Mind, Brain, Body, and Soul: A Review of the Electrophysiological Undercurrents for Dr. Frankenstein

Neural complexity is a common denominator of human consciousness across diverse regimes of cortical dynamics

What is the common denominator of consciousness across divergent regimes of cortical dynamics? Does consciousness show itself in decibels or in bits? To address these questions, we introduce a testbed for evaluating electroencephalogram (EEG) biomarkers of consciousness using dissociations between neural oscillations and consciousness caused by rare genetic disorders. Children with Angelman syndrome (AS) exhibit sleep-like neural dynamics during wakefulness. Conversely, children with duplication 15q11.2-13.1 syndrome (Dup15q) exhibit wake-like neural dynamics during non-rapid eye movement (NREM) sleep. To identify highly generalizable biomarkers of consciousness, we trained regularized logistic regression classifiers on EEG data from wakefulness and NREM sleep in children with AS using both entropy measures of neural complexity and spectral (i.e., neural oscillatory) EEG features. For each set of features, we then validated these classifiers using EEG from neurotypical (NT) children and abnormal EEGs from children with Dup15q. Our results show that the classification performance of entropy-based EEG biomarkers of conscious state is not upper-bounded by that of spectral EEG features, which are outperformed by entropy features. Entropy-based biomarkers of consciousness may thus be highly adaptable and should be investigated further in situations where spectral EEG features have shown limited success, such as detecting covert consciousness or anesthesia awareness.

Quantitative EEG During Critical Illness Correlates with Patterns of Long-Term Cognitive Impairment

OBJECTIVE

Many intensive care unit (ICU) survivors suffer disabling long-term cognitive impairment (LTCI) after critical illness. We compared EEG characteristics during critical illness with patients' 1-year neuropsychological outcomes.

METHODS

We performed a post hoc analysis of patients in the BRAIN-ICU study who had undergone EEG for clinical purposes during admission (n = 10). All survivors underwent formal cognitive assessments at 12-month follow-up. We evaluated EEGs by conventional visual inspection and computed 10 quantitative features. We explored associations between EEG and patterns of LTCI using Wilcoxon rank-sum tests and Spearman's rank correlations.

RESULTS

Of 521 Vanderbilt patients enrolled in the parent study, 24 had EEG recordings during admission. Ten survivors had EEG tracings available and completed follow-up cognitive testing. All but one inpatient EEG showed generalized background slowing. All patients demonstrated cognitive impairment in at least one domain at follow-up. The most common deficits occurred in delayed memory (DM-median index 62) and visuospatial/constructional (VC-median index 69) domains. Relative alpha power correlated with VC score (ρ = 0.78, P = .008). Peak interhemispheric coherence correlated negatively with DM (ρ = -0.81, P = .018).

CONCLUSIONS

Quantitative EEG features during critical illness correlated with domain-specific cognitive performance in our small cohort of ICU survivors. Further study in larger prospective cohorts is required to determine whether these relationships hold.

SIGNIFICANCE

EEG may serve as a prognostic biomarker predicting patterns of long-term cognitive impairment.

Clinical Correlates of Electroencephalographic Patterns in Critically Ill Patients

OBJECTIVE

The objective of this study was to determine the frequency and clinical correlates of different electroencephalographic patterns and their association with clinical outcomes in critically ill patients.

SUBJECTS AND METHODS

This retrospective cross-sectional study was performed in the Neurology Department of King Fahd Hospital of the University, Kingdom of Saudi Arabia and involved a review and analysis of medical records pertaining to 179 intensive care unit patients who underwent electroencephalography (EEG) in the June to November 2018 period.

