Multimodality monitoring in neurocritical care

Future of Artificial Intelligence in Surgery: A Narrative Review

Artificial intelligence (AI) is the capability of a machine to execute cognitive processes that are typically considered to be functions of the human brain. It is the study of algorithms that enable machines to reason and perform mental tasks, including problem-solving, object and word recognition, and decision-making. Once considered science fiction, AI today is a fact and an increasingly prevalent subject in both academic and popular literature. It is expected to reshape medicine, benefiting both healthcare professionals and patients. Machine learning (ML) is a subset of AI that allows machines to learn and make predictions by recognizing patterns, thus empowering the medical team to deliver better care to patients through accurate diagnosis and treatment. ML is expanding its footprint in a variety of surgical specialties, including general surgery, ophthalmology, cardiothoracic surgery, and vascular surgery, to name a few. In recent years, we have seen AI make its way into the operating theatres. Though it has not yet been able to replace the surgeon, it has the potential to become a highly valuable surgical tool. Rest assured that the day is not far off when AI shall play a significant intraoperative role, a projection that is currently marred by safety concerns. This review aims to explore the present application of AI in various surgical disciplines and how it benefits both patients and physicians, as well as the current obstacles and limitations facing its seemingly unstoppable rise.

The Role of Brain Tissue Oxygenation Monitoring in the Management of Subarachnoid Hemorrhage: A Scoping Review

Monitoring of brain tissue oxygenation (PbtO2) is an important component of multimodal monitoring in traumatic brain injury. Over recent years, use of PbtO2 monitoring has also increased in patients with poor-grade subarachnoid hemorrhage (SAH), particularly in those with delayed cerebral ischemia. The aim of this scoping review was to summarize the current state of the art regarding the use of this invasive neuromonitoring tool in patients with SAH. Our results showed that PbtO2 monitoring is a safe and reliable method to assess regional cerebral tissue oxygenation and that PbtO2 represents the oxygen available in the brain interstitial space for aerobic energy production (i.e., the product of cerebral blood flow and the arterio-venous oxygen tension difference). The PbtO2 probe should be placed in the area at risk of ischemia (i.e., in the vascular territory in which cerebral vasospasm is expected to occur). The most widely used PbtO2 threshold to define brain tissue hypoxia and initiate specific treatment is between 15 and 20 mm Hg. PbtO2 values can help identify the need for or the effects of various therapies, such as hyperventilation, hyperoxia, induced hypothermia, induced hypertension, red blood cell transfusion, osmotic therapy, and decompressive craniectomy. Finally, a low PbtO2 value is associated with a worse prognosis, and an increase of the PbtO2 value in response to treatment is a marker of good outcome.

Physiological Monitoring in Patients with Acute Brain Injury: A Multimodal Approach

Neurocritical care management of acute brain injury (ABI) is focused on identification, prevention, and management of secondary brain injury (SBI). Physiologic monitoring of the brain and other organ systems has a role to predict patient recovery or deterioration, guide individualized therapeutic interventions, and measure response to treatment, with the goal of improving patient outcomes. In this review, we detail how specific physiologic markers of brain injury and neuromonitoring tools are integrated and used in ABI patients to develop therapeutic approaches to prevent SBI.

Predictive modeling in neurocritical care using causal artificial intelligence

Artificial intelligence (AI) and digital twin models of various systems have long been used in industry to test products quickly and efficiently. Use of digital twins in clinical medicine caught attention with the development of Archimedes, an AI model of diabetes, in 2003. More recently, AI models have been applied to the fields of cardiology, endocrinology, and undergraduate medical education. The use of digital twins and AI thus far has focused mainly on chronic disease management, their application in the field of critical care medicine remains much less explored. In neurocritical care, current AI technology focuses on interpreting electroencephalography, monitoring intracranial pressure, and prognosticating outcomes. AI models have been developed to interpret electroencephalograms by helping to annotate the tracings, detecting seizures, and identifying brain activation in unresponsive patients. In this mini-review we describe the challenges and opportunities in building an actionable AI model pertinent to neurocritical care that can be used to educate the newer generation of clinicians and augment clinical decision making.

Role of Ultrasound in Neurocritical Care

Bedside point of care ultrasound has acquired an extremely significant role in diagnosis and management of neurocritical care, just as it has in other specialties. Easy availability and increasing expertise have allowed the intensivists to use it in a wide array of situations, such as confirming clinical findings as well as for interventional and prognostic purposes. At present, the clinical applications of ultrasonography (USG) in a neurosurgical patient include estimation of elevated intracranial pressure (ICP), assessment of cerebral blood flow (CBF) and velocities, diagnosis of intracranial mass lesion and midline shifts, and examination of pupils, apart from the systemic applications. Transcranial sonography has also found use in the diagnosis of the cerebral circulatory arrest. An increasing number of clinicians are now relying on the use of ultrasound in the neurointensive care unit for neurological as well as non-neurological indications. These uses include the diagnosis of shock, respiratory failure, deep vein thrombosis and performing bedside procedures.

Multimodal neurocritical monitoring

Neurocritical monitoring is important in caring for patients in the neurological intensive care unit. Although clinical neurologic examination is standard for neurocritical monitoring, changes found during the examination are often late signs and insufficient to detect and prevent secondary brain injury. Therefore, various neuromonitoring tools have been developed to monitor different physiologic parameters, such as cerebral oxygenation, cerebral blood flow, cerebral pressure, cerebral autoregulation, cerebral electric activity, and cerebral metabolism. In this review, we have discussed current commonly used neurocritical monitoring tools. No single monitor is sufficient and perfect for neurocritical monitoring. Multimodal neurocritical monitoring is the current trend. However, the lack of common formatting standards and uncertainty of improvement in patients' outcomes warrant further studies of multimodal neurocritical monitoring. Nevertheless, multimodal neurocritical monitoring considers individual pathophysiological variations in patients or their injuries and allows clinicians to tailor individualized management decisions.

Checklists to guide the supportive and critical care of tuberculous meningitis

The assessment and management of tuberculous meningitis (TBM) is often complex, yet no standardised approach exists, and evidence for the clinical care of patients, including those with critical illness, is limited. The roles of proformas and checklists are increasing in medicine; proformas provide a framework for a thorough approach to patient care, whereas checklists offer a priority-based approach that may be applied to deteriorating patients in time-critical situations. We aimed to develop a comprehensive assessment proforma and an accompanying 'priorities' checklist for patients with TBM, with the overriding goal being to improve patient outcomes. The proforma outlines what should be asked, checked, or tested at initial evaluation and daily inpatient review to assist supportive clinical care for patients, with an adapted list for patients in critical care. It is accompanied by a supporting document describing why these points are relevant to TBM. Our priorities checklist offers a useful and easy reminder of important issues to review during a time-critical period of acute patient deterioration. The benefit of these documents to patient outcomes would require investigation; however, we hope they will promote standardisation of patient assessment and care, particularly of critically unwell individuals, in whom morbidity and mortality remains unacceptably high.

