The impact of age on bispectral index values and EEG bispectrum during anaesthesia with desflurane and halothane in children

A practical guide for anesthetic management during intraoperative motor evoked potential monitoring

Postoperative motor dysfunction can develop after spinal surgery, neurosurgery and aortic surgery, in which there is a risk of injury of motor pathway. In order to prevent such devastating complication, intraoperative monitoring of motor evoked potentials (MEP) has been conducted. However, to prevent postoperative motor dysfunction, proper understanding of MEP monitoring and proper anesthetic managements are required. Especially, a variety of anesthetics and neuromuscular blocking agent are known to attenuate MEP responses. In addition to the selection of anesthetic regime to record the baseline and control MEP, the measures to keep the level of hypnosis and muscular relaxation at constant are crucial to detect the changes of MEP responses after the surgical manipulation. Once the changes of MEP are observed based on the institutional alarm criteria, multidisciplinary team members should share the results of MEP monitoring and respond to check the status of monitoring and recover the possible motor nerve injury. Prevention of MEP-related adverse effects is also important to be considered. The Working Group of Japanese Society of Anesthesiologists (JSA) developed this practical guide aimed to help ensure safe and successful surgery through appropriate anesthetic management during intraoperative MEP monitoring.

Variation of bispectral index in children aged 1-12 years under propofol anesthesia: an observational study

Background

The use of the bispectral index (BIS) is widespread in pediatric anesthesia, but few studies have attempted to perform a detailed evaluation of how BIS varies according to age in children under propofol anesthesia. This prospective study aimed to explore the exact relationship between BIS value and the age of 1- to 12-year-old children under propofol anesthesia.

Methods

This study enrolled 165 children (1 < yr. ≤ 12), scheduled for surgery under anesthesia, and divided them into 11 age groups. Of the 165 participants, 157 completed the study protocol. All patients were anesthetized with propofol for over 30 s. An observation period of 4 min followed. BIS values were recorded at 0 (immediately after propofol injection), 30, 40, 50, 60, 90, 120, 180, and 240 s after the injection. BIS values at each time point corresponding to the 11 age groups were compared using repeated measures ANOVA.

Results

BIS values significantly differed among the nine time points (p < 0.01) as well as among the different age groups (p < 0.01) after propofol administration. Post-hoc Bonferroni tests showed a difference in BIS values between groups 1–4 (1 < yr. ≤ 5) and groups 5–11(5 < yr. ≤ 12). BIS values were lower in the latter than in the former, from 50 to 240 s. The minimum BIS values in group 1 < yr. ≤ 5 and in group 5 < yr. ≤ 12 were recorded at 60 s as 49 ± 17 and 35 ± 14, respectively.

Conclusions

During propofol anesthesia, the BIS values were closely related to age, which can be divided into two groups: 1 < yr. ≤ 5 and 5 < yr. ≤ 12. BIS values of the older age group were lower than those of the younger age group at the same time points.

Trial registration

Registration number: chictr-roc-16008630. Registered on 12 June 2016. Retrospectively registered.

Minimum Alveolar Concentration of Desflurane for Maintaining BIS Below 50 in Children and Effect of Caudal Analgesia on it

Context:

Neuraxial techniques have sedative properties secondary to decreased inputs from sensory and motor afferents. We hypothesized that caudal analgesia decreases the requirement of desflurane as measured by bispectral index (BIS).

Aims:

This study aims to determine the minimum alveolar concentration (MAC) of desflurane for maintaining BIS below 50 (MACBIS₅₀) in children undergoing infraumbilical surgeries with laryngeal mask airway (LMA) and study the effect of caudal analgesia on the same.

Settings and Design:

This is prospective and observational study.

