Quantitative analysis of similarity between cerebral arterial blood volume and intracranial pressure pulse waveforms during intracranial pressure plateau waves

Introduction

Both intracranial pressure (ICP) and cerebral arterial blood volume (CaBV) have a pulsatile character related to the cardiac cycle. The evolution of the shape of ICP pulses under increasing ICP or decreasing intracranial compliance is well documented. Nevertheless, the exact origin of the alterations in the ICP morphology remains unclear.

Research question

Does ICP pulse waveform become similar to non-invasively estimated CaBV pulse during ICP plateau waves.

Material and methods

A total of 15 plateau waves recorded in 15 traumatic brain injured patients were analyzed. CaBV pulse waveforms were calculated using global cerebral blood flow model from transcranial Doppler cerebral blood flow velocity (CBFV) signals. The difference index (DI) was used to quantify the similarity between ICP and CaBV waveforms. DI was calculated as the sum of absolute sample-by-sample differences between ICP and CaBV waveforms, representing the area between the pulses.

Results

ICP increased (19.4 mm Hg [Q1-Q3: 18.2-23.4 mm Hg] vs. 42.7 mm Hg [Q1-Q3: 36.5-45.1 mm Hg], p < 0.001) while CBFV decreased (44.2 cm/s [Q1-Q3: 34.8-69.5 cm/s] vs. 32.9 cm/s [Q1-Q3: 24.7-68.2 cm/s], p = 0.002) during plateau waves. DI was smaller during the plateau waves (20.4 [Q1-Q3: 15.74-23.0]) compared to the baselines (26.3 [Q1-Q3: 24.2-34.7], p < 0.001).

Discussion and conclusion

The area between corresponding ICP and CaBV pulse waveforms decreased during the plateau waves which suggests they became similar in shape. CaBV may play a significant role in determining the shape of ICP pulses during the plateau waves and might be a driving force in formulating ICP elevation.

Focal brain oxygen, blood flow, and intracranial pressure measurements in relation to optimal cerebral perfusion pressure

OBJECTIVE

Different paradigms for neurocritical care of traumatic brain injury (TBI) have emerged in conjunction with advanced neuromonitoring technologies and derived metrics. The priority for optimizing these metrics is not currently clear. The goal of this study was to determine whether achieving cerebral perfusion pressure (CPPopt) also improves other metrics like brain oxygenation and brain blood flow.

METHODS

The authors performed a retrospective analysis of high-frequency data from patients with TBI who were treated at a single center and who had partial pressure of brain oxygen (PbtO2) measurements and/or brain blood flow measurements, while also undergoing intracranial pressure (ICP) monitoring. CPPopt was not calculated or targeted during patient care, but was retrospectively computed, as was the difference between the observed CPP and CPPopt.

RESULTS

A total of 22 patients with ICP, PbtO2, and/or brain blood flow monitoring were included in the analysis, and 245.7 days of measurements obtained every second were analyzed including 6,748,866 PbtO2 measurements, 3,296,405 blood flow measurements, and 10,264,770 ICP measurements. The data obtained every second were averaged by minute for analysis. In summative data, PbtO2 measurements peaked near CPPopt and were not improved above CPPopt. Blood flow measurements remained stable near CPPopt, decreased below it, and increased when CPP exceeded CPPopt. ICP decreased linearly with CPP without a specific relationship with CPPopt. In an inverse analysis, the percentage of CPP values at CPPopt, although significantly higher on the favorable side of contemporary treatment thresholds of PbtO2, ICP, and blood flow, was not found to be strongly correlated with the mean values of the physiological measurements obtained every minute (r = 0.27, r = 0.11, and r = 0.47 for ICP, PbtO2, and blood flow, respectively; p < 0.0001).

CONCLUSIONS

Although CPPopt was not targeted in the patients in this study, CPPopt was a physiologically significant value based on concurrent measurements of PbtO2 and blood flow. In summative data, achievement of CPPopt was associated with optimized PbtO2 and blood flow. Conversely, the correlation between achievement of CPPopt and the mean measurement value was not strong, strengthening the significance of CPPopt. In individual patients, achieving CPPopt is not always associated with optimal PbtO2 or blood flow. Further research should explore these relationships in treatment paradigms that specifically target CPPopt. These data do not support the premise that targeting and achieving CPPopt obviates the need for concurrent PbtO2 and blood flow monitoring. Although these data suggest that targeting CPPopt may be an appropriate initial treatment strategy, they do not provide evidence that CPPopt should be targeted with highest priority.

Time-domain methods for quantifying dynamic cerebral blood flow autoregulation: Review and recommendations. A white paper from the Cerebrovascular Research Network (CARNet)

Cerebral Autoregulation (CA) is an important physiological mechanism stabilizing cerebral blood flow (CBF) in response to changes in cerebral perfusion pressure (CPP). By maintaining an adequate, relatively constant supply of blood flow, CA plays a critical role in brain function. Quantifying CA under different physiological and pathological states is crucial for understanding its implications. This knowledge may serve as a foundation for informed clinical decision-making, particularly in cases where CA may become impaired. The quantification of CA functionality typically involves constructing models that capture the relationship between CPP (or arterial blood pressure) and experimental measures of CBF. Besides describing normal CA function, these models provide a means to detect possible deviations from the latter. In this context, a recent white paper from the Cerebrovascular Research Network focused on Transfer Function Analysis (TFA), which obtains frequency domain estimates of dynamic CA. In the present paper, we consider the use of time-domain techniques as an alternative approach. Due to their increased flexibility, time-domain methods enable the mitigation of measurement/physiological noise and the incorporation of nonlinearities and time variations in CA dynamics. Here, we provide practical recommendations and guidelines to support researchers and clinicians in effectively utilizing these techniques to study CA.

The time constant of the cerebral arterial bed: exploring age-related implications

The time constant of the cerebral arterial bed (τ) represents an estimation of the  transit time of flow from the point of insonation at the level of the middle cerebral artery to the arteriolar-capillary boundary, during a cardiac cycle. This study assessed differences in τ among healthy volunteers across different age groups. Simultaneous recordings of transcranial Doppler cerebral blood flow velocity (CBFV) and arterial blood pressure (ABP) were performed on two groups: young volunteers (below 30 years of age), and older volunteers (above 40 years of age). τ was estimated using mathematical transformation of ABP and CBFV pulse waveforms. 77 healthy volunteers [52 in the young group, and 25 in the old group] were included. Pulse amplitude of ABP was higher [16.7 (14.6-19.4) mmHg] in older volunteers as compared to younger ones [12.5 (10.9-14.4) mm Hg; p < 0.001]. CBFV was lower in older volunteers [59 (50-66) cm/s] as compared to younger ones [72 (63-78) cm/s p < 0.001]. τ was longer in the younger volunteers [217 (168-237) ms] as compared to the older volunteers [183 (149-211) ms; p = 0.004]. τ significantly decreased with age (rS =  - 0.27; p = 0.018). τ is potentially an integrative marker of the changes occurring in cerebral vasculature, as it encompasses the interplay between changes in compliance and resistance that occur with age.

Exploration of uncertainty of PRx time trends

Introduction

PRx can be used as surrogate measure of Cerebral Autoregulation (CA) in traumatic brain injury (TBI) patients. PRx can provide means for individualising cerebral perfusion pressure (CPP) targets, such as CPPopt. However, a recent Delphi consensus of clinicians concluded that consensus could not be reached on the accuracy, reliability, and validation of any current CA assessment method.

Research question

We aimed to quantify the short-term uncertainty of PRx time-trends and to relate this to other physiological measurements.

Material and methods

Intracranial pressure (ICP), arterial blood pressure (ABP), end-tidal CO2 (EtCO2) high-resolution recordings of 911 TBI patients were processed with ICM + software. Hourly values of metrics that describe the variability within modalities derived from ABP, ICP and EtCO2, were calculated for the first 24h of neuromonitoring. Generalized additive models were used to describe the time trend of the variability in PRx. Linear correlations were studied for describing the relationship between PRx variability and the other physiological modalities.

Results

The time profile of variability of PRx decreases over the first 12h and was higher for average PRx ∼0. Increased variability of PRx was not linearly linked with average ABP, ICP, or CPP. For coherence between slow waves of ABP and ICP >0.7, the variability in PRx decreased (R = -0.47, p < 0.001).

Discussion and conclusion

PRx is a highly variable parameter. PRx short-term dispersion was not related to average ICP, ABP or CPP. The determinants of uncertainty of PRx should be investigated to improve reliability of individualised CA assessment in TBI patients.

Mathematical modelling of cerebral haemodynamics and their effects on ICP

Introduction

Electrical-equivalence mathematical models that integrate vascular and cerebrospinal fluid (CSF) compartments perform well in simulations of dynamic cerebrovascular variations and their transient effects on intracranial pressure (ICP). However, ICP changes due to sustained vascular diameter changes have not been comprehensively examined. We hypothesise that changes in cerebrovascular resistance (CVR) alter the resistance of the bulk flow of interstitial fluid (ISF).

Research question

We hypothesise that changes in CVR alter the resistance of the bulk flow of ISF, thus allowing simulations of ICP in response to sustained vascular diameter changes.

Material and methods

A lumped parameter model with vascular and CSF compartments was constructed and converted into an electrical analogue. The flow and pressure responses to transient hyperaemic response test (THRT) and CSF infusion test (IT) were observed. Arterial blood pressure (ABP) was manipulated to simulate ICP plateau waves. The experiments were repeated with a modified model that included the ISF compartment.