Current Status and Recommendations in Multimodal Neuromonitoring

Every patient in neurocritical care evolves through two phases. Acute pathologies are addressed first. These include trauma, hemorrhagic or ischemic stroke, or neuroinfection. Soon after, the concentration shifts to identifying secondary pathologies like fever, seizures, and ischemia, which may exacerbate the brain injury. Frequent bedside examinations are not sufficient for timely detection and prevention of secondary brain injury (SBI) as per the International Multidisciplinary Consensus Conference on Multimodality Monitoring in Neurocritical Care. Multimodality monitoring (MMM) can help in tailoring treatment decisions to prevent such a brain injury. Multimodal neuromonitoring involves data-guided therapeutic interventions by employing various tools and data integration to understand brain physiology. Monitors provide real-time information on cerebral hemodynamics, oxygenation, metabolism, and electrophysiology. The monitors may be invasive/noninvasive and global/regional. We have reviewed such technologies in this write-up. Novel themes like bioinformatics, clinical research, and device development will also be discussed.

Machine Learning and Artificial Intelligence in Neurocritical Care: a Specialty-Wide Disruptive Transformation or a Strategy for Success

PURPOSE OF REVIEW

Neurocritical care combines the complexity of both medical and surgical disease states with the inherent limitations of assessing patients with neurologic injury. Artificial intelligence (AI) has garnered interest in the basic management of these complicated patients as data collection becomes increasingly automated.

RECENT FINDINGS

In this opinion article, we highlight the potential AI has in aiding the clinician in several aspects of neurocritical care, particularly in monitoring and managing intracranial pressure, seizures, hemodynamics, and ventilation. The model-based method and data-driven method are currently the two major AI methods for analyzing critical care data. Both are able to analyze the vast quantities of patient data that are accumulated in the neurocritical care unit. AI has the potential to reduce healthcare costs, minimize delays in patient management, and reduce medical errors. However, these systems are an aid to, not a replacement for, the clinician's judgment.

Checklists to guide the supportive and critical care of tuberculous meningitis

The assessment and management of tuberculous meningitis (TBM) is often complex, yet no standardised approach exists, and evidence for the clinical care of patients, including those with critical illness, is limited. The roles of proformas and checklists are increasing in medicine; proformas provide a framework for a thorough approach to patient care, whereas checklists offer a priority-based approach that may be applied to deteriorating patients in time-critical situations. We aimed to develop a comprehensive assessment proforma and an accompanying 'priorities' checklist for patients with TBM, with the overriding goal being to improve patient outcomes. The proforma outlines what should be asked, checked, or tested at initial evaluation and daily inpatient review to assist supportive clinical care for patients, with an adapted list for patients in critical care. It is accompanied by a supporting document describing why these points are relevant to TBM. Our priorities checklist offers a useful and easy reminder of important issues to review during a time-critical period of acute patient deterioration. The benefit of these documents to patient outcomes would require investigation; however, we hope they will promote standardisation of patient assessment and care, particularly of critically unwell individuals, in whom morbidity and mortality remains unacceptably high.

Usefulness of Intracranial Pressure and Mean Arterial Pressure for Predicting Neurological Prognosis in Cardiac Arrest Survivors Who Undergo Target Temperature Management

We aimed to compare the relationship of mean arterial pressure (MAP) and intracranial pressure (ICP) to predict the neurological prognosis in cardiac arrest (CA) survivors. We retrospectively examined out-of-hospital CA patients treated with targeted temperature management. ICP was measured using cerebrospinal fluid (CSF) pressure, whereas MAP was measured as blood pressure monitored through the radial or femoral artery during CSF pressure measurement. Primary outcome was 6-month neurological outcome. Of 92 enrolled patients, the favorable outcome group comprised 31 (34%) patients. The median and interquartile range of MAP were significantly higher and ICP was significantly lower in patients with favorable neurological outcomes than in those with unfavorable neurological outcomes (94.3 mmHg [80.0-105.3] vs. 82.0 mmHg [65.3-96.3], p = 0.021 and 9.4 mmHg [10.8-8.7] vs. 18.8 mmHg [20.0-15.7], p < 0.001, respectively). ICP showed the higher area under the receiver operating characteristic curve (area under curve [AUC] = 0.953, 95% confidence interval [CI] = 0.888-0.986) for neurological outcome prediction. MAP showed the lower AUC (0.648, 95% CI = 0.541-0.744). Higher accurate prognosis was predicted by ICP than MAP, and the prognostic performance was good. Prospective multicenter studies are required to confirm these results.

Artificial intelligence in neurocritical care

BACKGROUND

Neurocritical care combines the management of extremely complex disease states with the inherent limitations of clinically assessing patients with brain injury. As the management of neurocritical care patients can be immensely complicated, the automation of data-collection and basic management by artificial intelligence systems have garnered interest.

METHODS

In this opinion article, we highlight the potential artificial intelligence has in monitoring and managing several aspects of neurocritical care, specifically intracranial pressure, seizure monitoring, blood pressure, and ventilation.

RESULTS

The two major AI methods of analytical technique currently exist for analyzing critical care data: the model-based method and data driven method. Both of these methods have demonstrated an ability to analyze vast quantities of patient data, and we highlight the ways in which these modalities of artificial intelligence might one day play a role in neurocritical care.

CONCLUSIONS

While none of these artificial intelligence systems are meant to replace the clinician's judgment, these systems have the potential to reduce healthcare costs and errors or delays in medical management.

Analysis of cerebral blood flow and intracranial hypertension in critical patients with non-hepatic hyperammonemia

Hyperammonemia in adults is generally associated with cerebral edema, decreased cerebral metabolism, and increased cerebral blood flow. The aim of this study was to evaluate the association between non-hepatic hyperammonemia and intracranial hypertension assessed by Doppler flowmetry and measurement of the optic nerve sheath. A prospective cohort study in critically ill patients hospitalized in intensive care units of a University Hospital between March 2015 and February 2016. Clinical data and severity scores were collected and the Glasgow coma scale was recorded. Serial serum ammonia dosages were performed in all study patients. Transcranial Doppler evaluation was carried out for the first 50 consecutive results of each stratum of ammonemia: normal (<35 μmol/L), mild hyperammonemia (≥35 μmol/L and < 50 μmol/L), moderate hyperammonemia (≥50 μmol/L and < 100 μmol/L), and severe hyperammonemia (≥100 μmol/L). The measurement of the optic nerve sheath was performed at the same time as the Doppler examination if the patient scored less than 8 on the Glasgow coma scale. There was no difference in flow velocity in the cerebral arteries between patients with and without hyperammonemia. Patients with hyperammonemia presented longer ICU stay. Optic nerve sheath thickness was higher in the group with severe hyperammonemia and this group presented an association with intracranial hypertension. Higher mortality was observed in the severe hyperammonemia group. There was an association between severe hyperammonemia and signs of intracranial hypertension. No correlation was found between ammonia levels and cerebral blood flow velocity through the Doppler examination.

