Relationship between brain perfusion computed tomography variables and cerebral perfusion pressure in severe head trauma patients

Optimal cerebral perfusion pressure in aneurysmal subarachnoid hemorrhage and its relation to perfusion deficits on CT-perfusion

Preservation of optimal cerebral perfusion is a crucial part of the acute management after aneurysmal subarachnoid hemorrhage (aSAH). A few studies indicated possible benefits of maintaining a cerebral perfusion pressure (CPP) near the calculated optimal CPP (CPPopt), representing an individually optimal condition at which cerebral autoregulation functions at its best. This retrospective observational monocenter study was conducted to investigate, whether "suboptimal" perfusion with actual CPP deviating from CPPopt correlates with perfusion deficits detected by CT-perfusion (CTP). A consecutive cohort of aSAH-patients was reviewed and patients with available parameters for CPPopt-calculation, who simultaneously received CTP, were analyzed. By plotting the pressure reactivity index (PRx) versus CPP, CPP correlating the lowest PRx value was identified as CPPopt. Perfusion deficits on CTP were documented. In 86 out of 324 patients, the inclusion criteria were met. Perfusion deficits were detected in 47% (40/86) of patients. In 43% of patients, CPP was lower than CPPopt, which correlated with detected perfusion deficits (r = 0.23, p = 0.03). Perfusion deficits were found in 62% of patients with CPPCPPopt (OR 3, p = 0.01). These findings support the hypothesis, that a deviation of CPP from CPPopt is an indicator of suboptimal cerebral perfusion.

High spatial and temporal resolution cerebrovascular reactivity for humans and large mammals: A technological description of integrated fNIRS and niABP mapping system

Introduction: The process of cerebral vessels maintaining cerebral blood flow (CBF) fairly constant over a wide range of arterial blood pressure is referred to as cerebral autoregulation (CA). Cerebrovascular reactivity is the mechanism behind this process, which maintains CBF through constriction and dilation of cerebral vessels. Traditionally CA has been assessed statistically, limited by large, immobile, and costly neuroimaging platforms. However, with recent technology advancement, dynamic autoregulation assessment is able to provide more detailed information on the evolution of CA over long periods of time with continuous assessment. Yet, to date, such continuous assessments have been hampered by low temporal and spatial resolution systems, that are typically reliant on invasive point estimations of pulsatile CBF or cerebral blood volume using commercially available technology. Methods: Using a combination of multi-channel functional near-infrared spectroscopy and non-invasive arterial blood pressure devices, we were able to create a system that visualizes CA metrics by converting them to heat maps drawn on a template of human brain. Results: The custom Python heat map module works in "offline" mode to visually portray the CA index per channel with the use of colourmap. The module was tested on two different mapping grids, 8 channel and 24 channel, using data from two separate recordings and the Python heat map module was able read the CA indices file and represent the data visually at a preselected rate of 10 s. Conclusion: The generation of the heat maps are entirely non-invasive, with high temporal and spatial resolution by leveraging the recent advances in NIRS technology along with niABP. The CA mapping system is in its initial stage and development plans are ready to transform it from "offline" to real-time heat map generation.

Non-Invasive and Minimally-Invasive Cerebral Autoregulation Assessment: A Narrative Review of Techniques and Implications for Clinical Research

The process of cerebral vessels regulating constant cerebral blood flow over a wide range of systemic arterial pressures is termed cerebral autoregulation (CA). Static and dynamic autoregulation are two types of CA measurement techniques, with the main difference between these measures relating to the time scale used. Static autoregulation looks at the long-term change in blood pressures, while dynamic autoregulation looks at the immediate change. Techniques that provide regularly updating measures are referred to as continuous, whereas intermittent techniques take a single at point in time. However, a technique being continuous or intermittent is not implied by if the technique measures autoregulation statically or dynamically. This narrative review outlines technical aspects of non-invasive and minimally-invasive modalities along with providing details on the non-invasive and minimally-invasive measurement techniques used for CA assessment. These non-invasive techniques include neuroimaging methods, transcranial Doppler, and near-infrared spectroscopy while the minimally-invasive techniques include positron emission tomography along with magnetic resonance imaging and radiography methods. Further, the advantages and limitations are discussed along with how these methods are used to assess CA. At the end, the clinical considerations regarding these various techniques are highlighted.

Detection of cerebral hypoperfusion with a dynamic hyperoxia test using brain oxygenation pressure monitoring

Introduction

Brain multimodal monitoring including intracranial pressure (ICP) and brain tissue oxygen pressure (PbtO2) is more accurate than ICP alone in detecting cerebral hypoperfusion after traumatic brain injury (TBI). No data are available for the predictive role of a dynamic hyperoxia test in brain-injured patients from diverse etiology.

Aim

To examine the accuracy of ICP, PbtO2 and the oxygen ratio (OxR) in detecting regional cerebral hypoperfusion, assessed using perfusion cerebral computed tomography (CTP) in patients with acute brain injury.

Methods

Single-center study including patients with TBI, subarachnoid hemorrhage (SAH) and intracranial hemorrhage (ICH) undergoing cerebral blood flow (CBF) measurements using CTP, concomitantly to ICP and PbtO2 monitoring. Before CTP, FiO2 was increased directly from baseline to 100% for a period of 20 min under stable conditions to test the PbtO2 catheter, as a standard of care. Cerebral monitoring data were recorded and samples were taken, allowing the measurement of arterial oxygen pressure (PaO2) and PbtO2 at FiO2 100% as well as calculation of OxR (= ΔPbtO2/ΔPaO2). Regional CBF (rCBF) was measured using CTP in the tissue area around intracranial monitoring by an independent radiologist, who was blind to the PbtO2 values. The accuracy of different monitoring tools to predict cerebral hypoperfusion (i.e., CBF < 35 mL/100 g × min) was assessed using area under the receiver-operating characteristic curves (AUCs).

Results

Eighty-seven CTPs were performed in 53 patients (median age 52 [41–63] years—TBI, n = 17; SAH, n = 29; ICH, n = 7). Cerebral hypoperfusion was observed in 56 (64%) CTPs: ICP, PbtO2 and OxR were significantly different between CTP with and without hypoperfusion. Also, rCBF was correlated with ICP (r = − 0.27; p = 0.01), PbtO2 (r = 0.36; p < 0.01) and OxR (r = 0.57; p < 0.01). Compared with ICP alone (AUC = 0.65 [95% CI, 0.53–0.76]), monitoring ICP + PbO2 (AUC = 0.78 [0.68–0.87]) or ICP + PbtO2 + OxR (AUC = 0.80 (0.70–0.91) was significantly more accurate in predicting cerebral hypoperfusion. The accuracy was not significantly different among different etiologies of brain injury.

Conclusions

The combination of ICP and PbtO2 monitoring provides a better detection of cerebral hypoperfusion than ICP alone in patients with acute brain injury. The use of dynamic hyperoxia test could not significantly increase the diagnostic accuracy.

Selection of CT variables and prognostic models for outcome prediction in patients with traumatic brain injury

Background

Traumatic brain injuries (TBI) are associated with high risk of morbidity and mortality. Early outcome prediction in patients with TBI require reliable data input and stable prognostic models. The aim of this investigation was to analyze different CT classification systems and prognostic calculators in a representative population of TBI-patients, with known outcomes, in a neurointensive care unit (NICU), to identify the most suitable CT scoring system for continued research.

Materials and methods

We retrospectively included 158 consecutive patients with TBI admitted to the NICU at a level 1 trauma center in Sweden from 2012 to 2016. Baseline data on admission was recorded, CT scans were reviewed, and patient outcome one year after trauma was assessed according to Glasgow Outcome Scale (GOS). The Marshall classification, Rotterdam scoring system, Helsinki CT score and Stockholm CT score were tested, in addition to the IMPACT and CRASH prognostic calculators. The results were then compared with the actual outcomes.

