Predictive value of somatosensory evoked potentials for awakening from coma

Neural complexity and the spectral slope characterise auditory processing in wakefulness and sleep

Auditory processing and the complexity of neural activity can both indicate residual consciousness levels and differentiate states of arousal. However, how measures of neural signal complexity manifest in neural activity following environmental stimulation and, more generally, how the electrophysiological characteristics of auditory responses change in states of reduced consciousness remain under-explored. Here, we tested the hypothesis that measures of neural complexity and the spectral slope would discriminate stages of sleep and wakefulness not only in baseline electroencephalography (EEG) activity but also in EEG signals following auditory stimulation. High-density EEG was recorded in 21 participants to determine the spatial relationship between these measures and between EEG recorded pre- and post-auditory stimulation. Results showed that the complexity and the spectral slope in the 2-20 Hz range discriminated between sleep stages and had a high correlation in sleep. In wakefulness, complexity was strongly correlated to the 20-40 Hz spectral slope. Auditory stimulation resulted in reduced complexity in sleep compared to the pre-stimulation EEG activity and modulated the spectral slope in wakefulness. These findings confirm our hypothesis that electrophysiological markers of arousal are sensitive to sleep/wake states in EEG activity during baseline and following auditory stimulation. Our results have direct applications to studies using auditory stimulation to probe neural functions in states of reduced consciousness.

A Comprehensive Review and Practical Guide of the Applications of Evoked Potentials in Neuroprognostication After Cardiac Arrest

Cardiorespiratory arrest is a very common cause of morbidity and mortality nowadays, and many therapeutic strategies, such as induced coma or targeted temperature management, are used to reduce patient sequelae. However, these procedures can alter a patient's neurological status, making it difficult to obtain useful clinical information for the reliable estimation of neurological prognosis. Therefore, complementary investigations are conducted in the early stages after a cardiac arrest to clarify functional prognosis in comatose cardiac arrest survivors in the first few hours or days. Current practice relies on a multimodal approach, which shows its greatest potential in predicting poor functional prognosis, whereas the data and tools to identify patients with good functional prognosis remain relatively limited in comparison. Therefore, there is considerable interest in investigating alternative biological parameters and advanced imaging technique studies. Among these, somatosensory evoked potentials (SSEPs) remain one of the simplest and most reliable tools. In this article, we discuss the technical principles, advantages, limitations, and prognostic implications of SSEPs in detail. We will also review other types of evoked potentials that can provide useful information but are less commonly used in clinical practice (e.g., visual evoked potentials; short-, medium-, and long-latency auditory evoked potentials; and event-related evoked potentials, such as mismatch negativity or P300).

Neuromonitoring in Children with Traumatic Brain Injury

Traumatic brain injury remains a major cause of mortality and morbidity in children across the world. Current management based on international guidelines focuses on a fixed therapeutic target of less than 20 mm Hg for managing intracranial pressure and 40-50 mm Hg for cerebral perfusion pressure across the pediatric age group. To improve outcome from this complex disease, it is essential to understand the pathophysiological mechanisms responsible for disease evolution by using different monitoring tools. In this narrative review, we discuss the neuromonitoring tools available for use to help guide management of severe traumatic brain injury in children and some of the techniques that can in future help with individualizing treatment targets based on advanced cerebral physiology monitoring.

Neurological monitoring in ECMO patients: current state of practice, challenges and lessons

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) in critically ill patients serves as a management option for end-stage cardiorespiratory failure in medical and surgical conditions. Patients on ECMO are at a high risk of neurologic adverse events including intracranial hemorrhage (ICH), acute ischemic stroke (AIS), seizures, diffuse cerebral edema, and hypoxic brain injury. Standard approaches to neurological monitoring for patients receiving ECMO support can be challenging for multiple reasons, including the severity of critical illness, deep sedation, and/or paralysis. This narrative literature review provides an overview of the current landscape for neurological monitoring in this population.

METHODS

A literature search using PubMed was used to aid the understanding of the landscape of published literature in the area of neurological monitoring in ECMO patients.

RESULTS

Review articles, cohort studies, case series, and individual reports were identified. A total of 73 varied manuscripts were summarized and included in this review which presents the challenges and strategies for performing neurological monitoring in this population.

CONCLUSION

Neurological monitoring in ECMO is an area of interest to many clinicians, however, the literature is limited, heterogenous, and lacks consensus on the best monitoring practices. The evidence for optimal neurological monitoring that could impact clinical decisions and functional outcomes is lacking. Additional studies are needed to identify effective measures of neurological monitoring while on ECMO.

Prognostication after cardiac arrest: how EEG and evoked potentials may improve the challenge

About 80% of patients resuscitated from CA are comatose at ICU admission and nearly 50% of survivors are still unawake at 72 h. Predicting neurological outcome of these patients is important to provide correct information to patient's relatives, avoid disproportionate care in patients with irreversible hypoxic-ischemic brain injury (HIBI) and inappropriate withdrawal of care in patients with a possible favorable neurological recovery. ERC/ESICM 2021 algorithm allows a classification as "poor outcome likely" in 32%, the outcome remaining "indeterminate" in 68%. The crucial question is to know how we could improve the assessment of both unfavorable but also favorable outcome prediction. Neurophysiological tests, i.e., electroencephalography (EEG) and evoked-potentials (EPs) are a non-invasive bedside investigations. The EEG is the record of brain electrical fields, characterized by a high temporal resolution but a low spatial resolution. EEG is largely available, and represented the most widely tool use in recent survey examining current neuro-prognostication practices. The severity of HIBI is correlated with the predominant frequency and background continuity of EEG leading to "highly malignant" patterns as suppression or burst suppression in the most severe HIBI. EPs differ from EEG signals as they are stimulus induced and represent the summated activities of large populations of neurons firing in synchrony, requiring the average of numerous stimulations. Different EPs (i.e., somato sensory EPs (SSEPs), brainstem auditory EPs (BAEPs), middle latency auditory EPs (MLAEPs) and long latency event-related potentials (ERPs) with mismatch negativity (MMN) and P300 responses) can be assessed in ICU, with different brain generators and prognostic values. In the present review, we summarize EEG and EPs signal generators, recording modalities, interpretation and prognostic values of these different neurophysiological tools. Finally, we assess the perspective for futures neurophysiological investigations, aiming to reduce prognostic uncertainty in comatose and disorders of consciousness (DoC) patients after CA.

Predicting outcome of patients with prolonged disorders of consciousness using machine learning models based on medical complexity

Patients with severe acquired brain injury and prolonged disorders of consciousness (pDoC) are characterized by high clinical complexity and high risk to develop medical complications. The present multi-center longitudinal study aimed at investigating the impact of medical complications on the prediction of clinical outcome by means of machine learning models. Patients with pDoC were consecutively enrolled at admission in 23 intensive neurorehabilitation units (IRU) and followed-up at 6 months from onset via the Glasgow Outcome Scale-Extended (GOSE). Demographic and clinical data at study entry and medical complications developed within 3 months from admission were collected. Machine learning models were developed, targeting neurological outcomes at 6 months from brain injury using data collected at admission. Then, after concatenating predictions of such models to the medical complications collected within 3 months, a cascade model was developed. One hundred seventy six patients with pDoC (M: 123, median age 60.2 years) were included in the analysis. At admission, the best performing solution (k-Nearest Neighbors regression, KNN) resulted in a median validation error of 0.59 points [IQR 0.14] and a classification accuracy of dichotomized GOS-E of 88.6%. Coherently, at 3 months, the best model resulted in a median validation error of 0.49 points [IQR 0.11] and a classification accuracy of 92.6%. Interpreting the admission KNN showed how the negative effect of older age is strengthened when patients' communication levels are high and ameliorated when no communication is present. The model trained at 3 months showed appropriate adaptation of the admission prediction according to the severity of the developed medical complexity in the first 3 months. In this work, we developed and cross-validated an interpretable decision support tool capable of distinguishing patients which will reach sufficient independence levels at 6 months (GOS-E > 4). Furthermore, we provide an updated prediction at 3 months, keeping in consideration the rehabilitative path and the risen medical complexity.