RESULTS

Among the different etiologies, presence of spike and wave or sharp wave (SWs) was associated with encephalitis (P = .01) and large artery stroke (P = .01), whereas markedly attenuated EEG activity (p = .04) and burst suppression (P = .01) were associated with large artery stroke and hypoxic ischemic encephalopathy (HIE), respectively. Generalized theta activity (P = .01) was significantly found in patients of septic encephalopathy, while generalized delta activity (P = .02) and asymmetrical background (P = .04) were significantly associated with traumatic brain injury. Presence of periodic discharges in EEG was significantly associated with more adverse clinical outcomes (P = .001), whereas rhythmic delta activity (RDA) (P = .03), persistent focal slow wave activity (P = .01), and asymmetric background (P = .002) were found in patients who were discharged from hospital with sequelae of current illness.

CONCLUSION

Certain EEG patterns are associated with particular underlying etiologies like SWs for encephalitis, markedly attenuated EEG activity and burst suppression with large artery stroke and HIE, respectively. Whereas few EEG patterns, including periodic discharges, RDA, persistent focal slow wave activity have some prognostic value in critically ill patients. However, they cannot be used as markers for prognostic assessment of patients without considering other clinical and diagnostic variables. Further larger prospective studies with continuous EEG monitoring with control of confounding factors are needed.

Clinical and Radiological Correlates of Different Electroencephalographic Pattern in Hospitalized Patients

Objective. The present study aimed to determine the clinical and radiological correlates of different electroencephalographic (EEG) patterns in hospitalized patients. Subjects and Methods. In this retrospective study performed at the Neurology Department, King Fahd University Hospital, Kingdom of Saudi Arabia (KSA), data of 374 patients who underwent EEG were reviewed and analyzed. Results. Presence of focal spike and wave or sharp wave (SW) (P = .00), generalized theta activity (P = .00), generalized delta activity (P = .04), persistent focal slow wave activity (SWA) (P = .003) and asymmetric background (P = .01) in the EEG record was significantly associated with abnormal imaging findings. Specifically, generalized theta delta activity (P = .01) and markedly attenuated EEG activity (P = .007) were associated with presence of cortical lesions; whereas, triphasic waves (TWs) (P = .009), and generalized theta activity (P = .001) were found to be related with presence of subcortical lesions. While, generalized delta activity (P = .01) was the only correlate with extra-axial lesions. Conclusion. At present, certain EEG patterns cannot be precisely correlated with imaging findings, suggesting that intercurrent metabolic, infectious, and/or toxic contributors could be the confounding factors. Nonetheless, when EEG patterns are examined alongside magnetic resonance imaging findings and other clinically relevant data, these might be indicative of a group of diseases in some pertinent situations. Thus, further larger prospective clinical studies that incorporate continuous EEG monitoring, advanced radiology techniques, and laboratory analyses would be beneficial to elucidate their interplay for better firm up the correlations.

Multimodal Approach to Decision to Treat Critically Ill Patients With Periodic or Rhythmic Patterns Using an Ictal-Interictal Continuum Spectral Severity Score

We propose a comprehensive review of the subject of epileptiform and potentially harmful EEG patterns that lie on the interictal continuum (IIC) to help with therapeutic decision-making and target future research. This approach to "electro-physiological SE" encompasses five dimensions of the IIC: it characterizes a periodic or rhythmic pattern, not only regarding its ictal morphology and potential harm with secondary neuronal injury, but also addresses the "metabolic footprint," clinical repercussion, and epileptogenic potential. Recent studies have attempted to determine and qualify the ictal nature and the epileptogenic potential (i.e., risk of subsequent acute seizures) of particular IIC patterns and their intrinsic EEG characteristics. Others have correlated non-convulsive seizures with cognitive outcomes beyond mortality; non-convulsive seizures and sporadic, periodic, or rhythmic discharges to encephalopathy severity; and the spectrum of periodic or rhythmic patterns to measurable secondary brain injury. Equivocal periodic or rhythmic patterns on the IIC are frequently encountered in critical care neurology where clinicians often incorporate advanced neuroimaging, metabolic neuromonitoring, and anti-seizure drug short trials, in an effort to gauge these patterns. We propose portraying the IIC with a multiaxial graph to disambiguate each of these risks. Quantification along each axis may help calibrate therapeutic urgency. An adaptable scoring system assesses which quasi-ictal EEG patterns in this spectrum might reach the tipping point toward anti-seizure drug escalation, in neurocritically ill patients.