Results

Glasgow Coma Scale score on admission was 3–8 in 38%, 9–13 in 27.2%, and 14–15 in 34.8% of the patients. GOS after one year showed good recovery in 15.8%, moderate disability in 27.2%, severe disability in 24.7%, vegetative state in 1.3% and death in 29.7%. When adding the variables from the IMPACT base model to the CT scoring systems, the Stockholm CT score yielded the strongest relationship to actual outcome. The results from the prognostic calculators IMPACT and CRASH were divided into two subgroups of mortality (percentages); ≤50% (favorable outcome) and > 50% (unfavorable outcome). This yielded favorable IMPACT and CRASH scores in 54.4 and 38.0% respectively.

Conclusion

The Stockholm CT score and the Helsinki score yielded the closest relationship between the models and the actual outcomes in this consecutive patient series, representative of a NICU TBI-population. Furthermore, the Stockholm CT score yielded the strongest overall relationship when adding variables from the IMPACT base model and would be our method of choice for continued research when using any of the current available CT score models.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13049-021-00901-6.

Prognostic value of CT perfusion and permeability imaging in traumatic brain injury

BACKGROUND

Currently established prognostic models in traumatic brain injury (TBI) include noncontrast computed tomography (CT) which is insensitive to early perfusion alterations associated with secondary brain injury. Perfusion CT (PCT) on the other hand offers insight into early perfusion abnormalities. We hypothesized that adding CT perfusion and permeability data to the established outcome predictors improves the performance of the prognostic model.

METHODS

A prospective cohort study of consecutive 50 adult patients with head injury and Glasgow Coma Scale score of 12 or less was performed at a single Level 1 Trauma Centre. Perfusion CT was added to routine control CT 12 hours to 24 hours after admission. Region of interest analysis was performed in six major vascular territories on perfusion and permeability parametric maps. Glasgow Outcome Scale (GOS) was used 6 months later to categorize patients' functional outcomes to favorable (GOS score > 3) or unfavorable (GOS score ≤ 3). We defined core prognostic model, consisting of age, motor Glasgow Coma Scale score, pupillary reactivity, and CT Rotterdam Score. Next, we added perfusion and permeability data as predictors and compared updated models to the core model using cross-validated areas under the receiver operator curves (cv-AUC).

RESULTS

Significant advantage over core model was shown by the model, containing both mean cerebral extravascular-extracellular volume per unit of tissue volume and cerebral blood volume of the least perfused arterial territory in addition to core predictors (cv-AUC, 0.75; 95% confidence interval, 0.51-0.84 vs. 0.6; 95% confidence interval, 0.37-0.74).

CONCLUSION

The development of cerebral ischemia and traumatic cerebral edema constitutes the secondary brain injury and represents the target for therapeutic interventions. Our results suggest that adding CT perfusion and permeability data to the established outcome predictors improves the performance of the prognostic model in the setting of moderate and severe TBI.

LEVEL OF EVIDENCE

Prognostic study, level III.

Abnormalities on Perfusion CT and Intervention for Intracranial Hypertension in Severe Traumatic Brain Injury

The role of invasive intracranial pressure (ICP) monitoring in patients with severe traumatic brain injury (STBI) remain unclear. Perfusion computed tomography (CTP) provides crucial information about the cerebral perfusion status in these patients. We hypothesised that CTP abnormalities would be associated with the severity of intracranial hypertension (ICH). To investigate this hypothesis, twenty-eight patients with STBI and ICP monitors were investigated with CTP within 48 h from admission. Treating teams were blind to these results. Patients were divided into five groups based on increasing intervention required to control ICH and were compared. Group I required no intervention above routine sedation, group II required a single first tier intervention, group III required multiple different first-tier interventions, group IV required second-tier medical therapy and group V required second-tier surgical therapy. Analysis of the results showed demographics and injury severity did not differ among groups. In group I no patients showed CTP abnormality, while patients in all other groups had abnormal CTP (p = 0.003). Severe ischaemia observed on CTP was associated with increasing intervention for ICH. This study, although limited by small sample size, suggests that CTP abnormalities are associated with the need to intervene for ICH. Larger scale assessment of our results is warranted to potentially avoid unnecessary invasive procedures in head injury patients.

Cerebral Blood Flow Measurement in Healthy Children and Children Suffering Severe Traumatic Brain Injury-What Do We Know?

Traumatic brain injury is the leading cause of death in children. Children with severe TBI are in need of neurointensive care where the goal is to prevent secondary brain injury by avoiding secondary insults. Monitoring of cerebral blood flow (CBF) and autoregulation in the injured brain is crucial. However, there are limited studies performed in children to investigate this. Current studies report on age dependent increase in CBF with narrow age range. Low initial CBF following TBI has been correlated to poor outcome and may be more prevalent than hyperemia as previously suggested. Impaired cerebral pressure autoregulation is also detected and correlated with poor outcome but it remains to be elucidated if there is a causal relationship. Current studies are few and mainly based on small number of patients between the age of 0–18 years. Considering the changes of CBF and cerebral pressure autoregulation with increasing age, larger studies with more narrow age ranges and multimodality monitoring are required in order to generate data that can optimize the therapy and clinical management of children suffering TBI.

Advanced neuroimaging in traumatic brain injury: an overview

Traumatic brain injury (TBI) is a common condition with many potential acute and chronic neurological consequences. Standard initial radiographic evaluation includes noncontrast head CT scanning to rapidly evaluate for pathology that might require intervention. The availability of fast, relatively inexpensive CT imaging has fundamentally changed the clinician's ability to noninvasively visualize neuroanatomy. However, in the context of TBI, limitations of head CT without contrast include poor prognostic ability, inability to analyze cerebral perfusion status, and poor visualization of underlying posttraumatic changes to brain parenchyma. Here, the authors review emerging advanced imaging for evaluation of both acute and chronic TBI and include QuickBrain MRI as an initial imaging modality. Dynamic susceptibility-weighted contrast-enhanced perfusion MRI, MR arterial spin labeling, and perfusion CT are reviewed as methods for examining cerebral blood flow following TBI. The authors evaluate MR-based diffusion tensor imaging and functional MRI for prognostication of recovery post-TBI. Finally, MR elastography, MR spectroscopy, and convolutional neural networks are examined as future tools in TBI management. Many imaging technologies are being developed and studied in TBI, and some of these may hold promise in improving the understanding and management of TBI. ABBREVIATIONS ASL = arterial spin labeling; CNN = convolutional neural network; CTP = perfusion CT; DAI = diffuse axonal injury; DMN = default mode network; DOC = disorders of consciousness; DTI = diffusion tensor imaging; FA = fractional anisotropy; fMRI = functional MRI; GCS = Glasgow Coma Scale; MD = mean diffusivity; MRE = MR elastography; MRS = MR spectroscopy; mTBI = mild TBI; NAA = N-acetylaspartate; SWI = susceptibility-weighted imaging; TBI = traumatic brain injury; UHF = ultra-high field.

When a Slice Is Not Enough! Comparison of Whole-Brain versus Standard Limited-Slice Perfusion Computed Tomography in Patients with Severe Traumatic Brain Injury

Introduction: Cerebral perfusion computed tomography (PCT) provides crucial information in acute stroke and has an increasing role in traumatic brain injury (TBI) management. Most studies on TBI patients utilize 64-slice scanners, which are limited to four brain slices (limited-brain PCT, LBPCT). Newer 320-slice scanners depict the whole brain perfusion status (WBPCT). We aimed to identify the additional information gained with WBPCT when compared to LBPCT. Patients and methods: Forty-nine patients with severe TBI were investigated within 48 h from admission with WBPCT. Findings from LBPCT were compared with findings from WBPCT. Results: A perfusion abnormality was identified in 39 (80%) and 37 (76%) patients by WBPCT and LBPCT, respectively (p = 0.8). There were 90 and 68 perfusion abnormalities identified by WBPCT and LBPCT, respectively (p < 0.001). In the 39 patients with a perfusion abnormality detected by WBPCT, 15 (38%) had further perfusion abnormalities outside the LBPCT area of coverage. Thirty-six (92%) patients had a larger perfusion abnormality upon WBPCT compared with LBPCT. Additional information gained showed some statistically significant correlation with clinical outcome. Conclusions: In severe TBI patients, WBPCT provides extra information compared to LBPC. The limitations of LBPCT should be considered when evaluating studies reporting on PCT findings and their association with outcomes.

