The EEG signal: a window on the cortical brain activity

Predicting postoperative pain in children: an observational study using the pain threshold Index

Objective

While the pain threshold index (PTI) holds potential as a tool for monitoring analgesia-pain equilibrium, its precision in forecasting postoperative pain in children remains unconfirmed. This study's primary aim was to assess the PTI's predictive precision for postoperative pain.

Methods

Children (aged 2-16 years) undergoing general surgery under general anesthesia were included. Within 5 min prior to the patient's emergence from surgery, data including PTI, wavelet index (WLI), heart rates (HR) and mean arterial pressure (MAP) were collected. Subsequently, a 15-min pain assessment was conducted following the patient's awakening. The accuracy of these indicators in discerning between mild and moderate to severe postoperative pain was evaluated through receiver operating characteristic (ROC) analysis.

Results

The analysis encompassed data from 90 children. ROC analysis showed that PTI was slightly better than HR, MAP and WLI in predicting postoperative pain, but its predictive value was limited. The area under the curve (AUC) was 0.659 [0.537∼0.780] and the optimal threshold was 65[64-67]. Sensitivity and specificity were determined at 0.90 and 0.50, respectively. In a multivariable logistic regression model, a higher predictive accuracy was found for a multivariable predictor combining PTI values with gender, BMI, HR and MAP (AUC, 0.768; 95%CI, 0.669-0.866). Upon further scrutinizing the age groups, PTI's AUC was 0.796 for children aged 9-16, 0.656 for those aged 4-8, and 0.601 for younger individuals.

Conclusions

PTI, when used alone, lacks acceptable accuracy in predicting postoperative pain in children aged 2 to 16 years. However, when combined with other factors, it shows improved predictive accuracy. Notably, PTI appears to be more accurate in older children.

Intraoperative pediatric electroencephalography monitoring: an updated review

Intraoperative electroencephalography (EEG) monitoring under pediatric anesthesia has begun to attract increasing interest, driven by the availability of pediatric-specific EEG monitors and the realization that traditional dosing methods based on patient movement or changes in hemodynamic response often lead to imprecise dosing, especially in younger infants who may experience adverse events (e.g., hypotension) due to excess anesthesia. EEG directly measures the effects of anesthetics on the brain, which is the target end-organ responsible for inducing loss of consciousness. Over the past ten years, research on anesthesia and computational neuroscience has improved our understanding of intraoperative pediatric EEG monitoring and expanded the utility of EEG in clinical practice. We now have better insights into neurodevelopmental changes in the developing pediatric brain, functional connectivity, the use of non-proprietary EEG parameters to guide anesthetic dosing, epileptiform EEG changes during induction, EEG changes from spinal/regional anesthesia, EEG discontinuity, and the use of EEG to improve clinical outcomes. This review article summarizes the recent literature on EEG monitoring in perioperative pediatric anesthesia, highlighting several of the topics mentioned above.

Topographical Features of Pediatric Electroencephalography during High Initial Concentration Sevoflurane for Inhalational Induction of Anesthesia

BACKGROUND

High-density electroencephalographic (EEG) monitoring remains underutilized in clinical anesthesia, despite its obvious utility in unraveling the profound physiologic impact of these agents on central nervous system functioning. In school-aged children, the routine practice of rapid induction with high concentrations of inspiratory sevoflurane is commonplace, given its favorable efficacy and tolerance profile. However, few studies investigate topographic EEG during the critical timepoint coinciding with loss of responsiveness-a key moment for anesthesiologists in their everyday practice. The authors hypothesized that high initial sevoflurane inhalation would better precipitate changes in brain regions due to inhomogeneities in maturation across three different age groups compared with gradual stepwise paradigms utilized by other investigators. Knowledge of these changes may inform strategies for agent titration in everyday clinical settings.

METHODS

A total of 37 healthy children aged 5 to 10 yr underwent induction with 4% or greater sevoflurane in high-flow oxygen. Perturbations in anesthetic state were investigated in 23 of these children using 64-channel EEG with the Hjorth Laplacian referencing scheme. Topographical maps illustrated absolute, relative, and total band power across three age groups: 5 to 6 yr (n = 7), 7 to 8 yr (n = 8), and 9 to 10 yr (n = 8).

RESULTS

Spectral analysis revealed a large shift in total power driven by increased delta oscillations. Well-described topographic patterns of anesthesia, e.g., frontal predominance, paradoxical beta excitation, and increased slow activity, were evident in the topographic maps. However, there were no statistically significant age-related changes in spectral power observed in a midline electrode subset between the groups when responsiveness was lost compared to the resting state.

CONCLUSIONS

High initial concentration sevoflurane induction causes large-scale topographic effects on the pediatric EEG. Within the minute after unresponsiveness, this dosage may perturb EEG activity in children to an extent where age-related differences are not discernible.

EDITOR’S PERSPECTIVE

Mapping general anesthesia states based on electro-encephalogram transition phases

Cortical electro-encephalography (EEG) served as the clinical reference for monitoring unconsciousness during general anesthesia. The existing EEG-based monitors classified general anesthesia states as underdosed, adequate, or overdosed, lacking predictive power due to the absence of transition phases among these states. In response to this limitation, we undertook an analysis of the EEG signal during isoflurane-induced general anesthesia in mice. Adopting a data-driven approach, we applied signal processing techniques to track θ- and δ-band dynamics, along with iso-electric suppressions. Combining this approach with machine learning, we successfully developed an automated algorithm. The findings of our study revealed that the dampening of the δ-band occurred several minutes before the onset of significant iso-electric suppression episodes. Furthermore, a distinct γ-frequency oscillation was observed, persisting for several minutes during the recovery phase subsequent to isoflurane-induced overdose. As a result of our research, we generated a map summarizing multiple brain states and their transitions, offering a tool for predicting and preventing overdose during general anesthesia. The transition phases identified, along with the developed algorithm, have the potential to be generalized, enabling clinicians to prevent inadequate anesthesia and, consequently, tailor anesthetic regimens to individual patients.

Monitoring anesthesia depth with patient state index during pediatric surgery

BACKGROUND

Monitoring anesthesia depth in children is challenging. Pediatric anesthesiologists estimate general anesthesia depth using indirect methods such as pharmacokinetic models and neurovegetative reflexes. The application of processed electroencephalography may help to identify the correct anesthesia depth (i.e., patient state index between 25 and 50).

AIMS

To determine the median values of patient state index and spectral edge frequency 95% in children undergoing general anesthesia conducted according to indirect evaluation of depth. The relationships between patient state index and spectral edge frequency 95% and indirect monitoring of anesthesia depth, type of anesthesia, age subgroups, and postoperative delirium were also assessed.

METHODS

A prospective observational study on children (aged 1-18 years) undergoing surgery longer than 60 min. The SedLine monitor and the novel SedLine pediatric sensors (Masimo Inc., Irvine California) were applied. Patient state index levels were recorded for the duration of the anesthesia until the discharge to the ward at predefined time points.

RESULTS

In the 111 enrolled children, median patient state index level at the end of anesthesia induction was 25 (22-32) and ranged from 26 (23-34) to 28 (25-36) in the maintenance phase. Patient state index at extubation was 48 (35-60) and 69 (62-75) at discharge from the operatory room. Median right/left spectral edge frequency 95% values at the end of induction were 10 (6-14)/9 (5-14) Hz and median right/left spectral edge frequency 95% values in the maintenance phase ranged from 10 (6-14) to 12 (11-15) Hz in both hemispheres. At extubation, right/left spectral edge frequency 95% levels were 18 (15-21)/17 (15-21) Hz. We observed 39 episodes of burst suppression in 20 patients (19%). Median patient state index levels were not different between patients undergoing inhalational and intravenous anesthesia and between those undergoing general anesthesia and general anesthesia added to locoregional anesthesia. Children <2 years displayed significantly higher patient state index levels than older patients (p = .0004). The presence of a burst suppression episode was not associated with PAED levels (OR 1.58, 95% CI 0.14-16.74, p` = .18).