Results

Simulations of the THRT produced identical cerebral blood flow (CBF) responses. ICP generated by the new model reacted in a similar manner as the original model during ITs. Plateau pressure reached during ITs was however higher in the ISF model. Only the latter was successful in simulating the onset of ICP plateau waves in response to selective blood pressure manipulations.

Discussion and conclusion

Our simulations highlighted the importance of including the ISF compartment, which provides mechanism explaining sustained haemodynamic influences on ICP. Consideration of such interactions enables accurate simulations of the cerebrovascular effects on ICP.

The Effect of Recruitment Maneuvers on Cerebrovascular Dynamics and Right Ventricular Function in Patients with Acute Brain Injury: A Single-Center Prospective Study

BACKGROUND

Optimization of ventilatory settings is challenging for patients in the neurointensive care unit, requiring a balance between precise gas exchange control, lung protection, and managing hemodynamic effects of positive pressure ventilation. Although recruitment maneuvers (RMs) may enhance oxygenation, they could also exert profound undesirable systemic impacts.

METHODS

The single-center, prospective study investigated the effects of RMs (up-titration of positive end-expiratory pressure) on multimodal neuromonitoring in patients with acute brain injury. Our primary focus was on intracranial pressure and secondarily on cerebral perfusion pressure (CPP) and other neurological parameters: cerebral autoregulation [pressure reactivity index (PRx)] and regional cerebral oxygenation (rSO2). We also assessed blood pressure and right ventricular (RV) function evaluated using tricuspid annular plane systolic excursion. Results are expressed as the difference (Δ) from baseline values obtained after completing the RMs.

RESULTS

Thirty-two patients were enrolled in the study. RMs resulted in increased intracranial pressure (Δ = 4.8 mm Hg) and reduced CPP (ΔCPP = -12.8 mm Hg) and mean arterial pressure (difference in mean arterial pressure = -5.2 mm Hg) (all p < 0.001). Cerebral autoregulation worsened (ΔPRx = 0.31 a.u.; p < 0.001). Despite higher systemic oxygenation (difference in partial pressure of O2 = 4 mm Hg; p = 0.001) and unchanged carbon dioxide levels, rSO2 marginally decreased (ΔrSO2 = -0.5%; p = 0.031), with a significant drop in arterial content and increase in the venous content. RV systolic function decreased (difference in tricuspid annular plane systolic excursion = -0.1 cm; p < 0.001) with a tendency toward increased RV basal diameter (p = 0.06). Grouping patients according to ΔCPP or ΔPRx revealed that those with poorer tolerance to RMs had higher CPP (p = 0.040) and a larger RV basal diameter (p = 0.034) at baseline.

CONCLUSIONS

In patients with acute brain injury, RMs appear to have adverse effects on cerebral hemodynamics. These findings might be partially explained by RM's impact on RV function. Further advanced echocardiography monitoring is required to prove this hypothesis.

Short-term mild hyperventilation on intracranial pressure, cerebral autoregulation, and oxygenation in acute brain injury patients: a prospective observational study

Current guidelines suggest a target of partial pressure of carbon dioxide (PaCO2) of 32-35 mmHg (mild hypocapnia) as tier 2 for the management of intracranial hypertension. However, the effects of mild hyperventilation on cerebrovascular dynamics are not completely elucidated. The aim of this study is to evaluate the changes of intracranial pressure (ICP), cerebral autoregulation (measured through pressure reactivity index, PRx), and regional cerebral oxygenation (rSO2) parameters before and after induction of mild hyperventilation. Single center, observational study including patients with acute brain injury (ABI) admitted to the intensive care unit undergoing multimodal neuromonitoring and requiring titration of PaCO2 values to mild hypocapnia as tier 2 for the management of intracranial hypertension. Twenty-five patients were included in this study (40% female), median age 64.7 years (Interquartile Range, IQR = 45.9-73.2). Median Glasgow Coma Scale was 6 (IQR = 3-11). After mild hyperventilation, PaCO2 values decreased (from 42 (39-44) to 34 (32-34) mmHg, p < 0.0001), ICP and PRx significantly decreased (from 25.4 (24.1-26.4) to 17.5 (16-21.2) mmHg, p < 0.0001, and from 0.32 (0.1-0.52) to 0.12 (-0.03-0.23), p < 0.0001). rSO2 was statistically but not clinically significantly reduced (from 60% (56-64) to 59% (54-61), p < 0.0001), but the arterial component of rSO2 (ΔO2Hbi, changes in concentration of oxygenated hemoglobin of the total rSO2) decreased from 3.83 (3-6.2) μM.cm to 1.6 (0.5-3.1) μM.cm, p = 0.0001. Mild hyperventilation can reduce ICP and improve cerebral autoregulation, with minimal clinical effects on cerebral oxygenation. However, the arterial component of rSO2 was importantly reduced. Multimodal neuromonitoring is essential when titrating PaCO2 values for ICP management.

Red solid line: Patterns of terminal loss of cerebrovascular reactivity at the bedside

Introduction

Continuous monitoring of the pressure reactivity index (PRx) provides an estimation of dynamic cerebral autoregulation (CA) at the bedside in traumatic brain injury (TBI) patients. Visualising the time-trend of PRx with a risk bar chart in ICM + software at the bedside allows for better real-time interpretability of the autoregulation status. When PRx>0.3 is sustained for long periods, typically of at least half an hour, the bar shows a pattern called "red solid line" (RSL). RSL was previously described to precede refractory intracranial hypertension and brain death.

Research question

We aimed to describe pathophysiological changes in measured signals/parameters during RSL.

Material and methods

Observation of time-trends of PRx, intracranial pressure, cerebral perfusion pressure, brain oxygenation and compensatory reserve of TBI patients with RSL.

Results

Three pathophysiological patterns were identified: RSL precedes intracranial hypertension, RSL is preceded by intracranial hypertension, or RSL is preceded by brain hypoperfusion. In all cases, RSL was followed by death and the RSL onset was between 1 h and 1 day before the terminal event.

Discussion and conclusion

RSL precedes death in intensive care and could represent a marker for terminal clinical deterioration in TBI patients. These findings warrant further investigations in larger cohorts to characterise pathophysiological mechanisms underlying the RSL pattern and whether RSL has a significant relationship with outcome after TBI.

Observational study of intracranial pressure instability in patients with pseudotumour cerebri syndrome

Introduction

A fixed CSF pressure (CSFp) of 25 cmH2O (18 mmHg) has been utilised to date to define and classify pseudotumour cerebri syndrome (PTCS). Furthermore, ICP monitoring, and CSF infusion tests have not been frequently performed in this group of patients.

Research question

We aimed to report typical, unusual and unstable patterns of ICP in patients with PTCS.

Material and methods

We reviewed the recordings of CSF infusion tests and overnight ICP monitoring of patients with suspected or confirmed IIH between January 2003-December 2020.We excluded all patients with a shunt in situ and selected recordings that represented unstable patterns of ICP changes in PTCS.

Results

463 CSF infusion tests and 26 ICP monitorings of PTCS patients had been performed in this timeframe. We divided results of observed pattern into two group: those with known venous sinus measurements (Group A) and those without (Group B). Observed recordings formed a total of 5 and 4 different patterns respectively, based on the behaviour of ICP and slow waves at rest, overnight, and during infusion as well as in relationship to the clinical presentation of each patient.

Discussion and conclusion

Accurate monitoring of ICP in PTCS is quintessential. Full understanding of each element of its pathophysiology and their interaction would be essential and include quantification of the CSF pressure not only as a number, but also with consideration of its dynamic contents. Cerebral venous pressure measurements and/or monitoring may be useful. Consideration of the presence or absence of papilloedema in the context of disturbed CSF dynamics could reveal further diagnostic and therapeutic insights.

The effect of passive leg raising test on intracranial pressure and cerebral autoregulation in brain injured patients: a physiological observational study

BACKGROUND

The use of the passive leg raising (PLR) is limited in acute brain injury (ABI) patients with increased intracranial pressure (ICP) since the postural change of the head may impact on ICP and cerebral autoregulation. However, the PLR use may prevent a positive daily fluid balance, which had been recently associated to worse neurological outcomes. We therefore studied early and delayed effects of PLR on the cerebral autoregulation of patients recovering from ABI.

MATERIALS AND METHODS

This is a Prospective, observational, single-center study conducted in critically ill patients admitted with stable ABI and receiving invasive ICP monitoring, multimodal neuromonitoring and continuous hemodynamic monitoring. The fluid challenge consisted of 500 mL of crystalloid over 10 min; fluid responsiveness was defined as cardiac index increase ≥ 10%. Comparisons between different variables at baseline and after PLR were made by paired Wilcoxon signed-rank test. The correlation coefficients between hemodynamic and neuromonitoring variables were assessed using Spearman's rank test.

RESULTS

We studied 23 patients [12 patients (52.2%) were fluid responders]. The PLR significantly increased ICP [from 13.7 (8.3-16.4) to 15.4 (12.0-19.2) mmHg; p < 0.001], cerebral perfusion pressure (CPP) [from 51.1 (47.4-55.6) to 56.4 (49.6-61.5) mmHg; p < 0.001] and the pressure reactivity index (PRx) [from 0.12 (0.01-0.24) to 0.43 (0.34-0.46) mmHg; p < 0.001]. Regarding Near Infrared Spectroscopy (NIRS)-derived parameters, PLR significantly increased the arterial component of regional cerebral oxygen saturation (O2Hbi) [from 1.8 (0.8-3.7) to 4.3 (2.5-5.6) μM cm; p < 0.001], the deoxygenated hemoglobin (HHbi) [from 1.6 (0.2-2.9) to 2.7 (1.4-4.0) μM cm; p = 0.007] and total hemoglobin (cHbi) [from 3.6 (1.9-5.3) to 7.8 (5.2-10.3): p < 0.001]. In all the patients who had altered autoregulation after PLR, these changes persisted ten minutes afterwards. After the PLR, we observed a significant correlation between MAP and CPP and PRx.

