EEG Monitoring during Therapeutic Hypothermia in Neonates, Children, and Adults

Changes in the Term Neonatal Electroencephalogram with General Anesthesia: A Systematic Review with Narrative Synthesis

BACKGROUND

Although effects of general anesthesia on neuronal activity in the human neonatal brain are incompletely understood, electroencephalography provides some insight and may identify age-dependent differences.

METHODS

A systematic search (MEDLINE, Embase, PubMed, and Cochrane Library to November 2023) retrieved English language publications reporting electroencephalography during general anesthesia for cardiac or noncardiac surgery in term neonates (37 to 44 weeks postmenstrual age). Data were extracted, and risk of bias (ROBINS-I Cochrane tool) and quality of evidence (Grading of Recommendations Assessment, Development, and Evaluation [GRADE] checklist) were assessed.

RESULTS

From 1,155 abstracts, 9 publications (140 neonates; 55% male) fulfilled eligibility criteria. Data were limited, and study quality was very low. The occurrence of discontinuity, a characteristic pattern of alternating higher and lower amplitude electroencephalography segments, was reported with general anesthesia (94 of 119 neonates, 6 publications) and with hypothermia (23 of 23 neonates, 2 publications). Decreased power in the delta (0.5 to 4 Hz) frequency range was also reported with increasing anesthetic dose (22 neonates; 3 publications).

CONCLUSION

Although evidence gaps were identified, both increasing sevoflurane concentration and decreasing temperature are associated with increasing discontinuity.

EDITOR’S PERSPECTIVE

Color density spectral array findings on continuous EEG during therapeutic hypothermia in children with acute encephalopathy

BACKGROUND

Quantitative EEG is frequently used to monitor children affected by acute encephalopathy (AE), with the expectation of providing comprehensive insights into continuous EEG monitoring. However, the potential of quantitative EEG for estimating outcomes in this context remains unclear. We sought reliable prognostic markers within the color density spectral array (CDSA) of the continuous EEG for AE-affected children undergoing therapeutic hypothermia (TH).

METHODS

This retrospective study analyzed CDSA data from eight scalp electrodes of 15 AE-affected children undergoing TH. Two CDSA features were investigated-high-frequency lines (HFLs) and periodic elevation in the low frequency band (PLFB)-along with the corresponding EEG characteristics. The inter-rater reliability for CDSA was assessed by four pediatric neurologists. Outcomes were grouped into either no/mild or severe decline in motor and cognitive functions, then compared with CDSA features.

RESULTS

The median EEG recording time was 114 (81-151) h per child. While at least 41 % of HFLs corresponded to typical sleep spindles, 94 % of PLFB aligned with cyclic changes in the amplitude of delta/theta waves on the raw EEG. Inter-rater reliability was higher for HFLs than for PLFB (kappa values: 0.69 vs. 0.46). HFLs were significantly more prevalent in children with no/mild decline than in children with severe decline (p = 0.017), whereas PLFB did not differ significantly (p = 0.33).

CONCLUSIONS

This study provides preliminary evidence that reduced HFLs on CDSA predict unfavorable outcomes in AE-affected children undergoing TH. This suggests that maintaining high-frequency waves is critical for optimal brain function.

Quantitative EEG and prediction of outcome in neonatal encephalopathy: a review

Electroencephalogram (EEG) is an important biomarker for neonatal encephalopathy (NE) and has significant predictive value for brain injury and neurodevelopmental outcomes. Quantitative analysis of EEG involves the representation of complex EEG data in an objective, reproducible and scalable manner. Quantitative EEG (qEEG) can be derived from both a limited channel EEG (as available during amplitude integrated EEG) and multi-channel conventional EEG. It has the potential to enable bedside clinicians to monitor and evaluate details of cortical function without the necessity of continuous expert input. This is particularly useful in NE, a dynamic and evolving condition. In these infants, continuous, detailed evaluation of cortical function at the bedside is a valuable aide to management especially in the current era of therapeutic hypothermia and possible upcoming neuroprotective therapies. This review discusses the role of qEEG in newborns with NE and its use in informing monitoring and therapy, along with its ability to predict imaging changes and short and long-term neurodevelopmental outcomes. IMPACT: Quantitative representation of EEG data brings the evaluation of continuous brain function, from the neurophysiology lab to the NICU bedside and has a potential role as a biomarker for neonatal encephalopathy. Clinical and research applications of quantitative EEG in the newborn are rapidly evolving and a wider understanding of its utility is valuable. This overview summarizes the role of quantitative EEG at different timepoints, its relevance to management and its predictive value for short- and long-term outcomes in neonatal encephalopathy.