Subjects and Methods:

Thirty-nine American Society of Anesthesiologists physical status Classes I and II children in between 1 and 8 years of age undergoing elective infraumbilical surgery under general anesthesia were allocated randomly into two groups (Group C and Group D) after induction with sevoflurane and LMA insertion. In Group C, caudal block was performed with 0.75 mL/kg of 0.25% bupivacaine and BIS values were recorded after 10 min for 1 min at 10 s intervals. In Group D, BIS was recorded for desflurane for 1 min at 10 s intervals followed by a caudal block with the same dose.

Statistical Analysis Used:

Dixon up-down method with a step size of 0.5%, and probit analysis were used for analysis.

Results:

A total of 39 patients were enrolled. MAC of desflurane for maintaining MACBIS₅₀ was 5.57 (95% confidence interval [CI] 5.22–5.95) in Group D and 4.31 (95% CI 3.12–5.08) in Group C. The use of caudal anesthesia lowered the MAC of desflurane for maintaining MACBIS₅₀ in children by 22.36% (P < 0.001).

Conclusions:

The use of caudal analgesia significantly reduced MAC of desflurane for maintaining MACBIS₅₀ in children undergoing infraumbilical surgeries using LMA.

Intraoperative feasibility of bulbocavernosus reflex monitoring during untethering surgery in infants and children

Bulbocavernosus reflex (BCR) monitoring is used to assess the integrity of urinary and bowel function. In this study, we evaluated the feasibility of BCR monitoring during untethering surgery in infants and children to predict postoperative urinary and bowel dysfunction. The records of 22 patients ranging from 4 days to 10 years old (mean 2.7 ± 3.3 years) were reviewed. Anesthesia was maintained by propofol or sevoflurane/opioid without neuromuscular blockade. BCR waveforms induced by electrical stimulation (20-40 mA, train-of-four pulses with 500 Hz) to the penis or clitoris were recorded from bilateral external anal sphincters. To assess the sensitivity and specificity of BCR monitoring, we investigated the association between a significant continuous decrease in BCR amplitude at the end of surgery and postoperative urinary and bowel dysfunction after surgery. Reproducible baseline BCR waveforms were successfully recorded in 20 of 22 patients (90.9%). A significant continuous decrease in BCR amplitude was observed in 8 patients. The results of intraoperative BCR monitoring included three true-positives, twelve true-negatives, five false-positives, and zero false-negatives. Therefore, the sensitivity and specificity of BCR monitoring used to predict postoperative urinary and bowel dysfunction were 100 and 70.6%, respectively. BCR monitoring during untethering surgery in infants and children under general anesthesia was found to be a feasible method to prevent postoperative urinary and bowel dysfunction.

Effect of age on the performance of bispectral and entropy indices during sevoflurane pediatric anesthesia: a pharmacometric study

BACKGROUND

Bispectral index (BIS) and entropy monitors have been proposed for use in children, but research has not supported their validity for infants. However, effective monitoring of young children may be even more important than for adults, to aid appropriate anesthetic dosing and reduce the chance of adverse consequences. This prospective study aimed to investigate the relationships between age and the predictive performance of BIS and entropy monitors in measuring the anesthetic drug effects within a pediatric surgery setting.

METHODS

We concurrently recorded BIS and entropy (SE/RE) in 48 children aged 1 month-12 years, undergoing general anesthesia with sevoflurane and fentanyl. Nonlinear mixed effects modeling was used to characterize the concentration-response relationship independently between the three monitor indicators with sevoflurane. The model's goodness-of-fit was assessed by prediction-corrected visual predictive checks. Model fit with age was evaluated using absolute conditional individual weighted residuals (|CIWRES|). The ability of BIS and entropy monitors to describe the effect of anesthesia was compared with prediction probabilities (P_K ) in different age groups. Intraoperative and awakening values were compared in the age groups. The correlation between BIS and entropy was also calculated.

RESULTS

|CIWRES| vs age showed an increasing trend in the model's accuracy for all three indicators. P_K probabilities were similar for all three indicators within each age group, though lower in infants. The linear correlations between BIS and entropy in different age groups were lower for infants. Infants also tended to have lower values during surgery and at awakening than older children, while toddlers had higher values.