Health status monitoring for ICU patients based on locally weighted principal component analysis

BACKGROUND AND OBJECTIVES

Intelligent status monitoring for critically ill patients can help medical stuff quickly discover and assess the changes of disease and then make appropriate treatment strategy. However, general-type monitoring model now widely used is difficult to adapt the changes of intensive care unit (ICU) patients' status due to its fixed pattern, and a more robust, efficient and fast monitoring model should be developed to the individual.

METHODS

A data-driven learning approach combining locally weighted projection regression (LWPR) and principal component analysis (PCA) is firstly proposed and applied to monitor the nonlinear process of patients' health status in ICU. LWPR is used to approximate the complex nonlinear process with local linear models, in which PCA could be further applied to status monitoring, and finally a global weighted statistic will be acquired for detecting the possible abnormalities. Moreover, some improved versions are developed, such as LWPR-MPCA and LWPR-JPCA, which also have superior performance.

RESULTS

Eighteen subjects were selected from the Physiobank's Multi-parameter Intelligent Monitoring for Intensive Care II (MIMIC II) database, and two vital signs of each subject were chosen for online monitoring. The proposed method was compared with several existing methods including traditional PCA, Partial least squares (PLS), just in time learning combined with modified PCA (L-PCA), and Kernel PCA (KPCA). The experimental results demonstrated that the mean fault detection rate (FDR) of PCA can be improved by 41.7% after adding LWPR. The mean FDR of LWPR-MPCA was increased by 8.3%, compared with the latest reported method L-PCA. Meanwhile, LWPR spent less training time than others, especially KPCA.

CONCLUSIONS

LWPR is first introduced into ICU patients monitoring and achieves the best monitoring performance including adaptability to changes in patient status, sensitivity for abnormality detection as well as its fast learning speed and low computational complexity. The algorithm is an excellent approach to establishing a personalized model for patients, which is the mainstream direction of modern medicine in the following development, as well as improving the global monitoring performance.

Multimodality neuromonitoring in severe pediatric traumatic brain injury

Each year, the annual hospitalization rates of traumatic brain injury (TBI) in children in the United States are 57.7 per 100K in the <5 years of age and 23.1 per 100K in the 5-14 years age group. Despite this, little is known about the pathophysiology of TBI in children and how to manage it most effectively. Historically, TBI management has been guided by clinical examination. This has been assisted progressively by clinical imaging, intracranial pressure (ICP) monitoring, and finally a software that can calculate optimal brain physiology. Multimodality monitoring affords clinicians an early indication of secondary insults to the recovering brain including raised ICP and decreased cerebral perfusion pressure. From variables such as ICP and arterial blood pressure, correlations can be drawn to determine parameters of cerebral autoregulation (pressure reactivity index) and "optimal cerebral perfusion pressure" at which the vasculature is most reactive. More recently, significant advances using both direct and near-infrared spectroscopy-derived brain oxygenation plus cerebral microdialysis to drive management have been described. Here in, we provide a perspective on the state-of-the-art techniques recently implemented in clinical practice for pediatric TBI.

Brain Multimodality Monitoring: A New Tool in Neurocritical Care of Comatose Patients

Neurocritical care patients are at risk of developing secondary brain injury from inflammation, ischemia, and edema that follows the primary insult. Recognizing clinical deterioration due to secondary injury is frequently challenging in comatose patients. Multimodality monitoring (MMM) encompasses various tools to monitor cerebral metabolism, perfusion, and oxygenation aimed at detecting these changes to help modify therapies before irreversible injury sets in. These tools include intracranial pressure (ICP) monitors, transcranial Doppler (TCD), Hemedex™ (thermal diffusion probe used to measure regional cerebral blood flow), microdialysis catheter (used to measure cerebral metabolism), Licox™ (probe used to measure regional brain tissue oxygen tension), and continuous electroencephalography. Although further research is needed to demonstrate their impact on improving clinical outcomes, their contribution to illuminate the black box of the brain in comatose patients is indisputable. In this review, we further elaborate on commonly used MMM parameters, tools used to measure them, and the indications for monitoring per current consensus guidelines.

Development of a brain monitoring system for multimodality investigation in awake rats

Multimodal brain monitoring is an important approach to gain insight into brain function, modulation, and pathology. We have developed a unique micromachined neural probe capable of real-time continuous monitoring of multiple physiological, biochemical and electrophysiological variables. However, to date, it has only been used in anesthetized animals due to a lack of an appropriate interface for awake animals. We have developed a versatile headstage for recording the small neural signal and bridging the sensors to the remote sensing units for multimodal brain monitoring in awake rats. The developed system has been successfully validated in awake rats by simultaneously measuring four cerebral variables: electrocorticography, oxygen tension, temperature and cerebral blood flow. Reliable signal recordings were obtained with minimal artifacts from movement and environmental noise. For the first time, multiple variables of cerebral function and metabolism were simultaneously recorded from awake rats using a single neural probe. The system is envisioned for studying the effects of pharmacologic treatments, mapping the development of central nervous system diseases, and better understanding normal cerebral physiology.

Development and application of a microfabricated multimodal neural catheter for neuroscience

We present a microfabricated neural catheter for real-time continuous monitoring of multiple physiological, biochemical and electrophysiological variables that are critical to the diagnosis and treatment of evolving brain injury. The first generation neural catheter was realized by polyimide-based micromachining and a spiral rolling packaging method. The mechanical design and electrical operation of the microsensors were optimized and tailored for multimodal monitoring in rat brain such that the potential thermal, chemical and electrical crosstalk among the microsensors as well as errors from micro-environmental fluctuations are minimized. In vitro cytotoxicity analyses suggest that the developed neural catheters are minimally toxic to rat cortical neuronal cultures. In addition, in vivo histopathology results showed neither acute nor chronic inflammation for 7 days post implantation. The performance of the neural catheter was assessed in an in vivo needle prick model as a translational replica of a "mini" traumatic brain injury. It successfully monitored the expected transient brain oxygen, temperature, regional cerebral blood flow, and DC potential changes during the passage of spreading depolarization waves. We envisage that the developed multimodal neural catheter can be used to decipher the causes and consequences of secondary brain injury processes with high spatial and temporal resolution while reducing the potential for iatrogenic injury inherent to current use of multiple invasive probes.

