Clinical neurophysiologic monitoring and brain injury from cardiac arrest

Burst-Suppression EEG Reactivity to Photic Stimulation-A Translational Biomarker in Hypoxic-Ischemic Brain Injury

The reactivity of an electroencephalogram (EEG) to external stimuli is impaired in comatose patients showing burst-suppression (BS) patterns following hypoxic-ischemic brain injury (HIBI). We explored the reactivity of BS induced by isoflurane in rat models of HIBI and controls using intermittent photic stimulation (IPS) delivered to one eye. The relative time spent in suppression referred to as the suppression ratio (SR) was measured on the contralateral fronto-occipital cortical EEG channel. The BS reactivity (BSR) was defined as the decrease in the SR during IPS from the baseline before stimulation (SRPRE). We found that BSR increased with SRPRE. To standardize by anesthetic depth, we derived the BSR index (BSRi) as BSR divided by SRPRE. We found that the BSRi was decreased at 3 days after transient global cerebral ischemia in rats, which is a model of brain injury after cardiac arrest. The BSRi was also reduced 2 months after experimental perinatal asphyxia in rats, a model of birth asphyxia, which is a frequent neonatal complication in humans. Furthermore, Oxytocin attenuated BSRi impairment, consistent with a neuroprotective effect in this model. Our data suggest that the BSRi is a promising translational marker in HIBI which should be considered in future neuroprotection studies.

Hyperacute autonomic and cortical function recovery following cardiac arrest resuscitation in a rodent model

OBJECTIVE

There is a complex interaction between nervous and cardiovascular systems, but sparse data exist on brain-heart electrophysiological responses to cardiac arrest resuscitation. Our aim was to investigate dynamic changes in autonomic and cortical function during hyperacute stage post-resuscitation.

METHODS

Ten rats were resuscitated from 7-min cardiac arrest, as indicators of autonomic response, heart rate (HR), and its variability (HRV) were measured. HR was monitored through continuous electrocardiography, while HRV was assessed via spectral analysis, whereby the ratio of low-/high-frequency (LF/HF) power indicates the balance between sympathetic/parasympathetic activities. Cortical response was evaluated by continuous electroencephalography and quantitative analysis. Parameters were quantified at 5-min intervals over the first-hour post-resuscitation. Neurological outcome was assessed by Neurological Deficit Score (NDS, range 0-80, higher = better outcomes) at 4-h post-resuscitation.

RESULTS

A significant increase in HR was noted over 15-30 min post-resuscitation (p < 0.01 vs.15-min, respectively) and correlated with higher NDS (rs = 0.56, p < 0.01). LF/HF ratio over 15-20 min was positively correlated with NDS (rs = 0.75, p < 0.05). Gamma band power surged over 15-30 min post-resuscitation (p < 0.05 vs. 0-15 min, respectively), and gamma band fraction during this period was associated with NDS (rs ≥0.70, p < 0.05, respectively). Significant correlations were identified between increased HR and gamma band power during 15-30 min (rs ≥0.83, p < 0.01, respectively) and between gamma band fraction and LF/HF ratio over 15-20 min post-resuscitation (rs = 0.85, p < 0.01).

INTERPRETATIONS

Hyperacute recovery of autonomic and cortical function is associated with favorable functional outcomes. While this observation needs further validation, it presents a translational opportunity for better autonomic and neurologic monitoring during early periods post-resuscitation to develop novel interventions.

Clinical Significance of Gray to White Matter Ratio after Cardiopulmonary Resuscitation in Children

Cardiopulmonary resuscitation (CPR) successfully restores systemic circulation approximately 50% of the time; however, many successfully restored patients have severe neurologic damage. In adults, the gray matter to white matter attenuation ratio (GWR) in brain computed tomography (CT) correlates with the neurologic outcome. However, in children, the clinical significance of GWR still remains unclear. The aim of this study was to evaluate the clinical characteristics of children who underwent CPR for cardiac arrest according to the survival and to demonstrate the differentiation of grey/white matter by Hounsfield units of brain CT and to characterize the attenuations of grey and white matters. Methods: This is a retrospective single-center study. We enrolled those who underwent brain CT within 24 h after return of spontaneous circulation (ROSC) from January 2005 to June 2018. Brain CTs were taken within 24 h of ROSC. We measured the attenuation of grey and white matter in Hounsfield units and calculated GWR. They were compared with healthy controls. Patients were analyzed as follows: survivors vs. non-survivors and better neurologic outcome vs. worse neurologic outcome. Results: Among 100 pediatric patients who had CPR, 56 met inclusion criteria. There were 24 patients who survived and 32 non-survivors. Our study revealed that the incidence of seizure, duration of CPR, and instances of hypothermia were significantly different between survivors and non-survivors. In both survivors and non-survivors, the attenuation of the caudate nucleus, putamen, GWR-basal ganglia, and average GWR were significantly different from controls. In regression analyses, the medial cortex and average GWR were the significant variables to predict survival, and the receiver operating curves revealed areas under curve of 0.733 and 0.666, respectively. Also, the medial cortex 1 was the only variable that predicted the neurologic outcome. Conclusions: There was some predictive survival value of GWR and medial cortex at the centrum semiovale level in early brain CT within 24 h after cardiac arrest. Although we could not find the predictive value of GWR in the neurologic outcome of pediatric patients, we found that the absolute attenuation of the medial cortex was low in patients with worse neurologic outcomes. Further prospective, multicenter studies are needed to determine the predictive value of GWR and the medial cortex.