CONCLUSIONS

Performance of both monitors improves as age increases. Our results suggest a need for the development of new monitor algorithms or calibration to better account for the age-specific EEG dynamics of younger patients.

Dexmedetomidine Injection during Strabismus Surgery Reduces Emergence Agitation without Increasing the Oculocardiac Reflex in Children: A Randomized Controlled Trial

Objective

Dexmedetomidine is known to reduce the incidence of emergence agitation, which is a common complication after inhalational anesthesia like sevoflurane or desflurane in children. However, the dose of dexmedetomidine used for this purpose is reported variously and the most effective dose is not known. In this study, we tried to find the most effective dose of dexmedetomidine to reduce the incidence of emergence agitation in children undergoing strabismus surgery without the complications like oculocardiac reflex (OCR) or postoperative vomiting.

Methods

We randomized 103 pediatric patients aged 2–6 years and undergoing elective strabismus surgery into four groups. Anesthesia was induced with sevoflurane and maintained with desflurane. At the start of induction, dexmedetomidine, delivered at 0.25, 0.5, or 1 μg/kg, or saline was infused intravenously in the D0.25, D0.5, D1 groups, respectively. The primary outcome measure was the incidence of emergence agitation and the secondary outcome measure was the incidence of intraoperative OCR, postoperative vomiting, and desaturation events.

Results

The incidence of emergence agitation was 60, 48, 44, and 21% (P = 0.005) and the incidence of intraoperative OCR was 36, 36, 36, and 37% (P = 0.988) in the control, D0.25, D0.5, and D1 groups, respectively. And, postoperative vomiting rate and desaturation events were low in the all groups.

Conclusion

Dexmedetomidine decreased the incidence of emergence agitation without increasing intraoperative oculocardiac reflex. Dexmedetomidine delivered at 1 μg/kg was more effective at reducing emergence agitation than lower doses in children undergoing strabismus surgery under desflurane anesthesia.

Trial Registration

Clinical Research Information Service KCT0000141

Age-dependency of sevoflurane-induced electroencephalogram dynamics in children

BACKGROUND

General anaesthesia induces highly structured oscillations in the electroencephalogram (EEG) in adults, but the anaesthesia-induced EEG in paediatric patients is less understood. Neural circuits undergo structural and functional transformations during development that might be reflected in anaesthesia-induced EEG oscillations. We therefore investigated age-related changes in the EEG during sevoflurane general anaesthesia in paediatric patients.

METHODS

We analysed the EEG recorded during routine care of patients between 0 and 28 yr of age (n=54), using power spectral and coherence methods. The power spectrum quantifies the energy in the EEG at each frequency, while the coherence measures the frequency-dependent correlation or synchronization between EEG signals at different scalp locations. We characterized the EEG as a function of age and within 5 age groups: <1 yr old (n=4), 1-6 yr old (n=12), >6-14 yr old (n=14), >14-21 yr old (n=11), >21-28 yr old (n=13).

RESULTS

EEG power significantly increased from infancy through ∼6 yr, subsequently declining to a plateau at approximately 21 yr. Alpha (8-13 Hz) coherence, a prominent EEG feature associated with sevoflurane-induced unconsciousness in adults, is absent in patients <1 yr.

CONCLUSIONS

Sevoflurane-induced EEG dynamics in children vary significantly as a function of age. These age-related dynamics likely reflect ongoing development within brain circuits that are modulated by sevoflurane. These readily observed paediatric-specific EEG signatures could be used to improve brain state monitoring in children receiving general anaesthesia.

