulation capacity. Finally, we discuss the current evidence in using these modalities to support clinical decision making as well as potential insights into the future of advanced cerebral homeostatic assessments including neurovascular coupling.

Beyond intracranial pressure: monitoring cerebral perfusion and autoregulation in severe traumatic brain injury

PURPOSE OF REVIEW

Severe traumatic brain injury (TBI) remains the most prevalent neurological condition worldwide. Observational and interventional studies provide evidence to recommend monitoring of intracranial pressure (ICP) in all severe TBI patients. Existing guidelines focus on treating elevated ICP and optimizing cerebral perfusion pressure (CPP), according to fixed universal thresholds. However, both ICP and CPP, their target thresholds, and their interaction, need to be interpreted in a broader picture of cerebral autoregulation, the natural capacity to adjust cerebrovascular resistance to preserve cerebral blood flow in response to external stimuli.

RECENT FINDINGS

Cerebral autoregulation is often impaired in TBI patients, and monitoring cerebral autoregulation might be useful to develop personalized therapy rather than treatment of one size fits all thresholds and guidelines based on unidimensional static relationships.

SUMMARY

Today, there is no gold standard available to estimate cerebral autoregulation. Cerebral autoregulation can be triggered by performing a mean arterial pressure (MAP) challenge, in which MAP is increased by 10% for 20 min. The response of ICP (increase or decrease) will estimate the status of cerebral autoregulation and can steer therapy mainly concerning optimizing patient-specific CPP. The role of cerebral metabolic changes and its relationship to cerebral autoregulation is still unclear and awaits further investigation.

Secondary hyperperfusion injury following surgical evacuation for acute isolated epidural hematoma with concurrent cerebral herniation

Objective

Hemispherical cerebral swelling or even encephalocele after head trauma is a common complication and has been well elucidated previously. However, few studies have focused on the secondary brain hemorrhage or edema occurring regionally but not hemispherically in the cerebral parenchyma just underneath the surgically evacuated hematoma during or at a very early stage post-surgery.

Methods

In order to explore the characteristics, hemodynamic mechanisms, and optimized treatment of a novel peri-operative complication in patients with isolated acute epidural hematoma (EDH), clinical data of 157 patients with acute-isolated EDH who underwent surgical intervention were reviewed retrospectively. Risk factors including demographic characteristics, admission Glasgow Coma Score, preoperative hemorrhagic shock, anatomical location, and morphological parameters of epidural hematoma, as well as the extent and duration of cerebral herniation on physical examination and radiographic evaluation were considered.

Results

It suggested that secondary intracerebral hemorrhage or edema was determined in 12 of 157 patients within 6 h after surgical hematoma evacuation. It was featured by remarkable, regional hyperperfusion on the computed tomography (CT) perfusion images and associated with a relatively poor neurological prognosis. In addition to concurrent cerebral herniation, which was found to be a prerequisite for the development of this novel complication, multivariate logistic regression further showed four independent risk factors contributing to this type of secondary hyperperfusion injury: cerebral herniation that lasted longer than 2 h, hematomas that were located in the non-temporal region, hematomas that were thicker than 40 mm, and hematomas occurring in pediatric and elderly patients.

Conclusion

Secondary brain hemorrhage or edema occurring within an early perioperative period of hematoma-evacuation craniotomy for acute-isolated EDH is a rarely described hyperperfusion injury. Because it plays an important prognostic influence on patients' neurological recovery, optimized treatment should be given to block or reduce the consequent secondary brain injuries.

Traumatic brain injury: progress and challenges in prevention, clinical care, and research

Traumatic brain injury (TBI) has the highest incidence of all common neurological disorders, and poses a substantial public health burden. TBI is increasingly documented not only as an acute condition but also as a chronic disease with long-term consequences, including an increased risk of late-onset neurodegeneration. The first Lancet Neurology Commission on TBI, published in 2017, called for a concerted effort to tackle the global health problem posed by TBI. Since then, funding agencies have supported research both in high-income countries (HICs) and in low-income and middle-income countries (LMICs). In November 2020, the World Health Assembly, the decision-making body of WHO, passed resolution WHA73.10 for global actions on epilepsy and other neurological disorders, and WHO launched the Decade for Action on Road Safety plan in 2021. New knowledge has been generated by large observational studies, including those conducted under the umbrella of the International Traumatic Brain Injury Research (InTBIR) initiative, established as a collaboration of funding agencies in 2011. InTBIR has also provided a huge stimulus to collaborative research in TBI and has facilitated participation of global partners. The return on investment has been high, but many needs of patients with TBI remain unaddressed. This update to the 2017 Commission presents advances and discusses persisting and new challenges in prevention, clinical care, and research.