Increased QT Dispersion Is Linked to Worse Outcomes in Patients Hospitalized for Out-of-Hospital Cardiac Arrest

Background The incidence and mortality of out-of-hospital cardiac arrest (OHCA) remains high, but predicting outcomes is challenging. Being able to better assess prognosis of hospitalized patients after return of spontaneous circulation would enable improved management of survival expectations. In this study, we assessed the predictive value of ECG indexes in hospitalized patients with OHCA. Methods and Results PR interval and QT interval corrected by the Bazett formula (QTc) for all leads were calculated from standard 12-lead ECGs 24 hours after return of spontaneous circulation in 93 patients who were hospitalized following OHCA. PR interval and QT and QTc duration did not differentiate OHCA survivors and nonsurvivors. However, QT and QTc dispersion was significantly increased in patients who died during hospitalization compared with survivors discharged from the hospital (P<0.01). Logistic regression indicated a strong association between increased QT dispersion and in-hospital mortality (P<0.0001; area under the curve, 0.8918 for QT dispersion and 0.8673 for QTc dispersion). Multinomial logistic regression indicated that the increase of QTc dispersion correlated with worse Cerebral Performance Category scores at discharge (P<0.001; likelihood ratio, 51.42). There was also significant correlation between dispersion measures and serum potassium at the time of measurement and between dispersion measures and cumulative epinephrine administration. No difference existed regarding the number of measurable leads. Conclusions Lesser QT and QTc dispersion at 24 hours after return of spontaneous circulation was significantly associated with survival and neurologic status at discharge. Routine evaluation of QT and QTc dispersion during hospitalization following return of spontaneous circulation might improve outcome prognostication for patients hospitalized for OHCA.

Prediction of cognitive dysfunction after resuscitation - a systematic review

Cardiac arrest (CA) due to cardiovascular disease is the leading cause of death in developed countries. It is estimated that over 350,000 people in Europe suffer from out-of-hospital cardiac arrest. According to the literature, the longer the episode of cardiac arrest, the greater the risk of cognitive impairment, especially short-term memory, as well as immediate and delayed recall. Other common dysfunctions include attention deficits and executive function disorders. The aim of this systematic review was to summarize current research on cognitive impairment in patients after sudden cardiac arrest. The electronic databases PubMed/MEDLINE, OVID, Web of Science, and EBSCO were searched using the following key words: 'sudden cardiac arrest', 'out-of-hospital cardiac arrest', 'cognitive function', 'cognitive impairment', 'functional outcome', 'cardiopulmonary resuscitation'. The most recent studies from the last 7 years (2011-2018) were included. Cognitive disorders occurred in a broad range of cases: from 13% to even 100%. In one study, cognitive deficits did not occur at all. Amongst the reviewed articles only two studies were carried out on a large group of patients. The remaining studies were conducted on a small group of respondents; therefore there was no possibility to generalize the results to the entire population. The areas in which the most cognitive impairment occurred were memory, executive functions and visual-motor skills. One of the conclusions derived from the reviewed literature is the importance of continuous training of cognitive functions, especially for people with cardiovascular risk.

Neural oscillations demonstrate that general anesthesia and sedative states are neurophysiologically distinct from sleep

General anesthesia is a man-made neurophysiological state comprised of unconsciousness, amnesia, analgesia, and immobility along with maintenance of physiological stability. Growing evidence suggests that anesthetic-induced neural oscillations are a primary mechanism of anesthetic action. Each anesthetic drug class produces distinct oscillatory dynamics that can be related to the circuit mechanisms of drug action. Sleep is a naturally occurring state of decreased arousal that is essential for normal health. Physiological measurements (electrooculogram, electromyogram) and neural oscillatory (electroencephalogram) dynamics are used to empirically characterize sleep into rapid eye movement sleep and the three stages of non-rapid eye movement sleep. In this review, we discuss the differences between anesthesia- and sleep-induced altered states from the perspective of neural oscillations.

The Benefit of Neuromuscular Blockade in Patients with Postanoxic Myoclonus Otherwise Obscuring Continuous Electroencephalography (CEEG)

Introduction. Myoclonus status epilepticus is independently associated with poor outcome in coma patients after cardiac arrest. Determining if myoclonus is of cortical origin on continuous electroencephalography (CEEG) can be difficult secondary to the muscle artifact obscuring the underlying CEEG. The use of a neuromuscular blocker can be useful in these cases. Methods. Retrospective review of CEEG in patients with postanoxic myoclonus who received cisatracurium while being monitored. Results. Twelve patients (mean age: 53.3 years; 58.3% male) met inclusion criteria of clinical postanoxic myoclonus. The initial CEEG patterns immediately prior to neuromuscular blockade showed myoclonic artifact with continuous slowing (50%), burst suppression with myoclonic artifact (41.7%), and continuous myogenic artifact obscuring CEEG (8.3%). After intravenous administration of cisatracurium (0.1 mg–2 mg), reduction in artifact improved quality of CEEG recordings in 9/12 (75%), revealing previously unrecognized patterns: continuous EEG seizures (33.3%), lateralizing slowing (16.7%), burst suppression (16.7%), generalized periodic discharges (8.3%), and, in the patient who had an initially uninterpretable CEEG from myogenic artifact, continuous slowing. Conclusion. Short-acting neuromuscular blockade is useful in determining background cerebral activity on CEEG otherwise partially or completely obscured by muscle artifact in patients with postanoxic myoclonus. Fully understanding background cerebral activity is important in prognostication and treatment, particularly when there are underlying EEG seizures.

Cognitive impairment after sudden cardiac arrest

Aim

To evaluate the incidence and severity of the impairment of selected cognitive functions in patients after sudden cardiac arrest (SCA) in comparison to patients after myocardial infarction without SCA and healthy subjects and to analyze the influence of sociodemographic and clinical parameters and the duration of cardiac arrest on the presence and severity of the described disorders.

Material and methods

The study group comprised 30 cardiac arrest survivors, the reference group comprised 31 survivors of myocardial infarction without cardiac arrest, and the control group comprised 30 healthy subjects. The Mini-Mental State Examination (MMSE), the Digit Span test from the Wechsler Adult Intelligence Scale, Lauretta Bender’s Visual-Motor Gestalt Test, and the Benton Visual Retention Test (BVRT) were used to assess the presence of cognitive impairment. An original questionnaire developed by the author was used for overall mental state assessment.