A pilot study to determine whether visually evoked hemodynamic responses are preserved in children during inhalational anesthesia

BACKGROUND

Anesthetic depth is an important parameter to monitor during surgery, yet remains difficult to quantify, particularly in young children where developmental changes influence the electroencephalogram. A more fundamental physiological response to stimulation is the increase in cerebral blood flow secondary to increased metabolic demand, referred to as flow-metabolism coupling (FMC) and measurable using near-infrared spectroscopy (NIRS). Little is known about the effect of anesthesia on FMC; therefore, we studied visually evoked hemodynamic responses (VEHRs) using NIRS in children undergoing general anesthesia for minor surgical procedures.

METHOD

We recruited 23 children (aged 2-5 years), undergoing surgery requiring general anesthesia. VEHRs were measured for 30 min using NIRS, including 5 min of baseline recording after anesthetic induction. Parameters recorded using NIRS included the concentrations of oxygenated (oxy), deoxygenated (deoxy), and total hemoglobin (Hb), which were separated into epochs for evoked response analysis after filtration of motion artifact and baseline drift. Goodness-of-fit statistics and classification rules were used to determine the existence of evoked responses, and a modified Gaussian equation was used to model each evoked response.

RESULTS

Near-infrared spectroscopy data were recorded in 20/23 children, of whom nine showed a VEHR. No responses were seen in the baseline control data. When examining the relationship between VEHR and anesthetic agents, we noted that for 8/10 patients in whom preoperative or intraoperative fentanyl were administered and VEHRs were absent.

CONCLUSION

We have shown that VEHRs can be detected using NIRS in some anesthetized children. Administration of fentanyl was associated with an absence of VEHRs. The mechanism underlying this association is unclear.

Multiple feature extraction and classification of electroencephalograph signal for Alzheimers' with spectrum and bispectrum

In this paper, we have combined experimental neurophysiologic recording and statistical analysis to investigate the nonlinear characteristic and the cognitive function of the brain. Spectrum and bispectrum analyses are proposed to extract multiple effective features of electroencephalograph (EEG) signals from Alzheimer's disease (AD) patients and further applied to distinguish AD patients from the normal controls. Spectral analysis based on autoregressive Burg method is first used to quantify the power distribution of EEG series in the frequency domain. Compared to the control group, the relative power spectral density of AD group is significantly higher in the theta frequency band, while lower in the alpha frequency bands. In addition, median frequency of spectrum is decreased, and spectral entropy ratio of these two frequency bands undergoes drastic changes at the P3 electrode in the central-parietal brain region, implying that the electrophysiological behavior in AD brain is much slower and less irregular. In order to explore the nonlinear high order information, bispectral analysis which measures the complexity of phase-coupling is further applied to P3 electrode in the whole frequency band. It is demonstrated that less bispectral peaks appear and the amplitudes of peaks fall, suggesting a decrease of non-Gaussianity and nonlinearity of EEG in ADs. Notably, the application of this method to five brain regions shows higher concentration of the weighted center of bispectrum and lower complexity reflecting phase-coupling by bispectral entropy. Based on spectrum and bispectrum analyses, six efficient features are extracted and then applied to discriminate AD from the normal in the five brain regions. The classification results indicate that all these features could differentiate AD patients from the normal controls with a maximum accuracy of 90.2%. Particularly, different brain regions are sensitive to different features. Moreover, the optimal combination of features obtained by discriminant analysis may improve the classification accuracy. These results demonstrate the great promise for scape EEG spectral and bispectral features as a potential effective method for detection of AD, which may facilitate our understanding of the pathological mechanism of the disease.

Sevoflurane-induced changes in infants' quantifiable electroencephalogram parameters

BACKGROUND

Electroencephalogram (EEG) based depth of anesthesia algorithms developed in the adult population have not demonstrated the same reliability when applied to infants. This may be due to frequency changes occurring in the EEG during development. Amplitude-integrated EEG (aEEG) is based primarily in the time domain and hence may have greater utility in infants.

OBJECTIVE

To investigate the relationship between age adjusted Minimal Alveolar Concentration (MAC) multiples and aEEG in children under 2 years of age.