An automated bedside measure for monitoring neonatal cortical activity: a supervised deep learning-based electroencephalogram classifier with external cohort validation

BACKGROUND

Electroencephalogram (EEG) monitoring is recommended as routine in newborn neurocritical care to facilitate early therapeutic decisions and outcome predictions. EEG's larger-scale implementation is, however, hindered by the shortage of expertise needed for the interpretation of spontaneous cortical activity, the EEG background. We developed an automated algorithm that transforms EEG recordings to quantified interpretations of EEG background and provides simple intuitive visualisations in patient monitors.

METHODS

In this method-development and proof-of-concept study, we collected visually classified EEGs from infants recovering from birth asphyxia or stroke. We used unsupervised learning methods to explore latent EEG characteristics, which guided the supervised training of a deep learning-based classifier. We assessed the classifier performance using cross-validation and an external validation dataset. We constructed a novel measure of cortical function, brain state of the newborn (BSN), from the novel EEG background classifier and a previously published sleep-state classifier. We estimated clinical utility of the BSN by identification of two key items in newborn brain monitoring, the onset of continuous cortical activity and sleep-wake cycling, compared with the visual interpretation of the raw EEG signal and the amplitude-integrated (aEEG) trend.

FINDINGS

We collected 2561 h of EEG from 39 infants (gestational age 35·0-42·1 weeks; postnatal age 0-7 days). The external validation dataset included 105 h of EEG from 31 full-term infants. The overall accuracy of the EEG background classifier was 92% in the whole cohort (95% CI 91-96; range 85-100 for individual infants). BSN trend values were closely related to the onset of continuous EEG activity or sleep-wake cycling, and BSN levels showed robust difference between aEEG categories. The temporal evolution of the BSN trends showed early diverging trajectories in infants with severely abnormal outcomes.

INTERPRETATION

The BSN trend can be implemented in bedside patient monitors as an EEG interpretation that is intuitive, transparent, and clinically explainable. A quantitative trend measure of brain function might harmonise practices across medical centres, enable wider use of brain monitoring in neurocritical care, and might facilitate clinical intervention trials.

FUNDING

European Training Networks Funding Scheme, the Academy of Finland, Finnish Pediatric Foundation (Lastentautiensäätiö), Aivosäätiö, Sigrid Juselius Foundation, HUS Children's Hospital, HUS Diagnostic Center, National Health and Medical Research Council of Australia.

Amplitude Integrated Electroencephalography and Continuous Electroencephalography Monitoring Is Crucial in High-Risk Infants and Their Findings Correlate With Neurodevelopmental Outcomes

Background: To evaluate seizure diagnosis in sick infants in the neonatal intensive care unit (NICU) based on electroencephalography (EEG) monitoring combined with amplitude integrated electroencephalography (aEEG). Methods: We retrospectively reviewed EEG and aEEG findings and determined their correlations with neurodevelopmental outcomes at the age of >1 year in 65 patients with diagnosed seizures, encephalopathy, or both. Results: Seizure identification rate was 43.1%. The rate in nonstructural groups (hypocalcemic, hypoglycemic, and genetic seizures) was 71.4%, which was higher (p < 0.05) than the rate of 35.3% of structural brain lesion group [hypoxic-ischemic encephalopathy (HIE) and congenital brain structural malformation]. The aEEG background correlating with neurodevelopmental outcomes had 70.0% positive prediction value (PPV), 65.5%% negative prediction value (NPV), 67.7% specificity, and 67.9% sensitivity (p < 0.005). The aEEG background strongly (PPV, 93.8%; p < 0.005) correlated with the outcomes in HIE. For genetic seizures, the detected rate was high. The ictal recordings for the nonstructural seizures revealed downflected on the aEEG background initially, which differed from the structural lesion. Conclusions: EEG monitoring combined with aEEG can detect seizures, facilitating early treatment. EEG changes during seizures could exhibit delta-theta waves with or without clinical seizures in patients with brain lesions. In non-structural etiologies (hypocalcemic and KCNQ2 seizures), aEEG initially exhibited lower background during seizures that could aid in differentiating these EEG changes from those of other etiologies. The aEEG background was correlated with neurodevelopmental outcome and exhibited high PPV but not NPV in neonatal HIE.