CONCLUSIONS

NonpEEG-guided anesthesia in children led to median patient state index levels at the low range of recommended unconsciousness values with frequent episodes of burst suppression. Patient state index levels were generally higher in children below 2 years.

Comparative analysis of the effect of electromyogram to bispectral index and 95% spectral edge frequency under remimazolam and propofol anesthesia: a prospective, randomized, controlled clinical trial

Background

Bispectral index (BIS), an index used to monitor the depth of anesthesia, can be interfered with by the electromyogram (EMG) signal. The 95% spectral edge frequency (SEF95) also can reflect the sedation depth. Remimazolam in monitored anesthesia care results in higher BIS values than propofol, though in the same sedation level assessed by Modified Observers Assessment of Alertness and Sedation (MOAA/S). Our study aims to illustrate whether EMG is involved in remimazolam causing higher BIS value than propofol preliminarily and to explore the correlations among BIS, EMG, and SEF95 under propofol and remimazolam anesthesia.

Patients and methods

Twenty-eight patients were randomly divided into propofol (P) and remimazolam (RM) groups. Patients in the two groups received alfentanil 10 μg/kg, followed by propofol 2 mg/kg and remimazolam 0.15 mg/kg. Blood pressure (BP), heart rate (HR), and oxygen saturation (SpO2) were routinely monitored. The BIS, EMG, and SEF95 were obtained through BIS VISTATM. The primary outcomes were BIS, EMG, and the correlation between BIS and EMG in both groups. Other outcomes were SEF95, the correlation between BIS and SEF95, and the correlation between EMG and SEF95. And all the statistical and comparative analysis between these signals was conducted with SPSS 26.0 and GraphPad Prism 8.

Results

BIS values, EMG, and SEF95 were significantly higher in the RM group than in the P group (all p < 0.001). There was a strong positive correlation between BIS and EMG in the RM group (r = 0.416). Nevertheless, the BIS in the P group showed a weak negative correlation with EMG (r = -0.219). Both P (r = 0.787) and RM group (r = 0.559) had a reasonably significant correlation coefficient between BIS and SEF95. SEF95 almost did not correlate with EMG in the RM group (r = 0.101).

Conclusion

Bispectral index can be interfered with high EMG intensity under remimazolam anesthesia. However, EMG can hardly affect the accuracy of BIS under propofol anesthesia due to low EMG intensity and a weak negative correlation between EMG and BIS. Moreover, SEF95 may have a great application prospect in predicting the sedation condition of remimazolam.

Isometric force complexity may not fully originate from the nervous system

In humans and animals, spatial and temporal information from the nervous system are translated into muscle force enabling movements of body segments. To gain deeper understanding of this translation of information into movements, we investigated the motor control dynamics of isometric contractions in children, adolescents, young adults and older adults. Twelve children, thirteen adolescents, fourteen young adults, and fifteen older adults completed two minutes of submaximal isometric plantar- and dorsiflexion. Simultaneously, sensorimotor cortex EEG, tibialis anterior and soleus EMG and plantar- and dorsiflexion force was recorded. Surrogate analysis suggested that all signals were from a deterministic origin. Multiscale entropy analysis revealed an inverted U-shape relationship between age and complexity for the force but not for the EEG and EMG signals. This suggests that temporal information in from the nervous system is modulated by the musculoskeletal system during the transmission into force. The entropic half-life analyses indicated that this modulation increases the time scale of the temporal dependency in the force signal compared to the neural signals. Together this indicates that the information embedded in produced force does not exclusively reflect the information embedded in the underlying neural signal.

Study on the Psychological States of Olfactory Stimuli Using Electroencephalography and Heart Rate Variability

In the modern information society, people are constantly exposed to stress due to complex work environments and various interpersonal relationships. Aromatherapy is attracting attention as one of the methods for relieving stress using aroma. A method to quantitatively evaluate such an effect is necessary to clarify the effect of aroma on the human psychological state. In this study, we propose a method of using two biological indexes, electroencephalogram (EEG) and heart rate variability (HRV), to evaluate human psychological states during the inhalation of aroma. The purpose is to investigate the relationship between biological indexes and the psychological effect of aromas. First, we conducted an aroma presentation experiment using seven different olfactory stimuli while collecting data from EEG and pulse sensors. Next, we extracted the EEG and HRV indexes from the experimental data and analyzed them with respect to the olfactory stimuli. Our study found that olfactory stimuli have a strong effect on psychological states during aroma stimuli and that the human response to olfactory stimuli is immediate but gradually adapts to a more neutral state. The EEG and HRV indexes showed significant differences between aromas and unpleasant odors especially for male participants in their 20-30s, while the delta wave and RMSSD indexes showed potential for generalizing the method to evaluate psychological states influenced by olfactory stimuli across genders and generations. The results suggest the possibility of using EEG and HRV indexes to evaluate psychological states toward olfactory stimuli such as aroma. In addition, we visualized the psychological states affected by the olfactory stimuli on an emotion map, suggesting an appropriate range of EEG frequency bands for evaluating psychological states applied to the olfactory stimuli. The novelty of this research lies in our proposed method to provide a more detailed picture of the psychological responses to olfactory stimuli using the integration of biological indexes and emotion map, which contributes to the areas such as marketing and product design by providing insights into the emotional responses of consumers to different olfactory products.

Correlations between EEG and intestinal electrical stimulation

Many diseases affect the autonomous nervous system and the central nervous system simultaneously, for example Parkinson's disease or irritable bowel syndrome. To study neurophysiologic interactions between the intestinal electrical activity and the electroencephalography (EEG) pattern of the brain, we combined intestinal electrical stimulation (IES) and non-invasive telemetric full-band DC EEG recordings in an acute pig-model. Intestinal motility was monitored with accelerometers. Brain activity was analyzed with regard to network driven phenomena like phase amplitude coupling (PAC) within two time-windows: 1 min after IES (early response) and 3 min after stimulation (late response). Here we present the results for two stimulation sites (small intestine, colon) and two parietal scalp-EEG channels (right and left somatosensory cortex region). Electrical stimulation consisted of a 30 or 130 Hz pulse. In summary, the PAC modulation index at a parietal EEG recording position is decreased after IES. This effect is in line with an inhibitory effect of our IES protocol regarding peristalsis. The surprisingly strong effects of IES on network driven EEG patterns may be translated into new therapeutic techniques and/or diagnostic tools in the future. Furthermore, analytic tools, operating on sparse datasets, may be ideally suited for the integration in implantable intestinal pacemakers as feedback system.

Effects of anesthetic depth on postoperative pain and delirium: a meta-analysis of randomized controlled trials with trial sequential analysis

BACKGROUND

Whether anesthetic depth affects postoperative outcomes remains controversial. This meta-analysis aimed to evaluate the effects of deep vs. light anesthesia on postoperative pain, cognitive function, recovery from anesthesia, complications, and mortality.