METHODS

The aEEG, Spectral Edge Frequency 90% (SEF90) and Bispectral Index™ (BIS) were investigated in a prospective study of children <2 years of age. After anesthetic induction, and caudal block administration, EEG data were collected simultaneously with BrainZ BRM2™ and BIS™ monitors. Using a randomized crossover design, children received up to three age adjusted concentrations of sevoflurane: 0.75, 1 and 1.25 MAC. After 15 min of stable anesthetic delivery EEG readings were obtained. Prediction Probability (Pk ) and correlation coefficients were calculated for each EEG parameter.

RESULTS

From 51 children 102 stable anesthetics concentrations were obtained. For all age groups Pk of aEEG to multiple of age adjusted MAC was <0.72 indicating a poor predictive power for aEEG. In contrast for the SEF90 and BIS there was evidence for better predictive properties in children aged between 6 months and 2 years, with a Pk >0.81.

CONCLUSION

The aEEG is unlikely to be a useful measure of anesthesia depth in young children.

Higher-order spectrum in understanding nonlinearity in EEG rhythms

The fundamental nature of the brain's electrical activities recorded as electroencephalogram (EEG) remains unknown. Linear stochastic models and spectral estimates are the most common methods for the analysis of EEG because of their robustness, simplicity of interpretation, and apparent association with rhythmic behavioral patterns in nature. In this paper, we extend the use of higher-order spectrum in order to indicate the hidden characteristics of EEG signals that simply do not arise from random processes. The higher-order spectrum is an extension Fourier spectrum that uses higher moments for spectral estimates. This essentially nullifies all Gaussian random effects, therefore, can reveal non-Gaussian and nonlinear characteristics in the complex patterns of EEG time series. The paper demonstrates the distinguishing features of bispectral analysis for chaotic systems, filtered noises, and normal background EEG activity. The bispectrum analysis detects nonlinear interactions; however, it does not quantify the coupling strength. The squared bicoherence in the nonredundant region has been estimated to demonstrate nonlinear coupling. The bicoherence values are minimal for white Gaussian noises (WGNs) and filtered noises. Higher bicoherence values in chaotic time series and normal background EEG activities are indicative of nonlinear coupling in these systems. The paper shows utility of bispectral methods as an analytical tool in understanding neural process underlying human EEG patterns.

Comparison of use of an infrared anesthetic gas monitor and refractometry for measurement of anesthetic agent concentrations

OBJECTIVE

To assess agreement between anesthetic agent concentrations measured by use of an infrared anesthetic gas monitor (IAGM) and refractometry. SAMPLE-4 IAGMs of the same type and 1 refractometer.

PROCEDURES

Mixtures of oxygen and isoflurane, sevoflurane, desflurane, or N(2)O were used. Agent volume percent was measured simultaneously with 4 IAGMs and a refractometer at the common gas outlet. Measurements obtained with each of the 4 IAGMs were compared with the corresponding refractometer measurements via the Bland-Altman method. Similarly, Bland-Altman plots were also created with either IAGM or refractometer measurements and desflurane vaporizer dial settings.

RESULTS

Bias ± 2 SD for comparisons of IAGM and refractometer measurements was as follows: isoflurane, -0.03 ± 0.18 volume percent; sevoflurane, -0.19 ± 0.23 volume percent; desflurane, 0.43 ± 1.22 volume percent; and N(2)O, -0.21 ± 1.88 volume percent. Bland-Altman plots comparing IAGM and refractometer measurements revealed nonlinear relationships for sevoflurane, desflurane, and N(2)O. Desflurane measurements were notably affected; bias ± limits of agreement (2 SD) were small (0.1 ± 0.22 volume percent) at < 12 volume percent, but both bias and limits of agreement increased at higher concentrations. Because IAGM measurements did not but refractometer measurements did agree with the desflurane vaporizer dial settings, infrared measurement technology was a suspected cause of the nonlinear relationships.