CONCLUSIONS

In ABI patient with stable ICP, PLR test increased ICP, but mostly within safety values and thresholds. Despite this, cerebral autoregulation was importantly impaired, and this persisted up to 10 min after the end of the maneuvre. Our results discourage the use of PLR test in ABI even when ICP is stable.

Brain blood flow pulse analysis may help to recognize individuals who suffer from hydrocephalus

BACKGROUND

Normal pressure hydrocephalus (NPH) is often associated with altered cerebral blood flow. Recent research with the use of the ultrasonic method suggests specific changes in the shape of cardiac-related cerebral arterial blood volume (CaBV) pulses in NPH patients. Our study aims to provide a quantitative analysis of the shape of CaBV pulses, estimated based on transcranial Doppler ultrasonography (TCD) in NPH patients and healthy individuals.

METHODS

The CaBV pulses were estimated using TCD cerebral blood flow velocity signals recorded from probable NPH adults and age-matched healthy individuals at rest. The shape of the CaBV pulses was compared to a triangular shape with 27 similarity parameters calculated for every reliable CaBV pulse and compared between patients and volunteers. The diagnostic accuracy of the most prominent parameter for NPH classification was evaluated using the area under the receiver operating characteristic curve (AUC).

RESULTS

The similarity parameters were calculated for 31 probable NPH patients (age: 59 years (IQR: 47, 67 years), 14 females) and 23 healthy volunteers (age: 54 years (IQR: 43, 61 years), 18 females). Eighteen of 27 parameters were different between healthy individuals and NPH patients (p < 0.05). The most prominent differences were found for the ascending slope of the CaBV pulse with the AUC equal to 0.87 (95% confidence interval: 0.77, 0.97, p < 0.001).

CONCLUSIONS

The findings suggest that in NPH, the ascending slope of the CaBV pulse had a slower rise, was more like a straight line, and generally was less convex than in volunteers. Prospective research is required to verify the clinical utility of these findings.

Relationship between the shape of intracranial pressure pulse waveform and computed tomography characteristics in patients after traumatic brain injury

BACKGROUND

Midline shift and mass lesions may occur with traumatic brain injury (TBI) and are associated with higher mortality and morbidity. The shape of intracranial pressure (ICP) pulse waveform reflects the state of cerebrospinal pressure-volume compensation which may be disturbed by brain injury. We aimed to investigate the link between ICP pulse shape and pathological computed tomography (CT) features.

METHODS

ICP recordings and CT scans from 130 TBI patients from the CENTER-TBI high-resolution sub-study were analyzed retrospectively. Midline shift, lesion volume, Marshall and Rotterdam scores were assessed in the first CT scan after admission and compared with indices derived from the first 24 h of ICP recording: mean ICP, pulse amplitude of ICP (AmpICP) and pulse shape index (PSI). A neural network model was applied to automatically group ICP pulses into four classes ranging from 1 (normal) to 4 (pathological), with PSI calculated as the weighted sum of class numbers. The relationship between each metric and CT measures was assessed using Mann-Whitney U test (groups with midline shift > 5 mm or lesions > 25 cm3 present/absent) and the Spearman correlation coefficient. Performance of ICP-derived metrics in identifying patients with pathological CT findings was assessed using the area under the receiver operating characteristic curve (AUC).

RESULTS

PSI was significantly higher in patients with mass lesions (with lesions: 2.4 [1.9-3.1] vs. 1.8 [1.1-2.3] in those without; p << 0.001) and those with midline shift (2.5 [1.9-3.4] vs. 1.8 [1.2-2.4]; p < 0.001), whereas mean ICP and AmpICP were comparable. PSI was significantly correlated with the extent of midline shift, total lesion volume and the Marshall and Rotterdam scores. PSI showed AUCs > 0.7 in classification of patients as presenting pathological CT features compared to AUCs ≤ 0.6 for mean ICP and AmpICP.

CONCLUSIONS

ICP pulse shape reflects the reduction in cerebrospinal compensatory reserve related to space-occupying lesions despite comparable mean ICP and AmpICP levels. Future validation of PSI is necessary to explore its association with volume imbalance in the intracranial space and a potential complementary role to the existing monitoring strategies.

Analysis of intracranial pressure pulse waveform in studies on cerebrospinal compliance: a narrative review

Continuous monitoring of mean intracranial pressure (ICP) has been an essential part of neurocritical care for more than half a century. Cerebrospinal pressure-volume compensation, i.e. the ability of the cerebrospinal system to buffer changes in volume without substantial increases in ICP, is considered an important factor in preventing adverse effects on the patient's condition that are associated with ICP elevation. However, existing assessment methods are poorly suited to the management of brain injured patients as they require external manipulation of intracranial volume. In the 1980s, studies suggested that spontaneous short-term variations in the ICP signal over a single cardiac cycle, called the ICP pulse waveform, may provide information on cerebrospinal compensatory reserve. In this review we discuss the approaches that have been proposed so far to derive this information, from pulse amplitude estimation and spectral techniques to most recent advances in morphological analysis based on artificial intelligence solutions. Each method is presented with focus on its clinical significance and the potential for application in standard clinical practice. Finally, we highlight the missing links that need to be addressed in future studies in order for ICP pulse waveform analysis to achieve widespread use in the neurocritical care setting.

Creatinine Clearance in Acute Brain Injury: A Comparison of Methods

BACKGROUND

Currently, the measurement of glomerular filtration rate is very complex and costly, so its daily evaluation is performed using endogenous markers, of which creatinine is the most frequently used. It allows the estimation of glomerular filtration rate by means of its clearance or by formulas based on its serum and urine concentration. Augmented renal clearance (ARC) is frequent among critically ill patients and is defined as creatinine clearance (CrCl) > 130 ml/min/1.73 m2. The aim of this study was to compare measured CrCl (MCC) and estimated CrCl obtained with the Cockcroft-Gault formula (CG), the Modification of Diet in Renal Disease Study equation (MDRD), and the Chronic Kidney Disease Epidemiology Collaboration formula (CKD-EPI) in patients with severe traumatic brain injury and nontraumatic subarachnoid hemorrhage. The second aim was to assess the incidence of ARC in this population of neurocritical patients.

METHODS

This was a prospective, observational, single center study from a cohort of 74 patients admitted to the neurocritical intensive care unit due to traumatic brain injury or subarachnoid hemorrhage. Serum creatinine (at 7 a.m.) and a 6-h urine collection were analyzed, and CrCl was measured and estimated by using CG, MDRD, and CKD-EPI. The intraclass correlation coefficient (ICC) was evaluated for each pair, and Bland-Altman plots were used to assess clinical significance.

RESULTS

Among 74 patients, the median age was 53 (interquartile range [IQR] 36-65), and the median Glasgow Coma Scale score at admission was 6. The median MCC at admission was 176 (IQR 135-214). The medians of CG, MDRD and CKD-EPI were, respectively, 129 ml/min/1.73 m2 (IQR 95-176), 158 (IQR 115-202), and 116 (97-132). An ICC was applied to evaluate the correlation between MCC and estimated methods and showed a weak correlation between MCC and estimated CrCl obtained with the three different methods. The strongest ICC statistical correlation was found between MCC and MDRD, and the weakest correlation was found between MCC and CKD-EPI. Bland-Altman plots showed that differences between each pair were not clinically acceptable. ARC was present in 78% of measurements, using MCC. A weak correlation was observed between MCC and calculated CrCl. CG, MDRD, and CKD-EPI overestimated MCC when MCC ≤ 130 ml/min/1.73 m2 and underestimated it when MCC > 130 ml/min/1.73 m2.

CONCLUSIONS

In this population, there was a weak statistical correlation between measured and estimated methods. In patients with ARC, formulas underestimated MCC. MCC should probably be the preferred methodology for renal function assessment in the clinical setting to better adjust drug dosage and guarantee drug effectiveness.

Managing Idiopathic Normal Pressure Hydrocephalus: Need for a Change of Mindset

Idiopathic normal pressure hydrocephalus (iNPH) refers to a complex brain disorder characterized by ventricular enlargement and the classic Hakim's triad of gait and balance difficulties, urinary incontinence, and cognitive impairment. It predominantly affects older patients in the absence of an identified cause. As the elderly population continues to increase, iNPH becomes a growing concern in the complex spectrum of neuro-geriatric care, with significant socio-economic implications. However, unlike other well-structured management approaches for neurodegenerative disorders, the management of iNPH remains largely uncodified, leading to suboptimal care in many cases. In this article, we highlighted the challenges of current practice and identify key points for an optimal structuration of care for iNPH. Adopting a global approach to iNPH could facilitate a progressive shift in mindset, moving away from solely aiming to cure an isolated neurological disease with uncertain outcomes to providing comprehensive care that focuses on improving the daily life of frail patients with complex neurodegenerative burdens, using tailored goals.