METHODS

PubMed, EMBASE, and Cochrane CENTRAL databases were searched until January 2022 for randomized controlled trials comparing deep and light anesthesia in adult surgical patients. The co-primary outcomes were postoperative pain and delirium (assessed using the confusion assessment method). We conducted a meta-analysis using a random-effects model. We assessed publication bias using the Begg's rank correlation test and Egger's linear regression. We evaluated the evidence using the trial sequential analysis and Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology. We conducted subgroup analyses for pain scores at different postoperative time points and delirium according to cardiac or non-cardiac surgery.

RESULTS

A total of 26 trials with 10,743 patients were included. Deep anesthesia compared with light anesthesia (a mean difference in bispectral index of -12 to -11) was associated with lower pain scores at rest at 0 to 1 h postoperatively (weighted mean difference = -0.72, 95% confidence interval [CI] = -1.25 to -0.18, P  = 0.009; moderate-quality evidence) and an increased incidence of postoperative delirium (24.95% vs. 15.92%; risk ratio = 1.57, 95% CI = 1.28-1.91, P  < 0.0001; high-quality evidence). No publication bias was detected. For the exploratory secondary outcomes, deep anesthesia was associated with prolonged postoperative recovery, without affecting neurocognitive outcomes, major complications, or mortality. In the subgroup analyses, the deep anesthesia group had lower pain scores at rest and on movement during 24 h postoperatively, without statistically significant subgroup differences, and deep anesthesia was associated with an increased incidence of delirium after non-cardiac and cardiac surgeries, without statistically significant subgroup differences.

CONCLUSIONS

Deep anesthesia reduced early postoperative pain but increased postoperative delirium. The current evidence does not support the use of deep anesthesia in clinical practice.

Correlation between bispectral index and patient state index in children under sevoflurane anesthesia

BACKGROUND

Because the unanticipated arousal or hemodynamic instability during anesthesia may adversely affect the physical and emotional welfare of children, adequate management of the anesthesia depth is required. We aimed to compare Bispectral Index (BIS) and Patient State Index (PSI) in children during sevoflurane anesthesia and evaluate PSI as depth of anesthesia monitor in children aged 6 months-12 years.

METHODS

In this prospective observational study, children aged 6 months-12 years old scheduled for elective surgery under sevoflurane anesthesia were enrolled from November 2018 to June 2019. We monitored BIS and PSI at different sevoflurane concentrations. The primary outcome was the correlation between BIS and PSI. The correlation between BIS and PSI at different sevoflurane concentrations (at 1, 1.5, and 2 MACs) and at different age groups (6 months-2 years, 2-7 years, and 8-12 years) was also investigated.

RESULTS

Bispectral index and PSI showed a fair correlation (r = .430; 95% confidence interval [CI], 0.297-0.546; p < .001). Two values were fairly correlated at 1, 1.5, and 2 MAC (r = .544; 95% CI, 0.314-0.716; p < .001, r = .509; 95% CI, 0.283-0.699; p < .001, and r = .315; 95% CI, 0.047-0.522; p = 0.007). BIS and PSI values showed a fair correlation in 6 months - 2 year and 8-12 year groups (r = .696; 95% CI, 0.519-0.813; p < .001 and r = .297; 95% CI, -0.017 to 0.543; p < .021), but there was not significant correlation in 2-7 years group (r = .190; 95% CI, -0.015 to 0.374; p = .052).

CONCLUSIONS

There was a fair correlation between BIS and PSI in children under sevoflurane anesthesia. The use of BIS and PSI as an indicator for anesthesia depth by sevoflurane is not reliable in pediatric patients.

Electroencephalogram-derived pain index for evaluating pain during labor

Background

The discriminative ability of a point-of-care electroencephalogram (EEG)-derived pain index (Pi) for objectively assessing pain has been validated in chronic pain patients. The current study aimed to determine its feasibility in assessing labor pain in an obstetric setting.

Methods

Parturients were enrolled from the delivery room at the department of obstetrics in a tertiary hospital between February and June of 2018. Pi values and relevant numerical rating scale (NRS) scores were collected at different stages of labor in the presence or absence of epidural analgesia. The correlation between Pi values and NRS scores was analyzed using the Pearson correlation analysis. The receiver operating characteristic (ROC) curve was plotted to estimate the discriminative capability of Pi to detect labor pain in parturients.

Results

Eighty paturients were eligible for inclusion. The Pearson correlation analysis exhibited a positive correlation between Pi values and NRS scores in parturients (r = 0.768, P < 0.001). The ROC analysis revealed a cut-off Pi value of 18.37 to discriminate between mild and moderate-to-severe labor pain in parturients. Further analysis indicated that Pi values had the best diagnostic accuracy reflected by the highest area under the curve (AUC) of 0.857, with a sensitivity and specificity of 0.767 and 0.833, respectively, and a Youden index of 0.6. Subgroup analyses further substantiated the correlations between Pi values and NRS scores, especially in parturients with higher pain intensity.

Conclusion

This study indicates that Pi values derived from EEGs significantly correlate with the NRS scores, and can serve as a way to quantitatively and objectively evaluate labor pain in parturients.

fMRI-Informed EEG for brain mapping of imagined lower limb movement: Feasibility of a brain computer interface

BACKGROUND

EEG and fMRI have contributed greatly to our understanding of brain activity and its link to behaviors by helping to identify both when and where the activity occurs. This is particularly important in the development of brain-computer interfaces (BCIs), where feed forward systems gather data from imagined brain activity and then send that information to an effector. The purpose of this study was to develop and evaluate a computational approach that enables an accurate mapping of spatial brain activity (fMRI) in relation to the temporal receptors (EEG electrodes) associated with imagined lower limb movement.

NEW METHOD

EEG and fMRI data from 16 healthy, male participants while imagining lower limb movement were used for this purpose. A combined analysis of fMRI data and EEG electrode locations was developed to identify EEG electrodes with a high likelihood of capturing imagined lower limb movement originating from various clusters of brain activity. This novel feature selection tool was used to develop an artificial neural network model to classify right and left lower limb movement.

RESULTS

Results showed that left versus right lower limb imagined movement could be classified with 66.5% accuracy using this approach. Comparison with existing methods: Adopting a purely data-driven approach for feature selection to use in the right/left classification task resulted in the same accuracy (66.6%) but with reduced interpretability.

CONCLUSIONS

The developed fMRI-informed EEG approach could pave the way towards improved brain computer interfaces for lower limb movement while also being applicable to other systems where fMRI could be helpful to inform EEG acquisition and processing.

Using Electroencephalography (EEG) to Guide Propofol and Sevoflurane Dosing in Pediatric Anesthesia

Sevoflurane and propofol-based anesthetics are dosed according to vital signs, movement, and expired sevoflurane concentrations, which do not assess the anesthetic state of the brain and, therefore, risk underdose and overdose. Electroencephalography (EEG) measures cortical brain activity and can assess hypnotic depth, a key component of the anesthetic state. Application of sevoflurane and propofol pharmacology along with EEG parameters can more precisely guide dosing to achieve the desired anesthetic state for an individual pediatric patient. This article reviews the principles underlying EEG use for sevoflurane and propofol dosing in pediatric anesthesia and offers case examples to illustrate their use in individual patients.

Why do We Use the Concepts of Adult Anesthesia Pharmacology in Developing Brains? Will It Have an Impact on Outcomes? Challenges in Neuromonitoring and Pharmacology in Pediatric Anesthesia

BACKGROUND

Pediatric sedation and anesthesia techniques have plenty of difficulties and challenges. Data on the pharmacologic, electroencephalographic, and neurologic response to anesthesia at different brain development times are only partially known. New data in neuroscience, pharmacology, and intraoperative neuromonitoring will impact changing concepts and clinical practice. In this article, we develop a conversation to guide the debate and search for a view more attuned to the updated knowledge in neurodevelopment, electroencephalography, and clinical pharmacology for the anesthesiologic practice in the pediatric population.