A User-Configurable Headstage for Multimodality Neuromonitoring in Freely Moving Rats

Multimodal monitoring of brain activity, physiology, and neurochemistry is an important approach to gain insight into brain function, modulation, and pathology. With recent progress in micro- and nanotechnology, micro-nano-implants have become important catalysts in advancing brain research. However, to date, only a limited number of brain parameters have been measured simultaneously in awake animals in spite of significant recent progress in sensor technology. Here we have provided a cost and time effective approach to designing a headstage to conduct a multimodality brain monitoring in freely moving animals. To demonstrate this method, we have designed a user-configurable headstage for our micromachined multimodal neural probe. The headstage can reliably record direct-current electrocorticography (DC-ECoG), brain oxygen tension (PbrO₂), cortical temperature, and regional cerebral blood flow (rCBF) simultaneously without significant signal crosstalk or movement artifacts for 72 h. Even in a noisy environment, it can record low-level neural signals with high quality. Moreover, it can easily interface with signal conditioning circuits that have high power consumption and are difficult to miniaturize. To the best of our knowledge, this is the first time where multiple physiological, biochemical, and electrophysiological cerebral variables have been simultaneously recorded from freely moving rats. We anticipate that the developed system will aid in gaining further insight into not only normal cerebral functioning but also pathophysiology of conditions such as epilepsy, stroke, and traumatic brain injury.

Consensus statement on continuous EEG in critically ill adults and children, part II: personnel, technical specifications, and clinical practice

INTRODUCTION

Critical Care Continuous EEG (CCEEG) is a common procedure to monitor brain function in patients with altered mental status in intensive care units. There is significant variability in patient populations undergoing CCEEG and in technical specifications for CCEEG performance.

METHODS

The Critical Care Continuous EEG Task Force of the American Clinical Neurophysiology Society developed expert consensus recommendations on the use of CCEEG in critically ill adults and children.

RECOMMENDATIONS

The consensus panel describes the qualifications and responsibilities of CCEEG personnel including neurodiagnostic technologists and interpreting physicians. The panel outlines required equipment for CCEEG, including electrodes, EEG machine and amplifier specifications, equipment for polygraphic data acquisition, EEG and video review machines, central monitoring equipment, and network, remote access, and data storage equipment. The consensus panel also describes how CCEEG should be acquired, reviewed and interpreted. The panel suggests methods for patient selection and triage; initiation of CCEEG; daily maintenance of CCEEG; electrode removal and infection control; quantitative EEG techniques; EEG and behavioral monitoring by non-physician personnel; review, interpretation, and reports; and data storage protocols.

CONCLUSION

Recommended qualifications for CCEEG personnel and CCEEG technical specifications will facilitate standardization of this emerging technology.

Adaptive online monitoring for ICU patients by combining just-in-time learning and principal component analysis

Offline general-type models are widely used for patients' monitoring in intensive care units (ICUs), which are developed by using past collected datasets consisting of thousands of patients. However, these models may fail to adapt to the changing states of ICU patients. Thus, to be more robust and effective, the monitoring models should be adaptable to individual patients. A novel combination of just-in-time learning (JITL) and principal component analysis (PCA), referred to learning-type PCA (L-PCA), was proposed for adaptive online monitoring of patients in ICUs. JITL was used to gather the most relevant data samples for adaptive modeling of complex physiological processes. PCA was used to build an online individual-type model and calculate monitoring statistics, and then to judge whether the patient's status is normal or not. The adaptability of L-PCA lies in the usage of individual data and the continuous updating of the training dataset. Twelve subjects were selected from the Physiobank's Multi-parameter Intelligent Monitoring for Intensive Care II (MIMIC II) database, and five vital signs of each subject were chosen. The proposed method was compared with the traditional PCA and fast moving-window PCA (Fast MWPCA). The experimental results demonstrated that the fault detection rates respectively increased by 20 % and 47 % compared with PCA and Fast MWPCA. L-PCA is first introduced into ICU patients monitoring and achieves the best monitoring performance in terms of adaptability to changes in patient status and sensitivity for abnormality detection.

Multimodality monitoring, inflammation, and neuroregeneration in subarachnoid hemorrhage

BACKGROUND

Stroke, including subarachnoid hemorrhage (SAH), is one of the leading causes of morbidity and mortality worldwide. The mortality rate of poor-grade SAH ranges from 34% to 52%. In an attempt to improve SAH outcomes, clinical research on multimodality monitoring has been performed, as has basic science research on inflammation and neuroregeneration (which can occur due to injury-induced neurogenesis). Nevertheless, the current literature does not focus on the integrated study of these fields. Multimodality monitoring corresponds to physiological data obtained during clinical management by both noninvasive and invasive methods. Regarding inflammation and neuroregeneration, evidence suggests that, in all types of stroke, a proinflammatory phase and an anti-inflammatory phase occur consecutively; these phases affect neurogenesis, which is also influenced by other pathophysiological features of stroke, such as ischemia, seizures, and spreading depression.

OBJECTIVE

To assess whether injury-induced neurogenesis is a prognostic factor in poor-grade SAH that can be monitored and modulated.

METHODS

We propose a protocol for multimodality monitoring-guided hypothermia in poor-grade SAH in which cellular and molecular markers of inflammation and neuroregeneration can be monitored in parallel with clinical and multimodal data.

EXPECTED OUTCOMES

This study may reveal correlations between markers of inflammation and neurogenesis in blood and cerebrospinal fluid, based on clinical and multimodality monitoring parameters.

DISCUSSION

This protocol has the potential to lead to new therapies for acute, diffuse, and severe brain diseases.

Windowed multitaper correlation analysis of multimodal brain monitoring parameters

Although multimodal monitoring sets the standard in daily practice of neurocritical care, problem-oriented analysis tools to interpret the huge amount of data are lacking. Recently a mathematical model was presented that simulates the cerebral perfusion and oxygen supply in case of a severe head trauma, predicting the appearance of distinct correlations between arterial blood pressure and intracranial pressure. In this study we present a set of mathematical tools that reliably detect the predicted correlations in data recorded at a neurocritical care unit. The time resolved correlations will be identified by a windowing technique combined with Fourier-based coherence calculations. The phasing of the data is detected by means of Hilbert phase difference within the above mentioned windows. A statistical testing method is introduced that allows tuning the parameters of the windowing method in such a way that a predefined accuracy is reached. With this method the data of fifteen patients were examined in which we found the predicted correlation in each patient. Additionally it could be shown that the occurrence of a distinct correlation parameter, called scp, represents a predictive value of high quality for the patients outcome.