Results

The Bender test demonstrated a significant difference in the presence and severity of visual-motor skills between the study group and the control group, while BVRT and MMSE revealed increased incidence of cognitive impairment in the study group. The Bender and BVRT (D/D)/SS (version D, method D, scaled score) scales indicated cognitive impairment in 53.3% of these patients, while the BVRT (C/A)/SS test indicated cognitive impairment in 40%. For the reference group, the values were 32.3% and 12.9%, respectively. No correlation was found between the severity of cognitive impairment and the duration of cardiac arrest.

Conclusions

Impairment of visual-motor skills, short-term visual memory, concentration, and visual-motor coordination occurs much more frequently and is more severe in individuals after SCA than in healthy individuals. Impairment of memory trace storage and recall after delay occurs more frequently in patients after SCA than in patients after myocardial infarction without cardiac arrest and in healthy individuals. SCA duration did not have any influence on the severity of the described disorders.

Clinical Electroencephalography for Anesthesiologists: Part I: Background and Basic Signatures

The widely used electroencephalogram-based indices for depth-of-anesthesia monitoring assume that the same index value defines the same level of unconsciousness for all anesthetics. In contrast, we show that different anesthetics act at different molecular targets and neural circuits to produce distinct brain states that are readily visible in the electroencephalogram. We present a two-part review to educate anesthesiologists on use of the unprocessed electroencephalogram and its spectrogram to track the brain states of patients receiving anesthesia care. Here in part I, we review the biophysics of the electroencephalogram and the neurophysiology of the electroencephalogram signatures of three intravenous anesthetics: propofol, dexmedetomidine, and ketamine, and four inhaled anesthetics: sevoflurane, isoflurane, desflurane, and nitrous oxide. Later in part II, we discuss patient management using these electroencephalogram signatures. Use of these electroencephalogram signatures suggests a neurophysiologically based paradigm for brain state monitoring of patients receiving anesthesia care.

The human burst suppression electroencephalogram of deep hypothermia

OBJECTIVE

Deep hypothermia induces 'burst suppression' (BS), an electroencephalogram pattern with low-voltage 'suppressions' alternating with high-voltage 'bursts'. Current understanding of BS comes mainly from anesthesia studies, while hypothermia-induced BS has received little study. We set out to investigate the electroencephalogram changes induced by cooling the human brain through increasing depths of BS through isoelectricity.

METHODS

We recorded scalp electroencephalograms from eleven patients undergoing deep hypothermia during cardiac surgery with complete circulatory arrest, and analyzed these using methods of spectral analysis.

RESULTS

Within patients, the depth of BS systematically depends on the depth of hypothermia, though responses vary between patients except at temperature extremes. With decreasing temperature, burst lengths increase, and burst amplitudes and lengths decrease, while the spectral content of bursts remains constant.

CONCLUSIONS

These findings support an existing theoretical model in which the common mechanism of burst suppression across diverse etiologies is the cyclical diffuse depletion of metabolic resources, and suggest the new hypothesis of local micro-network dropout to explain decreasing burst amplitudes at lower temperatures.

SIGNIFICANCE

These results pave the way for accurate noninvasive tracking of brain metabolic state during surgical procedures under deep hypothermia, and suggest new testable predictions about the network mechanisms underlying burst suppression.

Continuous EEG monitoring in adults in the intensive care unit (ICU)

Continuous EEG monitoring in the ICU is different from planned EEG due to the rather urgent nature of the indications, explaining the fact that recording is started in certain cases by the clinical team in charge of the patient's care. Close collaboration between neurophysiology teams and intensive care teams is essential. Continuous EEG monitoring can be facilitated by quantified analysis systems. This kind of analysis is based on certain signal characteristics, such as amplitude or frequency content, but raw EEG data should always be interpreted if possible, since artefacts can sometimes impair quantified EEG analysis. It is preferable to work within a tele-EEG network, so that the neurophysiologist has the possibility to give an interpretation on call. Continuous EEG monitoring is thus useful in the diagnosis of non-convulsive epileptic seizures or purely electrical discharges and in the monitoring of status epilepticus when consciousness disorders persist after initial treatment. A number of other indications are currently under evaluation.

[French guidelines on electroencephalogram]

Electroencephalography allows the functional analysis of electrical brain cortical activity and is the gold standard for analyzing electrophysiological processes involved in epilepsy but also in several other dysfunctions of the central nervous system. Morphological imaging yields complementary data, yet it cannot replace the essential functional analysis tool that is EEG. Furthermore, EEG has the great advantage of being non-invasive, easy to perform and allows control tests when follow-up is necessary, even at the patient's bedside. Faced with the advances in knowledge, techniques and indications, the Société de Neurophysiologie Clinique de Langue Française (SNCLF) and the Ligue Française Contre l'Épilepsie (LFCE) found it necessary to provide an update on EEG recommendations. This article will review the methodology applied to this work, refine the various topics detailed in the following chapters. It will go over the summary of recommendations for each of these chapters and underline proposals for writing an EEG report. Some questions could not be answered by the review of the literature; in those cases, an expert advice was given by the working and reading groups in addition to the guidelines.

Changes in input strength and number are driven by distinct mechanisms at the retinogeniculate synapse

Recent studies have demonstrated that vision influences the functional remodeling of the mouse retinogeniculate synapse, the connection between retinal ganglion cells and thalamic relay neurons in the dorsal lateral geniculate nucleus (LGN). Initially, each relay neuron receives a large number of weak retinal inputs. Over a 2- to 3-wk developmental window, the majority of these inputs are eliminated, and the remaining inputs are strengthened. This period of refinement is followed by a critical period when visual experience changes the strength and connectivity of the retinogeniculate synapse. Visual deprivation of mice by dark rearing from postnatal day (P)20 results in a dramatic weakening of synaptic strength and recruitment of additional inputs. In the present study we asked whether experience-dependent plasticity at the retinogeniculate synapse represents a homeostatic response to changing visual environment. We found that visual experience starting at P20 following visual deprivation from birth results in weakening of existing retinal inputs onto relay neurons without significant changes in input number, consistent with homeostatic synaptic scaling of retinal inputs. On the other hand, the recruitment of new inputs to the retinogeniculate synapse requires previous visual experience prior to the critical period. Taken together, these findings suggest that diverse forms of homeostatic plasticity drive experience-dependent remodeling at the retinogeniculate synapse.