The intensive care delirium research agenda: a multinational, interprofessional perspective

Delirium, a prevalent organ dysfunction in critically ill patients, is independently associated with increased morbidity. This last decade has witnessed an exponential growth in delirium research in hospitalized patients, including those critically ill, and this research has highlighted that delirium needs to be better understood mechanistically to help foster research that will ultimately lead to its prevention and treatment. In this invited, evidence-based paper, a multinational and interprofessional group of clinicians and researchers from within the fields of critical care medicine, psychiatry, pediatrics, anesthesiology, geriatrics, surgery, neurology, nursing, pharmacy, and the neurosciences sought to address five questions: (1) What is the current standard of care in managing ICU delirium? (2) What have been the major recent advances in delirium research and care? (3) What are the common delirium beliefs that have been challenged by recent trials? (4) What are the remaining areas of uncertainty in delirium research? (5) What are some of the top study areas/trials to be done in the next 10 years? Herein, we briefly review the epidemiology of delirium, the current best practices for management of critically ill patients at risk for delirium or experiencing delirium, identify recent advances in our understanding of delirium as well as gaps in knowledge, and discuss research opportunities and barriers to implementation, with the goal of promoting an integrated research agenda.

Acute Symptomatic Seizures Caused by Electrolyte Disturbances

In this narrative review we focus on acute symptomatic seizures occurring in subjects with electrolyte disturbances. Quite surprisingly, despite its clinical relevance, this issue has received very little attention in the scientific literature. Electrolyte abnormalities are commonly encountered in clinical daily practice, and their diagnosis relies on routine laboratory findings. Acute and severe electrolyte imbalances can manifest with seizures, which may be the sole presenting symptom. Seizures are more frequently observed in patients with sodium disorders (especially hyponatremia), hypocalcemia, and hypomagnesemia. They do not entail a diagnosis of epilepsy, but are classified as acute symptomatic seizures. EEG has little specificity in differentiating between various electrolyte disturbances. The prominent EEG feature is slowing of the normal background activity, although other EEG findings, including various epileptiform abnormalities may occur. An accurate and prompt diagnosis should be established for a successful management of seizures, as rapid identification and correction of the underlying electrolyte disturbance (rather than an antiepileptic treatment) are of crucial importance in the control of seizures and prevention of permanent brain damage.

Prospective Cohort Study Evaluating the Prognostic Value of Simple EEG Parameters in Postanoxic Coma

We prospectively studied early bedside standard EEG characteristics in 61 acute postanoxic coma patients. Five simple EEG features, namely, isoelectric, discontinuous, nonreactive to intense auditory and nociceptive stimuli, dominant delta frequency, and occurrence of paroxysms were classified yes or no. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and area under the receiver operating characteristic curve (AUC) of each of these variables for predicting an unfavorable outcome, defined as death, persistent vegetative state, minimally conscious state, or severe neurological disability, as assessed 1 year after coma onset were computed as well as Synek's score. The outcome was unfavorable in 56 (91.8%) patients. Sensitivity, specificity, PPV, NPV, and AUC of nonreactive EEG for predicting an unfavorable outcome were 84%, 80%, 98%, 31%, and 0.82, respectively; and were all very close to the ones of Synek score>3, which were 82%, 80%, 98%, 29%, and 0.81, respectively. Specificities for predicting an unfavorable outcome were 100% for isoelectric, discontinuous, or dominant delta activity EEG. These 3 last features were constantly associated to unfavorable outcome. Absent EEG reactivity strongly predicted an unfavorable outcome in postanoxic coma, and performed as accurate as a Synek score>3. Analyzing characteristics of some simple EEG features may easily help nonneurophysiologist physicians to investigate prognostic issue of postanoxic coma patient. In this study (a) discontinuous, isoelectric, or delta-dominant EEG were constantly associated with unfavorable outcome and (b) nonreactive EEG performed prognostic as accurate as a Synek score>3.