CONCLUSIONS AND CLINICAL RELEVANCE

Given that the assumption of linearity is a cornerstone of anesthetic monitor calibration, this assumption should be confirmed before anesthetic monitors are used in experiments.

Equipment and monitoring--what is in the future to improve safety?

There have been a number of recent developments in the practice of anesthesia and intensive care aimed at improving outcome in terms of reducing both morbidity and mortality, as well as other less-defined factors, such as quality of service provision. Significant advances have been made in airway devices such as pediatric tracheal tube designs, Microcuff(®) tracheal tubes, and new laryngoscopes. Noninvasive monitoring devices, including continuous hemoglobin analysis and near infrared spectrometry, are being increasingly used in pediatric anesthesia. Other, 'scaled-down' versions from adult anesthesia care, however, have not universally been shown to result in improved safety and outcomes in pediatric anesthesia.

Anesthetic-specific electroencephalographic patterns during emergence from sevoflurane and isoflurane in infants and children

BACKGROUND

Devices that monitor the depth of anesthesia are increasingly used to titrate sedation and avoid awareness during anesthesia. Many of these monitors are based upon electroencephalography (EEG) collected from large adult reference populations and not pediatric populations (Anesthesiology, 86, 1997, 836; Journal of Anaesthesia, 92, 2004, 393; Anesthesiology, 99, 2003, 34). We hypothesized that EEG patterns in children would be different from those previously reported in adults and that they would show anesthetic-specific characteristics.

METHODS

This prospective observational study was approved by the Institutional Review Board, and informed written consent was obtained. Patients were randomized to receive maintenance anesthesia with isoflurane or sevoflurane. EEG data collection included at least 10 min at steady-state maintenance anesthesia. The EEG was recorded continuously through emergence until after extubation. A mixed model procedure was performed on global and regional power by pooled data analysis and by analyzing each anesthetic group separately. Statistical significance was defined as P < 0.05.

RESULTS

Thirty-seven children completed the study (ages 22 days-3.6 years). Isoflurane and sevoflurane had different effects on global and regional EEG power during emergence from anesthesia, and frontal predominance patterns were significantly different between these two anesthetic agents.

CONCLUSIONS

The principal finding of the present study was that there are anesthetic-specific and concentration-dependent EEG effects in children. Depth-of-anesthesia monitors that utilize algorithms based on the EEGs of adult reference populations therefore may not be appropriate for use in children.

Perioperative use of dexmedetomidine in an infant with familial dysautonomia

We present a case of a 10-month-old girl with familial dysautonomia, who was scheduled for the insertion of a gastrotomy tube via laparoscopy under general anaesthesia. We used a total i.v. anaesthetic technique including dexmedetomidine and titrated the drug to patients' haemodynamic status and BIS value. Vital signs remained virtually unchanged during the entire procedure, and the tracheal tube was removed at the end of the procedure. Postoperative course was uneventful. Careful planning of the anaesthetic management, understanding the physiological consequences, and being able to titrate the medications utilized are key to the decrease of complications encountered in these patients. We report the safe use of dexmedetomidine in an infant with this extremely rare condition.

Variation of bispectral index under TIVA with propofol in a paediatric population

BACKGROUND

In this prospective observational study, we aim to explore the relationship between age and bispectral index (BIS) values at different plasma concentrations of propofol.

METHODS

Fifty children aged from 3 to 15 yr were included. Anaesthesia was induced using a target-controlled infusion of propofol with the Kataria pharmacokinetic model together with a bolus of remifentanil followed by a continuous infusion rate at 0.2 microg kg(-1) min(-1). Target plasma propofol concentration was initially stabilized to 6 microg ml(-1) and continued for 6 min. The target was then decreased and stabilized to 4 microg ml(-1) and then to 2 microg ml(-1). BIS values, plasma propofol concentration, and EEG were continuously recorded. In order to explore the relationship between variations in propofol concentration and the EEG bispectrum, we used a multiple correspondence analysis (MCA). Results are shown in median (range).