Feasibility of bispectral index monitoring to guide early post-resuscitation cardiac arrest triage

INTRODUCTION

Triage after resuscitation from cardiac arrest is hindered by reliable early estimation of brain injury. We evaluated the performance of a triage model based on early bispectral index (BIS) findings and cardiac risk classes.

METHODS

Retrospective evaluation of serial patients resuscitated from cardiac arrest, unable to follow commands, and undergoing hypothermia. Patients were assigned to a cardiac risk group: STEMI, VT/VF shock, VT/VF no shock, or PEA/asystole, and to a neurological dysfunction group, based on the BIS score following first neuromuscular blockade (BISi), and classified as BISi>20, BISi 10-20, or BISi<10. Cause of death was described as neurological or circulatory.

RESULTS

BISi in 171 patients was measured at 267(±177)min after resuscitation and 35(±1.7)°C. BISi<10 suffered 82% neurological-cause and 91% overall mortality, BISi 10-20 35% neurological and 55% overall mortality, and BISi>20 12% neurological and 36% overall mortality. 33 patients presented with STEMI, 15 VT/VF-shock, 41 VT/VF-no shock, and 80 PEA/asystole. Among BISi>20 patients, 75% with STEMI underwent urgent cardiac catheterization (cath) and 94% had good outcome. When BISi>20 with VT/VF and shock, urgent cath was infrequent (33%), and 4 deaths (44%) were uniformly of circulatory etiology. Of 56 VT/VF patients without STEMI, 24 were BISi>20 but did not undergo urgent cath - 5(20.8%) of these had circulatory-etiology death. Circulatory-etiology death also occurred in 26.5% BIS>20 patients with PEA/asystole. When BISi<10, a neurological etiology death dominated independent of cardiac risk group.

CONCLUSIONS

Neurocardiac triage based on very early processed EEG (BIS) is feasible, and may identify patients appropriate for individualized post-resuscitation care. This and other triage models warrant further study.

Early brain computed tomography findings are associated with outcome in patients treated with therapeutic hypothermia after out-of-hospital cardiac arrest

Background

This study evaluated the association between the results of immediate brain computed tomography (CT) scans and outcome in patients who were treated with therapeutic hypothermia after cardiac arrest. The evaluation was based on the changes in the ratio of gray matter to white matter.

Methods

A total of 167 patients who were successfully resuscitated after cardiac arrest from March 2009 to December 2011 were included in this study. We selected 51 patients who received a brain CT scan within 1 hour after the return of spontaneous circulation (ROSC) and who had been treated with therapeutic hypothermia. Circular regions of measurement (10 mm²) were placed over regions of interest (ROIs), and the average attenuations in gray matter (GM) and white matter (WM) were recorded in the basal ganglia, at the level of the centrum semiovale and in the high convexity area. Three GM-to-WM ratios (GWRs) were calculated: one for the basal ganglia, one for the cerebrum and the average of the two. The neurological outcomes were assessed using the Cerebral Performance Category (CPC) scale at the time of hospital discharge, and a good neurological outcome was defined as a CPC score of 1 or 2.

Results

The average GWR was the strongest predictor of poor neurological outcome as determined using receiver operating characteristic curves (basal ganglia area under the curve (AUC) = 0.716; cerebrum AUC = 0.685; average AUC = 0.747). An average GWR < 1.14 predicted a poor neurological outcome with a sensitivity of 13.3% (95% confidence interval (CI) 3.8-30.7), a specificity of 100% (95% CI 83.9-100), a positive predictive value of 100% (95% CI 2.5-100), and a negative predictive value of 44.7% (CI 28.9-58.9).

Conclusions

Our study demonstrated that low GWRs in the immediate brain CT scans of patients treated with therapeutic hypothermia after ROSC were associated with poor neurological outcomes. Immediate brain CT scans could help predict outcome after cardiac arrest.

Fundamental interstrain differences in cortical activity between Wistar and Sprague-Dawley rats during global ischemia

Four-vessel occlusion (4VO), a frequently used model of global cerebral ischemia in rats, results in a dysfunction in wide brain areas, including the cerebral cortex and hippocampus. However, there are pronounced differences in response to global ischemia between the laboratory rat strains used in these studies. In the present work, the immediate acute effects of 4VO-induced global ischemia on the spontaneous electrocorticogram (ECoG) signals were analyzed in Wistar and Sprague-Dawley rats. The ECoG was isoelectric during the 10 min of global cerebral ischemia in Wistar rats and the first burst (FB) was seen 10-13 min after the start of reperfusion. In Sprague-Dawley rats, the FB was detected immediately after the start of 4VO or a few seconds later. The burst suppression ratio (BSR) in Wistar rats decreased to 45% in 5 min after FB, and after 25 min it was approximately 40%. In Sprague-Dawley rats, the BSR was 55% immediately after the FB and it decreased steeply to reach 0% by 10 min. There was also a significant difference between the two strains in the frequency composition of the ECoG pattern. The power spectral densities of the two strains differed virtually throughout the post-ischemic state. The histological results (Evans Blue, Cresyl Violet and Fluoro Jade C stainings) supplemented the electrophysiological data: the neuronal damage in the CA1 pyramids in Wistar rats was severe, whereas in the Sprague-Dawley animals it was only partial. These observations clearly demonstrate that the use of different rat strains (e.g. Wistar vs. Sprague-Dawley) can be a source of considerable variability in the results of acute experiments on global ischemia and it is important that the laboratory rats used in such experiments should be carefully chosen.