EEG differentiates left and right imagined Lower Limb movement

BACKGROUND

Identifying which EEG signals distinguish left from right leg movements in imagined lower limb movement is crucial to building an effective and efficient brain-computer interface (BCI). Past findings on this issue have been mixed, partly due to the difficulty in collecting and isolating the relevant information. The purpose of this study was to contribute to this new and important literature.

RESEARCH QUESTION

Can left versus right imagined stepping be differentiated using the alpha, beta, and gamma frequencies of EEG data at four electrodes (C1, C2, PO3, and PO4)?

METHODS

An experiment was conducted with a sample of 16 healthy male participants. They imagined left and right lower limb movements across 60 trials at two time periods separated by one week. Participants were fitted with a 64-electrode headcap, lay supine on a specially designed device and then completed the imagined task while observing a customized computer-generated image of a human walking to signify the left and right steps, respectively.

RESULTS

Findings showed that eight of the twelve frequency bands from 4 EEG electrodes were significant in differentiating imagined left from right lower limb movement. Using these data points, a neural network analysis resulted in an overall participant average test classification accuracy of left versus right movements at 63 %.

SIGNIFICANCE

Our study provides support for using the alpha, beta and gamma frequency bands at the sensorimotor areas (C1 and C2 electrodes) and incorporating information from the parietal/occipital lobes (PO3 and PO4 electrodes) for focused, real-time EEG signal processing to assist in creating a BCI for those with lower limb compromised mobility.

An approach to using pharmacokinetics and electroencephalography for propofol anesthesia for surgery in infants

Safe and effective techniques for propofol total intravenous anesthesia (TIVA) in infants are not well imbedded into clinical practice, resulting in practitioner unfamiliarity and potential for over- and under-dosing. In this education article, we describe our approach to TIVA dosing in infants and toddlers (birth to 36 months) which combines the use of pharmacokinetic models with EEG multi-parameter analysis. Pharmacokinetic models describe propofol and remifentanil effect site concentrations (Ce) over time in different age groups for a given dosing regimen. These models display substantial biological variability between individuals within age groups, impeding their application to clinical practice. Nevertheless, they reveal that younger infants require a higher propofol loading dose, a lower propofol maintenance dose, and a higher remifentanil dose compared with older infants. Proprietary EEG indices (eg, Bispectral Index) can serve as a biomarker of propofol Ce in adults and children to guide dosing to the individual patient; however, they are not recommended for infants as their validity remains uncertain this population. In our experience, EEG waveforms and processed parameters can reflect propofol Ce in infants, reflected by spectral edge frequency (SEF), density spectral array (DSA), and waveform patterns. In our practice, we use a "lookup table" of age-based dosing regimens or target-controlled infusion (TCI) based on the pharmacokinetic models to deliver a target propofol Ce and co-administer remifentanil and/or regional technique for analgesia. We analyze Electroencephalogram (EEG) waveforms, SEF, and DSA to adjust the propofol dose or TCI target concentration to the individual infant. EEG analysis mitigates against biological variability inherent in the pharmacokinetic models and has improved our experience with TIVA for infants.

Use of Processed Electroencephalography in the Clinical Setting

Purpose of Review

Processed electroencephalography (pEEG) is widely used in clinical practice. Few clinicians utilize the full potential of these devices. This brief review will address the improvements in patient management available from the utilization of all pEEG data.

Recent Findings

Anesthesiologists easily learn to recognize raw pEEG patterns that are consistent with an appropriate level of hypnotic effect. Power distribution within the waveform can be displayed in a visual format that identifies signatures of the principal anesthetic hypnotics. Opinion on the benefit of pEEG data in the mitigation of postoperative neurological impairment remains divided.

Summary

Looking beyond the index number can aid clinical decision making and improve confidence in the benefits of this monitoring modality.

An electroencephalography (EEG) study of short-term electromyography (EMG) biofeedback training in patients with myofascial pain syndrome in the upper trapezius

[Purpose] In the present study, electroencephalography was used to explore neural activity related to electromyography biofeedback training, focusing on pain perception before and after electromyography biofeedback. [Participants and Methods] Twenty-seven participants (female=23; mean age: 28.85 ± 4.99 years) with mild-to-moderate myofascial pain syndrome in the upper trapezius were recruited for this study. All participants underwent electroencephalography recording before, during, and after (0 and 15 min) electromyography biofeedback training. Quantitative electroencephalography analysis was performed to obtain the absolute power of the four main frequency bands. Pain scores before and after electromyography biofeedback were also evaluated by subjective rating. [Results] Electromyography biofeedback increased alpha power and decreased delta power 15 minutes after training, suggestive of relaxation. However, although a tendency for scores to decrease was observed, no significant improvements in pain scores were observed following the intervention. Such results may be due to the short duration of the biofeedback session and the subjective nature of pain assessments. [Conclusion] Despite no obvious changes in pain perception, brief electromyography biofeedback training may induce relaxation in patients with myofascial pain syndrome of the upper trapezius muscle.

Differential frontal alpha oscillations and mechanisms underlying loss of consciousness: a comparison between slow and fast propofol infusion rates

Mechanisms underlying loss of consciousness following propofol administration remain incompletely understood. The objective of this study was to compare frontal lobe electroencephalography activity and brainstem reflexes during intravenous induction of general anaesthesia, in patients receiving a typical bolus dose (fast infusion) of propofol compared with a slower infusion rate. We sought to determine whether brainstem suppression ('bottom-up') predominates over loss of cortical function ('top-down'). Sixteen ASA physical status-1 patients were randomly assigned to either a fast or slow propofol infusion group. Loss of consciousness and brainstem reflexes were assessed every 30 s by a neurologist blinded to treatment allocation. We performed a multitaper spectral analysis of all electroencephalography data obtained from each participant. Brainstem reflexes were present in all eight patients in the slow infusion group, while being absent in all patients in the fast infusion group, at the moment of loss of consciousness (p = 0.010). An increase in alpha band power was observed before loss of consciousness only in participants allocated to the slow infusion group. Alpha band power emerged several minutes after the loss of consciousness in participants allocated to the fast infusion group. Our results show a predominance of 'bottom-up' mechanisms during fast infusion rates and 'top-down' mechanisms during slow infusion rates. The underlying mechanisms by which propofol induces loss of consciousness are potentially influenced by the speed of infusion.

Pharmacologic Modulation of Noxious Stimulus-evoked Brain Activation in Cynomolgus Macaques Observed with Functional Neuroimaging

Maintaining effective analgesia during invasive procedures performed under general anesthesia is important for minimizing postoperative complications and ensuring satisfactory patient wellbeing and recovery. While patients under deep sedation may demonstrate an apparent lack of response to noxious stimulation, areas of the brain related to pain perception may still be activated. Thus, these patients may still experience pain during invasive procedures. The current study used anesthetized or sedated cynomolgus macaques and functional magnetic resonance imaging (fMRI) to assess the activation of the parts of the brain involved in pain perception during the application of peripheral noxious stimuli. Noxious pressure applied to the foot resulted in the bilateral activation of secondary somatosensory cortex (SII) and insular cortex (Ins), which are both involved in pain perception, in macaques under either propofol or pentobarbital sedation. No activation of SII/Ins was observed in macaques treated with either isoflurane or a combination of medetomidine, midazolam, and butorphanol. No movement or other reflexes were observed in response to noxious pressure during stimulation under anesthesia or sedation. The current findings show that despite the lack of visible behavioral symptoms of pain during anesthesia or sedation, brain activation suggests the presence of pain depending on the anesthetic agent used. These data suggest that fMRI could be used to noninvasively assess pain and to confirm the analgesic efficacy of currently used anesthetics. By assessing analgesic efficacy, researchers may refine their experiments, and design protocols that improve analgesia under anesthesia.