Burst suppression on processed electroencephalography as a predictor of postcoma delirium in mechanically ventilated ICU patients

OBJECTIVES

Many patients, due to a combination of illness and sedatives, spend a considerable amount of time in a comatose state that can include time in burst suppression. We sought to determine if burst suppression measured by processed electroencephalography during coma in sedative-exposed patients is a predictor of post-coma delirium during critical illness.

DESIGN

Observational convenience sample cohort.

SETTING

Medical and surgical ICUs in a tertiary care medical center.

PATIENTS

Cohort of 124 mechanically ventilated ICU patients.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Depth of sedation was monitored twice daily using the Richmond Agitation-Sedation Scale and continuously monitored by processed electroencephalography. When noncomatose, patients were assessed for delirium twice daily using Confusion Assessment Method for the ICU. Multiple logistic regression and Cox proportional hazards regression were used to assess associations between time in burst suppression and both prevalence and time to resolution of delirium, respectively, adjusting for time in deep sedation and a principal component score consisting of Acute Physiology and Chronic Health Evaluation II score and cumulative doses of sedatives while comatose. Of the 124 patients enrolled and monitored, 55 patients either never had coma or never emerged from coma, yielding 69 patients for whom we performed these analyses; 42 of these 69 (61%) had post-coma delirium. Most patients had burst suppression during coma, although often short-lived (median [interquartile range] time in burst suppression, 6.4 [1-58] min). After adjusting for covariates, even this short time in burst suppression independently predicted a higher prevalence of post-coma delirium (odds ratio, 4.16; 95% CI, 1.27-13.62; p = 0.02) and a lower likelihood (delayed) resolution of delirium (hazard ratio, 0.78; 95% CI, 0.53-0.98; p = 0.04).

CONCLUSIONS

Time in burst suppression during coma, as measured by processed electroencephalography, was an independent predictor of prevalence and time to resolution of postcoma/post-deep sedation delirium. These findings of this single-center investigation support lighter sedation strategies.

EEG patterns in hypoxic encephalopathies (post-cardiac arrest syndrome): fluctuations, transitions, and reactions

In patients with coma resulting from hypoxic encephalopathy (e.g., after cardiac arrest), the EEG may reflect the severity of brain dysfunction, although the exact relationship among the EEG changes, the extent of neuronal damage, and consequent prognosis is still under study. Many prognostications are based on particular EEG patterns at a time point, such as burst suppression or generalized periodic discharges, but with sequential, repeated, or with prolonged or continuous EEG monitoring, it has become increasingly clear that more information might be gleaned from EEG pattern changes over time. Short-term fluctuations (as opposed to permanent transitions), or preserved reactions to exogenous stimuli, have to be differentiated. This review presents many of the typical postanoxic EEG patterns, along with their evolution over time. This preliminary report illustrates the temporal dynamic changes of EEG over time. It is hoped that it will act as a starting point for prospective and systematic investigation to test whether EEG evolution and transitions add diagnostic and prognostic value.

Electroencephalography of encephalopathy in patients with endocrine and metabolic disorders

Patients with acute alteration in mental status from encephalopathy because of underlying metabolic-toxic or endocrine abnormalities are frequently seen in the acute hospital setting. A rapid diagnosis and correction of the underlying cause is essential as a prolonged state of encephalopathy portends a poor outcome. Correct diagnosis and management remain challenging because several encephalopathies may present similarly, and further laboratory, imaging, or other testing may not always reveal the underlying cause. EEG provides rapid additional information on the encephalopathic patient. It may help establish the diagnosis and is indispensable for identifying nonconvulsive status epilepticus, an important possible complication in this context. The EEG may assist the clinician in gauging the severity of brain dysfunction and may aid in predicting outcome. This review summarizes the current knowledge on EEG findings in selected metabolic and endocrine causes of encephalopathy and highlights distinct EEG features associated with particular etiologies.