[EEG in intensive care unit: which indications, which material?]

There is a growing development of continuous EEG monitoring (cEEG) in the intensive care unit (ICU) management of neurological patients. Its main objective is the detection of epileptic seizures or status epilepticus because the sensitivity of standard short-duration EEG recording in the ICU is poor. The aim of monitoring is to allow rapid recognition and treatment of epileptic complications in order to decrease secondary insults to the brain and improve outcome. Several studies have demonstrated that a large proportion of patients has epileptic crisis after subarachnoid haemorrhage, stroke or brain trauma, without any clinical manifestation. The EEG feature has also demonstrated a prognosis value but its value for clinical management needs further studies. Another application of EEG in the ICU is monitoring depth of anaesthesia or barbiturate treatment. Due to artifacts contamination, this is possible only in deeply sedated of paralyzed patients. The impact or cEEG monitoring on clinical management and its indications have to be further defined.

Application of electrophysiologic techniques in poor outcome prediction among patients with severe focal and diffuse ischemic brain injury

OBJECTIVE

To explore various electrophysiologic examinations as predictors for poor outcome in patients with severe ischemic brain injury, by comparing the prognostic ability of EEG, short-latency somatosensory evoked potentials (SLSEP), and brain stem auditory evoked potentials (BAEP).

METHODS

EEG, SLSEP, and BAEP were recorded in 161 patients with severe ischemic brain injuries (Glasgow Coma Scale ≤ 8), 77 with anoxic-ischemic encephalopathy after cardiopulmonary resuscitation, while 84 experienced massive hemispheric infarction at between 1 and 7 days after the onset. Outcomes were reviewed after 6 months using the Glasgow Outcome Scale.

RESULTS

Six months after the onset, poor outcomes (Glasgow Outcome Scale, 1-2) were identified in 66 and 54 patients among the anoxic-ischemic encephalopathy and the massive hemispheric infarction group, respectively. By using the prognostic authenticity analysis of predictors, unfavorable EEG patterns, lack of EEG reactivity, pathologic N20 of SLSEP, and pathologic wave V of BAEP showed the high sensitivity (92.4%-97.0%, 95% confidence interval [CI]: 82.5%-99.5%), while bilateral absence of SLSEP N20 showed the highest specificity (100%, 95% CI: 67.9%-100%) and positive predictive value (100%, 95% CI: 90.4%-100%) in the anoxic-ischemic encephalopathy group. In the massive hemispheric infarction group, unfavorable EEG patterns showed the highest sensitivity (96.3%, 95% CI: 86.2%-99.4%) while bilateral absence of SLSEP N20 and BAEP wave V showed the highest specificity (100%, 95% CI: 85.9%-100%) and positive predictive value (100%, 95% CI: 80.8%-100%).

CONCLUSIONS

The predictive power of electrophysiologic examinations is different according to the etiology of ischemic brain injury. Short-latency somatosensory evoked potentials (N20) can be considered the most powerful method to predict poor outcome in anoxic-ischemic encephalopathy. Combination of EEG (unfavorable EEG patterns) and SLSEP (N20)/BAEP (wave V) is best suited in massive hemispheric infarction to predict poor outcome.

Time jitter of somatosensory evoked potentials in recovery from hypoxic-ischemic brain injury

Impaired neural conductivity shown by delayed latency and reduced amplitude of characteristic peaks in somatosensory evoked potentials (SSEPs), has been used to monitor hypoxic-ischemic brain injury after cardiac arrest (CA). However, rather than characteristic peak deferral and suppression, the time jitter of the peak in SSEP related with time-variant neurological abnormalities is diminished by the commonly used ensemble average method. This paper utilizes the second order blind identification (SOBI) technique to extract characteristic peak information from one trial of SSEPs. Sixteen male Wistar rats were subjected to 7 or 9 min of asphyxial CA (n=8 per group). The SSEPs from median nerve stimulation were recorded for 4h after CA and then for 15 min periods at 24, 48 and 72 h. Neurological outcomes were evaluated by neurologic deficit score (NDS) at 72 h post-CA. The SSEP signal was analyzed offline with SOBI processing in Matlab. The N10 feature of SSEP was compared between good (NDS≥50) and bad (NDS<50) outcomes. After processed by SOBI, the N10 detection rate was significantly increased (p<0.001) from 90 min post-CA. Statistical difference of the latency variance of the N10 between good and bad outcome groups existed at 24, 48 and 72 h post-CA (p≤0.001). Our study is the first application using SOBI detecting variance in neural signals like SSEP. N10 latency variance, related with neurophysiological dysfunction, increased after hypoxic-ischemic injury. The SOBI technique is an efficient method in the identification of peak detection and offers a favorable alternative to reveal the neural transmission variation.

Prognosis after cardiac arrest and hypothermia: a new paradigm

Before the use of hypothermia as a treatment for comatose post-cardiac arrest patients, several prognostic variables were widely accepted as reliable and valid for the prediction of poor outcome. Recent studies using hypothermia have reported on patients with recovery of consciousness in spite of absent or extensor motor responses after 3 days, absent bilateral cortical N20 responses after 24 h, serum neuron-specific enolase levels greater than 33 μg/L, and early myoclonus status epilepticus. Hypothermia and its associated use of sedative and paralytic agents may delay neurologic recovery and affect the optimal timing of prognostic variables. Recent developments in brain imaging may provide additional objective prognostic information and deserve further study. Pending the results of future validation studies in patients treated with hypothermia, we recommend that irreversible management decisions not be made based on a single prognostic parameter, and, if there is uncertainty, these decisions be delayed for several days to allow for repeated testing.

Early CT signs in out-of-hospital cardiac arrest survivors: Temporal profile and prognostic significance

AIM

Although computed tomography (CT) signs of ischaemia, including loss of boundary (LOB) between grey matter and white matter and cortical sulcal effacement, in cardiac arrest (CA) survivors are known, their temporal profile and prognostic significance remains unclear; their clarification is necessary.