Perfusion Abnormalities are Frequently Detected by Early CT Perfusion and Predict Unfavourable Outcome Following Severe Traumatic Brain Injury

BACKGROUND

In patients with severe traumatic brain injury (TBI), early CT perfusion (CTP) provides additional information beyond the non-contrast CT (NCCT) and may alter clinical management. We hypothesized that this information may prognosticate functional outcome.

METHODS

Five-year prospective observational study was performed in a level-1 trauma centre on consecutive severe TBI patients. CTP (obtained in conjunction with first routine NCCT) was interpreted as: abnormal, area of altered perfusion more extensive than on NCCT, and the presence of ischaemia. Six months Glasgow Outcome Scale-Extended of four or less was considered an unfavourable outcome. Logistic regression analysis of CTP findings and core variables [preintubation Glasgow Coma Scale (GCS), Rotterdam score, base deficit, age] was conducted using Bayesian model averaging to identify the best predicting model for unfavourable outcome.

RESULTS

Fifty patients were investigated with CTP (one excluded for the absence of TBI) [male: 80%, median age: 35 (23-55), prehospital intubation: 7 (14.2%); median GCS: 5 (3-7); median injury severity score: 29 (20-36); median head and neck abbreviated injury scale: 4 (4-5); median days in ICU: 10 (5-15)]. Thirty (50.8%) patients had an unfavourable outcome. GCS was a moderate predictor of unfavourable outcome (AUC = 0.74), while CTP variables showed greater predictive ability (AUC for abnormal CTP = 0.92; AUC for area of altered perfusion more extensive than NCCT = 0.83; AUC for the presence of ischaemia = 0.81).

CONCLUSION

Following severe TBI, CTP performed at the time of the first follow-up NCCT, is a non-invasive and extremely valuable tool for early outcome prediction. The potential impact on management and its cost effectiveness deserves to be evaluated in large-scale studies.

LEVEL OF EVIDENCE III

Prospective study.

Pressure Autoregulation Measurement Techniques in Adult Traumatic Brain Injury, Part I: A Scoping Review of Intermittent/Semi-Intermittent Methods

The purpose of this study was to perform a systematic, scoping review of commonly described intermittent/semi-intermittent autoregulation measurement techniques in adult traumatic brain injury (TBI). Nine separate systematic reviews were conducted for each intermittent technique: computed tomographic perfusion (CTP)/Xenon-CT (Xe-CT), positron emission tomography (PET), magnetic resonance imaging (MRI), arteriovenous difference in oxygen (AVDO₂) technique, thigh cuff deflation technique (TCDT), transient hyperemic response test (THRT), orthostatic hypotension test (OHT), mean flow index (Mx), and transfer function autoregulation index (TF-ARI). MEDLINE^®, BIOSIS, EMBASE, Global Health, Scopus, Cochrane Library (inception to December 2016), and reference lists of relevant articles were searched. A two tier filter of references was conducted. The total number of articles utilizing each of the nine searched techniques for intermittent/semi-intermittent autoregulation techniques in adult TBI were: CTP/Xe-CT (10), PET (6), MRI (0), AVDO₂ (10), ARI-based TCDT (9), THRT (6), OHT (3), Mx (17), and TF-ARI (6). The premise behind all of the intermittent techniques is manipulation of systemic blood pressure/blood volume via either chemical (such as vasopressors) or mechanical (such as thigh cuffs or carotid compression) means. Exceptionally, Mx and TF-ARI are based on spontaneous fluctuations of cerebral perfusion pressure (CPP) or mean arterial pressure (MAP). The method for assessing the cerebral circulation during these manipulations varies, with both imaging-based techniques and TCD utilized. Despite the limited literature for intermittent/semi-intermittent techniques in adult TBI (minus Mx), it is important to acknowledge the availability of such tests. They have provided fundamental insight into human autoregulatory capacity, leading to the development of continuous and more commonly applied techniques in the intensive care unit (ICU). Numerous methods of intermittent/semi-intermittent pressure autoregulation assessment in adult TBI exist, including: CTP/Xe-CT, PET, AVDO₂ technique, TCDT-based ARI, THRT, OHT, Mx, and TF-ARI. MRI-based techniques in adult TBI are yet to be described, with the main focus of MRI techniques on metabolic-based cerebrovascular reactivity (CVR) and not pressure-based autoregulation.

Bedside cerebral microdialysis monitoring of delayed cerebral hypoperfusion in comatose patients with poor grade aneurysmal subarachnoid haemorrhage

BACKGROUND

Delayed cerebral ischaemia (DCI) is frequent after poor grade aneurysmal subarachnoid haemorrhage (SAH). Owing to the limited accuracy of clinical examination, DCI diagnosis is often based on multimodal monitoring. We examined the value of cerebral microdialysis (CMD) in this setting.

METHODS

20 comatose SAH participants underwent CMD monitoring-for hourly sampling of cerebral extracellular lactate/pyruvate ratio (LPR) and glucose-and brain perfusion CT (PCT). Patients were categorised as DCI when PCT (8±3 days after SAH) showed cerebral hypoperfusion, defined as cerebral blood flow <32.5 mL/100 g/min with a mean transit time >5.7 s. Clinicians were blinded to CMD data; for the purpose of the study, only patients who developed cerebral hypoperfusion in anterior and/or middle cerebral arteries were analysed.

RESULTS

DCI (n=9/20 patients) was associated with higher CMD LPR (51±36 vs 31±10 in patients without DCI, p=0.0007) and lower CMD glucose (0.64±0.34 vs 1.22±1.05, p=0.0005). In patients with DCI, CMD changes over the 18 hours preceding PCT diagnosis revealed a pattern of CMD LPR increase (coefficient +2.96 (95% CI 0.13 to 5.79), p=0.04) with simultaneous CMD glucose decrease (coefficient -0.06 (95% CI -0.08 to -0.01), p=0.03, mixed-effects multilevel regression model). No significant CMD changes were noted in patients without DCI.

CONCLUSIONS

In comatose patients with SAH, delayed cerebral hypoperfusion correlates with a CMD pattern of lactate increase and simultaneous glucose decrease. CMD abnormalities became apparent in the hours preceding PCT, thereby suggesting that CMD monitoring may anticipate targeted therapeutic interventions.

Clinical evaluation of post-operative cerebral infarction in traumatic epidural haematoma

BACKGROUND

Patients with traumatic epidural haematoma, undergoing the prompt and correct treatment, usually have favourable outcomes. However, secondary cerebral infarction may be life-threatening condition, as it is difficult to be identified before neurological impairment occurs.

OBJECTIVE

To evaluate the clinical data of patients with traumatic EDH and assess potential risk factors for post-operative cerebral infarction.

METHODS

The clinical data of patients with traumatic EDH were collected and analysed retrospectively.

RESULTS

The univariate analysis revealed 10 potential risk factors (the haematoma location, volume, the largest thickness and mid-line shift, basal cisterns compression, traumatic subarachnoid haemorrhage, pupil dilatation, pre-operative Glasgow Coma Scale score, ∆GCS and intraoperative brain pressure) for cerebral infarction with statistically significant difference. Of these factors, haematoma volume and basal cistern compression turned out to be the most significant risk factors through final multivariate logistic regression analysis.

CONCLUSION

The findings of this study can provide predictive factors for development of cerebral infarction and information for clinical decision-making and future studies.

Brain Vascular Imaging Techniques

Recent major improvements in a number of imaging techniques now allow for the study of the brain in ways that could not be considered previously. Researchers today have well-developed tools to specifically examine the dynamic nature of the blood vessels in the brain during development and adulthood; as well as to observe the vascular responses in disease situations in vivo. This review offers a concise summary and brief historical reference of different imaging techniques and how these tools can be applied to study the brain vasculature and the blood-brain barrier integrity in both healthy and disease states. Moreover, it offers an overview on available transgenic animal models to study vascular biology and a description of useful online brain atlases.