Functional and Prognostic Assessment in Comatose Patients: A Study Using Somatosensory Evoked Potentials

Aim

The functional prognosis of patients after coma following either cardiac arrest (CA) or acute structural brain injury (ABI) is often uncertain. These patients are associated with high mortality and disability. N20 and N70 somatosensory evoked potentials (SSEP) are used to predict prognosis. We evaluated the utility of SSEP (N20–N70) as an early indicator of long-term prognosis in these patients.

Methods

This was a retrospective cohort study of patients (n = 120) admitted to the intensive care unit (ICU) with a diagnosis of coma after CA (n = 60) or ABI (n = 60). An SSEP study was performed, including N20 and N70 at 24–72 h, after coma onset. Functional recovery was assessed 6–12 months later using the modified Glasgow scale (mGS). The study was approved by our local research ethics committee.

Results

In the CA and ABI groups, the absence of N20 (36% of CA patients and 41% of ABI patients; specificity = 100%) or N70 (68% of CA patients and 78% of ABI patients) was a strong indicator of poor outcome. Conversely, the presence of N70 was an indicator of a good outcome (AC: specificity = 84.2%, sensitivity = 92.7%; ABI: specificity = 64.2% sensitivity = 91.3%).

Conclusion

Somatosensory evoked potentials are useful early prognostic markers with high specificity (N20) and sensitivity (N70). Moreover, N70 has additional potential value for improving the prediction of good long-term functional outcomes.

Clinical Trial Registration:

[https://clinicaltrials.gov/], identifier [2018/01/001].

The Added Value of Somatosensory Potential N70 in Neurological Prognosis After Coma by Acute Brain Structural Injury: A Retrospective Study

Background:

Coma after acute brain structural injury (ABI) are associated with high mortality and disability. Somatosensory evoked potentials (SSEP) N20 and N70 are used to predict prognosis.

Purpose:

We assessed the utility of SSEP (N20-N70) as an early indicator of long-term functional prognosis in these patients.

Methods:

We conducted a retrospective cohort study of patients admitted to the intensive care unit (ICU) with a diagnosis of coma after ABI (n=60). An SSEP study including N20 and N70 was performed 24–72 hours after coma onset. Functional recovery was evaluated 6 to 12 months later using the Modified Glasgow Scale (mGS). The study was approved by our local research ethics committee.

Results:

The absence of N20 (41% specificity=100%) or N70 (78%) was a strong indicator of a poor outcome. In contrast, the presence of N70 was an indicator of a good outcome (specificity=64.2% sensitivity=91.3%).

Conclusion:

SSEP N20 and N70 are useful early prognostic markers with high specificity (N20) and sensitivity (N70). N70 has potential additional value for improving the prediction of good functional outcomes in the long term.

Evoked and Event-Related Potentials as Biomarkers of Consciousness State and Recovery

SUMMARY

The definition of consciousness has been the subject of great interest for many scientists and philosophers. To better understand how evoked potentials may be identified as biomarkers of consciousness and recovery, the different theoretical models sustaining neural correlates of consciousness are reviewed. A multimodal approach can help to better predict clinical outcome in patients presenting with disorders of consciousness. Evoked potentials are inexpensive and easy-to-implement bedside examination techniques. Evoked potentials are an integral part of prognostic evaluation, particularly in cases of cognitive motor dissociation. Prognostic criteria are well established in postanoxic disorders of consciousness, especially postcardiac arrest but are less well determined in other etiologies. In the early examination, bilateral absence of N20 in disorder of consciousness patients is strongly associated with unfavorable outcome (i.e., death or unresponsive wakefulness syndrome) especially in postanoxic etiologies. This predictive value is lower in other etiologies and probably also in children. Both N20 and mismatch negativity are proven outcome predictors for acute coma. Many studies have shown that mismatch negativity and P3a are characterized by a high prognostic value for awakening, but some patients presenting unresponsive wakefulness syndrome also process a P3a. The presence of long-latency event-related potential components in response to stimuli is indicative of a better recovery. All neurophysiological data must be integrated within a multimodal approach combining repeated clinical evaluation, neuroimaging, functional imaging, biology, and neurophysiology combining passive and active paradigms.

Neurophysiological Findings and Brain Injury Pattern in Patients on ECMO

Introduction. Brain injury is a major determinant of outcomes in extracorporeal membrane oxygenation (ECMO). Neurologic prognostication in ECMO has not been established. Absent electroencephalogram (EEG) reactivity and absent N20 on somatosensory evoked potential (SSEP) are associated with poor outcome in other types of brain injuries, especially following cardiopulmonary arrest. It is currently known if the same criteria are applicable in patients on ECMO. Methods. Continuous EEG (cEEG) was performed for patients with a Glasgow Coma Scale (GCS) <8 and SSEP data were performed for patients with a motor GCS < 4 in a prospective observational cohort undergoing ECMO at a tertiary center. EEG variables including reactivity were collected. SSEPs were categorized into absence, delay, or presence of N20. Poor outcome was defined as cerebral performance category 3 to 5 at discharge. Results. We present 13 consecutive patients who underwent both cEEG and SSEP. The median time from cannulation to EEG and SSEP were 3 (interquartile range [IQR] = 1-6) and 5 (IQR = 2-7) days, respectively. All patients were in coma and 12 (92%) had poor outcomes. Ten (77%) underwent brain computed tomography, the findings of which explained coma in only 2. Patients (n = 12) with poor outcome had poor variability, absent reactivity, and lack of sleep features with diffusely slow theta-delta background on the EEG. Despite poor outcomes, all had relatively preserved or normal N20 responses. One patient with preserved reactivity and sleep features on the EEG and intact SSEP had a good outcome. Conclusions. Absent EEG reactivity with the preservation of SSEP N20 was associated with poor outcome in comatose ECMO patients. We advise caution in interpreting electrophysiological tests in prognosticating ECMO patients until the patterns and outcomes are better understood.

Somatosensory evoked potentials in clinical practice: a review

The authors present a review of the current use of somatosensory evoked potentials (SSEPs) in neurological practice as a non-invasive neurophysiological technique. For this purpose we have reviewed articles published in English or Portuguese in the PubMed and LILACS databases. In this review, we address the role of SSEPs in neurological diseases that affect the central nervous system and the peripheral nervous system, especially in demyelinating diseases, for monitoring coma, trauma and the functioning of sensory pathways during surgical procedures. The latter, along with new areas of research, has become one of the most important applications of SSEPs.