In LMICs, the occurrence of TBI is driven by road traffic incidents, often involving vulnerable road users such as motorcyclists and pedestrians. In HICs, most TBI is caused by falls, particularly in older people (aged ≥65 years), who often have comorbidities. Risk factors such as frailty and alcohol misuse provide opportunities for targeted prevention actions. Little evidence exists to inform treatment of older patients, who have been commonly excluded from past clinical trials—consequently, appropriate evidence is urgently required. Although increasing age is associated with worse outcomes from TBI, age should not dictate limitations in therapy. However, patients injured by low-energy falls (who are mostly older people) are about 50% less likely to receive critical care or emergency interventions, compared with those injured by high-energy mechanisms, such as road traffic incidents.

Mild TBI, defined as a Glasgow Coma sum score of 13–15, comprises most of the TBI cases (over 90%) presenting to hospital. Around 50% of adult patients with mild TBI presenting to hospital do not recover to pre-TBI levels of health by 6 months after their injury. Fewer than 10% of patients discharged after presenting to an emergency department for TBI in Europe currently receive follow-up. Structured follow-up after mild TBI should be considered good practice, and urgent research is needed to identify which patients with mild TBI are at risk for incomplete recovery.

The selection of patients for CT is an important triage decision in mild TBI since it allows early identification of lesions that can trigger hospital admission or life-saving surgery. Current decision making for deciding on CT is inefficient, with 90–95% of scanned patients showing no intracranial injury but being subjected to radiation risks. InTBIR studies have shown that measurement of blood-based biomarkers adds value to previously proposed clinical decision rules, holding the potential to improve efficiency while reducing radiation exposure. Increased concentrations of biomarkers in the blood of patients with a normal presentation CT scan suggest structural brain damage, which is seen on MR scanning in up to 30% of patients with mild TBI. Advanced MRI, including diffusion tensor imaging and volumetric analyses, can identify additional injuries not detectable by visual inspection of standard clinical MR images. Thus, the absence of CT abnormalities does not exclude structural damage—an observation relevant to litigation procedures, to management of mild TBI, and when CT scans are insufficient to explain the severity of the clinical condition.

Although blood-based protein biomarkers have been shown to have important roles in the evaluation of TBI, most available assays are for research use only. To date, there is only one vendor of such assays with regulatory clearance in Europe and the USA with an indication to rule out the need for CT imaging for patients with suspected TBI. Regulatory clearance is provided for a combination of biomarkers, although evidence is accumulating that a single biomarker can perform as well as a combination. Additional biomarkers and more clinical-use platforms are on the horizon, but cross-platform harmonisation of results is needed. Health-care efficiency would benefit from diversity in providers.

In the intensive care setting, automated analysis of blood pressure and intracranial pressure with calculation of derived parameters can help individualise management of TBI. Interest in the identification of subgroups of patients who might benefit more from some specific therapeutic approaches than others represents a welcome shift towards precision medicine. Comparative-effectiveness research to identify best practice has delivered on expectations for providing evidence in support of best practices, both in adult and paediatric patients with TBI.

Progress has also been made in improving outcome assessment after TBI. Key instruments have been translated into up to 20 languages and linguistically validated, and are now internationally available for clinical and research use. TBI affects multiple domains of functioning, and outcomes are affected by personal characteristics and life-course events, consistent with a multifactorial bio-psycho-socio-ecological model of TBI, as presented in the US National Academies of Sciences, Engineering, and Medicine (NASEM) 2022 report. Multidimensional assessment is desirable and might be best based on measurement of global functional impairment. More work is required to develop and implement recommendations for multidimensional assessment. Prediction of outcome is relevant to patients and their families, and can facilitate the benchmarking of quality of care. InTBIR studies have identified new building blocks (eg, blood biomarkers and quantitative CT analysis) to refine existing prognostic models. Further improvement in prognostication could come from MRI, genetics, and the integration of dynamic changes in patient status after presentation.

Neurotrauma researchers traditionally seek translation of their research findings through publications, clinical guidelines, and industry collaborations. However, to effectively impact clinical care and outcome, interactions are also needed with research funders, regulators, and policy makers, and partnership with patient organisations. Such interactions are increasingly taking place, with exemplars including interactions with the All Party Parliamentary Group on Acquired Brain Injury in the UK, the production of the NASEM report in the USA, and interactions with the US Food and Drug Administration. More interactions should be encouraged, and future discussions with regulators should include debates around consent from patients with acute mental incapacity and data sharing. Data sharing is strongly advocated by funding agencies. From January 2023, the US National Institutes of Health will require upload of research data into public repositories, but the EU requires data controllers to safeguard data security and privacy regulation. The tension between open data-sharing and adherence to privacy regulation could be resolved by cross-dataset analyses on federated platforms, with the data remaining at their original safe location. Tools already exist for conventional statistical analyses on federated platforms, however federated machine learning requires further development. Support for further development of federated platforms, and neuroinformatics more generally, should be a priority.

This update to the 2017 Commission presents new insights and challenges across a range of topics around TBI: epidemiology and prevention (section 1 ); system of care (section 2 ); clinical management (section 3 ); characterisation of TBI (section 4 ); outcome assessment (section 5 ); prognosis (Section 6 ); and new directions for acquiring and implementing evidence (section 7 ). Table 1 summarises key messages from this Commission and proposes recommendations for the way forward to advance research and clinical management of TBI.