Cerebral Perfusion Pressure is Maintained in Acute Intracerebral Hemorrhage: A CT Perfusion Study

BACKGROUND AND PURPOSE

Although blood pressure reduction has been postulated to result in a fall in cerebral perfusion pressure in patients with intracerebral hemorrhage, the latter is rarely measured. We assessed regional cerebral perfusion pressure in patients with intracerebral hemorrhage by using CT perfusion source data.

MATERIALS AND METHODS

Patients with acute primary intracerebral hemorrhage were randomized to target systolic blood pressures of <150 mm Hg (n = 37) or <180 mm Hg (n = 36). Regional maps of cerebral blood flow, cerebral perfusion pressure, and cerebrovascular resistance were generated by using CT perfusion source data, obtained 2 hours after randomization.

RESULTS

Perihematoma cerebral blood flow (38.7 ± 11.9 mL/100 g/min) was reduced relative to contralateral regions (44.1 ± 11.1 mL/100 g/min, P = .001), but cerebral perfusion pressure was not (14.4 ± 4.6 minutes(-1) versus 14.3 ± 4.8 minutes(-1), P = .93). Perihematoma cerebrovascular resistance (0.34 ± 0.11 g/mL) was higher than that in the contralateral region (0.30 ± 0.10 g/mL, P < .001). Ipsilateral and contralateral cerebral perfusion pressure in the external (15.0 ± 4.6 versus 15.6 ± 5.3 minutes(-1), P = .15) and internal (15.0 ± 4.8 versus 15.0 ± 4.8 minutes(-1), P = .90) borderzone regions were all similar. Borderzone cerebral perfusion pressure was similar to mean global cerebral perfusion pressure (14.7 ± 4.7 minutes(-1), P ≥ .29). Perihematoma cerebral perfusion pressure did not differ between blood pressure treatment groups (13.9 ± 5.5 minutes(-1) versus 14.8 ± 3.4 minutes(-1), P = .38) or vary with mean arterial pressure (r = -0.08, [-0.10, 0.05]).

CONCLUSIONS

Perihematoma cerebral perfusion pressure is maintained despite increased cerebrovascular resistance and reduced cerebral blood flow. Aggressive antihypertensive therapy does not affect perihematoma or borderzone cerebral perfusion pressure. Maintenance of cerebral perfusion pressure provides physiologic support for the safety of blood pressure reduction in intracerebral hemorrhage.

Advances in neuro-monitoring

Neuromonitoring aims to detect harmful physiologic events, early enough to guide the treatment instituted. Evidences encourage us to implement multimodal monitoring, as no single monitor is capable of providing a complete picture of dynamic cerebral state. This review highlights the role of intracranial pressure monitoring, cerebral oxygenation (jugular venous oximetry, brain tissue oxygenation, near infrared oximetry, cerebral microdialysis) and cerebral blood flow monitoring (direct and indirect methods) in the management of neurologically injured patients. In this context, the recent developments of these monitors along with the relevant clinical implications have been discussed. Nevertheless, the diverse range of data obtained from these monitors needs to be integrated and simplified for the clinician. Hence, the future research should focus on identification of a most useful monitor for integration into multimodal system.

Resting functional imaging tools (MRS, SPECT, PET and PCT)

Functional imaging includes imaging techniques that provide information about the metabolic and hemodynamic status of the brain. Most commonly applied functional imaging techniques in patients with traumatic brain injury (TBI) include magnetic resonance spectroscopy (MRS), single photon emission computed tomography (SPECT), positron emission tomography (PET) and perfusion CT (PCT). These imaging modalities are used to determine the extent of injury, to provide information for the prediction of outcome, and to assess evidence of cerebral ischemia. In TBI, secondary brain damage mainly comprises ischemia and is present in more than 80% of fatal cases with traumatic brain injury (Graham et al., 1989; Bouma et al., 1991; Coles et al., 2004). In particular, while SPECT measures cerebral perfusion and MRS determines metabolism, PET is able to assess both perfusion and cerebral metabolism. This chapter will describe the application of these techniques in traumatic brain injury separately for the major groups of severity comprising the mild and moderate to severe group. The application in TBI and potential difficulties of each technique is described. The use of imaging techniques in children will be separately outlined.

Imaging evidence and recommendations for traumatic brain injury: advanced neuro- and neurovascular imaging techniques

SUMMARY

Neuroimaging plays a critical role in the evaluation of patients with traumatic brain injury, with NCCT as the first-line of imaging for patients with traumatic brain injury and MR imaging being recommended in specific settings. Advanced neuroimaging techniques, including MR imaging DTI, blood oxygen level-dependent fMRI, MR spectroscopy, perfusion imaging, PET/SPECT, and magnetoencephalography, are of particular interest in identifying further injury in patients with traumatic brain injury when conventional NCCT and MR imaging findings are normal, as well as for prognostication in patients with persistent symptoms. These advanced neuroimaging techniques are currently under investigation in an attempt to optimize them and substantiate their clinical relevance in individual patients. However, the data currently available confine their use to the research arena for group comparisons, and there remains insufficient evidence at the time of this writing to conclude that these advanced techniques can be used for routine clinical use at the individual patient level. TBI imaging is a rapidly evolving field, and a number of the recommendations presented will be updated in the future to reflect the advances in medical knowledge.

Imaging of cerebral blood flow in patients with severe traumatic brain injury in the neurointensive care

Ischemia is a common and deleterious secondary injury following traumatic brain injury (TBI). A great challenge for the treatment of TBI patients in the neurointensive care unit (NICU) is to detect early signs of ischemia in order to prevent further advancement and deterioration of the brain tissue. Today, several imaging techniques are available to monitor cerebral blood flow (CBF) in the injured brain such as positron emission tomography (PET), single-photon emission computed tomography, xenon computed tomography (Xenon-CT), perfusion-weighted magnetic resonance imaging (MRI), and CT perfusion scan. An ideal imaging technique would enable continuous non-invasive measurement of blood flow and metabolism across the whole brain. Unfortunately, no current imaging method meets all these criteria. These techniques offer snapshots of the CBF. MRI may also provide some information about the metabolic state of the brain. PET provides images with high resolution and quantitative measurements of CBF and metabolism; however, it is a complex and costly method limited to few TBI centers. All of these methods except mobile Xenon-CT require transfer of TBI patients to the radiological department. Mobile Xenon-CT emerges as a feasible technique to monitor CBF in the NICU, with lower risk of adverse effects. Promising results have been demonstrated with Xenon-CT in predicting outcome in TBI patients. This review covers available imaging methods used to monitor CBF in patients with severe TBI.

Temporal changes in CT perfusion values before and after cranioplasty in patients without symptoms related to external decompression: a pilot study

INTRODUCTION

Little is known about hemodynamic disturbances affecting cerebral hemispheres in traumatic brain injury (TBI) after cranioplasty.

METHODS

We prospectively investigated six stable TBI patients who underwent cranioplasty more than 90 days after effective decompressive craniectomy. Computerized tomography perfusion (CTP) studies and evaluation of clinical outcome were performed for each patient before cranioplasty and at 7 days and 3 months after surgery. Cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) were measured in multiple cortical circular regions positioned in cranioplasty-treated and contralateral hemispheres.

RESULTS

Neither complications associated with cranioplasty nor changes in outcome were observed. On the treated side, CBF and CBV values were higher before and 7 days after cranioplasty than at 3 months after surgery, whereas MTT values were lower at 7 days than at 3 months after surgical treatment.

CONCLUSIONS

Our results indicate that cortical perfusion progressively declines in the cranioplasty treated hemisphere but remains stable in the contralateral hemisphere after surgery and suggest that CTP can represent a promising tool for a longitudinal analysis of hemodynamic abnormalities occurring in TBI patients after cranioplasty. In addition, these data imply a possible role of cranioplasty in restoring flow to meet the prevailing metabolic demand.