Comparison of Two Methods of Anesthesia Using Patient State Index: Propofol Versus Sevoflurane During Interventional Neuroradiology Procedure

Background

Over the past few decades, interventional neuroradiology (INR) has been a rapidly growing and evolving area of neurosurgery. Sevoflurane and propofol are both suitable anesthetics for INR procedures. While the depth of anesthesia is widely monitored, few studies have examined the patient state index (PSI) during clinical neuroanesthesia.

Objectives

This study aimed to investigate the differences in PSI values and in hemodynamic variables between sevoflurane anesthetic and propofol anesthetic during INR procedures.

Methods

We reviewed the medical charts of the patients who underwent embolization of a non-ruptured intracranial aneurysm by a single operator at a single university hospital from May 2013 to December 2014. Sixty-five patients were included and divided into two groups: S group (sevoflurane anesthesia, n = 33) vs. P group (propofol anesthesia, n = 32). The PSI values, hemodynamic variables, and use of hemodynamic drugs between two groups were analyzed.

Results

There were significant differences between the PSI values obtained through different perioperative stages in the two groups (P < 0.0001). During the procedure, the PSI values were significantly lower in the P group than in the S group (P = 0.000). The P group patients had a more prolonged extubation time (P = 0.005) and more phenylephrine requirement than the S group patients (P = 0.007). More anti-hypertensive drugs were administered to the patients in the S group during extubation (P = 0.0197).

Conclusions

The PSI can be used to detect changes in anesthetics concentration and in the depth of anesthesia during INR procedures. Although the extubation was faster under sevoflurane anesthetic, propofol anesthetic showed rather smoother recovery.

Practicalities of Total Intravenous Anesthesia and Target-controlled Infusion in Children

Propofol administered in conjunction with an opioid such as remifentanil is used to provide total intravenous anesthesia for children. Drugs can be given as infusion controlled manually by the physician or as automated target-controlled infusion that targets plasma or effect site. Smart pumps programmed with pharmacokinetic parameter estimates administer drugs to a preset plasma concentration. A linking rate constant parameter (keo) allows estimation of effect site concentration. There are two parameter sets, named after the first author describing them, that are commonly used in pediatric target-controlled infusion for propofol (Absalom and Kataria) and one for remifentanil (Minto). Propofol validation studies suggest that these parameter estimates are satisfactory for the majority of children. Recommended target concentrations for both propofol and remifentanil depend on the type of surgery, the degree of surgical stimulation, the use of local anesthetic blocks, and the ventilatory status of the patient. The use of processed electroencephalographic monitoring is helpful in pediatric total intravenous anesthesia and target-controlled infusion anesthesia, particularly in the presence of neuromuscular blockade.

Comparative Evaluation of a New Depth of Anesthesia Index in ConView® System and the Bispectral Index during Total Intravenous Anesthesia: A Multicenter Clinical Trial

The performance of a new monitor for the depth of anesthesia (DOA), the Depth of Anesthesia Index (Ai) based on sample entropy (SampEn), 95% spectral edge frequency (95%SEF), and burst suppression ratio (BSR) was evaluated compared to Bispectral Index (BIS) during total intravenous anesthesia (TIVA). 144 patients in six medical centers were enrolled. General anesthesia was induced with stepwise-increased target-controlled infusion (TCI) of propofol until loss of consciousness (LOC). During surgery propofol was titrated according to BIS. Both Ai and BIS were recorded. Primary outcomes: the limits of agreement between Ai and BIS were -17.68 and 16.49, which were, respectively, -30.0% and 28.0% of the mean value of BIS. Secondary outcomes: prediction probability (Pk) of BIS and Ai was 0.943 and 0.935 (p=0.102) during LOC and 0.928 and 0.918 (p=0.037) during recovery of consciousness (ROC). And the values of BIS and Ai were 68.19 and 66.44 at 50%LOC, and 76.65 and 78.60 at 50%ROC. A decrease or an increase of Ai was significantly greater than that of BIS when consciousness changes (during LOC: -9.13±10.20 versus -5.83±9.63, p<0.001; during ROC: 10.88±11.51 versus 5.32±7.53, p<0.001). The conclusion is that Ai has similar characteristic of BIS as a DOA monitor and revealed the advantage of SampEn for indicating conscious level. This trial is registered at Chinese Clinical Trial Registry with ChiCTR-IOR-16009471.

Propofol pharmacokinetic and pharmacodynamic profile and its electroencephalographic interaction with remifentanil in children

BACKGROUND

Propofol and remifentanil are commonly combined during total intravenous anesthesia. The impact of remifentanil in this relationship is poorly quantified in children. Derivation of an integrated pharmacokinetic and pharmacodynamic propofol model, containing remifentanil pharmacodynamic interaction information, enables propofol effect-site target-controlled infusion in children with a better prediction of its hypnotic effect when both drugs are combined.

AIMS

We designed this study to derive an integrated propofol pharmacokinetic-pharmacodynamic model in children and to describe the pharmacodynamic interaction between propofol and remifentanil on the electroencephalographic bispectral index effect.

METHODS

Thirty children (mean age: 5.45 years, range 1.3-11.9; mean weight: 23.5 kg, range 8.5-61) scheduled for elective surgery with general anesthesia were studied. After sevoflurane induction, maintenance of anesthesia was based on propofol and remifentanil. Blood samples to measure propofol concentration were collected during anesthesia maintenance and up to 6 hours in the postoperative period. Bispectral index data were continuously recorded throughout the study. A pharmacokinetic-pharmacodynamic model was developed using population modeling. The Greco model was used to examine the pharmacokinetic-pharmacodynamic interaction between propofol and remifentanil for BIS response RESULTS: Propofol pharmacokinetic data from a previous study in 53 children were pooled with current data and simultaneously analyzed. Propofol pharmacokinetics were adequately described by a three-compartment distribution model with first-order elimination. Theory-based allometric relationships based on TBW improved the model fit. The Greco model supported an additive interaction between propofol and remifentanil. Remifentanil showed only a minor effect in BIS response.

CONCLUSION

We have developed an integrated propofol pharmacokinetic-pharmacodynamic model that can describe the pharmacodynamic interaction between propofol and remifentanil for BIS response. An additive interaction was supported by our modeling analysis.

Duration of Pupillary Unresponsiveness to Light: A Physiological Adjunct to Electroencephalography and Motor Seizure Duration Monitoring During Electroconvulsive Therapy

BACKGROUND

During electroconvulsive therapy (ECT) sessions, we observed that the time taken for the return of pupillary response to light (ROPL) outlasted both the electroencephalography (EEG) and the motor seizure duration after the delivery of the electrical stimulus to produce convulsions.

OBJECTIVE

The objective of this study was to investigate whether ROPL can be used as a marker of cessation of seizure activity in the brain after ECT and also to study the effect of atropine premedication on seizure activity during ECT.

METHODS

Forty-one patients underwent 82 sessions of ECT in a cross-over design study. The duration of motor seizure, EEG seizure, and time for ROPL was observed and compared.

RESULTS

The ROPL consistently outlasted EEG and motor seizures; the difference in their mean durations was statistically significant P < 0.05. There was good correlation among the 3 parameters. Atropine premedication did not alter the seizure activity and ROPL after ECT.