Somatosensory Evoked Potentials and Neuroprognostication After Cardiac Arrest

Improved understanding of post-cardiac arrest syndrome and clinical practices such as targeted temperature management have led to improved mortality in this cohort. Attention has now been placed on development of tools to aid in predicting functional outcome in comatose cardiac arrest survivors. Current practice uses a multimodal approach including physical examination, neuroimaging, and electrophysiologic data, with a primary utility in predicting poor functional outcome. These modalities remain confounded by self-fulfilling prophecy and the withdrawal of life-sustaining therapies. To date, a reliable measure to predict good functional outcome has not been established or validated, but the use of quantitative somatosensory evoked potential (SSEP) shows potential for this use. MEDLINE and EMBASE search using words "Cardiac Arrest" and "SSEP," "Somato sensory evoked potentials," "qSSEP," "quantitative SSEP," "targeted temperature management in cardiac arrest" was conducted. Relevant recent studies on targeted temperature management in cardiac arrest, plus studies on SSEP in cardiac arrest in the setting of hypothermia and without hypothermia, were included. In addition, animal studies evaluating the role of different components of SSEP in cardiac arrest were reviewed. SSEP is a specific indicator of poor outcomes in post-cardiac arrest patients but lacks sensitivity and has not clinically been established to foresee good outcomes. Novel methods of analyzing quantitative SSEP (qSSEP) signals have shown potential to predict good outcomes in animal and human studies. In addition, qSSEP has potential to track cerebral recovery and guide treatment strategy in post-cardiac arrest patients. Lying beyond the current clinical practice of dichotomized absent/present N20 peaks, qSSEP has the potential to emerge as one of the earliest predictors of good outcome in comatose post-cardiac arrest patients. Validation of qSSEP markers in prospective studies to predict good and poor outcomes in the cardiac arrest population in the setting of hypothermia could advance care in cardiac arrest. It has the prospect to guide allocation of health care resources and reduce self-fulfilling prophecy.

Somatosensory evoked potential amplitudes correlate with long-term consciousness recovery in patients with unresponsive wakefulness syndrome

OBJECTIVE

To prospectively investigate relationships of cortical somatosensory evoked potential (SEP) amplitudes with consciousness recovery and disability in the year following brain injury in patients with vegetative state/unresponsive wakefulness syndrome (VS/UWS).

METHODS

SEPs of 42 patients with VS/UWS were recorded 51.7 ± 23.3 days post-injury. N20-P25 amplitudes were compared between patients with and without consciousness recovery at 6 months and 1 year post-injury.

RESULTS

SEPs were present in 21 patients and bilaterally absent in 21 patients. N20-P25 amplitudes were significantly higher in patients who recovered consciousness than in those who died or did not recover consciousness at 6 months (median, 4.6 vs. 1.9 μV; P = 0.004) and 1 year (median, 4.6 vs. 2.1 μV; P = 0.02) after injury. The lowest N20-P25 amplitude in a patient who recovered consciousness was 2.15 μV. N20-P25 amplitudes correlated significantly with Coma Recovery Scale-Revised and Disability Rating Scale scores at 6 months and 1 year post-injury (both P < 0.05).

CONCLUSIONS

In patients with VS/UWS, SEP amplitudes are related to consciousness recovery and disability at 6 months and 1 year post-injury.

SIGNIFICANCE

The evaluation of SEP amplitudes can help to refine prognoses for patients with VS/UWS.

Reliability in the assessment of paediatric somatosensory evoked potentials post cardiac arrest

OBJECTIVE

To measure inter- and intra-rater agreement in the interpretation of cortical somatosensory evoked potential (SSEP) components following paediatric cardiac arrest (CA) in multi-professional neurophysiology teams.

METHODS

Thirteen professionals blinded to patient outcome interpreted 96 SSEPs in paediatric patients 24-/48-/72-hours following CA. Of these, 34 were duplicates used to assess intra-rater agreement. Consistent interpretations (absent/present/indeterminate) between scientists (who record/identify SSEP components) and neurophysiologists (who provide prognostic SSEP interpretation) were expressed as percentages. Rates of agreement were calculated using Fleiss' kappa coefficient (K).

RESULTS

Unanimous agreement between professionals was present in 40% (95%CI: 28-54%) of the interpreted SSEPs, with a K value of 0.62 (95%CI: 0.55-0.70) based on average agreement. Agreement was similar between neurophysiologists (K = 0.67; 95%CI: 0.57-0.77) and scientists (K = 0.62; 95%CI: 0.54-0.70) but lower in patients < 2 years old (K = 0.23; 95%CI: 0.14-0.33) and in those with poor outcome (K = 0.21; 95%CI: 0.07-0.35). No SSEP was unanimously interpreted as absent and 92% (95%CI: 89-95%) of duplicate SSEPs were interpreted consistently.

CONCLUSION

Despite substantial agreement when interpreting prognostic SSEPs, this was significantly lower in children with poor outcome and of younger age.

SIGNIFICANCE

Clinicians using SSEPs in the intensive care unit should be aware of the inter-rater variability when interpreting SSEPs as absent.

Defining catastrophic brain injury in children leading to coma and disorders of consciousness and the scope of the problem

PURPOSE OF REVIEW

Severe brain injury in children resulting in coma and disorders of consciousness (DOC) is a catastrophic event for the life and function of children and their families. The present article summarizes the recently published pediatric literature on validated diagnostic assessments, potential predictors of recovery, and outcome measures used in children with catastrophic brain injury (CBI). Literature search terms included variants of consciousness, diagnostic tests, predictors of outcome, and outcome measures.

RECENT FINDINGS

Developmentally appropriate diagnostic tools, outcome predictors, and outcome measures are lacking for children with CBI leading to coma and DOC. Individual case prognosis relies on serial clinical examinations and experience. Evidence regarding optimal diagnosis of the highest level of consciousness and management of children with CBI is needed. Global efforts through the ongoing Curing Coma Campaign are aimed at: developing common data elements for information capture; streamlining the classification of coma endotypes; describing trajectories with biomarkers to monitor recovery or disease progression; and devising effective treatments for adults and children.

SUMMARY

Standardized, developmentally appropriate diagnostic and outcome assessments for CBI in children are needed. Future research should use these content standards to update our understanding of children with CBI leading to coma and DOC, and evaluate effective practices using acute adjunctive and rehabilitation therapies.

Clinical and advanced neurophysiology in the prognostic and diagnostic evaluation of disorders of consciousness: review of an IFCN-endorsed expert group

The analysis of spontaneous EEG activity and evoked potentialsis a cornerstone of the instrumental evaluation of patients with disorders of consciousness (DoC). Thepast few years have witnessed an unprecedented surge in EEG-related research applied to the prediction and detection of recovery of consciousness after severe brain injury,opening up the prospect that new concepts and tools may be available at the bedside. This paper provides a comprehensive, critical overview of bothconsolidated and investigational electrophysiological techniquesfor the prognostic and diagnostic assessment of DoC.We describe conventional clinical EEG approaches, then focus on evoked and event-related potentials, and finally we analyze the potential of novel research findings. In doing so, we (i) draw a distinction between acute, prolonged and chronic phases of DoC, (ii) attempt to relate both clinical and research findings to the underlying neuronal processes and (iii) discuss technical and conceptual caveats.The primary aim of this narrative review is to bridge the gap between standard and emerging electrophysiological measures for the detection and prediction of recovery of consciousness. The ultimate scope is to provide a reference and common ground for academic researchers active in the field of neurophysiology and clinicians engaged in intensive care unit and rehabilitation.

Multicenter prospective study on predictors of short-term outcome in disorders of consciousness

OBJECTIVE

This international multicenter, prospective, observational study aimed at identifying predictors of short-term clinical outcome in patients with prolonged disorders of consciousness (DoC) due to acquired severe brain injury.