Neurotraumatology

Neurotraumatology has its roots in ancient history, but its modern foundations are the physical examination, imaging to localize the pathology, and thoughtful medical and surgical decision making. The neurobiology of cranial and spinal injury is similar, with the main goal of therapies being to limit secondary injury. Brain injury treatment focuses on minimizing parenchymal swelling within the confined cranial vault. Spine injury treatment has the additional consideration of spinal coumn stability. Current guidelines for non-operative and operative management are reviewed in this chapter.

Intracranial pressure monitoring, cerebral perfusion pressure estimation, and ICP/CPP-guided therapy: a standard of care or optional extra after brain injury?

Measurement of intracranial pressure (ICP) and mean arterial pressure (MAP) is used to derive cerebral perfusion pressure (CPP) and to guide targeted therapy of acute brain injury (ABI) during neurointensive care. Here we provide a narrative review of the evidence for ICP monitoring, CPP estimation, and ICP/CPP-guided therapy after ABI. Despite its widespread use, there is currently no class I evidence that ICP/CPP-guided therapy for any cerebral pathology improves outcomes; indeed some evidence suggests that it makes no difference, and some that it may worsen outcomes. Similarly, no class I evidence can currently advise the ideal CPP for any form of ABI. 'Optimal' CPP is likely patient-, time-, and pathology-specific. Further, CPP estimation requires correct referencing (at the level of the foramen of Monro as opposed to the level of the heart) for MAP measurement to avoid CPP over-estimation and adverse patient outcomes. Evidence is emerging for the role of other monitors of cerebral well-being that enable the clinician to employ an individualized multimodality monitoring approach in patients with ABI, and these are briefly reviewed. While acknowledging difficulties in conducting robust prospective randomized studies in this area, such high-quality evidence for the utility of ICP/CPP-directed therapy in ABI is urgently required. So, too, is the wider adoption of multimodality neuromonitoring to guide optimal management of ICP and CPP, and a greater understanding of the underlying pathophysiology of the different forms of ABI and what exactly the different monitoring tools used actually represent.

Clinical application of perfusion computed tomography in neurosurgery

OBJECT

Currently, perfusion CT (PCT) is a valuable imaging technique that has been successfully applied to the clinical management of patients with ischemic stroke and aneurysmal subarachnoid hemorrhage (SAH). However, recent literature and the authors' experience have shown that PCT has many more important clinical applications in a variety of neurosurgical conditions. Therefore, the authors share their experiences of its application in various diseases of the cerebrovascular, neurotraumatology, and neurooncology fields and review the pertinent literature regarding expanding PCT applications for neurosurgical conditions, including pitfalls and future developments.

METHODS

A pertinent literature search was conducted of English-language articles describing original research, case series, and case reports from 1990 to 2011 involving PCT and with relevance and applicability to neurosurgical disorders.

RESULTS

In the cerebrovascular field, PCT is already in use as a diagnostic tool for patients suspected of having an ischemic stroke. Perfusion CT can be used to identify and define the extent of the infarct core and ischemic penumbra core, and thus aid patient selection for acute reperfusion therapy. For patients with aneurysmal SAH, PCT provides assessment of early brain injury, cerebral ischemia, and infarction, in addition to vasospasm. It may also be used to aid case selection for aggressive treatment of patients with poor SAH grade. In terms of oncological applications, PCT can be used as an imaging biomarker to assess angiogenesis and response to antiangiogenetic treatments, differentiate between glioma grades, and distinguish recurrent tumor from radiation necrosis. In the setting of traumatic brain injury, PCT can detect and delineate contusions at an early stage. In patients with mild head injury, PCT results have been shown to correlate with the severity and duration of postconcussion syndrome. In patients with moderate or severe head injury, PCT results have been shown to correlate with patients' functional outcome.

CONCLUSIONS

Perfusion CT provides quantitative and qualitative data that can add diagnostic and prognostic value in a number of neurosurgical disorders, and also help with clinical decision making. With emerging new technical developments in PCT, such as characterization of blood-brain barrier permeability and whole-brain PCT, this technique is expected to provide more and more insight into the pathophysiology of many neurosurgical conditions.

Cerebral extracellular lactate increase is predominantly nonischemic in patients with severe traumatic brain injury

Growing evidence suggests that endogenous lactate is an important substrate for neurons. This study aimed to examine cerebral lactate metabolism and its relationship with brain perfusion in patients with severe traumatic brain injury (TBI). A prospective cohort of 24 patients with severe TBI monitored with cerebral microdialysis (CMD) and brain tissue oxygen tension (PbtO2) was studied. Brain lactate metabolism was assessed by quantification of elevated CMD lactate samples (>4 mmol/L); these were matched to CMD pyruvate and PbtO2 values and dichotomized as glycolytic (CMD pyruvate >119 μmol/L vs. low pyruvate) and hypoxic (PbtO2 <20 mm Hg vs. nonhypoxic). Using perfusion computed tomography (CT), brain perfusion was categorized as oligemic, normal, or hyperemic, and was compared with CMD and PbtO2 data. Samples with elevated CMD lactate were frequently observed (41±8%), and we found that brain lactate elevations were predominantly associated with glycolysis and normal PbtO2 (73±8%) rather than brain hypoxia (14±6%). Furthermore, glycolytic lactate was always associated with normal or hyperemic brain perfusion, whereas all episodes with hypoxic lactate were associated with diffuse oligemia. Our findings suggest predominant nonischemic cerebral extracellular lactate release after TBI and support the concept that lactate may be used as an energy substrate by the injured human brain.

Brain CT perfusion provides additional useful information in severe traumatic brain injury

BACKGROUND

The role of brain CT perfusion (CTP) imaging in severe traumatic brain injury (STBI) is unclear. We hypothesised that in STBI early CTP may provide additional information beyond the non contrast CT (NCCT).

METHODS

Subset analysis of an ongoing prospective observational study on trauma patients with STBI who did not require craniectomy and deteriorated or failed to improve neurologically during the first 48h from trauma. Subsequently to follow-up NCCT, a CTP was obtained. Additional findings were defined as an area of altered perfusion on CTP larger than the abnormal area detected by the simultaneous NCCT. Patients who had additional finding (A-CTP) were compared with patients who did not have additional findings (NA-CTP).

RESULTS

Study population was 30 patients [male: 90%, mean age: 38.6 (SD 16.9), blunt trauma: 100%; prehospital intubation: 6 (20%); lowest GCS before intubation: 5.1 (SD 2.0); mean ISS: 30.5 (SD 8.3); mean head and neck AIS: 4.4 (SD 0.8). Days in ICU: 10.2 (SD 6.3). Intracranial pressure (ICP) monitored in 12 (40%). Mean highest ICP in mmHg: 30.1 (SD14.1). There were five (17%) deaths. Findings of NCCT: primarily diffuse axonal injury (DAI) pattern in seven (23%), primarily haematoma in ten (33%), and primarily intracerebral contusion in nine (30%). CTP was performed 24.9 (SD 13) hours from trauma. There were 18 (60%) patients in the A-CTP group and 12 (40.0%) in NA-CTP. The A-CTP group was older (41.7 (SD16.9) vs 27.7 (SD 12.8): P<0.02) and showed on admission NCCT presence of cerebral contusion and absence of DAI. The degree of hypoperfusion was found to be severe enough to be in the ischaemic range in eight patients (27%). CTP altered clinical management in three patients (10%), who were diagnosed with massive and unsurvivable strokes despite minimal changes on NCCT.

CONCLUSION

When compared to NCCT, CTP provided additional diagnostic information in 60% of patients with STBI. CTP altered clinical management in 10% of patients.

Early cerebral circulation disturbance in patients suffering from different types of severe traumatic brain injury: a xenon CT and perfusion CT study

INTRODUCTION

Traumatic brain injury (TBI) is widely known to cause dynamic changes in cerebral blood flow (CBF). In particular, secondary brain insults have been reported to decrease CBF. The purpose of this study was to clarify the cerebral circulation in different types of TBI.