METHODS

Brain CT scans were obtained immediately after resuscitation in 75 non-traumatic CA survivors in a prospective fashion. They were divided into two groups according to the CA-return of spontaneous circulation (ROSC) interval: < or =20 min vs. >20 min. The incidence of the CT signs and predictability of these signs for outcome, assessed 6 months after CA, was evaluated and compared.

RESULTS

The incidence of the positive LOB sign was 24% in the < or =20-min group and 83% in the >20-min group, and the difference was statistically significant (p<0.001). The interval of 20 min seemed to be the time window for the LOB development. The incidence of the positive sulcal effacement sign was 0% in the < or =20 min group and 34% in the >20-min group, and the difference was statistically significant (p=0.004). A positive LOB sign was predictive of unfavourable outcome with an 81% sensitivity and 92% specificity. A positive sulcal effacement sign was predictive of unfavourable outcome with a 32% sensitivity and 100% specificity.

CONCLUSION

A time window may exist for ischaemic CT signs in CA survivors. The LOB sign may develop when the CA-ROSC interval exceeds 20 min, whereas the sulcal effacement sign may develop later. However, their temporal profile and outcome predictability should be verified by multicentre studies.

Diffusion-weighted magnetic resonance imaging for predicting the clinical outcome of comatose survivors after cardiac arrest: a cohort study

INTRODUCTION

The aim of this study was to examine whether the patterns of diffusion-weighted imaging (DWI) abnormalities and quantitative regional apparent diffusion coefficient (ADC) values can predict the clinical outcome of comatose patients following cardiac arrest.

METHODS

Thirty-nine patients resuscitated from out-of-hospital cardiac arrest were prospectively investigated. Within five days of resuscitation, axial DWIs were obtained and ADC maps were generated using two 1.5-T magnetic resonance scanners. The neurological outcomes of the patients were assessed using the Glasgow Outcome Scale (GOS) score at three months after the cardiac arrest. The brain injuries were categorised into four patterns: normal, isolated cortical injury, isolated deep grey nuclei injury, and mixed injuries (cortex and deep grey nuclei). Twenty-three subjects with normal DWIs served as controls. The ADC and percent ADC values (the ADC percentage as compared to the control data from the corresponding region) were obtained in various regions of the brains. We analysed the differences between the favourable (GOS score 4 to 5) and unfavourable (GOS score 1 to 3) groups with regard to clinical data, the DWI abnormalities, and the ADC and percent ADC values.

RESULTS

The restricted diffusion abnormalities in the cerebral cortex, caudate nucleus, putamen and thalamus were significantly different between the favourable (n = 13) and unfavourable (n = 26) outcome groups. The cortical pattern of injury was seen in one patient (3%), the deep grey nuclei pattern in three patients (8%), the cortex and deep grey nuclei pattern in 21 patients (54%), and normal DWI findings in 14 patients (36%). The cortex and deep grey nuclei pattern was significantly associated with the unfavourable outcome (20 patients with unfavourable vs. 1 patient with favourable outcomes, P < 0.001). In the 22 patients with quantitative ADC analyses, severely reduced ADCs were noted in the unfavourable outcome group. The optimal cutoffs for the mean ADC and the percent ADC values determined by receiver operating characteristic (ROC) curve analysis in the cortex, caudate nucleus, putamen, and thalamus predicted the unfavourable outcome with sensitivities of 67 to 93% and a specificity of 100%.

CONCLUSIONS

The patterns of brain injury in early diffusion-weighted imaging (DWI) (less than or equal to five days after resuscitation) and the quantitative measurement of regional ADC may be useful for predicting the clinical outcome of comatose patients after cardiac arrest.

Can early serum levels of S100B protein predict the prognosis of patients with out-of-hospital cardiac arrest?

OBJECTIVE

This study aims to know if the level of S100B protein at the initiation of cardiopulmonary resuscitation (CPR) and immediately after return of spontaneous circulation (ROSC) can predict clinical outcome.

MATERIALS AND METHODS

A prospective observational study from December 2004 to October 2006 was conducted in an urban tertiary hospital emergency department. Clinical demographics for out-of-hospital cardiac arrest patients were collected based on the Utstein style. Outcomes collected included ROSC for 20min, survival to admission, survival and Glasgow Outcome Scale (GOS) at 1 month. S100B protein was measured twice before starting CPR (first S100B) and immediately after ROSC (second S100B). We investigated the association between S100B protein levels and clinical outcomes using a multivariate logistic regression model.

RESULTS

A total of 151 patients were included (age: 60.2+/-16.8 years, male: 64.2%). Of these, 60 (39.7%) had ROSC and 46 (30.5%) survived to admission. After 1 month, 12 (8.0%) survived and only three patients showed good GOS (>/=4 points). The S100B levels were not different for ROSC, survival to admission and 1-month survival between survivors and non-survivors (p>0.05, first and second S100 B level). For the witnessed out-of-hospital cardiac arrest (OHCA) group (N=87), only the first S100B (1.22+/-0.85mugl(-1) vs. 3.91+/-4.25mugl(-1), p<0.001) showed significant difference for 1-month survival between survivors and non-survivors. The first S100B showed significant association with survival to emergency department (ED) but not 1-month survival (adjusted odds ratio (OR)=0.905, 95% confidence interval=0.821-0.998).

CONCLUSION

Higher levels of S100B at start of CPR were significantly associated with lower survival to admission, and not for 1-month survival.

Coma due to cardiac arrest: prognosis and contemporary treatment

Approximately 80% of patients who are successfully resuscitated from cardiac arrest do not regain consciousness immediately after return of spontaneous circulation, and may remain in a coma for hours or weeks, or even be in a persistent vegetative state. Recent investigations have focused on the identification of early clinical characteristics and biomarkers that can reliably predict emergence from coma in those who survive, and on therapies that might improve neurologic outcome from the ischemic brain injury that can be caused by cardiac arrest.