RESULTS

We found no statistical difference between BIS values with propofol 6 microg ml(-1) [23 (12-40)] and 4 microg ml(-1) [28 (9-67)]. At 2 microg ml(-1), BIS was significantly different [52 (24-71)], but a significant correlation between the age of children and BIS values was found (r2=0.66; P<0.01). There was little change in children's position between 6 and 4 microg ml(-1) in the structure model of the MCA. From 4 to 2 microg ml(-1), the position of children moved only on axis 2.

CONCLUSIONS

These results showed the difficulty to interpret BIS values because of the absence of significant change for higher plasma propofol concentration variation or because of the link with age for the lower plasma concentration.

The electroencephalograph during anesthesia and emergence in infants and children

BACKGROUND

The characteristics of the electroencephalogram (EEG) during anesthesia in children are poorly described. An understanding of the EEG during anesthesia may help explain and predict the performance of EEG-derived depth of anesthesia monitors in children. This study aims to describe the association between age and some basic characteristics of the EEG during nonstandardized anesthesia in children and infants.

METHODS

Sixty-four children aged 9 days to 12 years were enrolled in this observational physiological study. Anesthesia was given at the discretion of the anesthetist. EEG was recorded from after induction to emergence using a BRM2 brain monitor ''BrainZ Instruments, Auckland, New Zealand'' in parietal and frontal montages. For comparison, 90% spectral edge frequency (SEF-90) and power were determined at three points (equilibrium during anesthesia, when the volatile agent was discontinued and at emergence), and children were divided into three age groups (0-6 months, 6-24 months and 2-12 years).

RESULTS

Fifty-seven children had artifact-free EEG data. From equilibrium to emergence the mean forehead power decreased substantially in children aged 2-12 years (3171-153 microV(2), P < 0.001) and 6-24 months (756-140 microV(2), P < 0.001) but no difference was found in infants aged 0-6 months (93-63 microV(2), P = 0.4). From equilibrium to emergence mean forehead spectral edge frequency increased in children aged 2-12 years (10.8-13.7 Hz, P = 0.01) but no change was found in children aged 6-24 months (12.7-12.7 Hz, P = 0.9) or 0-6 months (9.45-7.26 Hz, P = 0.08). Throughout emergence, infants demonstrated a discontinuous EEG pattern with intermittent bursts separated with low amplitude.

CONCLUSIONS

During anesthesia, the EEG in infants is fundamentally different from the EEG in older children. This study supports the need for specific infant-derived algorithms if EEG-derived anesthesia depth monitors are to be used in infants.

Awareness, dreaming and unconscious memory formation during anaesthesia in children

Recent studies have reported an incidence of awareness in children of around 1%, while older studies reported incidences varying from 0% to 5%. Measuring awareness in children requires techniques specifically adapted to a child's cognitive development and variations in incidence may be partly explained by the measures used. The causes and consequences of awareness in children remain poorly defined, though a consistent finding is that many children do not seem distressed by their memories. There are, however, some published reports of persistent psychological symptoms after episodes of childhood awareness. Compared to explicit memory, implicit memory is more robust in young children; however there is no evidence yet for implicit memory formation during anaesthesia in children. Children less than 3 years of age do not form explicit memory, although toddlers, infants and even neonates have signs of consciousness and implicit memory formation. In these very young children the relevance of awareness remains largely unknown.