Clinical and electroencephalographic correlates of acute encephalopathy

The term encephalopathy encompasses a wide variety of syndromes caused by a large number of different toxic, metabolic, and degenerative derangements. Despite advances in intensive medical care and new diagnostic procedures, encephalopathy remains a frequent and underrecognized critical medical condition with high morbidity and mortality. Electroencephalography (EEG) enables rapid bedside electrophysiological measurements of brain dysfunction and complements clinical and neuroimaging assessment of encephalopathic patients. Both progressive slowing of EEG background activity with increasing cerebral compromise and decreased EEG reactivity to external stimuli provide important diagnostic and prognostic information. The aim of this review was to provide an overview of the diagnostic and prognostic value of EEG in encephalopathic patients.

The applicability of ambulatory electroencephalography (AEEG) in healthy horses and horses with abnormal behaviour or clinical signs of epilepsy

BACKGROUND

Short-duration electroencephalography (EEG) recordings in horses are helpful in diagnosing intracranial disorders. Potentially, long-duration ambulatory EEG (AEEG) recordings in horses will enhance the chance of detecting abnormal brain activity independent of the presence of an insult.

OBJECTIVE

The objective of this study was to test if AEEG recordings in unsedated horses can be acquired and benefit diagnosing abnormal brain activity.

ANIMALS AND METHODS

Recordings were taken from 8 adult control horses and 10 patients suspected of intracranial abnormalities. Self-adhesive electrodes and the 'Porti-5' recording system were used. Filter settings were 0.5 Hz high pass and 35 Hz low pass. The records were analysed offline at a 50-200 μV/division and 10 seconds/division scale. Abnormal activity was defined as a spike or sharp wave, a period of generalised slow wave rhythmical activity or a generalised fast rhythmical discharge. The recording time ranged from 5 to 49 hours.

RESULTS

In the control group, one horse showed pathological activity. In the patient group, six out of nine horses showed abnormal activity during the recordings. Magnetic resonance imaging confirmed the presence of an intracranial mass in one patient. Long-term recordings of high quality can be obtained in unsedated horses by allowing daily activity using AEEG, resulting in a reasonable chance of recording (inter)ictal abnormal brain activity indicating epileptic or seizure-like activity in the absence of clinical signs or seizures.

CONCLUSIONS

It is concluded that abnormal behaviour can be expressed intermittently, and with the availability of AEEG a useful tool is added to the diagnostic scenario for horses.

Sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a diffuse brain dysfunction that occurs secondary to infection in the body without overt CNS infection. SAE is frequently encountered in critically ill patients in intensive care units, and in up to 70% of patients with severe systemic infection. The severity of SAE can range from mild delirium to deep coma. Seizures and myoclonus are infrequent and cranial nerves are almost always spared, but most severe cases have an associated critical illness neuromyopathy. Development of SAE probably involves a number of mechanisms that are not mutually exclusive and vary from patient to patient. Substantial neurological and psychological morbidities often occur in survivors. Mortality is almost always due to multiorgan failure rather than neurological complications, and is almost 70% in patients with severe SAE. Further research into the pathophysiology, management and prevention of SAE is needed. This Review discusses the epidemiology and clinical presentation of SAE. Recent evidence for SAE pathophysiology is outlined and a diagnostic approach to patients with this syndrome is presented. Lastly, prognosis and management of SAE is discussed.

Disturbed oscillatory brain dynamics in subcortical ischemic vascular dementia

Background

White matter hyperintensities (WMH) can lead to dementia but the underlying physiological mechanisms are unclear. We compared relative oscillatory power from electroencephalographic studies (EEGs) of 17 patients with subcortical ischemic vascular dementia, based on extensive white matter hyperintensities (SIVD-WMH) with 17 controls to investigate physiological changes underlying this diagnosis.

Results

Differences between the groups were large, with a decrease of relative power of fast activity in patients (alpha power 0.25 ± 0.12 versus 0.38 ± 0.13, p = 0.01; beta power 0.08 ± 0.04 versus 0.19 ± 0.07; p<0.001) and an increase in relative powers of slow activity in patients (theta power 0.32 ± 0.11 versus 0.14 ± 0.09; p<0.001 and delta power 0.31 ± 0.14 versus 0.23 ± 0.09; p<0.05). Lower relative beta power was related to worse cognitive performance in a linear regression analysis (standardized beta = 0.67, p<0.01).