METHODS

Sixty-nine patients with TBI were divided into four groups, the subdural hematoma group, the contusion/intracerebral hematoma group, the diffuse axonal injury group, and the diffuse brain swelling group. In these patients, we simultaneously performed Xe-CT and perfusion CT to evaluate the cerebral circulation on post-injury days 1-3. We measured CBF using Xe-CT and mean transit time using perfusion CT and calculated the cerebral blood volume using the AZ-7000 W98 computer system.

RESULTS

There were no significant differences in the Glasgow Coma Scale score on arrival or the Glasgow Outcome Scale score between the groups. The patients who had suffered focal TBI displayed more significant cerebral circulation disturbances than those that had suffered diffuse TBI. We were able to evaluate the cerebral circulation of TBI patients using these parameters.

CONCLUSION

Moderate hypothermia therapy, which decreases CBF, the cerebral metabolic rate oxygen consumption (CMRO2), and intracranial pressure might be effective against the types of TBI accompanied by cerebral circulation disturbance. We have to use all possible measures including hypothermia therapy to treat severe TBI patients according to the type of TBI that they have suffered.

Emerging imaging tools for use with traumatic brain injury research

This article identifies emerging neuroimaging measures considered by the inter-agency Pediatric Traumatic Brain Injury (TBI) Neuroimaging Workgroup. This article attempts to address some of the potential uses of more advanced forms of imaging in TBI as well as highlight some of the current considerations and unresolved challenges of using them. We summarize emerging elements likely to gain more widespread use in the coming years, because of 1) their utility in diagnosis, prognosis, and understanding the natural course of degeneration or recovery following TBI, and potential for evaluating treatment strategies; 2) the ability of many centers to acquire these data with scanners and equipment that are readily available in existing clinical and research settings; and 3) advances in software that provide more automated, readily available, and cost-effective analysis methods for large scale data image analysis. These include multi-slice CT, volumetric MRI analysis, susceptibility-weighted imaging (SWI), diffusion tensor imaging (DTI), magnetization transfer imaging (MTI), arterial spin tag labeling (ASL), functional MRI (fMRI), including resting state and connectivity MRI, MR spectroscopy (MRS), and hyperpolarization scanning. However, we also include brief introductions to other specialized forms of advanced imaging that currently do require specialized equipment, for example, single photon emission computed tomography (SPECT), positron emission tomography (PET), encephalography (EEG), and magnetoencephalography (MEG)/magnetic source imaging (MSI). Finally, we identify some of the challenges that users of the emerging imaging CDEs may wish to consider, including quality control, performing multi-site and longitudinal imaging studies, and MR scanning in infants and children.

Common data elements in radiologic imaging of traumatic brain injury

Traumatic brain injury (TBI) has a poorly understood pathology. Patients suffer from a variety of physical and cognitive effects that worsen as the type of trauma worsens. Some noninvasive insights into the pathophysiology of TBI are possible using magnetic resonance imaging (MRI), computed tomography (CT), and many other forms of imaging as well. A recent workshop was convened to evaluate the common data elements (CDEs) that cut across the imaging field and given the charge to review the contributions of the various imaging modalities to TBI and to prepare an overview of the various clinical manifestations of TBI and their interpretation. Technical details regarding state-of-the-art protocols for both MRI and CT are also presented with the hope of guiding current and future research efforts as to what is possible in the field. Stress was also placed on the potential to create a database of CDEs as a means to best record information from a given patient from the reading of the images.

Neuromonitoring for Traumatic Brain Injury in Neurosurgical Intensive Care

The primary aim of neuromonitoring in patients with traumatic brain injury is early detection of secondary brain insults so that timely interventions can be instituted to prevent or treat secondary brain injury. Intracranial pressure monitoring has been a stalwart in neuromonitoring and is still very much the main parameter to guide therapy in brain injured patients in many centres. Cerebral oxygenation is also established as an important parameter for monitoring: global cerebral oxygenation is reliably measured using jugular venous oxygen saturation while brain tissue oxygen tension measurement allows focal brain oxygenation to be monitored. Near-infrared spectroscopy allows a non-invasive option for monitoring of regional cerebral oxygenation. Cerebral microdialysis makes focal measurements of markers of cellular metabolism and cellular injury and death possible, and it is in transition from being a research tool to being an important clinical tool in neuromonitoring. Multimodal monitoring allows different parameters of brain physiology and function to be monitored and can improve identification and prediction of secondary cerebral insults. Multimodal monitoring can potentially improve outcomes in patients with traumatic brain injury by promoting customised treatment strategies for individual patients in place of the commonplace practice of strict adherence to achieving the same standard physiological targets for every patient.

Radiation dose reduction in time-resolved CT angiography using highly constrained back projection reconstruction

Recently dynamic, time-resolved three-dimensional computed tomography angiography (CTA) has been introduced to the neurological imaging community. However, the radiation dose delivered to patients in time-resolved CTA protocol is a high and potential risk associated with the ionizing radiation dose. Thus, minimizing the radiation dose is highly desirable for time-resolved CTA. In order to reduce the radiation dose delivered during dynamic, contrast-enhanced CT applications, we introduce here the CT formulation of HighlY constrained back PRojection (HYPR) imaging. We explore the radiation dose reduction approaches of both acquiring a reduced number of projections for each image and lowering the tube current used during acquisition. We then apply HYPR image reconstruction to produce image sets at a reduced patient dose and with low image noise. Numerical phantom experiments and retrospective analysis of in vivo canine studies are used to assess the accuracy and quality of HYPR reduced dose image sets and validate our approach. Experimental results demonstrated that a factor of 6-8 times radiation dose reduction is possible when the HYPR algorithm is applied to time-resolved CTA exams.

Cerebral perfusion CT: technique and clinical applications

Perfusion computed tomography (PCT) is an imaging technique that allows rapid, noninvasive, quantitative evaluation of cerebral perfusion by generating maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). The concepts behind this imaging technique were developed in the 1980s', but its widespread clinical use was allowed by the recent introduction of rapid, large-coverage multidetector-row CT scanners. Key clinical applications for PCT include the diagnosis of cerebral ischemia and infarction, and evaluation of vasospasm after subarachnoid hemorrhage. PCT measurements of cerebrovascular reserve after acetazolamide challenges in patients with vascular stenoses permit evaluation of candidacy for bypass surgery and endovascular treatment. PCT has also been used to assess cerebral perfusion after head trauma and microvascular permeability in the setting of intracranial neoplasm. Some controversy exists regarding this technique, including questions regarding correct selection of an arterial input vessel, the accuracy of quantitative results, and the reproducibility of results. This article provides an overview of PCT, including details of technique, major clinical applications, and limitations.

Perfusion-CT for early assessment of traumatic cerebral contusions

INTRODUCTION

To investigate the value of perfusion-CT (PCT) for assessment of traumatic cerebral contusions (TCC) and to compare the abilities of early noncontrast CT and PCT modalities to evaluate tissue viability.

METHODS

PCT studies performed in 30 patients suffering from TCC during the acute phase of their illness were retrospectively reviewed. Cerebral blood flow (CBF), volume (CBV) and mean transit time (MTT) were measured in three different areas: the hemorrhagic core of the TCC, the surrounding hypodense area and the perilesional normal-appearing parenchyma. TCC area was measured on CBF-, CBV- and MTT-derived maps and compared with the areas measured using the same slice obtained with CT scans performed on admission, at the time of PCT (follow-up CT) and at 1 week.

RESULTS

TCC were characterized by low CBF and CBV values (9.2+/-6.6 ml/100 g per min and 0.9+/-0.7 ml/100 g, respectively) and a significant prolongation of MTT (11.9+/-10.7 s) in the hemorrhagic core whereas PCT parameters were more variable in the hypodense area. The TCC whole area showed a noticeable growth of the lesions during the first week of admission. In comparison with early noncontrast CT, CBV and CBF maps proved to be more congruent with the findings of noncontrast CT scans at 1 week.