METHODS

Patients in vegetative state/unresponsive wakefulness syndrome (VS/UWS) or in minimally conscious state (MCS) were enrolled within 3 months from their brain injury in 12 specialized medical institutions. Demographic, anamnestic, clinical, and neurophysiologic data were collected at study entry. Patients were then followed up for assessing the primary outcome, that is, clinical diagnosis according to standardized criteria at 6 months postinjury.

RESULTS

We enrolled 147 patients (44 women; mean age 49.4 [95% confidence interval 46.1-52.6] years; VS/UWS 71, MCS 76; traumatic 55, vascular 56, anoxic 36; mean time postinjury 59.6 [55.4-63.6] days). The 6-month follow-up was complete for 143 patients (VS/UWS 70; MCS 73). With respect to study entry, the clinical diagnosis improved in 72 patients (VS/UWS 27; MCS 45). Younger age, shorter time postinjury, higher Coma Recovery Scale-Revised total score, and presence of EEG reactivity to eye opening at study entry predicted better outcome, whereas etiology, clinical diagnosis, Disability Rating Scale score, EEG background activity, acoustic reactivity, and P300 on event-related potentials were not associated with outcome.

CONCLUSIONS

Multimodal assessment could identify patients with higher likelihood of clinical improvement in order to help clinicians, families, and funding sources with various aspects of decision-making. This multicenter, international study aims to stimulate further research that drives international consensus regarding standardization of prognostic procedures for patients with DoC.

Progression Prediction of Mild Cervical Spondylotic Myelopathy by Somatosensory-evoked Potentials

STUDY DESIGN

Retrospective study to correlate classification of somatosensory-evoked potentials (SEPs) with symptomatic progress of patients with mild cervical spondylotic myelopathy (CSM).

OBJECTIVE

The aim of this study was to evaluate the usefulness of SEPs for predicting symptomatic progress of mild CSM.

SUMMARY OF BACKGROUND DATA

SEPs have been used for clinical diagnosis and intraoperative neuromonitoring in patients with CSM. However, the prognostic value of SEPs in predicting the progression of CSM remains unclear.

METHODS

A total of 200 patients with a clinical diagnosis of mild CSM were enrolled between September 2014 and February 2018. All patients received clinical assessment with the modified Japanese Orthopedic Association scale (mJOA), magnetic resonance imaging, and SEP tests in the first clinical visit and at 1-year follow-up. A classification of upper and lower limbs SEP was developed. At 1-year follow-up, patients with symptom decline >2 points in mJOA were considered progressive myelopathy cases. The relationship of progressive myelopathy and classifications of SEP was investigated.

RESULTS

Fifty-four of 200 cases presented with progressive myelopathy. The incidence of progressive myelopathy was 2.6%, 27.7%, 23.8%, 86.7%, and 100% in Class I, II, III, IV, and V of upper SEPs, respectively, and 18.8%, 39.4%, 42.3%, and 62.5% in Class I, II, III, and IV of lower SEPs, respectively. For the combination classification of upper and lower SEPs, the incidence of progressive myelopathy was 0%, 13.7%, 24.3%, 91.1%, and 100% in Class I, II, III, IV, and V, respectively. There was a significant correlation of the incidence of progressive myelopathy with SEP classification for the upper SEPs (r = 0.94, P < 0.01) and the combination SEPs (r = 0.95, P < 0.01).

CONCLUSION

The incidence of progressive degenerative myelopathy increased with the upper and combination SEP classifications. Thus, classification of SEPs could predict the clinical decline in mJOA in CSM, reflecting the probability of worsening of myelopathy.

LEVEL OF EVIDENCE

4.

SSEP retains its value as predictor of poor outcome following cardiac arrest in the era of therapeutic hypothermia

OBJECTIVES

To re-evaluate the role of median nerve somatosensory evoked potentials (SSEPs) and bilateral loss of the N20 cortical wave as a predictor of unfavorable outcome in comatose patients following cardiac arrest (CA) in the therapeutic hypothermia (TH) era.

METHODS

Review the results and conclusions drawn from isolated case reports and small series of comatose patients following CA in which the bilateral absence of N20 response has been associated with recovery, and evaluate the proposal that SSEP can no longer be considered a reliable and accurate predictor of unfavorable neurologic outcome.

RESULTS

There are many methodological limitations in those patients reported in the literature with severe post anoxic encephalopathy who recover despite having lost their N20 cortical potential. These limitations include lack of sufficient clinical and neurologic data, severe core body hypothermia, specifics of electrophysiologic testing, technical issues such as background noise artifacts, flawed interpretations sometimes related to interobserver inconsistency, and the extreme variability in interpretation and quality of SSEP analysis among different clinicians and hospitals.

CONCLUSIONS

The absence of the SSEP N20 cortical wave remains one of the most reliable early prognostic tools for identifying unfavorable neurologic outcome in the evaluation of patients with severe anoxic-ischemic encephalopathy whether or not they have been treated with TH. When confounding factors are eliminated the false positive rate (FPR) approaches zero.

Short-Latency Positive Peak Following N20 Somatosensory Evoked Potential Is Superior to N20 in Predicting Neurologic Outcome After Out-of-Hospital Cardiac Arrest

OBJECTIVES

The absence of N20 somatosensory evoked potential after cardiac arrest is related to poor outcome. However, discrimination between the low-amplitude and the absence of N20 is challenging. P25 and P30 are short-latency positive peaks with latencies between 25 and 30 ms following N20 (P25/30). P25/30 is evident even with an ambiguous N20 in patients with good outcome. Therefore, we evaluated the predictive value of P25/30 after cardiac arrest.

DESIGN

A retrospective observational study.

SETTING

University-affiliated hospital.

SUBJECTS

Comatose survivors after out-of-hospital cardiac arrest treated by hypothermic targeted temperature management.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

The specificity and the positive predictive value of P25/30 and N20 in predicting poor outcome were the same, showing a rate of 100%. The sensitivity of P25/30 in predicting poor outcome (90.12% [95% CI, 81.5-95.6%]) was higher than that of N20 (70.37% [95% CI, 59.2-80%]). Also, the negative predictive value of P25/30 in predicting poor outcome (81.4% [95% CI, 69.4-89.4%]) was higher than that of N20 (59.3% [95% CI, 51-67.1%]). The P25/30-based adjusted model showed a larger area under the curve (0.98 [95% CI, 0.95-1]) compared with the N20-based adjusted model (0.95 [95% CI, 0.91-0.98]) (p = 0.02).

CONCLUSIONS

The absence of P25/30 is related to poor outcome with a higher sensitivity, negative predictive value than the absence of N20.

[A case of post-cardiac arrest syndrome presenting with lateralized periodic discharges evolving to a cyclic seizure pattern on electroencephalogram]

A 53-year-old man with hypertension experienced sudden cardiopulmonary arrest. Ambulance crews detected ventricular fibrillation that responded to defibrillation. Cardiopulmonary resuscitation resulted in return of spontaneous circulation (ROSC) after 30 minutes. At admission to our hospital, he was in a comatose state. Therapeutic hypothermia was performed for two days with other supportive care. However, despite these therapies, he remained comatose, and a diagnosis of post-cardiac arrest syndrome (PCAS) was made. On the sixth hospital day, an electroencephalogram (EEG) showed lateralized periodic discharges (LPDs) in the right occipital area evolving to electrographic seizures. Over roughly 15 minutes, this evolution process repeated 10 times, demonstrating a cyclic seizure pattern. Intravenous administration of 10 mg diazepam resulted in temporal attenuation of the high-amplitude discharges followed by LPDs re-emergence accompanying a low-amplitude fast rhythm on the background activity (LPDs+). Antiepileptic drugs administration was continued, along with supportive care. He opened his eyes on the 11th hospital day, after which his general conditions showed a good recovery. He was discharged on the 30th day without any sequelae.