Conclusions

This pattern of disturbance in oscillatory brain activity indicate loss of connections between neurons, providing a first step in the understanding of cognitive dysfunction in SIVD-WMH.

Control of sleep and wakefulness

This review summarizes the brain mechanisms controlling sleep and wakefulness. Wakefulness promoting systems cause low-voltage, fast activity in the electroencephalogram (EEG). Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations. Local, activity-dependent factors modulate the amplitude and frequency of cortical slow oscillations. Non-rapid-eye-movement (NREM) sleep results in conservation of brain energy and facilitates memory consolidation through the modulation of synaptic weights. Rapid-eye-movement (REM) sleep results from the interaction of brain stem cholinergic, aminergic, and GABAergic neurons which control the activity of glutamatergic reticular formation neurons leading to REM sleep phenomena such as muscle atonia, REMs, dreaming, and cortical activation. Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. Genetic studies suggest that brain mechanisms controlling waking and NREM sleep are strongly conserved throughout evolution, underscoring their enormous importance for brain function. Sleep disruption interferes with the normal restorative functions of NREM and REM sleep, resulting in disruptions of breathing and cardiovascular function, changes in emotional reactivity, and cognitive impairments in attention, memory, and decision making.

Performance of the hepatic encephalopathy scoring algorithm in a clinical trial of patients with cirrhosis and severe hepatic encephalopathy

OBJECTIVES

The grading of hepatic encephalopathy (HE) is based on a combination of indicators that reflect the state of consciousness, intellectual function, changes in behavior, and neuromuscular alterations seen in patients with liver failure.

METHODS

We modified the traditional West Haven criteria (WHC) to provide an objective assessment of the cognitive parameters to complement the subjective clinical ratings for the performance of extracorporeal albumin dialysis (ECAD) using a molecular adsorption recirculating system in patients with cirrhosis and severe (grade III / IV) encephalopathy. The HE Scoring Algorithm (HESA) combined clinical indicators with those derived from simple neuropsychological tests,the latter more often used in milder grades of HE (I / II). The performance of each indicator was compared across grades and sites.

RESULTS

Results of HESA were also compared with the Glasgow Coma Scale. A total of 597 evaluations were performed in patients randomized to ECAD plus standard medical therapy or the latter only. Most parameters exhibited significant separation between grades; the most effective indicators were lack of verbal, eye, and motor response (grade IV), somnolence and disorientation to place (grade III), and lethargy and disorientation to time (grade II). Two clinical and four neuropsychological indicators were useful to classify patients as grade I. The Glasgow Coma Scale differed among the four stages of the WHC, but the differences between grades I and II were small and not clinically useful.

CONCLUSION

HESA extends the traditional WHC for grading HE. In the absence of a "gold" standard, the most useful indicators noted in this trial should be further validated.

Bioreactors for guiding muscle tissue growth and development

Muscle tissue bioreactors are devices which are employed to guide and monitor the development of engineered muscle tissue. These devices have a modern history that can be traced back more than a century, because the key elements of muscle tissue bioreactors have been studied for a very long time. These include barrier isolation and culture of cells, tissues and organs after isolation from a host organism; the provision of various stimuli intended to promote growth and maintain the muscle, such as electrical and mechanical stimulation; and the provision of a perfusate such as culture media or blood derived substances. An accurate appraisal of our current progress in the development of muscle bioreactors can only be made in the context of the history of this endeavor. Modern efforts tend to focus more upon the use of computer control and the application of mechanical strain as a stimulus, as well as substrate surface modifications to induce cellular organization at the early stages of culture of isolated muscle cells.