Application of Tsallis entropy to EEG: quantifying the presence of burst suppression after asphyxial cardiac arrest in rats

Burst suppression (BS) activity in EEG is clinically accepted as a marker of brain dysfunction or injury. Experimental studies in a rodent model of brain injury following asphyxial cardiac arrest (CA) show evidence of BS soon after resuscitation, appearing as a transitional recovery pattern between isoelectricity and continuous EEG. The EEG trends in such experiments suggest varying levels of uncertainty or randomness in the signals. To quantify the EEG data, Shannon entropy and Tsallis entropy (TsEn) are examined. More specifically, an entropy-based measure named TsEn area (TsEnA) is proposed to reveal the presence and the extent of development of BS following brain injury. The methodology of TsEnA and the selection of its parameter are elucidated in detail. To test the validity of this measure, 15 rats were subjected to 7 or 9 min of asphyxial CA. EEG recordings immediately after resuscitation from CA were investigated and characterized by TsEnA. The results show that TsEnA correlates well with the outcome assessed by evaluating the rodents after the experiments using a well-established neurological deficit score (Pearson correlation = 0.86, p << 0.01 ). This research shows that TsEnA reliably quantifies the complex dynamics in BS EEG, and may be useful as an experimental or clinical tool for objective estimation of the gravity of brain damage after CA.

Continuous electroencephalogram monitoring in the intensive care unit

Because of recent technical advances, it is now possible to record and monitor the continuous digital electroencephalogram (EEG) of many critically ill patients simultaneously. Continuous EEG monitoring (cEEG) provides dynamic information about brain function that permits early detection of changes in neurologic status, which is especially useful when the clinical examination is limited. Nonconvulsive seizures are common in comatose critically ill patients and can have multiple negative effects on the injured brain. The majority of seizures in these patients cannot be detected without cEEG. cEEG monitoring is most commonly used to detect and guide treatment of nonconvulsive seizures, including after convulsive status epilepticus. In addition, cEEG is used to guide management of pharmacological coma for treatment of increased intracranial pressure. An emerging application for cEEG is to detect new or worsening brain ischemia in patients at high risk, especially those with subarachnoid hemorrhage. Improving quantitative EEG software is helping to make it feasible for cEEG (using full scalp coverage) to provide continuous information about changes in brain function in real time at the bedside and to alert clinicians to any acute brain event, including seizures, ischemia, increasing intracranial pressure, hemorrhage, and even systemic abnormalities affecting the brain, such as hypoxia, hypotension, acidosis, and others. Monitoring using only a few electrodes or using full scalp coverage, but without expert review of the raw EEG, must be done with extreme caution as false positives and false negatives are common. Intracranial EEG recording is being performed in a few centers to better detect seizures, ischemia, and peri-injury depolarizations, all of which may contribute to secondary injury. When cEEG is combined with individualized, physiologically driven decision making via multimodality brain monitoring, intensivists can identify when the brain is at risk for injury or when neuronal injury is already occurring and intervene before there is permanent damage. The exact role and cost-effectiveness of cEEG at the current time remains unclear, but we believe it has significant potential to improve neurologic outcomes in a variety of settings.

Diagnostic and prognostic use of bispectral index in coma, vegetative state and related disorders

PRIMARY OBJECTIVE

This study investigates (1) the utility of the bispectral index (BIS) to distinguish levels of consciousness in severely brain damaged patients and, particularly, disentangle vegetative state (VS) from minimally conscious state (MCS), as compared to other EEG parameters; (2) the prognostic value of BIS with regards to recovery after 1 year.

RESEARCH DESIGN

Multi-centric prospective study.

METHOD AND PROCEDURES

Unsedated patients recovering from coma were followed until death or transferal. Automated electrophysiological and standardized behavioural assessments were carried out twice a week. EEG recordings were categorized according to level of consciousness (coma, VS, MCS and Exit MCS). Outcome was assessed at 1 year post-insult.

MAIN OUTCOMES AND RESULTS

One hundred and fifty-six EEG epochs obtained in 43 patients were included in the analyses. BIS showed a higher correlation with behavioural scales as compared to other EEG parameters. Moreover, BIS values differentiated levels of consciousness and distinguished VS from MCS while other EEG parameters did not. Finally, higher BIS values were found in patients who recovered at 1 year post-insult as compared to patients who did not recover.

CONCLUSION

EEG-BIS recording is an interesting additional method to help in the diagnosis as well as in the prognosis of severely brain injured patients recovering from coma.

Post-cardiac arrest syndrome: Epidemiology, pathophysiology, treatment, and prognostication: A scientific statement from the International Liaison Committee on Resuscitation; the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; the Council on Stroke (Part 1)

AIM OF THE REVIEW

To review the epidemiology, pathophysiology, treatment and prognostication in relation to the post-cardiac arrest syndrome.

METHODS

Relevant articles were identified using PubMed, EMBASE and an American Heart Association EndNote master resuscitation reference library, supplemented by hand searches of key papers. Writing groups comprising international experts were assigned to each section. Drafts of the document were circulated to all authors for comment and amendment.

RESULTS

The 4 key components of post-cardiac arrest syndrome were identified as (1) post-cardiac arrest brain injury, (2) post-cardiac arrest myocardial dysfunction, (3) systemic ischaemia/reperfusion response, and (4) persistent precipitating pathology.

CONCLUSIONS

A growing body of knowledge suggests that the individual components of the postcardiac arrest syndrome are potentially treatable.

Differential effect of first versus second concussive episodes on wavelet information quality of EEG

OBJECTIVE

Recent reports have suggested that long-term residual brain dysfunctions from mild traumatic brain injury (MTBI) that are often overlooked by clinical criteria may be detected using advanced research methods. The aim of the present study was to examine the feasibility of EEG wavelet information quality measures (EEG-IQ) in monitoring alterations of brain functions as well as to determine the differential rate of recovery between the first and second concussive episodes.