Early-SEPs' amplitude reduction is reliable for poor-outcome prediction after cardiac arrest?

OBJECTIVE

The bilateral absence of cortical Somatosensory Evoked Potentials (SEPs), after cardiac arrest (CA), is a high reliable predictor of poor outcome but it is present in no more than 40% of patients. An amplitude reduction of cortical SEPs was found in about 30% of subjects, but few papers analysed its prognostic significance. The aim of our study is to identify a value of SEP amplitude reduction below which all the CA patients had poor outcome and the relationship between SEP and Electroencephalogram (EEG) patterns.

MATERIAL AND METHODS

We analysed comatose patients in whom SEPs and EEG were recorded at 6-12 hours after CA. We evaluated the sensitivity at specificity of 100% of SEP amplitude in predicting the non-recovery of consciousness by plotting Receiver Operating Characteristic (ROC) curves. We also analysed the relationship between SEP amplitude and EEG patterns. Outcome was evaluated at 6 months by Glasgow Outcome Scale.

RESULTS

We analysed 119 subjects. According to the ROC analysis (area under the curve = 0.95/CI 0.91-0.99), all patients with a cortical SEP amplitude <0.65 μV did not recover consciousness (GOS 1-2), with a sensitivity of 71.8%. Severe EEG abnormalities (suppression and burst-suppression patterns) were also observed in all these patients.

CONCLUSION

Not only the absence but also a bilateral amplitude reduction of cortical SEPs (<0.65 μV) is associated with ominous prognosis (death or non-recovery of consciousness) with a very high predictive value. However, we emphasize that great caution should be applied before adopting amplitude reduction as a criterion for the poor prognosis of CA patients.

Cervical Spinal Cord Stimulation for the Vegetative State: A Preliminary Result of 12 Cases

OBJECTIVES

Data on the treatment of the vegetative state (VS) with cervical spinal cord stimulation (cSCS) are limited and prognostic factors are inconclusive. In this study, we present our experience of treating 12 VS patients with cSCS and discuss the prognostic factors.

METHODS

Twelve VS patients were enrolled. Preoperative assessments included CT/MRI, PET, brainstem auditory evoked potentials (BAEPs), somatosensory evoked potentials (SEPs), and electroencephalogram (EEG). cSCS surgeries were performed at West China Hospital. The electrode was implanted in the epidural space of the C2-4 vertebrae. Levels of consciousness were evaluated based on the Coma Recovery Scale-Revised (CRS-R) at baseline and during follow-up.

RESULTS

The average follow-up was 11.1 months. The average CRS-R score at the last evaluation was 10.8, which was significantly improved compared with the baseline score (6.25). Five patients achieved responsive outcomes (three recovered and two evolved to a minimally conscious state) and seven achieved unresponsive outcomes (six remained in VS and one died). Age, preoperative CRS-R score, the interval between acute comatose injury and cSCS, and the Vth wave of BAEPs did not differ significantly between the responsive group and the unresponsive group. Appearance of the N20 of SEPs and multifocal abnormalities on CT/MRI and PET were significantly associated with a better outcome, while the etiology of ischemia and anoxia (IAA) was significantly associated with a poor outcome.

CONCLUSIONS

cSCS should be a glimmer of hope for VS patients. Patients whose N20 is elicited or whose CT/MRI or PET demonstrates multifocal abnormalities are more likely to benefit from cSCS, whereas those with an IAA etiology have a lower likelihood of recovery after cSCS.

Neurophysiology contributes to outcome prediction after cardiac arrest

This "Points of View" paper discusses the role of neurophysiology in predicting outcome in patients who have initially survived a cardiac arrest but remain in coma. The authors, from different clinical backgrounds, discuss their individual approaches to neuroprognostication.

Value and mechanisms of EEG reactivity in the prognosis of patients with impaired consciousness: a systematic review

Background

Electroencephalography (EEG) is a well-established tool for assessing brain function that is available at the bedside in the intensive care unit (ICU). This review aims to discuss the relevance of electroencephalographic reactivity (EEG-R) in patients with impaired consciousness and to describe the neurophysiological mechanisms involved.

Methods

We conducted a systematic search of the term “EEG reactivity and coma” using the PubMed database. The search encompassed articles published from inception to March 2018 and produced 202 articles, of which 42 were deemed relevant, assessing the importance of EEG-R in relationship to outcomes in patients with impaired consciousness, and were therefore included in this review.

Results

Although definitions, characteristics and methods used to assess EEG-R are heterogeneous, several studies underline that a lack of EEG-R is associated with mortality and unfavorable outcome in patients with impaired consciousness. However, preserved EEG-R is linked to better odds of survival. Exploring EEG-R to nociceptive, auditory, and visual stimuli enables a noninvasive trimodal functional assessment of peripheral and central sensory ascending pathways that project to the brainstem, the thalamus and the cerebral cortex. A lack of EEG-R in patients with impaired consciousness may result from altered modulation of thalamocortical loop activity by afferent sensory input due to neural impairment. Assessing EEG-R is a valuable tool for the diagnosis and outcome prediction of severe brain dysfunction in critically ill patients.

Conclusions

This review emphasizes that whatever the etiology, patients with impaired consciousness featuring a reactive electroencephalogram are more likely to have a favorable outcome, whereas those with a nonreactive electroencephalogram are prone to having an unfavorable outcome. EEG-R is therefore a valuable prognostic parameter and warrants a rigorous assessment. However, current assessment methods are heterogeneous, and no consensus exists. Standardization of stimulation and interpretation methods is needed.

Anoxic-Ischemic Brain Injury

Improvements in cardiopulmonary resuscitation and intensive care medicine have led to declining mortality rates for patients with out-of-hospital cardiac arrest, but overall it is still a minority that achieves good outcomes. Estimating neurologic prognosis for patients that remain comatose after resuscitation remains a challenge and the need for accurate and early prognostic predictors is crucial. A thoughtful approach is required and should take into account information acquired from multiple tests in association with neurologic examination. No decision should be made based on a single predictor. In addition to clinical examination, somatosensory evoked potentials, electroencephalogram, serum biomarkers, and neuroimaging provide complimentary information to inform prognosis.

Repeated injections of human umbilical cord blood-derived mesenchymal stem cells significantly promotes functional recovery in rabbits with spinal cord injury of two noncontinuous segments

Background

Spinal cord injuries (SCIs) are sustained by an increasing number of patients each year worldwide. The treatment of SCIs has long been a hard nut to crack for doctors around the world. Mesenchymal stem cells (MSCs) have shown benefits for the repair of SCI and recovery of function. Our present study aims to investigate the effects of intravenously infused human umbilical cord blood-derived MSCs (hUCB-MSCs) on functional recovery after subacute spinal cord compression injury of two noncontinuous segments. In addition, we compared the effects of single infusion and repeated intravenous (i.v.) injections on the recovery of spinal cord function.