Perioperative microdialysis in meningioma surgery: correlation of cerebral metabolites with clinical outcome

BACKGROUND

Brain tumour resection requires surgical manoeuvres that may cause an ischaemic injury to peritumoral tissue. The aim of the present study was to examine whether putative alterations in peritumoral tissue biochemistry, monitored by microdialysis, correlate with clinical outcome in patients undergoing craniotomy for meningioma resection.

METHODS

In 34 patients undergoing meningioma resection (35 % male; mean age ± SD: 54.3 ± 12.1 years), microdialysis measurements were taken perioperatively from peritumoral brain parenchyma. Standard metabolites (glucose, lactate, pyruvate, glycerol and the lactate:pyruvate ratio) were quantified in relation to clinical outcome assessed by the Glasgow Coma Scale (GCS) and the Karnofsky Performance Status scale.

RESULTS

Higher postoperative glucose and pyruvate levels were found in patients with a favourable outcome (GCS not deteriorated or Karnofsky score > 80). Multiple logistic regression analysis (age, preoperative physical status, metabolite levels as independent variables) showed that lower postoperative glucose and pyruvate levels as well as higher lactate:pyruvate ratio values were independently associated with an unfavourable outcome as defined by Karnofsky score <80 [(OR: 0.084, 95 % CI: 0.01-0.98, p = 0.049), (OR: 0.97, 95 % CI: 0.95-0.99, p = 0.050), (OR: 1.21, 95 % CI: 1.04-1.42, p = 0.015) respectively], as well as with death [(OR: 0.08, 95 % CI: 0.01-0.97, p = 0.046), (OR: 0.94, 95 % CI: 0.89-0.99, p = 0.016), (OR: 1.07, 95 % CI: 1.00-1.15, p = 0.05) respectively].

CONCLUSIONS

Postoperative levels of glucose and pyruvate and the lactate:pyruvate ratio appear to correlate with clinical outcome in patients undergoing meningioma resection. The present findings provide support for the utility of microdialysis as a prognostic tool in brain tumour surgery.

Critical care for patients with massive ischemic stroke

Malignant cerebral edema following ischemic stroke is life threatening, as it can cause inadequate blood flow and perfusion leading to irreversible tissue hypoxia and metabolic crisis. Increased intracranial pressure and brain shift can cause herniation syndrome and finally brain death. Multiple randomized clinical trials have shown that preemptive decompressive hemicraniectomy effectively reduces mortality and morbidity in patients with malignant middle cerebral artery infarction. Another life-saving decompressive surgery is suboccipital craniectomy for patients with brainstem compression by edematous cerebellar infarction. In addition to decompressive surgery, cerebrospinal fluid drainage by ventriculostomy should be considered for patients with acute hydrocephalus following stroke. Medical treatment begins with sedation, analgesia, and general measures including ventilatory support, head elevation, maintaining a neutral neck position, and avoiding conditions associated with intracranial hypertension. Optimization of cerebral perfusion pressure and reduction of intracranial pressure should always be pursued simultaneously. Osmotherapy with mannitol is the standard treatment for intracranial hypertension, but hypertonic saline is also an effective alternative. Therapeutic hypothermia may also be considered for treatment of brain edema and intracranial hypertension, but its neuroprotective effects have not been demonstrated in stroke. Barbiturate coma therapy has been used to reduce metabolic demand, but has become less popular because of its systemic adverse effects. Furthermore, general medical care is critical because of the complex interactions between the brain and other organ systems. Some challenging aspects of critical care, including ventilator support, sedation and analgesia, and performing neurological examinations in the setting of a minimal stimulation protocol, are addressed in this review.

The evolution of neurocritical care

Although neurocritical care as a subspecialty is a relatively young field of medicine, its origins can be traced back to ancient times. This article focuses on the progression of neurocritical care from prehistoric trepanation procedures, through the development of mechanical ventilation, management of increased intracranial pressure, and traumatic brain injury, to the establishment of the first "real" intensive care units, and finally to modern monitoring in neurocritical care, management of post-cardiac arrest patients, and the diagnosis of brain death. This article also focuses on the future direction of neurocritical care.

Prospective evaluation of intravascular volume status in critically ill patients: does inferior vena cava collapsibility correlate with central venous pressure?

BACKGROUND

In search of a standardized noninvasive assessment of intravascular volume status, we prospectively compared the sonographic inferior vena cava collapsibility index (IVC-CI) and central venous pressures (CVPs). Our goals included the determination of CVP behavior across clinically relevant IVC-CI ranges, examination of unitary behavior of IVC-CI with changes in CVP, and estimation of the effect of positive end-expiratory pressure (PEEP) on the IVC-CI/CVP relationship.

METHODS

Prospective, observational study was performed in surgical/medical intensive care unit patients between October 2009 and July 2013. Patients underwent repeated sonographic evaluations of IVC-CI. Demographics, illness severity, ventilatory support, CVP, and patient positioning were recorded. Correlations were made between CVP groupings (<7, 7-12, 12-18, 19+) and IVC-CI ranges (<25, 25-49, 50-74, 75+). Comparison of CVP (2-unit quanta) and IVC-CI (5-unit quanta) was performed, followed by assessment of per-unit ΔIVC-CI/ΔCVP behavior as well as examination of the effect of PEEP on the IVC-CI/CVP relationship.

RESULTS

We analyzed 320 IVC-CI/CVP measurement pairs from 79 patients (mean [SD] age, 55.8 [16.8] years; 64.6% male; mean [SD] Acute Physiology and Chronic Health Evaluation II, 11.7 [6.21]). Continuous data for IVC-CI/CVP correlated poorly (R = 0.177, p < 0.01) and were inversely proportional, with CVP less than 7 noted in approximately 10% of the patients for IVC-CIs less than 25% and CVP less than 7 observed in approximately 85% of patients for IVC-CIs greater than or equal to 75%. Median ΔIVC-CI per unit CVP was 3.25%. Most measurements (361 of 320) were collected in mechanically ventilated patients (mean [SD] PEEP, 7.76 [4.11] cm H2O). PEEP-related CVP increase was approximately 2 mm Hg to 2.5 mm Hg for IVC-CIs greater than 60% and approximately 3 mm Hg to 3.5 mm Hg for IVC-CIs less than 30%. PEEP also resulted in lower IVC-CIs at low CVPs, which reversed with increasing CVPs. When IVC-CI was examined across increasing PEEP ranges, we noted an inverse relationship between the two variables, but this failed to reach statistical significance.