Cerebral Autoregulation, Cerebral Hemodynamics, and Injury Biomarkers, in Patients with COVID-19 Treated with Veno-Venous Extracorporeal Membrane Oxygenation

BACKGROUND

This study aimed to describe the cerebrovascular dynamics, in particular cerebral autoregulation (CA), and cerebral biomarkers as neuron-specific enolase (NSE) in patients with a diagnosis of coronavirus disease 2019 and acute respiratory distress syndrome as well as undergoing veno-venous extracorporeal membrane treatment.

METHODS

This was a single center, observational study conducted in the intensive care unit of the University Hospital in Wroclaw from October 2020 to February 2022. Transcranial Doppler recordings of the middle cerebral artery conducted for at least 20 min were performed. Cerebral autoregulation (CA) was estimated by using the mean velocity index (Mxa), calculated as the moving correlation coefficient between slow-wave oscillations in cerebral blood flow velocity and arterial blood pressure. Altered CA was defined as a positive Mxa. Blood samples for the measurement of NSE were obtained at the same time as transcranial Doppler measurements.

RESULTS

A total of 16 patients fulfilled the inclusion criteria and were enrolled in the study. The median age was 39 (34-56) years. Altered CA was found in 12 patients, and six out of seven patients who died had altered CA. A positive Mxa was a significant predictor of mortality, with a sensitivity of 85.7%. We found that three out of five patients with pathological changes in brain computed tomography and six out of ten patients with neurological complications had altered CA. NSE was a significant predictor of mortality (cutoff value: 28.9 µg/L); area under the curve = 0.83, p = 0.006), with a strong relationship between increased level of NSE and altered CA, χ2 = 6.24; p = 0.035; φ = 0.69.

CONCLUSIONS

Patients with coronavirus disease 2019-related acute respiratory distress syndrome, requiring veno-venous extracorporeal membrane treatment, are likely to have elevated NSE levels and altered CA. The CA was associated with NSE values in this group. This preliminary analysis suggests that advanced neuromonitoring and evaluation of biomarkers should be considered in this population.

Are We Ready for Clinical Therapy based on Cerebral Autoregulation? A Pro-con Debate

Cerebral autoregulation (CA) is a physiological mechanism that maintains constant cerebral blood flow regardless of changes in cerebral perfusion pressure and prevents brain damage caused by hypoperfusion or hyperperfusion. In recent decades, researchers have investigated the range of systemic blood pressures and clinical management strategies over which cerebral vasculature modifies intracranial hemodynamics to maintain cerebral perfusion. However, proposed clinical interventions to optimize autoregulation status have not demonstrated clear clinical benefit. As future trials are designed, it is crucial to comprehend the underlying cause of our inability to produce robust clinical evidence supporting the concept of CA-targeted management. This article examines the technological advances in monitoring techniques and the accuracy of continuous assessment of autoregulation techniques used in intraoperative and intensive care settings today. It also examines how increasing knowledge of CA from recent clinical trials contributes to a greater understanding of secondary brain injury in many disease processes, despite the fact that the lack of robust evidence influencing outcomes has prevented the translation of CA-guided algorithms into clinical practice.

Intracranial pressure for clinicians: it is not just a number

BACKGROUND

Invasive intracranial pressure (ICP) monitoring is a standard practice in severe brain injury cases, where it allows to derive cerebral perfusion pressure (CPP); ICP-tracing can also provide additional information about intracranial dynamics, forecast episodes of intracranial hypertension and set targets for a tailored therapy to prevent secondary brain injury. Nevertheless, controversies about the advantages of an ICP clinical management are still debated.

FINDINGS

This article reviews recent research on ICP to improve the understanding of the topic and uncover the hidden information in this signal that may be useful in clinical practice. Parameters derived from time-domain as well as frequency domain analysis include compensatory reserve, autoregulation estimation, pulse waveform analysis, and behavior of ICP in time. The possibility to predict the outcome and apply a tailored therapy using a personalised perfusion pressure target is also described.

CONCLUSIONS

ICP is a crucial signal to monitor in severely brain injured patients; a bedside computer can empower standard monitoring giving new metrics that may aid in clinical management, establish a personalized therapy, and help to predict the outcome. Continuous collaboration between engineers and clinicians and application of new technologies to healthcare, is vital to improve the accuracy of current metrics and progress towards better care with individualized dynamic targets.

Analysis of intracranial pressure pulse waveform in traumatic brain injury patients: a CENTER-TBI study

OBJECTIVE

Intracranial pressure (ICP) pulse waveform analysis may provide valuable information about cerebrospinal pressure-volume compensation in patients with traumatic brain injury (TBI). The authors applied spectral methods to analyze ICP waveforms in terms of the pulse amplitude of ICP (AMP), high frequency centroid (HFC), and higher harmonics centroid (HHC) and also used a morphological classification approach to assess changes in the shape of ICP pulse waveforms using the pulse shape index (PSI).

METHODS

The authors included 184 patients from the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) High-Resolution Sub-Study in the analysis. HFC was calculated as the average power-weighted frequency within the 4- to 15-Hz frequency range of the ICP power density spectrum. HHC was defined as the center of mass of the ICP pulse waveform harmonics from the 2nd to the 10th. PSI was defined as the weighted sum of artificial intelligence-based ICP pulse class numbers from 1 (normal pulse waveform) to 4 (pathological waveform).

RESULTS

AMP and PSI increased linearly with mean ICP. HFC increased proportionally to ICP until the upper breakpoint (average ICP of 31 mm Hg), whereas HHC slightly increased with ICP and then decreased significantly when ICP exceeded 25 mm Hg. AMP (p < 0.001), HFC (p = 0.003), and PSI (p < 0.001) were significantly greater in patients who died than in patients who survived. Among those patients with low ICP (< 15 mm Hg), AMP, PSI, and HFC were greater in those with poor outcome than in those with good outcome (all p < 0.001).

CONCLUSIONS

Whereas HFC, AMP, and PSI could be used as predictors of mortality, HHC may potentially serve as an early warning sign of intracranial hypertension. Elevated HFC, AMP, and PSI were associated with poor outcome in TBI patients with low ICP.

The lower limit of reactivity as a potential individualised cerebral perfusion pressure target in traumatic brain injury: a CENTER-TBI high-resolution sub-study analysis

BACKGROUND

A previous retrospective single-centre study suggested that the percentage of time spent with cerebral perfusion pressure (CPP) below the individual lower limit of reactivity (LLR) is associated with mortality in traumatic brain injury (TBI) patients. We aim to validate this in a large multicentre cohort.

METHODS

Recordings from 171 TBI patients from the high-resolution cohort of the CENTER-TBI study were processed with ICM+ software. We derived LLR as a time trend of CPP at a level for which the pressure reactivity index (PRx) indicates impaired cerebrovascular reactivity with low CPP. The relationship with mortality was assessed with Mann-U test (first 7-day period), Kruskal-Wallis (daily analysis for 7 days), univariate and multivariate logistic regression models. AUCs (CI 95%) were calculated and compared using DeLong's test.

RESULTS

Average LLR over the first 7 days was above 60 mmHg in 48% of patients. %time with CPP < LLR could predict mortality (AUC 0.73, p =  < 0.001). This association becomes significant starting from the third day post injury. The relationship was maintained when correcting for IMPACT covariates or for high ICP.

CONCLUSIONS

Using a multicentre cohort, we confirmed that CPP below LLR was associated with mortality during the first seven days post injury.

Effects of positive end-expiratory pressure on cerebral hemodynamics in acute brain injury patients

Background: Cerebral autoregulation is the mechanism that allows to maintain the stability of cerebral blood flow despite changes in cerebral perfusion pressure. Maneuvers which increase intrathoracic pressure, such as the application of positive end-expiratory pressure (PEEP), have been always challenged in brain injured patients for the risk of increasing intracranial pressure (ICP) and altering autoregulation. The primary aim of this study is to assess the effect of PEEP increase (from 5 to 15 cmH2O) on cerebral autoregulation. Secondary aims include the effect of PEEP increase on ICP and cerebral oxygenation. Material and Methods: Prospective, observational study including adult mechanically ventilated patients with acute brain injury requiring invasive ICP monitoring and undergoing multimodal neuromonitoring including ICP, cerebral perfusion pressure (CPP) and cerebral oxygenation parameters obtained with near-infrared spectroscopy (NIRS), and an index which expresses cerebral autoregulation (PRx). Additionally, values of arterial blood gases were analyzed at PEEP of 5 and 15 cmH2O. Results are expressed as median (interquartile range). Results: Twenty-five patients were included in this study. The median age was 65 years (46-73). PEEP increase from 5 to 15 cmH2O did not lead to worsened autoregulation (PRx, from 0.17 (-0.003-0.28) to 0.18 (0.01-0.24), p = 0.83). Although ICP and CPP changed significantly (ICP: 11.11 (6.73-15.63) to 13.43 (6.8-16.87) mm Hg, p = 0.003, and CPP: 72.94 (59.19-84) to 66.22 (58.91-78.41) mm Hg, p = 0.004), these parameters did not reach clinically relevant levels. No significant changes in relevant cerebral oxygenation parameters were observed. Conclusion: Slow and gradual increases of PEEP did not alter cerebral autoregulation, ICP, CPP and cerebral oxygenation to levels triggering clinical interventions in acute brain injury patients.

Towards autoregulation-oriented management after traumatic brain injury: increasing the reliability and stability of the CPPopt algorithm

PURPOSE

CPPopt denotes a Cerebral Perfusion Pressure (CPP) value at which the Pressure-Reactivity index, reflecting the global state of Cerebral Autoregulation, is best preserved. CPPopt has been investigated as a potential dynamically individualised CPP target in traumatic brain injury patients admitted in intensive care unit. The prospective bedside use of the concept requires ensured safety and reliability of the CPP recommended targets based on the automatically-generated CPPopt. We aimed to: Increase stability and reliability of the CPPopt automated algorithm by fine-tuning; perform outcome validation of the adjusted algorithm in a multi-centre TBI cohort.