Ictal and interictal electroencephalographic findings can contribute to early diagnosis and prompt treatment in KCNQ2-associated epileptic encephalopathy

BACKGROUND

KCNQ2-associated epilepsy is most common in neonatal genetic epilepsy. A prompt diagnosis to initialize early treatment is important.

METHODS

We studied the electroencephalographic (EEG) changes including automated EEGs and conventional EEGs monitoring of 10 nonconsanguineous cases with KCNQ2 mutations, identified among 162 (6%) childhood epilepsy. We compared 11 (25%) non-KCNQ2 seizures videoed from 44 automated EEG and EEG monitoring.

RESULTS

Patients with KCNQ2 seizures had received more antiepileptic treatments than patients in non-KCNQ2 group. Seizures were detected in all patients with KCNQ2 epileptic encephalopathy (EE); the detection rate in KCNQ2 group was more than in patients with non-KCNQ2. The ictal recordings showed 3 newborns presented with initial lower amplitudes (<15 μV) and fast activity (>20 Hz), evolving into higher-amplitude theta-delta waves. Two patient's ictal seizures showed recurrent focal tonic movements of the unilateral limbs associated with slowly continuous spikes in the contralateral hemisphere. The interictal EEGs in 5 KCNQ2 EE were burst-suppression. In 5 patients with familial KCNQ2 mutations, the interictal EEGs showed focal paroxysmal activity. Compared with 11 non-KCNQ2 EEG of ictal seizures, the differences are ictal EEGs initially appeared manifesting theta-delta waves without fast activities. In KCNQ2 seizures, patients with mutations locating in the selectivity filter controlling K⁺ permeability had severe EEG patterns and poor neurodevelopmental outcomes.

CONCLUSION

Ictal EEGs in KCNQ2 seizures are unique and different from the EEGs of seizures with other etiologies. An EEG monitoring can be a valuable tool for early diagnosing KCNQ2-associated seizures and for supporting prompt treatments.

Effects of Cortical Cooling on Activity Across Layers of the Rat Barrel Cortex

Moderate cortical cooling is known to suppress slow oscillations and to evoke persistent cortical activity. However, the cooling-induced changes in electrical activity across cortical layers remain largely unknown. Here, we performed multi-channel local field potential (LFP) and multi-unit activity (MUA) recordings with linear silicone probes through the layers of single cortical barrel columns in urethane-anesthetized rats under normothermia (38°C) and during local cortical surface cooling (30°C). During cortically generated slow oscillations, moderate cortical cooling decreased delta wave amplitude, delta-wave occurrence, the duration of silent states, and delta wave-locked MUA synchronization. Moderate cortical cooling increased total time spent in the active state and decreased total time spent in the silent state. Cooling-evoked changes in the MUA firing rate in cortical layer 5 (L5) varied from increase to decrease across animals, and the polarity of changes in L5 MUA correlated with changes in total time spent in the active state. The decrease in temperature reduced MUA firing rates in all other cortical layers. Sensory-evoked MUA responses also decreased during cooling through all cortical layers. The cooling-dependent slowdown was detected at the fast time-scale with a decreased frequency of sensory-evoked high-frequency oscillations (HFO). Thus, moderate cortical cooling suppresses slow oscillations and desynchronizes neuronal activity through all cortical layers, and is associated with reduced firing across all cortical layers except L5, where cooling induces variable and non-consistent changes in neuronal firing, which are common features of the transition from slow-wave synchronization to desynchronized activity in the barrel cortex.

Continuous Electroencephalography Monitoring in Critically Ill Infants and Children

Continuous video electroencephalography (CEEG) monitoring of critically ill infants and children has expanded rapidly in recent years. Indications for CEEG include evaluation of patients with altered mental status, characterization of paroxysmal events, and detection of electrographic seizures, including monitoring of patients with limited neurological examination or conditions that put them at high risk for electrographic seizures (e.g., cardiac arrest or extracorporeal membrane oxygenation cannulation). Depending on the inclusion criteria and clinical characteristics of the population studied, the percentage of pediatric patients with electrographic seizures varies from 7% to 46% and with electrographic status epilepticus from 1% to 23%. There is also evidence that epileptiform and background CEEG patterns may provide important information about prognosis in certain clinical populations. Quantitative EEG techniques are emerging as a tool to enhance the value of CEEG to provide real-time bedside data for management and prognosis. Continued research is needed to understand the clinical value of seizure detection and identification of other CEEG patterns on the outcomes of critically ill infants and children.