Methods

A total of 43 adult rabbits were randomly divided into four groups: control, single injection (SI), repeated injection at a 3-day (3RI) or repeated injection at a 7-day interval (7RI) groups. Non-immunosuppressed rabbits in the transplantation groups were infused with either a single complete dose or three divided doses of 2 × 10⁶ hUCB-MSCs (3-day or 7-day intervals) on the first day post decompression. Behavioural scores and somatosensory evoked potentials (SEPs) were used to evaluate hindlimb functional recovery. The survival and differentiation of the transplanted human cells and the activation of the host glial and inflammatory reaction in the injured spinal cord were studied by immunohistochemical staining.

Results

Our results showed that hUCB-MSCs survived, proliferated, and primarily differentiated into oligodendrocytes in the injured area. Treatment with hUCB-MSCs reduced the extent of astrocytic activation, increased axonal preservation, potentially promoted axonal regeneration, decreased the number of Iba-1+ and TUNEL+ cells, increased the amplitude and decreased the onset latency of SEPs and significantly promoted functional improvement. However, these effects were more pronounced in the 3RI group compared with the SI and 7RI groups.

Conclusions

Our results suggest that treatment with i.v. injected hUCB-MSCs after subacute spinal cord compression injury of two noncontinuous segments can promote functional recovery through the differentiation of hUCB-MSCs into specific cell types and the enhancement of anti-inflammatory, anti-astrogliosis, anti-apoptotic and axonal preservation effects. Furthermore, the recovery was more pronounced in the rabbits repeatedly injected with cells at 3-day intervals. The results of this study may provide a novel and useful treatment strategy for the transplantation treatment of SCI.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0879-0) contains supplementary material, which is available to authorized users.

Noninvasive Neuromonitoring: Current Utility in Subarachnoid Hemorrhage, Traumatic Brain Injury, and Stroke

Noninvasive neuromonitoring is increasingly being used to monitor the course of primary brain injury and limit secondary brain damage of patients in the neurocritical care unit. Proposed advantages over invasive neuromonitoring methods include a lower risk of infection and bleeding, no need for surgical installation, mobility and portability of some devices, and safety. The question, however, is whether noninvasive neuromonitoring is practical and trustworthy enough already. We searched the recent literature and reviewed English-language studies on noninvasive neuromonitoring in subarachnoid hemorrhage, traumatic brain injury, and ischemic and hemorrhagic stroke between the years 2010 and 2015. We found 88 studies that were eligible for review including the methods transcranial ultrasound, electroencephalography, evoked potentials, near-infrared spectroscopy, bispectral index, and pupillometry. Noninvasive neuromonitoring cannot yet completely replace invasive methods in most situations, but has great potential being complementarily integrated into multimodality monitoring, for guiding management, and for limiting the use of invasive devices and in-hospital transports for imaging.

Combining early post-resuscitation EEG and HRV features improves the prognostic performance in cardiac arrest model of rats

OBJECTIVE

Early and reliable prediction of neurological outcome remains a challenge for comatose survivors of cardiac arrest (CA). The purpose of this study was to evaluate the predictive ability of EEG, heart rate variability (HRV) features and the combination of them for outcome prognostication in CA model of rats.

METHODS

Forty-eight male Sprague-Dawley rats were randomized into 6 groups (n=8 each) with different cause and duration of untreated arrest. Cardiopulmonary resuscitation was initiated after 5, 6 and 7min of ventricular fibrillation or 4, 6 and 8min of asphyxia. EEG and ECG were continuously recorded for 4h under normothermia after resuscitation. The relationships between features of early post-resuscitation EEG, HRV and 96-hour outcome were investigated. Prognostic performances were evaluated using the area under receiver operating characteristic curve (AUC).

RESULTS

All of the animals were successfully resuscitated and 27 of them survived to 96h. Weighted-permutation entropy (WPE) and normalized high frequency (nHF) outperformed other EEG and HRV features for the prediction of survival. The AUC of WPE was markedly higher than that of nHF (0.892 vs. 0.759, p<0.001). The AUC was 0.954 when WPE and nHF were combined using a logistic regression model, which was significantly higher than the individual EEG (p=0.018) and HRV (p<0.001) features.

CONCLUSIONS

Earlier post-resuscitation HRV provided prognostic information complementary to quantitative EEG in the CA model of rats. The combination of EEG and HRV features leads to improving performance of outcome prognostication compared to either EEG or HRV based features alone.

Prognostication in Anoxic Brain Injury

Cardiac arrest is a common cause of coma with frequent poor outcomes. Palliative medicine teams are often called upon to discuss the scope of treatment and future care in cases of anoxic brain injury. Understanding prognostic tools in this setting would help medical teams communicate more effectively with patients’ families and caregivers and may promote improved quality of life overall. This article reviews multiple tools that are useful in determining outcomes in the setting of postarrest anoxic brain injury.

Somatosensory evoked potentials after decompressive craniectomy for traumatic brain injury

Somatosensory evoked potentials (SSEPs) are used for neuroprognosis after severe traumatic brain injury (TBI). However decompressive craniectomy (DC), involving removal of a portion of the skull to alleviate elevated intracranial pressure, is associated with an increase in SSEP amplitude. Accordingly, SSEPs are not available for neuroprognosis over the hemisphere with DC. We aim to determine the degree to which SSEP amplitudes are increased in the absence of cranial bone. This will serve as a precursor for translation to clinically prognostic ranges. Intra-operative SSEPs were performed before and after bone flap replacement in 22 patients with severe TBI. SSEP measurements were also performed in a comparison non-traumatic group undergoing craniotomy for tumor resection. N20/P25 amplitudes and central conduction time were measured with the bone flap in (BI) and out (BO). Linear regressions, adjusting for skull thickness and study arm, were performed to evaluate the contribution of bone presence to SSEP amplitudes. Latencies were not different between BO or BI trials in either group. Mean N20/P25 amplitudes recorded with BO were statistically different (p = 0.0001) from BI in both cohorts, showing an approximate doubling in BO amplitudes. For contralateral-ipsilateral montages r² was 0.28 and for frontal pole montages r² was 0.62. Cortical SSEP amplitudes are influenced by the presence of cortical bone as is particularly evident in frontal pole montages. Larger, longitudinal trials to assess feasibility of neuroprognosis over the hemisphere with DC in severe TBI patients are warranted.

Bilateral loss of cortical SEPs predict severe MRI lesions in neonatal hypoxic ischemic encephalopathy treated with hypothermia

OBJECTIVE

The introduction of therapeutic hypothermia for neonatal hypoxic-ischemic encephalopathy calls for reevaluation of the prognostic role of somatosensory evoked potentials (SEPs).

METHODS

Among 80 consecutive neonates undergoing hypothermia for hypoxic-ischemic encephalopathy, 58 performed SEPs and MRI at 4-14 days of life and were recruited in this multicenter study. SEPs were scored as: 0 (bilaterally/unilaterally recorded N20) or 1 (bilaterally absent N20). The severity of brain injury was scored using MRI.

RESULTS

Bilaterally absent N20 was observed in 10/58 neonates (17%); all had moderate/severe MRI abnormalities; 36/48 neonates (75%) with score 0 at SEPs had normal MRI. The positive predictive value of SEPs on MRI outcome was of 1.00, while the negative predictive value 0.72, sensitivity 0.48, specificity 1.00, with an accuracy of 0.78 (p < .001).

CONCLUSIONS

Bilateral absence of cortical SEPs predicts moderate/severe MRI pattern of injury.