METHODS

ICM + software was used to derive CPPopt and fine-tune the algorithm. Parameters for improvement of the algorithm were selected based on qualitative and quantitative assessment of stability and reliability metrics. Patients enrolled in the Collaborative European Neuro Trauma Effectiveness Research in TBI (CENTER-TBI) high-resolution cohort were included for retrospective validation. Yield and stability of the new algorithm were compared to the previous algorithm using Mann-U test. Area under the curves for mortality prediction at 6 months were compared with the DeLong Test.

RESULTS

CPPopt showed higher stability (p < 0.0001), but lower yield compared to the previous algorithm [80.5% (70-87.5) vs 85% (75.7-91.2), p < 0.001]. Deviation of CPPopt could predict mortality with an AUC of [AUC = 0.69 (95% CI 0.59-0.78), p < 0.001] and was comparable with the previous algorithm.

CONCLUSION

The CPPopt calculation algorithm was fine-tuned and adapted for prospective use with acceptable lower yield, improved stability and maintained prognostic power.

Is Lumbar Puncture Needed? - Noninvasive Assessment of ICP Facilitates Decision Making in Patients with Suspected Idiopathic Intracranial Hypertension

PURPOSE

 Idiopathic intracranial hypertension (IIH) usually occurs in obese women of childbearing age. Typical symptoms are headache and sight impairment. Lumbar puncture (LP) is routinely used for both diagnosis and therapy (via cerebrospinal fluid drainage) of IIH. In this study, noninvasively assessed intracranial pressure (nICP) was compared to LP pressure (LPP) in order to clarify its feasibility for the diagnosis of IIH.

MATERIALS AND METHODS

 nICP was calculated using continuous signals of arterial blood pressure and cerebral blood flow velocity in the middle cerebral artery, a method which has been introduced recently. In 26 patients (f = 24, m = 2; age: 33 ± 11 years), nICP was assessed one hour prior to LPP. If LPP was > 20 cmH₂O, lumbar drainage was performed, LPP was measured again, and also nICP was reassessed.

RESULTS

 In total, LPP and nICP correlated with R = 0.85 (p < 0.001; N = 38). The mean difference of nICP-LPP was 0.45 ± 4.93 cmH₂O. The capability of nICP to diagnose increased LPP (LPP > 20 cmH₂O) was assessed by ROC analysis. The optimal cutoff for nICP was close to 20 cmH₂O with both a sensitivity and specificity of 0.92. Presuming 20 cmH₂O as a critical threshold for the indication of lumbar drainage, the clinical implications would coincide in both methods in 35 of 38 cases.

CONCLUSION

 The TCD-based nICP assessment seems to be suitable for a pre-diagnosis of increased LPP and might eliminated the need for painful lumbar puncture if low nICP is detected.

Neurocritical care management supported by multimodal brain monitoring after acute brain injury

OBJECTIVE

To evaluate the association between different intensive care units and levels of brain monitoring with outcomes in acute brain injury.

METHODS

Patients with traumatic brain injury and subarachnoid hemorrhage admitted to intensive care units were included. Neurocritical care unit management was compared to general intensive care unit management. Patients managed with multimodal brain monitoring and optimal cerebral perfusion pressure were compared with general management patients. A good outcome was defined as a Glasgow outcome scale score of 4 or 5.

RESULTS

Among 389 patients, 237 were admitted to the neurocritical care unit, and 152 were admitted to the general intensive care unit. Neurocritical care unit management patients had a lower risk of poor outcome (OR = 0.228). A subgroup of 69 patients with multimodal brain monitoring (G1) was compared with the remaining patients (G2). In the G1 and G2 groups, 59% versus 23% of patients, respectively, had a good outcome at intensive care unit discharge; 64% versus 31% had a good outcome at 28 days; 76% versus 50% had a good outcome at 3 months (p < 0.001); and 77% versus 58% had a good outcome at 6 months (p = 0.005). When outcomes were adjusted by SAPS II severity score, using good outcome as the dependent variable, the results were as follows: for G1 compared to G2, the OR was 4.607 at intensive care unit discharge (p < 0.001), 4.22 at 28 days (p = 0.001), 3.250 at 3 months (p = 0.001) and 2.529 at 6 months (p = 0.006). Patients with optimal cerebral perfusion pressure management (n = 127) had a better outcome at all points of evaluation. Mortality for those patients was significantly lower at 28 days (p = 0.001), 3 months (p < 0.001) and 6 months (p = 0.001).

CONCLUSION

Multimodal brain monitoring with autoregulation and neurocritical care unit management were associated with better outcomes and should be considered after severe acute brain injury.

Accuracy of Intracranial Pressure Monitoring-Single Centre Observational Study and Literature Review

Intracranial hypertension and adequacy of brain blood flow are primary concerns following traumatic brain injury. Intracranial pressure (ICP) monitoring is a critical diagnostic tool in neurocritical care. However, all ICP sensors, irrespective of design, are subject to systematic and random measurement inaccuracies that can affect patient care if overlooked or disregarded. The wide choice of sensors available to surgeons raises questions about performance and suitability for treatment. This observational study offers a critical review of the clinical and experimental assessment of ICP sensor accuracy and comments on the relationship between actual clinical performance, bench testing, and manufacturer specifications. Critically, on this basis, the study offers guidelines for the selection of ICP monitoring technologies, an important clinical decision. To complement this, a literature review on important ICP monitoring considerations was included. This study utilises illustrative clinical and laboratory material from 1200 TBI patients (collected from 1992 to 2019) to present several important points regarding the accuracy of in vivo implementation of contemporary ICP transducers. In addition, a thorough literature search was performed, with sources dating from 1960 to 2021. Sources considered to be relevant matched the keywords: "intraparenchymal ICP sensors", "fiberoptic ICP sensors", "piezoelectric strain gauge sensors", "external ventricular drains", "CSF reference pressure", "ICP zero drift", and "ICP measurement accuracy". Based on single centre observations and the 76 sources reviewed in this paper, this material reports an overall anticipated measurement accuracy for intraparenchymal transducers of around ± 6.0 mm Hg with an average zero drift of <2.0 mm Hg. Precise ICP monitoring is a key tenet of neurocritical care, and accounting for zero drift is vital. Intraparenchymal piezoelectric strain gauge sensors are commonly implanted to monitor ICP. Laboratory bench testing results can differ from in vivo observations, revealing the shortcomings of current ICP sensors.

Neurological and respiratory effects of lung protective ventilation in acute brain injury patients without lung injury: brain vent, a single centre randomized interventional study

INTRODUCTION

Lung protective ventilation (LPV) comprising low tidal volume (VT) and high positive end-expiratory pressure (PEEP) may compromise cerebral perfusion in acute brain injury (ABI). In patients with ABI, we investigated whether LPV is associated with increased intracranial pressure (ICP) and/or deranged cerebral autoregulation (CA), brain compensatory reserve and oxygenation.

METHODS

In a prospective, crossover study, 30 intubated ABI patients with normal ICP and no lung injury were randomly assigned to receive low VT [6 ml/kg/predicted (pbw)]/at either low (5 cmH₂O) or high PEEP (12 cmH₂O). Between each intervention, baseline ventilation (VT 9 ml/kg/pbw and PEEP 5 cmH₂O) were resumed. The safety limit for interruption of the intervention was ICP above 22 mmHg for more than 5 min. Airway and transpulmonary pressures were continuously monitored to assess respiratory mechanics. We recorded ICP by using external ventricular drainage or a parenchymal probe. CA and brain compensatory reserve were derived from ICP waveform analysis.

RESULTS

We included 27 patients (intracerebral haemorrhage, traumatic brain injury, subarachnoid haemorrhage), of whom 6 reached the safety limit, which required interruption of at least one intervention. For those without intervention interruption, the ICP change from baseline to "low VT/low PEEP" and "low VT/high PEEP" were 2.2 mmHg and 2.3 mmHg, respectively, and considered clinically non-relevant. None of the interventions affected CA or oxygenation significantly. Interrupted events were associated with high baseline ICP (p < 0.001), low brain compensatory reserve (p < 0.01) and mechanical power (p < 0.05). The transpulmonary driving pressure was 5 ± 2 cmH₂O in both interventions. Partial arterial pressure of carbon dioxide was kept in the range 34-36 mmHg by adjusting the respiratory rate, hence, changes in carbon dioxide were not associated with the increase in ICP.

CONCLUSIONS

The present study found that most patients did not experience any adverse effects of LPV, neither on ICP nor CA. However, in almost a quarter of patients, the ICP rose above the safety limit for interrupting the interventions. Baseline ICP, brain compensatory reserve, and mechanical power can predict a potentially deleterious effect of LPV and can be used to personalize ventilator settings. Trial registration NCT03278769 . Registered September 12, 2017.

Studying Trends of Auto-Regulation in Severe Head Injury in Paediatrics (STARSHIP): protocol to study cerebral autoregulation in a prospective multicentre observational research database study

INTRODUCTION

Studying cerebral autoregulation, particularly PRx (Pressure Reactivity Index), is commonly employed in adult traumatic brain injury (TBI) and gives real-time information about intracranial pathophysiology, which can help in patient management. Experience in paediatric TBI (PTBI) is limited to single-centre studies despite disproportionately higher incidence of morbidity and mortality in PTBI than in adult TBI.