CONCLUSION

IVC-CI and CVP correlate inversely, with each 1 mm Hg of CVP corresponding to 3.3% median ΔIVC-CI. Low IVC-CI (<25%) is consistent with euvolemia/hypervolemia, while IVC-CI greater than 75% suggests intravascular volume depletion. The presence of PEEP results in 2 mm Hg to 3.5 mm Hg of CVP increase across the IVC-CI spectrum and lower collapsibility at low CVPs. Although IVC-CI decreased with increasing degrees of PEEP, this failed to reach statistical significance. While this study represents a step forward in the area of intravascular volume estimation using IVC-CI, our findings must be applied with caution owing to some methodologic limitations.

LEVEL OF EVIDENCE

Diagnostic study, level III. Prognostic study, level III.

Decreased risk of secondary brain herniation with intracranial pressure monitoring in patients with haemorrhagic stroke

BACKGROUND

Intracranial-pressure (ICP) monitoring is considered standard care for severe traumatic brain injury and is used frequently, but the efficacy of treatment based on monitoring in patients with hemorrhagic stroke has not been rigorously assessed. In this study, we investigated the clinical value of ICP monitoring in patients with hemorrhagic stroke.

METHODS

We conducted a randomized, unblinded, controlled trial in which 90 patients with hemorrhagic stroke were randomly assigned to ICP monitoring or a control group. The primary outcome was a composite of incidence rate of hematoma enlargement and secondary brain herniation. The secondary outcome was neurological status assessed using the Glasgow Outcome Scale scores at 6 months post-onset. Characteristics of the patients at baseline and outcome measurements were also compared between the two groups.

RESULTS

There was no significant between-group difference in the incidence of hematoma enlargement (control group, 38.6% vs. ICP monitoring group, 32.6%; P > 0.05). The incidence rate of secondary brain herniation in the ICP monitoring group was significantly lower compared with the control group (10.9% vs. 20.5%, P = 0.04). Six-month mortality was 6.5% in the ICP group and 9.1% in the control group (P < 0.05), and neurological outcome was better in the ICP group compared with the control group (P < 0.05).

CONCLUSION

The dynamic ICP value may be more sensitive and effective in preventing secondary brain herniation in patients with hemorrhagic stroke compared with guidance directed by clinical signs and radiological indicators.

Ultrasound-based imaging in neurocritical care patients: a review of clinical applications

OBJECTIVE

To analyze the diagnostic, monitoring, and procedural applications of ultrasound (US) imaging in neurocritical care (NCC) patients.

METHOD

US imaging has been extensively validated in various subset of critically ill patients, but not specifically in the NCC population. We reviewed the clinical applications of US imaging for heart, vascular, brain, and lung evaluation and for possible procedural uses in NCC patients. Major neurosurgical books, journals, testimonials, authors' personal experience, and scientific databases were analyzed.

RESULTS

Cardiac US imaging provides accurate information at NCC arrival to stratify risk factors, including presence of atrial septal defect/patent formen ovale, abnormal ventricular function, or pericardial effusion, and to monitor cardiac anatomy and function during the NCC stay for guiding goal-directed therapy. Vascular US in NCC patients has three especially relevant indications: to screen anatomy and flow in extracranial supra-aortic arteries, to diagnose deep vein thrombosis, and to optimize the safety of central venous catheterization. Brain US has important clinical applications in the NCC, including transcranial Doppler and emerging techniques for cerebral blood flow evaluation with contrast-enhanced US imaging. Lung US, as demonstrated in other intensive care unit patients, provides accurate diagnosis of anatomical and functional abnormalities and enables diagnosis of pleural effusion, pneumothorax, lung consolidation, pulmonary abscess and interstitial-alveolar syndrome, and lung recruitment/derecruitment. US imaging can effectively guide percutaneous tracheostomy.

CONCLUSION

In conclusion, US imaging is an important diagnostic tool that provides real-time information at the bedside to stratify risk, monitor for complications, and guide invasive procedures in NCC patients.

Continuous detection of cerebral vasodilatation and vasoconstriction using intracranial pulse morphological template matching

Although accurate and continuous assessment of cerebral vasculature status is highly desirable for managing cerebral vascular diseases, no such method exists for current clinical practice. The present work introduces a novel method for real-time detection of cerebral vasodilatation and vasoconstriction using pulse morphological template matching. Templates consisting of morphological metrics of cerebral blood flow velocity (CBFV) pulse, measured at middle cerebral artery using Transcranial Doppler, are obtained by applying a morphological clustering and analysis of intracranial pulse algorithm to the data collected during induced vasodilatation and vasoconstriction in a controlled setting. These templates were then employed to define a vasodilatation index (VDI) and a vasoconstriction index (VCI) for any inquiry data segment as the percentage of the metrics demonstrating a trend consistent with those obtained from the training dataset. The validation of the proposed method on a dataset of CBFV signals of 27 healthy subjects, collected with a similar protocol as that of training dataset, during hyperventilation (and CO₂ rebreathing tests) shows a sensitivity of 92% (and 82%) for detection of vasodilatation (and vasoconstriction) and the specificity of 90% (and 92%), respectively. Moreover, the proposed method of detection of vasodilatation (vasoconstriction) is capable of rejecting all the cases associated with vasoconstriction (vasodilatation) and outperforms other two conventional techniques by at least 7% for vasodilatation and 19% for vasoconstriction.

Validation of frontal near-infrared spectroscopy as noninvasive bedside monitoring for regional cerebral blood flow in brain-injured patients

OBJECT

Near-infrared spectroscopy (NIRS) offers noninvasive bedside measurement of direct regional cerebral arteriovenous (mixed) brain oxygenation. To validate the accuracy of this monitoring technique, the authors analyzed the statistical correlation of NIRS and CT perfusion with respect to regional cerebral blood flow (CBF) measurements.

METHODS

The authors retrospectively reviewed all cases in which NIRS measurements were obtained at a single, academic neurointensive care unit from February 2008 to June 2011 in which CT perfusion was performed at the same time as NIRS data was collected. Regions of interest were obtained 2.5 cm below the NIRS bifrontal scalp probe on CT perfusion with an average volume between 2 and 4 ml, with mean CBF values used for purposes of analysis. Linear regression analysis was performed for NIRS and CBF values.

RESULTS

The study included 8 patients (2 men, 6 women), 6 of whom suffered subarachnoid hemorrhage, 1 ischemic stroke, and 1 intracerebral hemorrhage and brain edema. Mean CBF measured by CT perfusion was 61 ml/100 g/min for the left side and 60 ml/100 g/min for the right side, while mean NIRS values were 75 on the right and 74 on the left. Linear regression analysis demonstrated a statistically significant probability value (p<0.0001) comparing NIRS frontal oximetry and CT perfusion-obtained CBF values.