SIGNIFICANCE

Therapeutic hypothermia does not seem to significantly affect prognostic reliability of SEPs.

Cognitive Event-Related Potentials during the Sub-Acute Phase of Severe Traumatic Brain Injury and Their Relationship to Outcome

Predicting outcome in the early phase after severe traumatic brain injury (sTBI) is a major clinical challenge, particularly identifying patients with potential for good cognitive outcome. The current single-center prospective study aimed to explore presence and normalization of electroencephalography (EEG)-based event-related potentials (ERPs) in the early phase followings TBI, and their relationship to functional and cognitive outcome 6 months post-injury. Fourteen adult patients (eight males) with sTBI were recruited from the neurointensive care unit (mean age = 38.2 years [standard deviation (SD) = 14.7]; mean lowest Glasgow Coma Scale (GCS) score within first 24 h = 5.4, SD = 1.87). EEG recordings were conducted biweekly at three time-points applying an ERP paradigm encompassing a passive condition involving hearing their own name randomly interspersed between an unfamiliar name (UN), and an active condition with instruction to count their own name. Functional and cognitive outcome 6 months post-injury was measured with Glasgow Outcome Scale-Extended (GOSE) and neuropsychological tests of attention and memory. Ten patients demonstrated a significantly enhanced cognitive P3 in the active counting task compared with passive listening across recordings, and six presented with normalization of P3 in the counting task. Moreover, P3 amplitude to the counting task at the third time-point was positively correlated with both functional outcome (GOSE) and cognition (verbal learning, attentional set-shifting, and switching) 6 months post-injury. ERP can index cognitive capacities in the early phase following sTBI, and the cognitive P3 component in an active design is associated with functional and cognitive outcome, demonstrating that the cognitive P3 may yield valuable information of residual cognition and provide supplementary prognostic information.

Somatosensory evoked potentials in patients with high-grade aneurysmal subarachnoid hemorrhage

OBJECTIVE The aim of this prospective study was to investigate the value of somatosensory evoked potentials (SEPs) in predicting outcome in patients with high-grade aneurysmal subarachnoid hemorrhage (SAH). METHODS Between January 2013 and January 2015, 48 patients with high-grade SAH (Hunt and Hess Grade III, IV, or V) who were admitted within 3 days after hemorrhage were enrolled in the study. Right and left median and tibial nerve SEPs were recorded on Day 3 after hemorrhage and recorded again 2 weeks later. Glasgow Outcome Scale (GOS) scores were determined 6 months after hemorrhage and dichotomized as poor (Scores 1-3) or good (Scores 4-5). Results of SEP measurements were dichotomized (present or missing cortical responses or normal or prolonged latencies) for each nerve and side. These variables were summed and tested using logistic regression and a receiver operating characteristic curve to assess the value of SEPs in predicting long-term outcome. RESULTS At the 6-month follow-up visit, 29 (60.4%) patients had a good outcome, and 19 (39.6%) had a poor outcome. The first SEP measurement did not correlate with clinical outcome (area under the curve [AUC] 0.69, p = 0.52). At the second measurement of median nerve SEPs, all patients with a good outcome had cortical responses present bilaterally, and none of them had bilateral prolonged latencies (p = 0.014 and 0.003, respectively). In tibial nerve SEPs, 7.7% of the patients with a good GOS score had one or more missing cortical responses, and bilateral prolonged latencies were found in 23% (p = 0.001 and 0.034, respectively). The second measurement correlated with the outcome regarding each of the median and tibial nerve SEPs and the combination of both (AUC 0.75 [p = 0.010], 0.793 [p = 0.003], and 0.81 [p = 0.001], respectively). CONCLUSIONS Early SEP measurement after SAH did not correlate with clinical outcome, but measurement of median and tibial nerve SEPs 2 weeks after a hemorrhage did predict long-term outcome in patients with high-grade SAH.

Brainstem Monitoring in the Neurocritical Care Unit: A Rationale for Real-Time, Automated Neurophysiological Monitoring

Patients with severe traumatic brain injury or large intracranial space-occupying lesions (spontaneous cerebral hemorrhage, infarction, or tumor) commonly present to the neurocritical care unit with an altered mental status. Many experience progressive stupor and coma from mass effects and transtentorial brain herniation compromising the ascending arousal (reticular activating) system. Yet, little progress has been made in the practicality of bedside, noninvasive, real-time, automated, neurophysiological brainstem, or cerebral hemispheric monitoring. In this critical review, we discuss the ascending arousal system, brain herniation, and shortcomings of our current management including the neurological exam, intracranial pressure monitoring, and neuroimaging. We present a rationale for the development of nurse-friendly-continuous, automated, and alarmed-evoked potential monitoring, based upon the clinical and experimental literature, advances in the prognostication of cerebral anoxia, and intraoperative neurophysiological monitoring.

Automatic and continuous assessment of ERPs for mismatch negativity detection

Accurate and fast detection of event related potential (ERP) components is an unresolved issue in neuroscience and critical health care. Mismatch negativity (MMN) is a component of the ERP to an odd stimulus in a sequence of identical stimuli which has good correlation with coma awakening. All of the previous studies for MMN detection are based on visual inspection of the averaged ERPs (over a long recording time) by a skilled neurophysiologist. However, in practical situations, such an expert may not be available or familiar with all aspects of evoked potential methods. Further, we may miss important clinically essential events due to the implicit averaging process used to acquire the ERPs. In this paper we propose a practical machine learning approach for automatic and continuous assessment of the ERPs for detecting the presence of the MMN component. The proposed method is realized in a classification framework. Performance of the proposed method is demonstrated on 22 healthy subjects through a leave-one subject-out strategy where the MMN components are identified with about 93% accuracy.

Prognostic utility of neuroinjury biomarkers in post out-of-hospital cardiac arrest (OHCA) patient management

Despite aggressive intervention, patients who survive an out-of-hospital cardiac arrest (OHCA) generally have very poor prognoses, with nationwide survival rates of approximately 10-20%. Approximately 90% of survivors will have moderate to severe neurological injury ranging from moderate cognitive impairment to brain death. Currently, few early prognostic indicators are considered reliable enough to support patients' families and clinicians' in their decisions regarding medical futility. Blood biomarkers of neurological injury after OHCA may be of prognostic value in these cases. When most bodily tissues are oxygen-deprived, cellular metabolism switches from aerobic to anaerobic respiration. Neurons are a notable exception, however, being dependent solely upon aerobic respiration. Thus, after several minutes without circulating oxygen, neurons sustain irreversible damage, and certain measurable biomarkers are released into the circulation. Prior studies have demonstrated value in blood biomarkers in prediction of survival and neurologic impairment after OHCA. We hypothesize that understanding peptide biomarker kinetics in the early return of spontaneous circulation (ROSC) period, especially in the setting of refractory cardiac arrest, may assist clinicians in determining prognosis earlier in acute resuscitation. Specifically, during and after immediate resuscitation and return of ROSC, clinicians and families face a series of important questions regarding patient prognosis, futility of care and allocation of scarce resources such as the early initiation of extracorporeal cardiopulmonary resuscitation (ECPR). The ability to provide early prognostic information in this setting is highly valuable. Currently available, as well as potential biomarkers that could be good candidates in prognostication of neurological outcomes after OHCA or in the setting of refractory cardiac arrest will be reviewed and discussed.