Prognostic value of continuous electroencephalography in children undergoing therapeutic hypothermia after cardiac arrest: A pilot study

OBJECTIVE

To determine the prognostic value of continuous electroencephalography (EEG) in children undergoing therapeutic hypothermia after cardiac arrest.

METHOD

We retrospectively reviewed medical records and continuous EEG of all patients undergoing therapeutic hypothermia after cardiac arrest from November 2013 to September 2016. Demographic, clinical data and immediate complications were collected. Characteristics of continuous EEG including EEG background, time to normal trace (TTNT) and electrographic seizures were reviewed by investigators. Cerebral performance category scales at 6 months' follow up were evaluated and divided into good (grade 1-2) and poor (grade 3-5) outcome groups.

RESULT

Six patients were included (two boys and four girls) with median age of 19.5 months (range13-128 months). Five patients (83.3%) presented with cardiac arrest from near-drowning and one patient with underlying acute lymphocytic leukemia presented an in-hospital cardiac arrest. Initial EKG rhythm was asystole in 3 patients (50%), pulseless activity in 1 patient (16.7%) and initially unknown in 2 patients (33.3%). Two patients (33.3%) who had EEG reactivity and TTNT within 5minutes and 2.5hours had good neurological outcome (CPC1). Four patients (66.7%) with absent EEG reactivity had poor neurological outcome (CPC4, 5 in 3 and 1 children respectively). Three patients from the poor outcome group had electrographic seizures, of whom 2/3 progressed to status epilepticus. Three out of four patients in the poor outcome group had the following complications: pneumonia, bleeding and pancreatitis.

CONCLUSION

Early TTNT and EEG reactivity help to predict good neurological outcome in children undergoing therapeutic hypothermia after cardiac arrest. Seizures and status epilepticus may predict poor neurological outcome.

Optimal Duration of Continuous Video-Electroencephalography in Term Infants With Hypoxic-Ischemic Encephalopathy and Therapeutic Hypothermia

Continuous video-electroencephalography (EEG) is an important diagnostic and prognostic tool in newborns with hypoxic-ischemic encephalopathy undergoing therapeutic hypothermia. The optimal duration of continuous video-EEG during whole-body hypothermia is not known. We conducted a retrospective study of 35 neonates with hypoxic-ischemic encephalopathy undergoing whole-body hypothermia with continuous video-EEG. EEG ictal changes were detected in 9/35 infants (26%). Of these 9 infants, the seizures were initially observed within 30 minutes of EEG monitoring in 6 (67%), within 24 hours in 2 (22%), and during rewarming in 1 infant (11%). No new seizures were detected between 24-72 hours of therapeutic hypothermia. Background suppression was detected in 14 infants (40%) by 24 hours. In neonates with hypoxic-ischemic encephalopathy undergoing therapeutic hypothermia, continuous video-EEG has the highest diagnostic yield within the first 24 hours and during the rewarming phase. In the absence of prior seizures or antiepileptic therapy, limiting continuous video-EEG to these periods in resource-limited settings may reduce cost during therapeutic hypothermia.

Analgesia, sedation, and neuromuscular blockade during targeted temperature management after cardiac arrest

The approach to sedation, analgesia, and neuromuscular blockade during targeted temperature management (TTM) remains largely unstudied, forcing clinicians to adapt previous research from other patient environments. During TTM, very little data guide drug selection, doses, and specific therapeutic goals. Sedation should be deep enough to prevent awareness during neuromuscular blockade, but titration is complex as metabolism and clearance are delayed for almost all drugs during hypothermia. Deeper sedation is associated with prolonged intensive care unit (ICU) and ventilator therapy, increased delirium and infection, and delayed wakening which can confound early critical neurological assessments, potentially resulting in erroneous prognostication and inappropriate withdrawal of life support. We review the potential therapeutic goals for sedation, analgesia, and neuromuscular blockade during TTM; the adverse events associated with that treatment; data suggesting that TTM and organ dysfunction impair drug metabolism; and controversies and potential benefits of specific monitoring. We also highlight the areas needing better research to guide our therapy.