METHODS

Student-athletes at high risk for MTBI (n=265) were tested prior to concussive episodes as a baseline. From this subject pool, twenty one athletes who suffered from two concussive episodes within one athletic season and were tested on days 7, 14 and 21 post-first and second injuries using a within-subjects design. Specifically, EEG was recorded and processed using wavelet entropy (EEG-IQ) algorithm along with a battery of neuropsychological (NS) tests. Spatial distribution of EEG-IQ and its dynamics in conjunction with NS data were analyzed prior to and after MTBI.

RESULTS

No neuropsychological deficits were present in concussed subjects beyond 7 days post-injury after first and second concussions. However, EEG-IQ measures were significantly reduced primarily at temporal, parietal and the occipital regions (ROIs) after first and especially after second MTBI (p<0.01) beyond 7 days post-injury. Rate of recovery of EEG-IQ measures was significantly slower after second MTBI compared to those after the first concussion (p<0.01).

CONCLUSIONS

EEG-IQ measures may reveal alterations in the brain of concussed individuals that are most often overlooked by current assessment tools. In this regard, EEG-IQ may potentially be a valuable tool for assessing and monitoring residual brain dysfunction in "asymptomatic" MTBI subjects.

SIGNIFICANCE

The results demonstrate the potential utility of EEG-IQ measures to classify concussed individuals at various stages of recovery.

Post-cardiac arrest syndrome: epidemiology, pathophysiology, treatment, and prognostication. A Scientific Statement from the International Liaison Committee on Resuscitation; the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; the Council on Stroke

AIM OF THE REVIEW

To review the epidemiology, pathophysiology, treatment and prognostication in relation to the post-cardiac arrest syndrome.

METHODS

Relevant articles were identified using PubMed, EMBASE and an American Heart Association EndNote master resuscitation reference library, supplemented by hand searches of key papers. Writing groups comprising international experts were assigned to each section. Drafts of the document were circulated to all authors for comment and amendment.

RESULTS

The 4 key components of post-cardiac arrest syndrome were identified as (1) post-cardiac arrest brain injury, (2) post-cardiac arrest myocardial dysfunction, (3) systemic ischaemia/reperfusion response, and (4) persistent precipitating pathology.

CONCLUSIONS

A growing body of knowledge suggests that the individual components of the post-cardiac arrest syndrome are potentially treatable.

Post-cardiac arrest temperature manipulation alters early EEG bursting in rats

OBJECTIVES

Hypothermia improves outcomes after cardiac arrest (CA), while hyperthermia worsens injury. EEG recovers through periodic bursting from isoelectricity after CA, the duration of which is associated with outcome in normothermia. We quantified burst frequency to study the effect of temperature on early EEG recovery after CA.

METHODS

Twenty-four rats were divided into three groups, based on 6h of hypothermia (T=33 degrees C), normothermia (T=37 degrees C), or hyperthermia (T=39 degrees C) immediately post-resuscitation from 7-min asphyxial CA. Temperature was maintained using surface cooling and re-warming. Neurological recovery was defined by 72-h neurological deficit score (NDS).

RESULTS

Burst frequency was higher during the first 90min in rats treated with hypothermia (25.6+/-12.2min(-1)) and hyperthermia (22.6+/-8.3min(-1)) compared to normothermia (16.9+/-8.5min(-1)) (p<0.001). Burst frequency correlated strongly with 72-h NDS in normothermic rats (p<0.05) but not in hypothermic or hyperthermic rats. The 72-h NDS of the hypothermia group (74, 61-74; median, 25-75th percentile) was significantly higher than the normothermia (49, 47-61) and hyperthermia (43, 0-50) groups (p<0.001).

CONCLUSIONS

In normothermic rats resuscitated from CA, early EEG burst frequency is strongly associated with neurological recovery. Increased bursting followed by earlier restitution of continuous EEG activity with hypothermia may represent enhanced recovery, while heightened metabolic rate and worsening secondary injury is likely in the hyperthermia group. These factors may confound use of early burst frequency for outcome prediction.

Hypothermia effects on neurovascular coupling and cerebral metabolic rate of oxygen

Neuronal activation is accompanied by a local increase in cerebral blood flow (CBF) and in cerebral metabolic rate of oxygen (CMRO(2)), caused by neurovascular and neurometabolic coupling. Hypothermia is used as a neuroprotective approach in surgical patients and therapeutically after cardiac arrest or stroke. The effect of hypothermia on neurovascular coupling is of interest for evaluating brain function in these patients, but has not been determined so far. It is not clear whether functional hyperaemia actually operates at subnormal temperatures. In addition, decreasing brain temperature reduces spontaneous CMRO(2) following a known quantitative relationship (Q(10)). Q(10) determination may serve to validate a recently introduced CMRO(2) measurement approach relying on optical measurements of CBF and hemoglobin concentration. We applied this method to investigate hypothermia in a functional study of the somatosensory cortex. Anesthetized Wistar rats underwent surgical implantation of a closed cranial window. Using laser Doppler flowmetry and optical spectroscopy, relative changes in CBF and hemoglobin concentration were measured continuously. At the same time, an electroencephalogram (EEG) was recorded from the measurement site. By the application of ice packs, whole-body hypothermia was induced, followed by rewarming. Spontaneous EEG, CBF and CMRO(2) were measured, interleaved by blocks of electrical forepaw stimulation. The Q(10) obtained from spontaneous CMRO(2) changes of 4.4 (95% confidence interval 3.7-5.1) was close to published values, indicating the reliability of the CMRO(2) measurement. Lowering brain temperature decreased functional changes of CBF and CMRO(2) as well as amplitudes of somatosensory evoked potentials (SEP) to the same degree. In conclusion, neurovascular and neurometabolic coupling is preserved during hypothermia.