Chronic disorders of consciousness

Over the last 20 years, studies have provided greater insight into disorders of consciousness (DOC), also known as altered state of consciousness. Increased brain residual functions have been identified in patients with DOC due to the successful application of novel next-generation imaging technologies. Many unconscious patients have now been confirmed to retain considerable cognitive functions. It is hoped that greater insight regarding the psychological state of patients may be achieved through the use of functional magnetic resonance imaging and brain-computer interfaces. However, issues surrounding the research and treatment of DOC remain problematic. These include differing opinions on the definition of consciousness, difficulties in diagnosis, assessment, prognosis and/or treatment, and newly emerging ethical, legal and social issues. To overcome these, appropriate care must be offered to patients with DOC by clinicians and families, as DOC patients may now be considered to live in more than just a vegetative state. The present article reviews the controversy surrounding the definition of consciousness and the reliability of novel technologies, prognostic prediction, communication with DOC patients and treatment methods. The ethical and social issues surrounding the treatment of DOC and future perspectives are also considered.

What is the optimal sequence of decompression for multilevel noncontinuous spinal cord compression injuries in rabbits?

Background

In recent years, multilevel spinal cord injuries (SCIs) have gained a substantial amount of attention from clinicians and researchers. Multilevel noncontinuous SCI patients cannot undergo the multiple steps of a one-stage operation because of a poor general condition or a lack of proper surgical approaches. The surgeon subsequently faces the decision of whether to initially relieve the rostral or caudal compression. In this study, we established a spinal cord compression model involving two noncontinuous segments in rabbits to evaluate the effects of differences in decompression order on the functional recovery of the spinal cord.

Methods

A Fogarty catheter was inserted into the epidural space through a hole in T6-7 and advanced 3 cm rostrally or caudally. Following successful model establishment, which was demonstrated by an evaluation of evoked potentials, balloons of different volumes (40 μl or 50 μl) were inflated in the experimental groups, whereas no balloons were inflated in the control group. The experimental groups underwent the first decompression in the rostral or caudal area at 1 week post-injury; the second decompression was performed at 2 weeks post-injury. For 6 weeks post-injury, the animals were tested to determine behavioral scores, somatosensory evoked potentials (SEPs) and radiographic imaging changes; histological and apoptosis assay results were subsequently analyzed.

Results

The behavioral test results and onset latency of the SEPs indicated that there were significant differences between priority rostral decompression (PRD) and priority caudal decompression (PCD) in the 50-μl compression group at 6 weeks post-injury; however, there were no significant differences between the two procedures in the 40-μl group at the same time point. Moreover, there were no significant peak-to-peak amplitude differences between the two procedures in the 50-μl compression group.

Conclusions

The findings of this study suggested that preferential rostral decompression was more beneficial than priority caudal decompression with respect to facilitating spinal cord functional recovery in rabbits with severe paraplegia and may provide clinicians with a reference for the clinical treatment of multiple-segment spinal cord compression injuries.

Global cerebral ischemia due to circulatory arrest: insights into cellular pathophysiology and diagnostic modalities

Circulatory arrest (CA) remains a major unresolved public health problem in the United States; the annual incidence of which is ~0.50 to 0.55 per 1000 population. Despite seminal advances in therapeutic approaches over the past several decades, brain injury continues to be the leading cause of morbidity and mortality after CA. In brief, CA typically results in global cerebral ischemia leading to delayed neuronal death in the hippocampal pyramidal cells as well as in the cortical layers. The dynamic changes occurring in neurons after CA are still unclear, and predicting these neurological changes in the brain still remains a difficult issue. It is hypothesized that the "no-flow" period produces a cytotoxic cascade of membrane depolarization, Ca²⁺ ion influx, glutamate release, acidosis, and resultant activation of lipases, nucleases, and proteases. Furthermore, during reperfusion injury, neuronal death occurs due to the generation of free radicals by interfering with the mitochondrial respiratory chain. The efficacy of many pharmacological agents for CA patients has often been disappointing, reflecting our incomplete understanding of this enigmatic disease. The primary obstacles to the development of a neuroprotective therapy in CA include uncertainties with regard to the precise cause(s) of neuronal dysfunction and what to target. In this review, we summarize our knowledge of the pathophysiology as well as specific cellular changes in brain after CA and revisit the most important neurofunctional, neuroimaging techniques, and serum biomarkers as potent predictors of neurologic outcome in CA patients.

Patterns of use of somatosensory-evoked potentials for comatose patients in Canada

PURPOSE

To measure how frequently somatosensory-evoked potentials (SEPs) are used in comatose patients after traumatic brain injury (TBI) and hypoxic ischemic encephalopathy (HIE), how SEPs contribute to outcome prediction and clinical decision making, and how available they are to clinicians.

METHODS

A novel factual and scenario-based survey instrument to measure patterns of SEPs use in comatose patients due to HIE or TBI was distributed to critical care, neurology, and neurosurgical physicians across Canada. The analysis was based on 86 completed surveys from specialists in neurology (36), neurosurgery (24), and critical care (22).

RESULTS

Most (73%) of respondents reported that SEPs were available. When provided clinical vignettes, only 36% indicated that they would use them in TBI and 49% would use them in HIE. When respondents ranked the various methods available for establishing prognosis for awakening, SEP was ranked after cerebral blood flow and magnetic resonance imaging. The majority did not accurately estimate chances of awakening when SEP responses were bilaterally absent.

CONCLUSIONS

There are significant opportunities to optimize the use of SEPs in comatose patients including standardizing SEP testing and reporting, better communicating results to critical care physicians, and improving the understanding regarding the recommended use and interpretation of these tests.

Bedside functional brain imaging in critically-ill children using high-density EEG source modeling and multi-modal sensory stimulation

Acute brain injury is a common cause of death and critical illness in children and young adults. Fundamental management focuses on early characterization of the extent of injury and optimizing recovery by preventing secondary damage during the days following the primary injury. Currently, bedside technology for measuring neurological function is mainly limited to using electroencephalography (EEG) for detection of seizures and encephalopathic features, and evoked potentials. We present a proof of concept study in patients with acute brain injury in the intensive care setting, featuring a bedside functional imaging set-up designed to map cortical brain activation patterns by combining high density EEG recordings, multi-modal sensory stimulation (auditory, visual, and somatosensory), and EEG source modeling. Use of source-modeling allows for examination of spatiotemporal activation patterns at the cortical region level as opposed to the traditional scalp potential maps. The application of this system in both healthy and brain-injured participants is demonstrated with modality-specific source-reconstructed cortical activation patterns. By combining stimulation obtained with different modalities, most of the cortical surface can be monitored for changes in functional activation without having to physically transport the subject to an imaging suite. The results in patients in an intensive care setting with anatomically well-defined brain lesions suggest a topographic association between their injuries and activation patterns. Moreover, we report the reproducible application of a protocol examining a higher-level cortical processing with an auditory oddball paradigm involving presentation of the patient's own name. This study reports the first successful application of a bedside functional brain mapping tool in the intensive care setting. This application has the potential to provide clinicians with an additional dimension of information to manage critically-ill children and adults, and potentially patients not suited for magnetic resonance imaging technologies.

•

We demonstrate the use of high-density EEG combined with multi-modality sensory stimulation and source modeling to generate functional brain activation maps.

•

This is the first demonstration of source-level monitoring of functional brain responses in multiple modalities in children with acute brain injuries in ICU.

•

The set-up is designed to examine higher-level cortical processing by using an auditory oddball paradigm involving the subject’s own name.