CONCLUSIONS

The ROPL after ECT stimulus is a good bedside monitor for termination of seizure activity and can be a valuable adjunct to surface EEG in monitoring the duration of epileptic activity after delivery of ECT.

Does High Frequency Transcutaneous Electrical Nerve Stimulation (TENS) Affect EEG Gamma Band Activity?

BACKGROUND

Transcutaneous electrical nerve stimulation (TENS) is a noninvasive, inexpensive and safe analgesic technique used for relieving acute and chronic pain. However, despite all these advantages, there has been very little research into the therapeutic effects of TENS on brain activity. To the best of our knowledge, there is no evidence on the effect of high frequency TENS on the gamma band activity.

OBJECTIVE

Investigation of the effect of high frequency TENS on the electroencephalographic (EEG) gamma band activity after inducing ischemic pain in healthy volunteers is considered.

MATERIAL AND METHODS

The modified version of Submaximal effort tourniquet test was carried out to induce tonic pain in 15 right-handed healthy volunteers. The high frequency TENS (150µs in duration, frequency of 100 Hz) was applied for 20 minutes. Pain intensity was assessed at using Visual Analog Scale (VAS) in two conditions (after-pain, after-TENS). EEG gamma band activity was recorded by a 19-channel EEG in three conditions (baseline, after-pain and after- TENS). The repeated measure ANOVA and paired-sample T- tests were used for data analysis.

RESULTS

EEG analysis showed an increase in gamma total power after inducing pain as compared to baseline and a decrease after the application of TENS (mean±SD: .043±.029 to .088±.042 to .038±.022 μV² ).The analysis of VAS values demonstrated that the intensity of induced pain (mean±SD: 51.53±9.86) decreased after the application of TENS (mean±SD: 18.66±10.28). All these differences were statistically significant (p<.001).

CONCLUSION

The results of this study revealed that the high frequency TENS can reduce the enhanced gamma band activity after the induction of tonic pain in healthy volunteers. This finding might help as a functional brain biomarker which could be useful for pain treatment, specifically for EEG-based neurofeedback approaches.

Different effects of propofol and dexmedetomidine sedation on electroencephalogram patterns: Wakefulness, moderate sedation, deep sedation and recovery

Sedation induces changes in electroencephalography (EEG) dynamics. However, the distinct EEG dynamic characteristics at comparable sedation levels have not been well studied, resulting in potential interpretation errors in EEG monitoring during sedation. We aimed to analyze the EEG dynamics of dexmedetomidine and propofol at comparable sedation levels and to explore EEG changes with increased sedation levels for each agent. We measured the Bispectral Index (BIS) and 20-channel EEG under dexmedetomidine and propofol sedation from wakefulness, moderate sedation, and deep sedation to recovery in healthy volunteers (n = 10) in a randomized, 2-day, crossover study. Observer's Assessment of Alertness and Sedation (OAA/S) score was used to assess sedation levels. Despite similar changes in increased delta oscillations, multiple differences in the EEG spatiotemporal dynamics were observed between these two agents. During moderate sedation, both dexmedetomidine and propofol induced increased spindle power; however, dexmedetomidine decreased the global alpha/beta/gamma power, whereas propofol decreased the alpha power in the occipital area and increased the global spindle/beta/gamma power. During deep sedation, dexmedetomidine was associated with increased fronto-central spindle power and decreased global alpha/beta/gamma power, but propofol was associated with increased theta/alpha/spindle/beta power, which was maximized in the frontal area. The transition of topographic alpha/spindle/beta power distribution from moderate sedation to deep sedation completely differed between these two agents. Our study demonstrated that there was a distinct hierarchy of EEG changes with increased sedation depths by propofol and dexmedetomidine. Differences in EEG dynamics at the same sedation level might account for differences in the BIS value and reflect the different sedation mechanisms. EEG-based clinical sedation monitoring should consider the effect of drug types on EEG dynamics.

Abnormally low Bispectral index and severe hypoglycemia during maintenance of and recovery from general anesthesia in diabetic retinopathy surgery: two case reports

Background

Hypoglycemia is one of the most fatal complications during the perioperative period. General anesthesia or sedation can mask a hypoglycemia-altered mental status. Acute hypoglycemia might result in permanent brain injury. There is no way to detect hypoglycemia during general anesthesia, except for intermittent blood glucose monitoring.

Case presentation

Hypoglycemia is associated with changes in electroencephalogram readings. Here, we report two cases of patients with an abnormally low Bispectral Index (BIS) associated with diabetic retinopathy surgery, one in the recovery stage of general anesthesia and the other in the maintenance of general anesthesia. Hemodynamics were stable. Severe hypoglycemia (1.6 mmol/L and 2.2 mmol/L) was then detected. BIS increased with the correction of severe hypoglycemia.

Conclusions

For diabetic patients, when the intraoperative BIS value is abnormally low, hypoglycemia should be considered. Severe hypoglycemia may be presented in BIS monitoring during general anesthesia.

Simultaneous Video-EEG-ECG Monitoring to Identify Neurocardiac Dysfunction in Mouse Models of Epilepsy

In epilepsy, seizures can evoke cardiac rhythm disturbances such as heart rate changes, conduction blocks, asystoles, and arrhythmias, which can potentially increase risk of sudden unexpected death in epilepsy (SUDEP). Electroencephalography (EEG) and electrocardiography (ECG) are widely used clinical diagnostic tools to monitor for abnormal brain and cardiac rhythms in patients. Here, a technique to simultaneously record video, EEG, and ECG in mice to measure behavior, brain, and cardiac activities, respectively, is described. The technique described herein utilizes a tethered (i.e., wired) recording configuration in which the implanted electrode on the head of the mouse is hard-wired to the recording equipment. Compared to wireless telemetry recording systems, the tethered arrangement possesses several technical advantages such as a greater possible number of channels for recording EEG or other biopotentials; lower electrode costs; and greater frequency bandwidth (i.e., sampling rate) of recordings. The basics of this technique can also be easily modified to accommodate recording other biosignals, such as electromyography (EMG) or plethysmography for assessment of muscle and respiratory activity, respectively. In addition to describing how to perform the EEG-ECG recordings, we also detail methods to quantify the resulting data for seizures, EEG spectral power, cardiac function, and heart rate variability, which we demonstrate in an example experiment using a mouse with epilepsy due to Kcna1 gene deletion. Video-EEG-ECG monitoring in mouse models of epilepsy or other neurological disease provides a powerful tool to identify dysfunction at the level of the brain, heart, or brain-heart interactions.

Motor imagery learning across a sequence of trials in stroke patients

PURPOSE

In brain-computer interfaces (BCIs), electrical brain signals during motor imagery are utilized as commands connecting the brain to a computer. To use BCI in patients with stroke, unique brain signal changes should be characterized during motor imagery process. This study aimed to examine the trial-dependent motor-imagery-related activities in stroke patients.

METHODS

During the recording of electroencephalography (EEG) signals, 12 chronic stroke patients and 11 age-matched healthy controls performed motor imagery finger tapping at 1.3 sec intervals. Trial-dependent brain signal changes were assessed by analysis of the mu and beta bands.

RESULTS

Neuronal activity in healthy controls was observed over bilateral hemispheres at the mu and beta bands regardless of changes in the trials, whereas neuronal activity in stroke patients was mainly seen over the ipsilesional hemisphere at the beta band. With progression to repeated trials, healthy controls displayed a decrease in cortical activity in the contralateral hemisphere at the mu band and in bilateral hemispheres at the beta band. In contrast, stroke patients showed a decreasing trend in cortical activity only over the ipsilesional hemisphere at the beta band.