CONCLUSIONS

The authors demonstrated a linear correlation for frontal NIRS cerebral oxygenation measurements compared with regional CBF on CT perfusion imaging. Thus, frontal NIRS cerebral oxygenation measurement may serve as a useful, noninvasive, bedside intensive care unit monitoring tool to assess brain oxygenation in a direct manner.

Interrater reliability of ICU EEG research terminology

BACKGROUND

Standardized research terminology critical to the establishment of a multicenter intensive care unit (ICU) electroencephalogram (EEG) database was originally proposed in 2005 and has been modified many times since. However, interrater agreement (IRA) of the revised terminology has not been investigated.

METHODS

After a brief tutorial, investigators of ICU EEG research centers (n = 16) took an 82-question EEG certification test comprising 10-second EEG samples, which assessed the use of main term 1 (pattern location), main term 2 (pattern type), and modifiers from the most recently revised terminology.

RESULTS

Kappa values for main terms 1 and 2 were 0.87 and 0.92, respectively. Agreement was 93% for determination of amplitude and 80% for determination of frequency. Kappa values for each of the "plus" modifiers (fast, rhythmic, and sharp/spike activity) were 0.54, 0.62, and 0.16 respectively.

CONCLUSIONS

Main terms 1 and 2 have high IRA and are reasonable for use in multicenter research. There is a suggestion that assessment of amplitude has good reliability, while assessment of frequency may have less reliability. The fast and rhythmic "plus" modifiers have moderate IRA, while sharp/spike modifier has only slight IRA implying that further refinement and assessment of terminology modifiers may be necessary.

The relationship between intracranial pressure and brain oxygenation in children with severe traumatic brain injury

BACKGROUND

Intracranial pressure (ICP) monitoring is a cornerstone of care for severe traumatic brain injury (TBI). Management of ICP can help ensure adequate cerebral blood flow and oxygenation. However, studies indicate that brain hypoxia may occur despite normal ICP and the relationship between ICP and brain oxygenation is poorly defined. This is particularly important for children in whom less is known about intracranial dynamics.

OBJECTIVE

To examine the relationship between ICP and partial pressure of brain tissue oxygen (PbtO2) in children with severe TBI (Glasgow Coma Scale score ≤ 8) admitted to Red Cross War Memorial Children's Hospital, Cape Town.

METHODS

The relationship between time-linked hourly and high-frequency ICP and PbtO2 data was examined using correlation, regression, and generalized estimating equations. Thresholds for ICP were examined against reduced PbtO2 using age bands and receiver-operating characteristic curves.

RESULTS

Analysis using more than 8300 hourly (n = 75) and 1 million high-frequency data points (n = 30) demonstrated a weak relationship between ICP and PbtO2 (r = 0.05 and r = 0.04, respectively). No critical ICP threshold for low PbtO2 was identified. Individual patients revealed a strong relationship between ICP and PbtO2 at specific times, but different relationships were evident over longer periods.

CONCLUSION

The relationship between ICP and PbtO2 appears complex, and several factors likely influence both variables separately and in combination. Although very high ICP is associated with reduced PbtO2, in general, absolute ICP has a poor relationship with PbtO2. Because reduced PbtO2 is independently associated with poor outcome, a better understanding of ICP and PbtO2 management in pediatric TBI seems to be needed.

Position of probe determines prognostic information of brain tissue PO2 in severe traumatic brain injury

BACKGROUND

Monitoring brain tissue PO2 (PbtO2) is part of multimodality monitoring of patients with traumatic brain injury (TBI). However, PbtO2 measurement is a sampling of only a small area of tissue surrounding the sensor tip.

OBJECTIVE

To examine the effect of catheter location on the relationship between PbtO2 and neurological outcome.

METHODS

A total of 405 patients who had PbtO2 monitoring as part of standard management of severe traumatic brain injury were studied. The relationships between probe location and resulting PbtO2 and outcome were examined.

RESULTS

When the probe was located in normal brain, PbtO2 averaged 30.8 ± 18.2 compared with 25.6 ± 14.8 mm Hg when placed in abnormal brain (P < .001). Factors related to neurological outcome in the best-fit logistic regression model were age, PbtO2 probe position, postresuscitation motor Glasgow Coma Scale score, and PbtO2 trend pattern. Although average PbtO2 was significantly related to outcome in univariate analyses, it was not significant in the final logistic model. However, the interaction between PbtO2 and probe position was statistically significant. When the PbtO2 probe was placed in abnormal brain, the average PbtO2 was higher in those with a favorable outcome, 28.8 ± 12.0 mm Hg, compared with those with an unfavorable outcome, 19.5 ± 13.7 mm Hg (P = .01). PbtO2 and outcome were not related when the probe was placed in normal-appearing brain.

CONCLUSION

These results suggest that the location of the PbtO2 probe determines the PbtO2 values and the relationship of PbtO2 to neurological outcome.

Controversies in the management of adults with severe traumatic brain injury

Despite progress in the management of adults with severe traumatic brain injury, several controversies persist. Among the unresolved issues of greatest concern to neurocritical care clinicians and scientists are the following: (1) the best use of technological advances and the data obtained from multimodality monitoring; (2) the use of mannitol and hypertonic saline in the management of increased intracranial pressure; (3) the use of decompressive craniectomy and barbiturate coma in refractory increased intracranial pressure; (4) therapeutic hypothermia as a neuroprotectant; (5) anemia and the role of blood transfusion; and (6) venous thromboembolism prophylaxis in severe traumatic brain injury. Each of these strategies for managing severe traumatic brain injury, including the postulated mechanism(s) of action and beneficial effects of each intervention, adverse effects, the state of the science, and critical care nursing implications, is discussed.

Implementation of cerebral microdialysis at a community-based hospital: A 5-year retrospective analysis

Background:

Cerebral microdialysis (MD) provides valuable information about brain metabolism under normal and pathologic conditions. The CMA 600 microdialysis analyzer received US Food and Drug Administration (FDA) approval for clinical use in the United States in 2005. Since then, cerebral MD has been increasingly utilized nationally in the multimodal monitoring of traumatic brain injury (TBI), stroke, aneurysmal subarachnoid hemorrhage, and brain tumors. We describe a 5-year, single-institutional experience using cerebral MD at a community-based hospital, Legacy Emanuel Medical Center (LEMC). Implications for the adoption and utility of MD in medical centers with limited resources are discussed.

Methods:

This is a retrospective chart review and data analysis of 174 consecutive patients who had cerebral MD as part of multimodal brain monitoring. All cerebral MD catheters were placed by board-certified, attending neurosurgeons at LEMC. Clinical severity in the TBI patients was reported using initial Glasgow Coma Scale (GCS); radiologic severity was graded with the Marshall CT grading scale. Measures of the risks of MD placement included post-placement hemorrhage, cerebral infection, and dislodgement.