PROJECT

We describe the protocol to study cerebral autoregulation using PRx in PTBI. The project called Studying Trends of Auto-Regulation in Severe Head Injury in Paediatrics is a multicentre prospective ethics approved research database study from 10 centres across the UK. Recruitment started in July 2018 with financial support from local/national charities (Action Medical Research for Children, UK).

METHODS AND ANALYSIS

The first phase of the project is powered to detect optimal thresholds of PRx associated with favourable outcome in PTBI by recruiting 135 patients (initial target of 3 years which has changed to 5 years due to delays related to COVID-19 pandemic) from 10 centres in the UK with outcome follow-up to 1-year postictus. The secondary objectives are to characterise patterns of optimal cerebral perfusion pressure in PTBI and compare the fluctuations in these measured parameters with outcome. The goal is to create a comprehensive research database of a basic set of high-resolution (full waveforms resolution) neuromonitoring data in PTBI for scientific use.

ETHICS AND DISSEMINATION

Favourable ethical approval has been provided by Health Research Authority, Southwest-Central Bristol Research Ethics Committee (Ref: 18/SW/0053). Results will be disseminated via publications in peer-reviewed medical journals and presentations at national and international conferences.

TRIAL REGISTRATION NUMBER

NCT05688462.

Effects of short-term hyperoxemia on cerebral autoregulation and tissue oxygenation in acute brain injured patients

Introduction: Potential detrimental effects of hyperoxemia on outcomes have been reported in critically ill patients. Little evidence exists on the effects of hyperoxygenation and hyperoxemia on cerebral physiology. The primary aim of this study is to assess the effect of hyperoxygenation and hyperoxemia on cerebral autoregulation in acute brain injured patients. We further evaluated potential links between hyperoxemia, cerebral oxygenation and intracranial pressure (ICP). Methods: This is a single center, observational, prospective study. Acute brain injured patients [traumatic brain injury (TBI), subarachnoid hemorrhage (SAH), intracranial hemorrhage (ICH)] undergoing multimodal brain monitoring through a software platform (ICM+) were included. Multimodal monitoring consisted of invasive ICP, arterial blood pressure (ABP) and near infrared spectrometry (NIRS). Derived parameters of ICP and ABP monitoring included the pressure reactivity index (PRx) to assess cerebral autoregulation. ICP, PRx, and NIRS-derived parameters (cerebral regional saturation of oxygen, changes in concentration of regional oxy- and deoxy-hemoglobin), were evaluated at baseline and after 10 min of hyperoxygenation with a fraction of inspired oxygen (FiO₂) of 100% using repeated measures t-test or paired Wilcoxon signed-rank test. Continuous variables are reported as median (interquartile range). Results: Twenty-five patients were included. The median age was 64.7 years (45.9-73.2), and 60% were male. Thirteen patients (52%) were admitted for TBI, 7 (28%) for SAH, and 5 (20%) patients for ICH. The median value of systemic oxygenation (partial pressure of oxygen-PaO₂) significantly increased after FiO₂ test, from 97 (90-101) mm Hg to 197 (189-202) mm Hg, p < 0.0001. After FiO₂ test, no changes were observed in PRx values (from 0.21 (0.10-0.43) to 0.22 (0.15-0.36), p = 0.68), nor in ICP values (from 13.42 (9.12-17.34) mm Hg to 13.34 (8.85-17.56) mm Hg, p = 0.90). All NIRS-derived parameters reacted positively to hyperoxygenation as expected. Changes in systemic oxygenation and the arterial component of cerebral oxygenation were significantly correlated (respectively ΔPaO₂ and ΔO₂Hbi; r = 0.49 (95% CI = 0.17-0.80). Conclusion: Short-term hyperoxygenation does not seem to critically affect cerebral autoregulation.

Peak appearance time in pulse waveforms of intracranial pressure and cerebral blood flow velocity

The shape of the pulse waveforms of intracranial pressure (ICP) and cerebral blood flow velocity (CBFV) typically contains three characteristic peaks. It was reported that alterations in cerebral hemodynamics may influence the shape of the pulse waveforms by changing peaks' configuration. However, the changes in peak appearance time (PAT) in ICP and CBFV pulses are only described superficially. We analyzed retrospectively ICP and CBFV signals recorded in traumatic brain injury patients during decrease in ICP induced by hypocapnia (n = 11) and rise in ICP during episodes of ICP plateau waves (n = 8). All three peaks were manually annotated in over 48 thousand individual pulses. The changes in PAT were compared between periods of vasoconstriction (expected during hypocapnia) and vasodilation (expected during ICP plateau waves) and their corresponding baselines. Correlation coefficient (r_S) analysis between mean ICP and mean PATs was performed in each individual recording. Vasodilation prolonged PAT of the first peaks of ICP and CBFV pulses and the third peak of CBFV pulse. It also accelerated PAT of the third peak of ICP pulse. In contrast, vasoconstriction shortened appearance time of the first peaks of ICP and CBFV pulses and the second peak of ICP pulses. Analysis of individual recordings demonstrated positive association between changes in PAT of all three peaks in the CBFV pulse and mean ICP (r_S range: 0.32-0.79 for significant correlations). Further study is needed to test whether PAT of the CBFV pulse may serve as an indicator of changes in ICP-this may open a perspective for non-invasive monitoring of alterations in mean ICP.

Cerebral multimodality monitoring in adult neurocritical care patients with acute brain injury: A narrative review

Cerebral multimodality monitoring (MMM) is, even with a general lack of Class I evidence, increasingly recognized as a tool to support clinical decision-making in the neuroscience intensive care unit (NICU). However, literature and guidelines have focused on unimodal signals in a specific form of acute brain injury. Integrating unimodal signals in multiple signal monitoring is the next step for clinical studies and patient care. As such, we aimed to investigate the recent application of MMM in studies of adult patients with traumatic brain injury (TBI), subarachnoid hemorrhage (SAH), intracerebral hemorrhage (ICH), acute ischemic stroke (AIS), and hypoxic ischemic brain injury following cardiac arrest (HIBI). We identified continuous or daily updated monitoring modalities and summarized the monitoring setting, study setting, and clinical characteristics. In addition, we discussed clinical outcome in intervention studies. We identified 112 MMM studies, including 11 modalities, over the last 7 years (2015-2022). Fifty-eight studies (52%) applied only two modalities. Most frequently combined were ICP monitoring (92 studies (82%)) together with PbtO₂ (63 studies (56%). Most studies included patients with TBI (59 studies) or SAH (53 studies). The enrollment period of 34 studies (30%) took more than 5 years, whereas the median sample size was only 36 patients (q1- q3, 20-74). We classified studies as either observational (68 studies) or interventional (44 studies). The interventions were subclassified as systemic (24 studies), cerebral (10 studies), and interventions guided by MMM (11 studies). We identified 20 different systemic or cerebral interventions. Nine (9/11, 82%) of the MMM-guided studies included clinical outcome as an endpoint. In 78% (7/9) of these MMM-guided intervention studies, a significant improvement in outcome was demonstrated in favor of interventions guided by MMM. Clinical outcome may be improved with interventions guided by MMM. This strengthens the belief in this application, but further interdisciplinary collaborations are needed to overcome the heterogeneity, as illustrated in the present review. Future research should focus on increasing sample sizes, improved data collection, refining definitions of secondary injuries, and standardized interventions. Only then can we proceed with complex outcome studies with MMM-guided treatment.

Feasibility of non-invasive neuromonitoring in general intensive care patients using a multi-parameter transcranial Doppler approach

PURPOSE

To assess the feasibility of Transcranial Doppler ultrasonography (TCD) neuromonitoring in a general intensive care environment, in the prognosis and outcome prediction of patients who are in coma due to a variety of critical conditions.

METHODS

The prospective trial was performed between March 2017 and March 2019 Addenbrooke's Hospital, Cambridge, UK. Forty adult patients who failed to awake appropriately after resuscitation from cardiac arrest or were in coma due to conditions such as meningitis, seizures, sepsis, metabolic encephalopathies, overdose, multiorgan failure or transplant were eligible for inclusion. Gathered data included admission diagnosis, duration of ventilation, length of stay in the ICU, length of stay in hospital, discharge status using Cerebral Performance Categories (CPC). All patients received intermittent extended TCD monitoring following inclusion in the study. Parameters of interest included TCD-based indices of cerebral autoregulation, non-invasive intracranial pressure, autonomic system parameters (based on heart rate variability), critical closing pressure, the cerebrovascular time constant and indices describing the shape of the TCD pulse waveform.

RESULTS

Thirty-seven patients were included in the final analysis, with 21 patients classified as good outcome (CPC 1-2) and 16 as poor neurological outcomes (CPC 3-5). Three patients were excluded due to inadequacies identified in the TCD acquisition. The results indicated that irrespective of the primary diagnosis, non-survivors had significantly disturbed cerebral autoregulation, a shorter cerebrovascular time constant and a more distorted TCD pulse waveform (all p<0.05).

CONCLUSIONS

Preliminary results from the trial indicate that multi-parameter TCD neuromonitoring increases outcome-predictive power and TCD-based indices can be applied to general intensive care monitoring.

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.