Early Electroencephalographic Findings Correlate With Neurologic Outcome in Children Following Cardiac Arrest

OBJECTIVES

To determine the clinical and electroencephalographic findings associated with prognosis in nonneonate children following cardiac arrest.

DESIGN

Retrospective observational study.

SETTING

PICU and cardiac ICU.

PATIENTS

Nonneonate children with a history of cardiac arrest more than 2 minutes.

INTERVENTIONS

Electroencephalographic monitoring within 72 hours of return of spontaneous circulation.

MEASUREMENTS AND MAIN RESULTS

Clinical and features, neurophysiologic data, and Pediatric Cerebral Performance Category scores were collected. Electroencephalographic traces were reviewed in a blinded manner, all seizures and electroencephalographic findings noted, and the electroencephalography was scored at 1 hour, 24 hours, and continuous electroencephalographic end. Discrete data regarding specific characteristics of the electroencephalographic background and seizures were studied. Univariate and multivariate analyses were performed to identify associations between clinical variables, electroencephalographic findings, and Pediatric Cerebral Performance Category score at hospital discharge. Multivariate analysis of 73 children revealed duration of cardiac arrest less than 20 minutes or continuous electroencephalographic background activity within 12 hours postreturn of spontaneous circulation were associated with good short term neurologic outcome. Change in electroencephalographic background score over time and electroencephalographic data collected after the initial hour were not associated with outcome.

CONCLUSIONS

Following pediatric cardiac arrest, an initially normal electroencephalography or generalized slowing of the electroencephalographic background was associated with good neurologic outcome at hospital discharge.

Functional mitochondrial analysis in acute brain sections from adult rats reveals mitochondrial dysfunction in a rat model of migraine

Mitochondrial dysfunction has been implicated in many neurological disorders that only develop or are much more severe in adults, yet no methodology exists that allows for medium-throughput functional mitochondrial analysis of brain sections from adult animals. We developed a technique for quantifying mitochondrial respiration in acutely isolated adult rat brain sections with the Seahorse XF Analyzer. Evaluating a range of conditions made quantifying mitochondrial function from acutely derived adult brain sections from the cortex, cerebellum, and trigeminal nucleus caudalis possible. Optimization of this technique demonstrated that the ideal section size was 1 mm wide. We found that sectioning brains at physiological temperatures was necessary for consistent metabolic analysis of trigeminal nucleus caudalis sections. Oxygen consumption in these sections was highly coupled to ATP synthesis, had robust spare respiratory capacities, and had limited nonmitochondrial respiration, all indicative of healthy tissue. We demonstrate the effectiveness of this technique by identifying a decreased spare respiratory capacity in the trigeminal nucleus caudalis of a rat model of chronic migraine, a neurological disorder that has been associated with mitochondrial dysfunction. This technique allows for 24 acutely isolated sections from multiple brain regions of a single adult rat to be analyzed simultaneously with four sequential drug treatments, greatly advancing the ability to study mitochondrial physiology in adult neurological disorders.

Continuous electroencephalographic monitoring in critically ill patients: indications, limitations, and strategies

OBJECTIVE

Continuous electroencephalography as a bedside monitor of cerebral activity has been used in a range of critically ill patients. This review compiles the indications, limitations, and strategies for continuous electroencephalography in the ICU.

DATA SOURCE

The authors searched the electronic MEDLINE database.

STUDY SELECTION AND DATA EXTRACTION

References from articles of special interest were selected.

DATA SYNTHESIS AND CONCLUSION

Electroencephalographically-defined suppression is routinely used as the basis for titration of pharmacologic therapy in refractory status epilepticus and intracranial hypertension. The increasing use of continuous electroencephalography reveals a clinically underappreciated burden of epileptiform and epileptic activity in patients with primary acute neurologic disorders, and also in critically ill patients with acquired encephalopathy. Status epilepticus is reported with continuous electroencephalography in 1% to 10% of patients with ischemic stroke, 8% to 14% with traumatic brain injury, 10% to 14% with subarachnoid hemorrhage, 1% to 21% with intracerebral hemorrhage, and 30% of patients following cardiorespiratory arrest. These figures underscore the importance of continuous electroencephalography in the critically ill. The interpretation of continuous electroencephalography in the ICU is challenged by electroencephalography artifacts and the frequent subtle differences between ictal and interictal patterns.