CONCLUSION

PCT confirmed the results of xenon-CT studies and was shown to allow better evaluation of tissue viability than noncontrast CT. These findings suggest that PCT could be implemented in the future for the early assessment of patients with traumatic brain injury.

The implications of cerebral ischemia and metabolic dysfunction for treatment strategies in neurointensive care

PURPOSE OF REVIEW

This review outlines recent observations made in a clinical setting that document the extent and degree of cerebral ischemia and metabolic dysfunction after acute brain injury. The intent is to guide clinicians in considering how best to monitor and treat brain metabolism in the intensive care unit.

RECENT FINDINGS

Recent findings have documented that following brain injury there is a heterogeneous distribution of disturbed metabolism with some areas of the brain rendered severely oligemic or ischemic while other areas are less affected. Areas that are not truly ischemic, however, still appear to be at risk of excitotoxic injury. Various methods of monitoring the brain are compared and discussed, including positron emission tomography, brain parenchymal oxygenation monitoring, brain microdialysis, and continuous electroencephalography; important caveats are also presented. These methods are complementary and provide information about oxygen utilization and other aspects of brain metabolism. Integration of these methods into a practical clinical protocol is discussed.

SUMMARY

The intensive care of acute brain injury has entered a new era in which monitoring of brain metabolism will permit targeted therapy and may possibly minimize iatrogenic adverse effects by making better use of our powerful therapies.

[Brain perfusion and metabolism imaging techniques]

Due to recent efforts in improving spatial and temporal resolution in imaging techniques, it is now possible to get relevant information about brain perfusion and metabolism in humans. This information can significantly impact on brain pathophysiology, diagnosis assessment and therapy options, particularly in patients having brain ischemia. Among these imaging and metabolism techniques are dynamic perfusion computed tomography, perfusion MRI, positron emission tomography and NMR spectroscopic imaging. The goal of this article is an overview of these four techniques, with their own technical description, advantages and drawbacks. Details are provided about brain parameters given by each technique and their clinical relevance, the accessibility of the technique in the emergency setting and the optimal window to use it during the patient's evolution.

Cerebral perfusion computerized tomography: influence of reference vessels, regions of interest and interobserver variability

INTRODUCTION

There are still no standardized guidelines for perfusion computerized tomography (PCT) analysis.

METHODS

A total of 61 PCT studies were analyzed using either the anterior cerebral artery (ACA) or the middle cerebral artery (MCA) as the arterial reference, and the superior sagittal sinus (SSS) or the vein of Galen (VG) as the venous reference. The sizes of regions of interest (ROI) were investigated comparing PCT results obtained using a hemispheric ROI combined with vascular pixel elimination with those obtained using five smaller ROIs located over the cortex and basal ganglia. In addition, interobserver variations were explored using a standardized protocol.

RESULTS

MCA-based measurements of cerebral blood flow (CBF) and blood volume (CBV) were in accordance with those obtained with the ACA except in 16 patients with ischemic stroke, in whom CBF was overestimated by the ipsilateral MCA. Venous maximal intensity was significantly lower with the VG when compared with the SSS, resulting in overestimation of CBF and CBV. However, in 13.3% of patients the VG ROI yielded higher maximal intensities than the SSS ROI. There was no difference in PCT results between hemispheric ROI and averaged separate ROI when vascular pixel elimination was used. Finally, interobserver variations were as high as 11% for CBF and 12% for CBV.

CONCLUSION

The present results suggest that pathological rather than anatomical considerations should dictate the choice of the arterial ROI. For venous ROI, although SSS seems to be adequate in most instances, deep cerebral veins may occasionally generate higher maximal intensities and should therefore be selected. Importantly, significant user-dependency should be taken into account.

Cerebral vascular autoregulation assessed by perfusion-CT in severe head trauma patients

PURPOSE

To use perfusion-CT technique in order to characterize cerebral vascular autoregulation in a population of severe head trauma patients with features of cerebral edema either on the admission or on the follow-up conventional noncontrast cerebral CT.

MATERIAL AND METHODS

A total of 80 perfusion-CT examinations were obtained in 42 severe head trauma patients with features of cerebral edema on conventional noncontrast cerebral CT, either on admission or during follow-up. Perfusion-CT results, i.e. the regional cerebral blood volume (rCBV) and flow (rCBF), were correlated with the mean arterial pressure (MAP) measured during each perfusion-CT examination. Ratios were defined to integrate the concept of cerebral vascular autoregulation, and cluster analysis performed, which allowed identification of different subgroups of patients. MAP values and perfusion-CT results in these groups were compared using Kruskal-Wallis and Wilcoxon (Mann-Whitney) tests. Moreover, the functional outcome of the 42 patients was evaluated 3 months after trauma on the basis of the Glasgow Outcome Scale (GOS) score and similarly compared between groups.

RESULTS

Three main groups of patients were identified: 1) 22 perfusion-CT examinations were collected in 13 patients, characterized by high rCBV and rCBF values and by significant dependence of perfusion-CT rCBV and rCBF results on MAP values (p<0.001), 2) 23 perfusion-CT examinations collected in 19 patients showing perfusion-CT results similar to control trauma subjects, and 3) 33 perfusion-CT collected in 16 patients, with low rCBV and rCBF values and near-independence of perfusion-CT results with respect to MAP values. The first group was interpreted as showing impaired cerebral vascular autoregulation, which was preserved in the third group. The second group was associated with the best functional outcome; it was linked to the first group, because eight patients went from one group to the other from admission to follow-up.

CONCLUSION

Perfusion-CT in severe head trauma patients was able to provide direct and quantitative assessment of cerebral vascular autoregulation with a single measurement. It could hence be used as a guide for brain edema therapy, as well as to monitor the treatment efficiency.

Contrast ultrasonographic assessment of cerebral perfusion in patients undergoing decompressive craniectomy for traumatic brain injury

Object

The aims of this study were to determine whether contrast-enhanced ultrasonography (CEU) could be used for noninvasive evaluation of cerebral perfusion in patients with traumatic brain injury (TBI) and to assess the effect of decompressive surgery on cerebral perfusion as measured by CEU.

Methods

Contrast-enhanced ultrasonography with intravenous administration of a microbubble contrast agent was performed in six patients with TBI undergoing decompressive craniectomy. Contrast-enhanced ultrasonography was performed through a bur hole before craniectomy and through the calvarial defect immediately after craniectomy and on postoperative Days 1 and 2. For the latter two studies, patients were placed in the recumbent position and at a 35° incline to investigate changes in perfusion produced by modulation of intracranial pressure (ICP). Cerebral microvascular blood flow increased by almost threefold immediately after craniectomy, from a mean of 7.5 ± 6.9 (standard deviation [SD]) to 20.9 ± 11.6 (p < 0.05), and further improved on postoperative Day 1 (mean 37.1 ± 13.9 [SD], p < 0.05, compared with postcraniectomy microvascular blood flow) without subsequent change on Day 2. The change in microvascular perfusion correlated inversely with the initial ICP (p < 0.01), indicating less recovery of flow when preoperative ICP was markedly elevated. On postoperative Days 1 and 2, head-of-bed elevation produced an increase in microvascular perfusion on CEU (mean 37 ± 11 compared with 51 ± 20, p < 0.05) and a small decrease in ICP (mean 16 ± 5 mm Hg compared with 12 ± 4 mm Hg, p < 0.05). In patients with parenchymal hematoma, CEU provided spatial information on perfusion abnormalities in the hemorrhagic core and surrounding tissues.

Conclusions

Contrast-enhanced ultrasonography has potential for the intraoperative and bedside assessment of cerebral perfusion in patients with TBI. The technique may be appropriate for evaluating responses to therapies aimed at preventing secondary ischemia and for assessing regional perfusion abnormalities.