Inducing oscillations in positive end-expiratory pressure improves assessment of cerebrovascular pressure reactivity in patients with traumatic brain injury

The cerebral pressure reactivity index (PRx), through intracranial pressure (ICP) measurements, informs clinicians about the cerebral autoregulation (CA) status in adult-sedated patients with traumatic brain injury (TBI). Using PRx in clinical practice is currently limited by variability over shorter monitoring periods. We applied an innovative method to reduce the PRx variability by ventilator-induced slow (1/min) positive end-expiratory pressure (PEEP) oscillations. We hypothesized that, as seen in a previous animal model, the PRx variability would be reduced by inducing slow arterial blood pressure (ABP) and ICP oscillations without other clinically relevant physiological changes. Patients with TBI were ventilated with a static PEEP for 30 min (PRx period) followed by a 30-min period of slow [1/min (0.0167 Hz)] +5 cmH2O PEEP oscillations (induced (iPRx period). Ten patients with TBI were included. No clinical monitoring was discontinued and no additional interventions were required during the iPRx period. The PRx variability [measured as the standard deviation (SD) of PRx] decreased significantly during the iPRx period from 0.25 (0.22-0.30) to 0.14 (0.09-0.17) (P = 0.006). There was a power increase around the induced frequency (1/min) for both ABP and ICP (P = 0.002). In conclusion, 1/min PEEP-induced oscillations reduced the PRx variability in patients with TBI with ICP levels <22 mmHg. No other clinically relevant physiological changes were observed. Reduced PRx variability might improve CA-guided perfusion management by reducing the time to find "optimal" perfusion pressure targets. Larger studies with prolonged periods of PEEP-induced oscillations are required to take it to routine use.NEW & NOTEWORTHY Cerebral autoregulation assessment requires sufficient slow arterial blood pressure (ABP) waves. However, spontaneous ABP waves may be insufficient for reliable cerebral autoregulation estimations. Therefore, we applied a ventilator "sigh-function" to generate positive end-expiratory pressure oscillations that induce slow ABP waves. This method demonstrated a reduced variability of the pressure reactivity index, commonly used as continuous cerebral autoregulation measure in a traumatic brain injury population.

Clinical Outcomes After Ventriculo-Peritoneal Shunting in Patients With Classic vs. Complex NPH

Objective

Normal pressure hydrocephalus (NPH) is a neurological condition characterized by a clinical triad of gait disturbance, cognitive impairment, and urinary incontinence in conjunction with ventriculomegaly. Other neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and vascular dementia share some overlapping clinical features. However, there is evidence that patients with comorbid NPH and Alzheimer's or Parkinson's disease may still exhibit good clinical response after CSF diversion. This study aims to evaluate clinical responses after ventriculo-peritoneal shunt (VPS) in a cohort of patients with coexisting NPH and neurodegenerative disease.

Methods

The study has two components; (i) a pilot study was performed that specifically focused upon patients with Complex NPH and following the inclusion of the Complex NPH subtype into consideration for the clinical NPH programme, (ii) a retrospective snapshot study was performed to confirm and characterize differences between Classic and Complex NPH patients being seen consecutively over the course of 1 year within a working subspecialist NPH clinic. We studied the characteristics of patients with Complex NPH, utilizing clinical risk stratification and multimodal biomarkers.

Results

There was no significant difference between responders and non-responders to CSF diversion on comorbidity scales. After VPS insertion, significantly more Classic NPH patients had improved cognition compared to Complex NPH patients (p = 0.005). Improvement in gait and urinary symptoms did not differ between the groups. 26% of the Classic NPH group showed global improvement of the triad, and 42% improved in two domains. Although only 8% showed global improvement of the triad, all Complex NPH patients improved in gait.

Conclusions

Our study has demonstrated that the presence of neurodegenerative disorders co-existing with NPH should not be the sole barrier to the consideration of high-volume tap test or lumbar drainage via a specialist NPH programme. Further characterization of distinct cohorts of NPH with differing degrees of CSF responsiveness due to overlay from neurodegenerative or comorbidity risk burden may aid toward more precise prognostication and treatment strategies. We propose a simplistic conceptual framework to describe NPH by its Classic vs. Complex subtypes to promote the clinical paradigm shift toward subspecialist geriatric neurosurgery by addressing needs for rapid screening tools at the clinical-research interface.

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.

Diffusion Tensor Imaging Profiles Can Distinguish Diffusivity and Neural Properties of White Matter Injury in Hydrocephalus vs. Non-hydrocephalus Using a Strategy of a Periodic Table of DTI Elements

Background:

The aim of this study was to create a simplistic taxonomy to improve transparency and consistency in, and reduce complexity of, interpreting diffusion tensor imaging (DTI) profiles in white matter disruption. Using a novel strategy of a periodic table of DTI elements, we examined if DTI profiles could demonstrate neural properties of disruption sufficient to characterize white matter changes specific for hydrocephalus vs. non-hydrocephalus, and to distinguish between cohorts of neural injury by their differing potential for reversibility.

Methods

DTI datasets from three clinical cohorts representing pathological milestones from reversible to irreversible brain injury were compared to those of healthy controls at baseline, over time and with interventions. The final dataset comprised patients vs. controls in the following groupings: mild traumatic brain injury (mTBI), n = 24 vs. 27, normal pressure hydrocephalus (NPH), n = 16 vs. 9 and Alzheimer's disease (AD), n = 27 vs. 47. We generated DTI profiles from fractional anisotropy (FA) and mean, axial and radial diffusivity measures (MD, L1 and L2 and 3 respectively), and constructed an algorithm to map changes consistently to a periodic table of elements, which fully described their diffusivity and neural properties.

Results

Mapping tissue signatures to a periodic table of DTI elements rapidly characterized cohorts by their differing patterns of injury. At baseline, patients with mTBI displayed the most preserved tracts. In NPH, the magnitude of changes was dependent on “familial” DTI neuroanatomy, i.e., potential for neural distortion from risk of ventriculomegaly. With time, patients with Alzheimer's disease were significantly different to controls across multiple measures. By contrast, patients with mTBI showed both loss of integrity and pathophysiological processes of neural repair. In NPH, some patterns of injury, such as “stretch/compression” and “compression” were more reversible following intervention than others; these neural profile properties suggested “microstructural resilience” to injury.

Conclusion

Using the novel strategy of a periodic table of DTI elements, our study has demonstrated it is possible to distinguish between different cohorts along the spectrum of brain injury by describing neural profile properties of white matter disruption. Further work to contribute datasets of disease toward this proposed taxonomic framework would enhance the translatability of DTI profiles to the clinical-research interface.

Evaluation of Outcomes Among Patients With Traumatic Intracranial Hypertension Treated With Decompressive Craniectomy vs Standard Medical Care at 24 Months: A Secondary Analysis of the RESCUEicp Randomized Clinical Trial

Importance

Trials often assess primary outcomes of traumatic brain injury at 6 months. Longer-term data are needed to assess outcomes for patients receiving surgical vs medical treatment for traumatic intracranial hypertension.

Objective

To evaluate 24-month outcomes for patients with traumatic intracranial hypertension treated with decompressive craniectomy or standard medical care.

Design, Setting, and Participants

Prespecified secondary analysis of the Randomized Evaluation of Surgery With Craniectomy for Uncontrollable Elevation of Intracranial Pressure (RESCUEicp) randomized clinical trial data was performed for patients with traumatic intracranial hypertension (>25 mm Hg) from 52 centers in 20 countries. Enrollment occurred between January 2004 and March 2014. Data were analyzed between 2018 and 2021. Eligibility criteria were age 10 to 65 years, traumatic brain injury (confirmed via computed tomography), intracranial pressure monitoring, and sustained and refractory elevated intracranial pressure for 1 to 12 hours despite pressure-controlling measures. Exclusion criteria were bilateral fixed and dilated pupils, bleeding diathesis, or unsurvivable injury.

Interventions

Patients were randomly assigned 1:1 to receive a decompressive craniectomy with standard care (surgical group) or to ongoing medical treatment with the option to add barbiturate infusion (medical group).

Main Outcomes and Measures

The primary outcome was measured with the 8-point Extended Glasgow Outcome Scale (1 indicates death and 8 denotes upper good recovery), and the 6- to 24-month outcome trajectory was examined.

Results

This study enrolled 408 patients: 206 in the surgical group and 202 in the medical group. The mean (SD) age was 32.3 (13.2) and 34.8 (13.7) years, respectively, and the study population was predominantly male (165 [81.7%] and 156 [80.0%], respectively). At 24 months, patients in the surgical group had reduced mortality (61 [33.5%] vs 94 [54.0%]; absolute difference, -20.5 [95% CI, -30.8 to -10.2]) and higher rates of vegetative state (absolute difference, 4.3 [95% CI, 0.0 to 8.6]), lower or upper moderate disability (4.7 [-0.9 to 10.3] vs 2.8 [-4.2 to 9.8]), and lower or upper severe disability (2.2 [-5.4 to 9.8] vs 6.5 [1.8 to 11.2]; χ27 = 24.20, P = .001). For every 100 individuals treated surgically, 21 additional patients survived at 24 months; 4 were in a vegetative state, 2 had lower and 7 had upper severe disability, and 5 had lower and 3 had upper moderate disability, respectively. Rates of lower and upper good recovery were similar for the surgical and medical groups (20 [11.0%] vs 19 [10.9%]), and significant differences in net improvement (≥1 grade) were observed between 6 and 24 months (55 [30.0%] vs 25 [14.0%]; χ22 = 13.27, P = .001).

Conclusions and Relevance

At 24 months, patients with surgically treated posttraumatic refractory intracranial hypertension had a sustained reduction in mortality and higher rates of vegetative state, severe disability, and moderate disability. Patients in the surgical group were more likely to improve over time vs patients in the medical group.