CONCLUSIONS

Trial-dependent changes during motor imagery learning presented in a different manner in stroke patients. Understanding motor imagery learning in stroke patients is crucial for enhancing the effectiveness of motor-imagery-based BCIs.

A Prospective Study of Age-dependent Changes in Propofol-induced Electroencephalogram Oscillations in Children

BACKGROUND

In adults, frontal electroencephalogram patterns observed during propofol-induced unconsciousness consist of slow oscillations (0.1 to 1 Hz) and coherent alpha oscillations (8 to 13 Hz). Given that the nervous system undergoes significant changes during development, anesthesia-induced electroencephalogram oscillations in children may differ from those observed in adults. Therefore, we investigated age-related changes in frontal electroencephalogram power spectra and coherence during propofol-induced unconsciousness.

METHODS

We analyzed electroencephalogram data recorded during propofol-induced unconsciousness in patients between 0 and 21 yr of age (n = 97), using multitaper spectral and coherence methods. We characterized power and coherence as a function of age using multiple linear regression analysis and within four age groups: 4 months to 1 yr old (n = 4), greater than 1 to 7 yr old (n = 16), greater than 7 to 14 yr old (n = 30), and greater than 14 to 21 yr old (n = 47).

RESULTS

Total electroencephalogram power (0.1 to 40 Hz) peaked at approximately 8 yr old and subsequently declined with increasing age. For patients greater than 1 yr old, the propofol-induced electroencephalogram structure was qualitatively similar regardless of age, featuring slow and coherent alpha oscillations. For patients under 1 yr of age, frontal alpha oscillations were not coherent.

CONCLUSIONS

Neurodevelopmental processes that occur throughout childhood, including thalamocortical development, may underlie age-dependent changes in electroencephalogram power and coherence during anesthesia. These age-dependent anesthesia-induced electroencephalogram oscillations suggest a more principled approach to monitoring brain states in pediatric patients.

Electroencephalographic study of chlorpromazine alone or combined with alpha-lipoic acid in a model of schizophrenia induced by ketamine in rats

Schizophrenia is characterized by behavioral symptoms, brain function impairments and electroencephalographic (EEG) changes. Dysregulation of immune responses and oxidative imbalance underpins this mental disorder. The present study aimed to investigate the effects of the typical antipsychotic chlorpromazine (CP) alone or combined with the natural antioxidant alpha-lipoic acid (ALA) on changes in the hippocampal average spectral power induced by ketamine (KET). Three days after stereotactic implantation of electrodes, male Wistar rats were divided into groups treated for 10 days with saline (control) or KET (10 mg/kg, IP). CP (1 or 5 mg/kg, IP) alone or combined with ALA (100 mg/kg, P.O.) was administered 30 min before KET or saline. Hippocampal EEG recordings were taken on the 1st, 5th and 10th days of treatment immediately after the last drug administration. KET significantly increased average spectral power of delta and gamma-high bands on the 5th and 10th days of treatment when compared to control. Gamma low-band significantly increased on the 1st, 5th and 10th days when compared to control group. This effect of KET was prevented by CP alone or combined with ALA. Indeed, the combination of ALA 100 + CP1 potentiated the inhibitory effects of CP1 on gamma low-band oscillations. In conclusion, our results showed that KET presents excitatory and time-dependent effects on hippocampal EEG bands activity. KET excitatory effects on EEG were prevented by CP alone and in some situations potentiated by its combination with ALA.

Bispectral index under propofol anesthesia in children: a comparative randomized study between TIVA and TCI

BACKGROUND

In children, only a few studies have compared different modes of propofol infusion during a total intravenous anesthesia (TIVA) with propofol and remifentanil. The aim of this study was to compare Bispectral Index (BIS) profiles (percentage of time spent at adequate BIS values) between four modes of propofol infusion: titration of the infusion rate on clinical signs (TIVA0 ), titration of the infusion rate on the BIS (TIVABIS ), target controlled infusion (TCI) guided by the BIS either with the Kataria model (TCI KBIS ) or the Schnider model (TCI SBIS ).

METHODS

Sixty-six children (aged from 4 to 14 years) were prospectively randomized into one of the four groups. In the TIVA0 group, the anesthesiologist was blinded to the BIS. In each group, the percentage of time with adequate BIS values (45-55), the bias, and imprecision were calculated.

RESULTS

The propofol consumption was similar in the four groups. During the maintenance phase, the percentage of time spent in the targeted BIS range was significantly lower in the TIVA0 group compared to the three other groups (TIVA0 : 31% ± 22, TIVABIS : 59% ± 17, TCI KBIS : 53% ± 12, TCI SBIS : 56% ± 17). The bias was not statistically different between the four groups, but the imprecision was larger for the TIVA0 group. Compared to the Kataria model, the Schnider model was associated with shorter time delay to reach the desired BIS, to eyes opening, and to tracheal extubation.

CONCLUSIONS

Propofol administration using manual infusion guided by clinical signs was associated with higher risks of over- or underdosage when compared to BIS-guided administrations. When propofol infusion was guided by the BIS, no major difference was found between TIVA and TCI (either with the Kataria or the Schnider model). This study highlights the need of a pharmacodynamic feedback during propofol anesthesia in children.

Sleep/Wake Modulation of Polysomnographic Patterns has Prognostic Value in Pediatric Unresponsive Wakefulness Syndrome

STUDY OBJECTIVE

Sleep patterns of pediatric patients in unresponsive wakefulness syndrome (UWS) have been poorly investigated, and the prognostic potential of polysomnography (PSG) in these subjects is still uncertain. The goal of the study was to identify quantitative PSG indices to be applied as possible prognostic markers in pediatric UWS.

METHODS

We performed PSG in 27 children and adolescents with UWS due to acquired brain damage in the subacute phase. Patients underwent neurological examination and clinical assessment with standardized scales. Outcome was assessed after 36 mo. PSG tracks were scored for sleep stages and digitally filtered. The spectral difference between sleep and wake was computed, as the percent difference at specific spectral frequencies. We computed (1) the ratio between percent power in the delta and alpha frequency bands, (2) the ratio between alpha and theta frequency bands, and (3) the power ratio index, during wake and sleep, as proposed in previous literature. The predictive role of several clinical and PSG measures was tested by logistic regression.

RESULTS

Correlation was found between the differential measures of electroencephalographic activity during sleep and wake in several frequency bands and the clinical scales (Glasgow Outcome Score, Level of Cognitive Functioning Assessment Scale, and Disability Rating Scale) at follow-up; the Sleep Patterns for Pediatric Unresponsive Wakefulness Syndrome (SPPUWS) scores correlated with the differential measures, and allowed outcome prediction with 96.3% of accuracy.

CONCLUSIONS

The differential measure of electroencephalographic activity during sleep and wake in the beta band and, more incisively, SPPUWS can help in determining the capability to recover from pediatric UWS well before the confirmation provided by suitable clinical scales.

Polysomnographic Sleep Patterns in Children and Adolescents in Unresponsive Wakefulness Syndrome

OBJECTIVES

We aimed (i) to search for qualitative sleep patterns for pediatric unresponsive wakefulness syndrome (SPPUWS) in prolonged polysomnographic (PSG) recordings in children and adolescents with subacute severe disorders of consciousness due to an acquired brain damage; (ii) to investigate the clinical relevance of SPPUWS and of possible neurophysiological markers (rapid eye movement sleep and sleep spindles) in PSG recordings of pediatric patients with unresponsive wakefulness syndrome (UWS).