Comparative overview of brain perfusion imaging techniques

Numerous imaging techniques have been developed and applied to evaluate brain hemodynamics. Among these are: Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), Xenon-enhanced Computed Tomography (XeCT), Dynamic Perfusion-computed Tomography (PCT), Magnetic Resonance Imaging Dynamic Susceptibility Contrast (DSC), Arterial Spin-Labeling (ASL), and Doppler Ultrasound. These techniques give similar information about brain hemodynamics in the form of parameters such as cerebral blood flow (CBF) or volume (CBV). All of them are used to characterize the same types of pathological conditions. However, each technique has its own advantages and drawbacks. This article addresses the main imaging techniques dedicated to brain hemodynamics. It represents a comparative overview, established by consensus among specialists of the various techniques. For clinicians, this paper should offers a clearer picture of the pros and cons of currently available brain perfusion imaging techniques, and assist them in choosing the proper method in every specific clinical setting.

Cerebral blood flow monitoring in clinical practice

The brain depends on a continuous flow of blood to provide it with oxygen and glucose needed to maintain normal function and structural integrity, thus cerebral blood flow is normally tightly regulated. A decrease in cerebral blood flow to ischemic levels may be tolerated for only minutes to hours, depending on the severity of the ischemia. If cerebral blood flow ceases completely, brain cell death occurs within minutes. A variety of conditions are encountered clinically, such as stroke or traumatic brain injury, where an actual or potential alteration in cerebral blood flow puts the brain at risk for ischemia and infarction. In this article, the physiology of cerebral blood flow will be presented as a basis for understanding cerebral blood flow regulation and the rationale for clinical interventions to optimize cerebral blood flow. Techniques currently available to assess cerebral blood flow and clinical situations in which cerebral blood flow is measured will be discussed. Clinical interventions will be presented briefly.

Brain tissue oxygen monitoring in intracerebral hemorrhage

INTRODUCTION

Brain tissue oxygen (PbrO2) monitoring is an emerging technique for detection of secondary brain injury in neurocritical care. Although it has been extensively reported in traumatic brain injury and aneurysmal subarachnoid hemorrhage, its use in nontraumatic intracerebral hemorrhage (ICH) has not been well described. We report complementary preliminary studies in a large animal model and in patients that demonstrate the feasibility of PbrO2 monitoring after ICH.

METHODS

To assess early events after ICH, Licox Clark-type oxygen probes were inserted in the bilateral frontal white matter of four anesthetized swine that subsequently underwent right parietal hematoma formation in an experimental model of ICH. Intracranial pressure (ICP) was monitored as well. Seven patients with acute ICH, who were undergoing ICP monitoring as part of standard neurocritical care, had placement of a frontal oxygen probe, with subsequent monitoring for up to 7 days.

RESULTS

In the swine ICH model, a rise in ICP early after hematoma formation was accompanied by a decrease in ipsilateral and contralateral PbrO2. Secondary increases in hematoma volume resulted in further decreases in PbrO2 over the first hour after ICH. In patients undergoing oxygen monitoring, low PbrO2 (<15 mmHg) was common. In these patients, changes in FiO2, mean arterial pressure, and cerebral perfusion pressure (but not ICP) predicted subsequent change in PbrO2.

CONCLUSION

Brain tissue oxygen monitoring is feasible in ICH patients, as well as in a swine model of ICH. Translational research that emphasizes complementary information derived from human and animal studies may yield additional insights not available from either alone.

Managing head injured patients

PURPOSE OF REVIEW

In this article we aim to review the recent literature concerning the management of traumatic brain injury patients, summarize the main findings, and discuss the impact of these findings on clinical practice.

RECENT FINDINGS

Several authors have focused on the development of more reliable and informative tools to predict outcome in traumatic brain injury as well as refining the definition of cerebral ischemia in last year's literature. The validity of the current cerebral perfusion pressure management guidelines has also come under scrutiny. It appears that a one size fits all therapy is not a suitable approach for traumatic brain injury patients. An individualized approach, depending on the integrity of pressure autoregulation mechanisms, would be more advisable. Clinical trials investigating brain protective treatments in head injured patients have been disappointing so far. Increasing the homogeneity of patients entering brain protective studies might be an answer. Finally, the use of hyperoxia as well as factors contributing to secondary brain injury such as the occurrence of hyperthermia, with or without an infectious process, have been assessed in head injury patients.

SUMMARY

The key term for the management of traumatic brain injury patients in the early twenty-first century will clearly be 'individualized therapy'. The search of an ideal cerebral perfusion pressure target that would fit every head-injured patients is a utopia. More energy should be focused on the development of reliable tools for outcome prediction and outcome assessment for traumatic brain injured patients. That, and a better targeting of patients entering brain protective trials, should increase the likelihood of demonstrating a significant salvaging effect of a particular treatment in humans.

Comparative overview of brain perfusion imaging techniques

BACKGROUND AND PURPOSE

Numerous imaging techniques have been developed and applied to evaluate brain hemodynamics. Among these are positron emission tomography, single photon emission computed tomography, Xenon-enhanced computed tomography, dynamic perfusion computed tomography, MRI dynamic susceptibility contrast, arterial spin labeling, and Doppler ultrasound. These techniques give similar information about brain hemodynamics in the form of parameters such as cerebral blood flow or cerebral blood volume. All of them are used to characterize the same types of pathological conditions. However, each technique has its own advantages and drawbacks.

SUMMARY OF REVIEW

This article addresses the main imaging techniques dedicated to brain hemodynamics. It represents a comparative overview established by consensus among specialists of the various techniques.

CONCLUSIONS

For clinicians, this article should offer a clearer picture of the pros and cons of currently available brain perfusion imaging techniques and assist them in choosing the proper method for every specific clinical setting.

Multimodality monitoring and telemonitoring in neurocritical care: from microdialysis to robotic telepresence

PURPOSE OF REVIEW

This review will highlight the state-of-the-art in brain monitoring in neurointensive care and define methods of integrating this technology into patient care using telemedicine methods.

RECENT FINDINGS

Several new methods of brain monitoring have been established over the last several years including continuous EEG monitoring, brain tissue oxygenation, jugular venous oxygenation, and cerebral microdialysis. Observational research using these monitors has documented that the brain metabolism, blood flow and function are dynamic after a primary insult. The dynamic nature of the brain can predispose the brain to secondary insults that can occur in the setting of intensive care. Several variables of brain metabolism and function can be monitored and directly impact treatment decisions as well as provide diagnostic and prognostic information. General treatment guidelines for brain injury and brain hemorrhage were developed, in part, prior to implementation of use of these monitors, and there is a trend away from adoption of a one-size-fits-all approach and a trend towards monitor-guided therapy. Dealing with the data provided by multimodality monitoring can be overwhelming. Efficient use of such information requires methods to integrate diverse sets of information, and methods to access the online monitoring information remotely and at any time, day or night. Such remote access integration methods will be reviewed.

SUMMARY

Multimodality and telemedicine techniques have advanced the state of knowledge about brain function in critically ill patients, and are presently being implemented to direct therapy. Increasing complexity of care will become commonplace, but will be facilitated by computer-enhanced tools that permit the intensivist to integrate this information into an improved treatment regimen.

Réunion de neuroanesthésie-réanimation. Prise en charge anesthésique du patient en hypertension intracrânienne aiguë

Transcranial Doppler and, if possible, measurement of intracranial pressure (ICP) allow preoperative diagnosis of acute intracranial hypertension (ICH) after brain trauma. The main goal of the anaesthesiologist is to prevent the occurrence of secondary brain injuries and to avoid cerebral ischaemia. Treatment of high ICP is mainly achieved with osmotherapy. High-dose mannitol administration (1.4 to 2 g/kg given in bolus doses) may be considered a better option than conventional doses, especially before emergency evacuation of a cerebral mass lesion. Hypertonic saline seems as effective as mannitol without rebound effect and without diuresis increase. Haemostasis should be normalized before neurosurgery and invasive blood pressure monitoring is mandatory. For anaesthesia induction, thiopental or etomidate may be used. In case of ICH, halogenated and nitrous oxide should be avoided. Until the dura is open, mean arterial pressure should be maintained around 90 mmHg (or cerebral perfusion pressure around 70 mmHg). If a long-lasting (several hours) extracranial surgery is necessary, ICP should be monitored and treatment of ICH should have been instituted before.