Results:

Between July 2005 and July 2010, 248 cerebral MD catheters were placed in 174 patients undergoing multimodal brain monitoring. One hundred and eighty-five catheters were placed at the time of open craniotomy. None were associated with cranial infection. Patients ranged in age from 5 months to 90 years, with a mean of 49 years. The male to female ratio was 1.4:1. The underlying pathologies were: TBI (126), cerebral vascular accident (24), aneurysmal subarachnoid hemorrhage (17), and tumor (7).

Conclusions:

Cerebral MD was readily implemented in a community-based hospital. No cerebral hemorrhages or infections were attributed to cerebral MD. Examples of how MD may be a useful adjunct in the clinical decision making of patients with brain injuries are presented.

Computerized data analysis of neuromonitoring parameters identifies patients with reduced cerebral compliance as seen on CT

OBJECTIVE

Computer-assisted analysis of neuromonitoring parameters may provide important decision-making support to the neurointensivist. A recently developed mathematical model for the simulation of cerebral autoregulation and brain swelling showed that in the case of an intact autoregulation but diminished cerebral compliance, a negative correlation between arterial blood pressure (ABP) and intracranial pressure (ICP) occurs. The goal of our study was to verify these simulation results in an appropriate patient cohort.

METHODS

Simultaneously measured data (ABP, ICP) of 6 patients (1 female; 5 male) with severe head trauma (n = 5) and stroke (n = 1) were used to calculate time resolved multitaper cross coherence. Further, we calculated the Hilbert phases of both signals, defining a negative correlation in case of a mean Hilbert phase difference greater than 130°. To validate the results, CT scans performed during the critical phases identified were analyzed.

RESULTS

In five out of six datasets we found long lasting events of negative correlation between ABP and ICP. In all patients, corresponding CT scans demonstrated changes in the intracranial compartment characterized by diminished cerebral compliance.

CONCLUSIONS

Our data indicate that complex multidimensional data analysis of neuromonitoring parameters can identify complication-specific data patterns with a high degree of accuracy.

Hypothermia for acute brain injury--mechanisms and practical aspects

Hypothermia is widely accepted as the gold-standard method by which the body can protect the brain. Therapeutic cooling--or targeted temperature management (TTM)--is increasingly being used to prevent secondary brain injury in patients admitted to the emergency department and intensive care unit. Rapid cooling to 33 °C for 24 h is considered the standard of care for minimizing neurological injury after cardiac arrest, mild-to-moderate hypothermia (33-35 °C) can be used as an effective component of multimodal therapy for patients with elevated intracranial pressure, and advanced cooling technology can control fever in patients who have experienced trauma, haemorrhagic stroke, or other forms of severe brain injury. However, the practical application of therapeutic hypothermia is not trivial, and the treatment carries risks. Development of clinical management protocols that focus on detection and control of shivering and minimize the risk of other potential complications of TTM will be essential to maximize the benefits of this emerging therapeutic modality. This Review provides an overview of the potential neuroprotective mechanisms of hypothermia, practical considerations for the application of TTM, and disease-specific evidence for the use of this therapy in patients with acute brain injuries.

Neurocritical care monitoring correlates with neuropathology in a swine model of pediatric traumatic brain injury

BACKGROUND

Small-animal models have been used in traumatic brain injury (TBI) research to investigate the basic mechanisms and pathology of TBI. Unfortunately, successful TBI investigations in small-animal models have not resulted in marked improvements in clinical outcomes of TBI patients.

OBJECTIVE

To develop a clinically relevant immature large-animal model of pediatric neurocritical care following TBI.

METHODS

Eleven 4-week-old piglets were randomly assigned to either rapid axial head rotation without impact (n = 6) or instrumented sham (n = 5). All animals had an intracranial pressure monitor, brain tissue oxygen tension (Pbto(2)) probe, and cerebral microdialysis probe placed in the frontal lobe and data collected for 6 hours following injury.

RESULTS

Injured animals had sustained elevations in intracranial pressure and lactate-pyruvate ratio (LPR), and decreased Pbto(2) compared with sham. Pbto(2) and LPR from separate frontal lobes had strong linear correlation in both sham and injured animals. Neuropathologic examination demonstrated significant axonal injury and infarct volumes in injured animals compared with sham at 6 hours postinjury. Averaged over time, Pbto(2) in both injured and sham animals had a strong inverse correlation with total injury volume. Average LPR had a strong correlation with total injury volume.

CONCLUSION

LPR and Pbto(2) can be utilized as serial nonterminal secondary markers in our injury model for neuropathology, and as evaluation metrics for novel interventions and therapeutics in the acute postinjury period. This translational model bridges a vital gap in knowledge between TBI studies in small-animal models and clinical trials in the pediatric TBI population.

Correlation of transcranial color Doppler to n20 somatosensory evoked potential detects ischemic penumbra in subarachnoid hemorrhage

Background:

Normal subjects present interhemispheric symmetry of middle cerebral artery (MCA) mean flow velocity and N20 cortical somatosensory evoked potential (SSEP). Subarachnoid haemorrhage (SAH) can modify this pattern, since high regional brain vascular resistances increase blood flow velocity, and impaired regional brain perfusion reduces N20 amplitude. The aim of the study is to investigate the variability of MCA resistances and N20 amplitude between hemispheres in SAH.

Methods:

Measurements of MCA blood flow velocity (vMCA) by transcranial color-Doppler and median nerve SSEP were bilaterally performed in sixteen patients. MCA vascular changes on the compromised hemisphere were calculated as a ratio of the reciprocal of mean flow velocity (1/vMCA) to contralateral value and correlated to the simultaneous variations of interhemispheric ratio of N20 amplitude, within each subject. Data were analysed with respect to neuroimaging of MCA supplied areas.

Results:

Both interhemispheric ratios of 1/vMCA and N20 amplitude were detected >0.65 (p <0,01) in patients without neuroimages of injury. Both ratios became <0.65 (p <0.01) when patients showed unilateral images of ischemic penumbra and returned >0.65 if penumbra disappeared. The two ratios no longer correlated after structural lesion developed, as N20 detected in the damaged side remained pathological (ratio <0.65), whereas 1/vMCA reverted to symmetric interhemispheric state (ratio >0.65), suggesting a luxury perfusion.

Conclusion:

Variations of interhemispheric ratios of MCA resistance and cortical N20 amplitude correlate closely in SAH and allow identification of the reversible ischemic penumbra threshold, when both ratios become <0.65. The correlation is lost when structural damage develops.