METHODS

We performed a PSG study in 27 children with UWS due to acquired brain damage in the subacute phase. Patients received a full neurological examination and a clinical assessment with standardized scales. In addition, outcome was assessed after 36 months.

RESULTS

We identified 6 PSG patterns (SPPUWS) corresponding to increasing neuroelectrical complexity. The presence of an organized sleep pattern, as well as rapid eye movement sleep and sleep spindles, in the subacute stage appeared highly predictive of a more favorable outcome. Correlation was found between SPPUWS and recovery, as assessed by several clinical and rehabilitation scales.

CONCLUSIONS

Polysomnography can be used as a prognostic tool, as it can help determine the capability to recover from a pediatric UWS and predict outcome well before the confirmation provided by suitable clinical scales.

Spindle Oscillations in Sleep Disorders: A Systematic Review

Measurement of sleep microarchitecture and neural oscillations is an increasingly popular technique for quantifying EEG sleep activity. Many studies have examined sleep spindle oscillations in sleep-disordered adults; however reviews of this literature are scarce. As such, our overarching aim was to critically review experimental studies examining sleep spindle activity between adults with and without different sleep disorders. Articles were obtained using a systematic methodology with a priori criteria. Thirty-seven studies meeting final inclusion criteria were reviewed, with studies grouped across three categories: insomnia, hypersomnias, and sleep-related movement disorders (including parasomnias). Studies of patients with insomnia and sleep-disordered breathing were more abundant relative to other diagnoses. All studies were cross-sectional. Studies were largely inconsistent regarding spindle activity differences between clinical and nonclinical groups, with some reporting greater or less activity, while many others reported no group differences. Stark inconsistencies in sample characteristics (e.g., age range and diagnostic criteria) and methods of analysis (e.g., spindle bandwidth selection, visual detection versus digital filtering, absolute versus relative spectral power, and NREM2 versus NREM3) suggest a need for greater use of event-based detection methods and increased research standardization. Hypotheses regarding the clinical and empirical implications of these findings, and suggestions for potential future studies, are also discussed.

Age-dependent electroencephalogram (EEG) patterns during sevoflurane general anesthesia in infants

Electroencephalogram (EEG) approaches may provide important information about developmental changes in brain-state dynamics during general anesthesia. We used multi-electrode EEG, analyzed with multitaper spectral methods and video recording of body movement to characterize the spatio-temporal dynamics of brain activity in 36 infants 0-6 months old when awake, and during maintenance of and emergence from sevoflurane general anesthesia. During maintenance: (1) slow-delta oscillations were present in all ages; (2) theta and alpha oscillations emerged around 4 months; (3) unlike adults, all infants lacked frontal alpha predominance and coherence. Alpha power was greatest during maintenance, compared to awake and emergence in infants at 4-6 months. During emergence, theta and alpha power decreased with decreasing sevoflurane concentration in infants at 4-6 months. These EEG dynamic differences are likely due to developmental factors including regional differences in synaptogenesis, glucose metabolism, and myelination across the cortex. We demonstrate the need to apply age-adjusted analytic approaches to develop neurophysiologic-based strategies for pediatric anesthetic state monitoring.

Propofol concentration to induce general anesthesia in children aged 3-11 years with the Kataria effect-site model

BACKGROUND

The propofol pharmacokinetic model derived by Kataria et al. was recently modified to perform effect-site target-controlled infusion (TCI). Effect-site concentration (Ce) targets to induce general anesthesia with this model in children have not been described. The aim of this study was to identify propofol Ce targets associated with success rates of 50% (Ce50) and 95% (Ce95) among children 3-11 years of age.

METHODS

Forty-two children were assigned to one of seven groups of six patients each according to propofol target Ce. After fentanyl administration propofol TCI was started with an assigned Ce target. A successful response was defined as loss of eyelash reflex and bispectral index < 50, 45 s after reaching the assigned Ce. Logistic regression analysis was performed to calculate propofol Ce50 and Ce95.

RESULTS

Twenty-eight children had a successful response with the assigned propofol Ce. In these patients, a significant decrease in mean arterial blood pressure (79-59, P < 0.0001) and in heart rate (95-83, P < 0.0001) was observed. Propofol Ce and age showed a statistically significant effect in the logistic regression model. The overall calculated propofol Ce50 and Ce95 were 3.8 μg·ml(-1) (95% CI: 3.1-4.4 μg·ml(-1) ) and 6.1 μg·ml(-1) (95% CI: 4.6-7.6 μg·ml(-1) ), respectively.

CONCLUSION

Our results identified useful propofol targets to be used with the Kataria effect-site model to induce anesthesia in children between 3 and 11 years. The recommended targets should be reduced progressively with increasing age most probably due to PK model misspecifications.

Voxel-based dipole orientation constraints for distributed current estimation

Distributed electroencephalography source localization is a highly ill-posed problem. With measurements on the order of 10(2), and unknowns in the range of 10(4)-10(5), the range of feasible solutions is quite large. One approach to reducing ill-posedness is to intelligently reduce the number of unknowns. Restricting solutions to gray matter is one approach. A further step is to use the anatomy of each patient to identify and constrain the orientation of the dipole within each voxel. While dipole orientation constraints for cortical patch-based approaches have been proposed, to our knowledge, no solutions for full volumetric localizations have been presented. Patch techniques account for patch surface area, but place dipoles only on the surface, rather than throughout the cortex. Variability in human cortical thickness means that thicker regions of cortex will potentially contribute more to the EEG signal, and should be accounted for in modeling. Additionally, patch models require cortical surface identification techniques, which can separate them from the extensive literature on voxel-based MR image processing, and require additional adaptation to incorporate more complex information. We present a volumetric approach for computing voxel-based distributed estimates of cortical activity with constrained dipole orientations. Using a tissue thickness estimation approach, we obtain estimates of the cortical surface normal at each voxel. These let us constrain the inverse problem, and yield localizations with reduced spatial blurring and better identification of signal magnitude within the cortex. This is demonstrated for a series of simulated and experimental data using patient-specific bioelectric models.

Electroencephalography and analgesics

To assess centrally mediated analgesic mechanisms in clinical trials with pain patients, objective standardized methods such as electroencephalography (EEG) has many advantages. The aim of this review is to provide the reader with an overview of present findings in analgesics assessed with spontaneous EEG and evoked brain potentials (EPs) in humans. Furthermore, EEG methodologies will be discussed with respect to translation from animals to humans and future perspectives in predicting analgesic efficacy. We searched PubMed with MeSH terms 'analgesics', 'electroencephalography' and 'evoked potentials' for relevant articles. Combined with a search in their reference lists 15 articles on spontaneous EEG and 55 papers on EPs were identified. Overall, opioids produced increased activity in the delta band in the spontaneous EEG, but increases in higher frequency bands were also seen. The EP amplitudes decreased in the majority of studies. Anticonvulsants used as analgesics showed inconsistent results. The N-methyl-D-aspartate receptor antagonist ketamine showed an increase in the theta band in spontaneous EEG and decreases in EP amplitudes. Tricyclic antidepressants increased the activity in the delta, theta and beta bands in the spontaneous EEG while EPs were inconsistently affected. Weak analgesics were mainly investigated with EPs and a decrease in amplitudes was generally observed. This review reveals that both spontaneous EEG and EPs are widely used as biomarkers for analgesic drug effects. Methodological differences are common and a more uniform approach will further enhance the value of such biomarkers for drug development and prediction of treatment response in individual patients.