Trial Registration

ISRCTN Identifier: 66202560.

Comparative effectiveness of intracranial hypertension management guided by ventricular versus intraparenchymal pressure monitoring: a CENTER-TBI study

OBJECTIVE

To compare outcomes between patients with primary external ventricular device (EVD)-driven treatment of intracranial hypertension and those with primary intraparenchymal monitor (IP)-driven treatment.

METHODS

The CENTER-TBI study is a prospective, multicenter, longitudinal observational cohort study that enrolled patients of all TBI severities from 62 participating centers (mainly level I trauma centers) across Europe between 2015 and 2017. Functional outcome was assessed at 6 months and a year. We used multivariable adjusted instrumental variable (IV) analysis with "center" as instrument and logistic regression with covariate adjustment to determine the effect estimate of EVD on 6-month functional outcome.

RESULTS

A total of 878 patients of all TBI severities with an indication for intracranial pressure (ICP) monitoring were included in the present study, of whom 739 (84%) patients had an IP monitor and 139 (16%) an EVD. Patients included were predominantly male (74% in the IP monitor and 76% in the EVD group), with a median age of 46 years in the IP group and 48 in the EVD group. Six-month GOS-E was similar between IP and EVD patients (adjusted odds ratio (aOR) and 95% confidence interval [CI] OR 0.74 and 95% CI [0.36-1.52], adjusted IV analysis). The length of intensive care unit stay was greater in the EVD group than in the IP group (adjusted rate ratio [95% CI] 1.70 [1.34-2.12], IV analysis). One hundred eighty-seven of the 739 patients in the IP group (25%) required an EVD due to refractory ICPs.

CONCLUSION

We found no major differences in outcomes of patients with TBI when comparing EVD-guided and IP monitor-guided ICP management. In our cohort, a quarter of patients that initially received an IP monitor required an EVD later for ICP control. The prevalence of complications was higher in the EVD group.

PROTOCOL

The core study is registered with ClinicalTrials.gov , number NCT02210221, and the Resource Identification Portal (RRID: SCR_015582).

Clinical determinants of cerebrovascular reactivity in very preterm infants during the transitional period

BACKGROUND

Preterm infants are at enhanced risk of brain injury due to altered cerebral haemodynamics during postnatal transition. This observational study aimed to assess the clinical determinants of transitional cerebrovascular reactivity and its association with intraventricular haemorrhage (IVH).

METHODS

Preterm infants <32 weeks underwent continuous monitoring of cerebral oxygenation and heart rate over the first 72 h after birth. Serial cranial and cardiac ultrasound assessments were performed to evaluate the ductal status and to diagnose IVH onset. The moving correlation coefficient between cerebral oxygenation and heart rate (TOHRx) was calculated. Linear mixed-effect models were used to analyse the impact of relevant clinical variables on TOHRx. The association between TOHRx and IVH development was also assessed.

RESULTS

Seventy-seven infants were included. A haemodynamically significant patent ductus arteriosus (hsPDA) (β = 0.044, 95% CI: 0.007-0.081) and ongoing dopamine treatment (β = 0.096, 95% CI: 0.032-0.159) were associated with increasing TOHRx, indicating impaired cerebrovascular reactivity. A significant association between TOHRx, mean arterial blood pressure (β = -0.004, 95% CI: -0.007, -0.001) and CRIB-II score (β = 0.007, 95% CI: 0.001-0.015) was also observed. TOHRx was significantly higher in infants developing high-grade IVH compared to those without IVH.

CONCLUSIONS

Dopamine treatment, low blood pressure, hsPDA and high CRIB-II are associated with impaired cerebrovascular reactivity during postnatal transition, with potential implications on IVH development.

IMPACT

The correlation coefficient between cerebral oxygenation and heart rate (TOHRx) provides a non-invasive estimation of cerebrovascular reactivity, whose failure has a potential pathogenic role in the development of IVH in preterm infants. This study shows that cerebrovascular reactivity during the transitional period improves over time and is affected by specific clinical and therapeutic factors, whose knowledge could support the development of individualized neuroprotective strategies in at-risk preterm infants. The evidence of increased TOHRx in infants developing high-grade compared to low-grade or no IVH during the transitional period further supports the role of impaired cerebrovascular reactivity in IVH pathophysiology.

Hydrocephalus and the neuro-intensivist: CSF hydrodynamics at the bedside

Hydrocephalus (HCP) is far more complicated than a simple disorder of cerebrospinal fluid (CSF) circulation. HCP is a common complication in patients with subarachnoid hemorrhage (SAH) and after craniectomy. Clinical measurement in HCP is mainly related to intracranial pressure (ICP) and cerebral blood flow. The ability to obtain quantitative variables that describe CSF dynamics at the bedside before potential shunting may support clinical intuition with a description of CSF dysfunction and differentiation between normal pressure hydrocephalus and brain atrophy. This review discusses the advanced research on HCP and how CSF is generated, stored and absorbed within the context of a mathematical model developed by Marmarou. Then, we proceed to explain the main quantification analysis of CSF dynamics using infusion techniques for deciding on definitive treatment. We consider that such descriptions of multiple parameters of measurements need to be significantly appreciated by the caring neuro-intensivist, for better understanding of the complex pathophysiology and clinical management and finally, improve of the prognosis of these patients with HCP.

In this review article, we present current and novel theories of CSF circulation and pathophysiology of hydrocephalus, along with results from infusion studies for evaluating CSF dynamics at the bedside.

Prolonged Automated Robotic TCD Monitoring in Acute Severe TBI: Study Design and Rationale

BACKGROUND

Transcranial Doppler ultrasonography (TCD) is a portable, bedside, noninvasive diagnostic tool used for the real-time assessment of cerebral hemodynamics. Despite the evident utility of TCD and the ability of this technique to function as a stethoscope to the brain, its use has been limited to specialized centers because of the dearth of technical and clinical expertise required to acquire and interpret the cerebrovascular parameters. Additionally, the conventional pragmatic episodic TCD monitoring protocols lack dynamic real-time feedback to guide time-critical clinical interventions. Fortunately, with the recent advent of automated robotic TCD technology in conjunction with the automated software for TCD data processing, we now have the technology to automatically acquire TCD data and obtain clinically relevant information in real-time. By obviating the need for highly trained clinical personnel, this technology shows great promise toward a future of widespread noninvasive monitoring to guide clinical care in patients with acute brain injury.

METHODS

Here, we describe a proposal for a prospective observational multicenter clinical trial to evaluate the safety and feasibility of prolonged automated robotic TCD monitoring in patients with severe acute traumatic brain injury (TBI). We will enroll patients with severe non-penetrating TBI with concomitant invasive multimodal monitoring including, intracranial pressure, brain tissue oxygenation, and brain temperature monitoring as part of standard of care in centers with varying degrees of TCD availability and experience. Additionally, we propose to evaluate the correlation of pertinent TCD-based cerebral autoregulation indices such as the critical closing pressure, and the pressure reactivity index with the brain tissue oxygenation values obtained invasively.

CONCLUSIONS

The overarching goal of this study is to establish safety and feasibility of prolonged automated TCD monitoring for patients with TBI in the intensive care unit and identify clinically meaningful and pragmatic noninvasive targets for future interventions.

Relationship Between Baroreflex and Cerebral Autoregulation in Patients With Cerebral Vasospasm After Aneurysmal Subarachnoid Hemorrhage

Introduction: Common consequences following aneurysmal subarachnoid hemorrhage (aSAH) are cerebral vasospasm (CV), impaired cerebral autoregulation (CA), and disturbance in the autonomic nervous system, as indicated by lower baroreflex sensitivity (BRS). The compensatory interaction between BRS and CA has been shown in healthy volunteers and stable pathological conditions such as carotid atherosclerosis. The aim of this study was to investigate whether the inverse correlation between BRS and CA would be lost in patients after aSAH during vasospasm. A secondary objective was to analyze the time-trend of BRS after aSAH.

Materials and Methods: Retrospective analysis of prospectively collected data was performed at the Neuro-Critical Care Unit of Addenbrooke's Hospital (Cambridge, UK) between June 2010 and January 2012. The cerebral blood flow velocity (CBFV) was measured in the middle cerebral artery using transcranial Doppler ultrasonography (TCD). The arterial blood pressure (ABP) was monitored invasively through an arterial line. CA was quantified by the correlation coefficient (Mxa) between slow oscillations in ABP and CBFV. BRS was calculated using the sequential cross-correlation method using the ABP signal.

Results: A total of 73 patients with aSAH were included. The age [median (lower-upper quartile)] was 58 (50–67). WFNS scale was 2 (1–4) and the modified Fisher scale was 3 (1–3). In the total group, 31 patients (42%) had a CV and 42 (58%) had no CV. ABP and CBFV were higher in patients with CV during vasospasm compared to patients without CV (p = 0.001 and p < 0.001). There was no significant correlation between Mxa and BRS in patients with CV, neither during nor before vasospasm. In patients without CV, a significant, although moderate correlation was found between BRS and Mxa (r_S = 0.31; p = 0.040), with higher BRS being associated with worse CA. Multiple linear regression analysis showed a significant worsening of BRS after aSAH in patients with CV (R_p = −0.42; p < 0.001).

Conclusions: Inverse compensatory correlation between BRS and CA was lost in patients who developed CV after aSAH, both before and during vasospasm. The impact of these findings on the prognosis of aSAH should be investigated in larger studies.