Presence of electroencephalogram burst suppression in sedated, critically ill patients is associated with increased mortality

OBJECTIVES

This study investigates the possibility of a relationship between oversedation and mortality in mechanically ventilated patients. The presence of burst suppression, a pattern of severely decreased brain wave activity on the electroencephalogram, may be unintentionally induced by heavy doses of sedatives. Burst suppression has never been studied as a potential risk factor for death in patients without a known neurologic disorder or injury.

DESIGN

Post hoc analysis of a prospectively observational cohort study.

SETTING

Medical intensive care units of a tertiary care, university-based medical center.

PATIENTS

A total of 125 mechanically ventilated, adult, critically ill patients.

MEASUREMENTS AND MAIN RESULTS

A validated arousal scale (Richmond Agitation-Sedation Scale) was used to measure sedation level, and the bispectral index monitor was used to capture electroencephalogram data. Burst suppression occurred in 49 of 125 patients (39%). For analysis, the patients were divided into those with burst suppression (49 of 125, 39%) and those without burst suppression (76 of 125, 61%). All baseline variables were similar between the two groups, with the overall cohort demonstrating a high severity of illness (Acute Physiology and Chronic Health Evaluation II scores of 27.4 +/- 8.2) and 98% receiving sedation. Of those with burst suppression, 29 of 49 (59%) died within 6 months compared with 25 of 76 (33%) who did not demonstrate burst suppression. Using time-dependent Cox regression to adjust for clinically important covariates (age, Charlson comorbidity score, baseline dementia, Acute Physiology and Chronic Health Evaluation II, Sequential Organ Failure Assessment, coma, and delirium), patients who experienced burst suppression were found to have a statistically significant higher 6-month mortality [Hazard's ratio = 2.04, 95% confidence interval, 1.12-3.70, p = 0.02].

CONCLUSION

The presence of burst suppression, which was unexpectedly high in this medical intensive care unit population, was an independent predictor of increased risk of death at 6 months. This association should be studied prospectively on a larger scale in mechanically ventilated, critically ill patients.

EEG with triphasic waves in Borrelia burgdorferi meningoencephalitis

We describe a case of encephalopathy in which the clinical picture and triphasic waves in the EEG indicated a metabolic cause. However, the illness was caused by neuroborreliosis. The occurrence of triphasic waves in the EEG is a strong evidence of metabolic encephalopathy, but triphasic waves are not specific for metabolic encephalopathy. Triphasic waves have been described in a number of non-metabolic encephalopaties and structural brain lesions. To our knowledge, this is the first report of triphasic waves in Borrelia burgdorferi meningoencephalitis.

Electroencephalographic Assessment of Coma

SUMMARY

Altered mental status ranging from confusion to deep unresponsiveness can be described as coma. Electroencephalography is an important tool in assessing comatose patients. Some EEG patterns are seen with lighter stages of coma and have a good prognosis, whereas others are seen in deep, often irreversible coma. These EEG patterns carry a much more grave prognosis. This paper discusses the various EEG features seen in coma, ranging from intermittent rhythmic delta activity to electrocerebral inactivity. A discussion regarding etiology and prognosis is presented after the EEG pattern is described in detail. Special EEG features, such as alpha coma, beta coma, spindle coma, etc., are discussed toward the end.

Approach to the comatose patient

BACKGROUND

Coma is a medical emergency and may constitute a diagnostic and therapeutic challenge for the intensivist.

OBJECTIVE

To review currently available data on the etiology, diagnosis, and outcome of coma. To propose an evidence-based approach for the clinical management of the comatose patient.

DATA SOURCE

Search of Medline and Cochrane databases; manual review of bibliographies from selected articles and monographs.

DATA SYNTHESIS AND CONCLUSIONS

Coma and other states of impaired consciousness are signs of extensive dysfunction or injury involving the brainstem, diencephalon, or cerebral cortex and are associated with a substantial risk of death and disability. Management of impaired consciousness includes prompt stabilization of vital physiologic functions to prevent secondary neurologic injury, etiological diagnosis, and the institution of brain-directed therapeutic or preventive measures. Neurologic prognosis is determined by the underlying etiology and may be predicted by the combination of clinical signs and electrophysiological tests.