Brain activity modeling in general anesthesia: enhancing local mean-field models using a slow adaptive firing rate

In this paper, an enhanced local mean-field model that is suitable for simulating the electroencephalogram (EEG) in different depths of anesthesia is presented. The main building elements of the model (e.g., excitatory and inhibitory populations) are taken from Steyn-Ross [M. L. Steyn-Ross, Phys. Rev. E 64, 011917 (2001), D. A. Steyn-Ross, Phys. Rev. E 64, 011918 (2001)] and Bojak and Liley [I. Bojak and D. T. Liley, Phys. Rev. E 71, 041902 (2005)] mean-field models and a new slow ionic mechanism is included in the main model. Generally, in mean-field models, some sigmoid-shape functions determine firing rates of neural populations according to their mean membrane potentials. In the enhanced model, the sigmoid function corresponding to excitatory population is redefined to be also a function of the slow ionic mechanism. This modification adapts the firing rate of neural populations to slow ionic activities of the brain. When an anesthetic drug is administered, the slow mechanism may induce neural cells to alternate between two levels of activity referred to as up and down states. Basically, the frequency of up-down switching is in the delta band (0-4 Hz) and this is the main reason behind high amplitude, low frequency fluctuations of EEG signals in anesthesia. Our analyses show that the enhanced model may have different working states driven by anesthetic drug concentration. The model is settled in the up state in the waking period, it may switch to up and down states in moderate anesthesia while in deep anesthesia it remains in the down state.

Effect of age and sedative agent on the accuracy of bispectral index in detecting depth of sedation in children

OBJECTIVE

This study evaluated age- and sedative agent-related differences in bispectral index across observed sedation levels in a large sample of children < 18 years of age.

PATIENTS AND METHODS

With institutional review board approval and waiver of consent, data from 4 independently conducted studies were combined in a secondary analysis of 3373 observations from 248 children aged 1 month to 18 years. In these studies, bispectral index values of sedated children were recorded in a blinded fashion, and sedation depth was scored using the University of Michigan Sedation Scale (UMSS). Bispectral index was evaluated across UMSS scores for several age groups and during use of each sedative agent (with/without opioids).

RESULTS

There was a moderate inverse correlation between bispectral index and UMSS for all age groups. There were significant differences in bispectral index across UMSS and between each sedation level except UMSS 3 to 4 in all the age groups and UMSS 0 to 1 in infants. The mean bispectral index and the cutoff values on the receiver-operating-characteristic curve for mild, moderate, and deep sedation were significantly lower in infants < or = 6 months compared with older children at each sedation level. Bispectral index was reasonably sensitive and specific in differentiating mild (UMSS 0-1) from deeper (UMSS 3-4) levels of sedation but poorly differentiated between moderate and deep levels of sedation in all age groups. There was a moderate correlation between bispectral index and UMSS during the use of chloral hydrate, pentobarbital, propofol, and midazolam but poor correlation during ketamine or opioid use. Bispectral index values were significantly lower during deep sedation with propofol and pentobarbital compared with midazolam and chloral hydrate.

CONCLUSIONS

Our findings suggest that, although bispectral index may differentiate light from deep sedation in most children, bispectral index must be interpreted cautiously in sedated children, with particular consideration given to patient age and use of sedative agents.

Monitoring the anaesthetic depth in children - an update

PURPOSE OF REVIEW

There are several commercially available electroencephalogram-derived devices for monitoring anaesthesia depth. This article reviews all published studies describing their use in children; first assessing studies of performance in measuring anaesthesia depth in observational, physiological studies and then describing relevant outcome studies. There is also a brief discussion of why they might be useful, what physiological problems may arise and what the reader should be wary of in the methodology of these studies. The subject is approached from a clinical perspective.

RECENT FINDINGS

There are several physiological studies suggesting that for older children the bispectral index, entropy, Narcotrend index, cerebral state index and A-line ARX index all change with induction of anaesthesia, and have reasonable correlations with doses of anaesthetic agent. There is consistent evidence that the performances are substantially poorer in infants. Some of these devices have been demonstrated to reduce anaesthesia drug consumption and hasten recovery in older children.

SUMMARY

The bispectral index is the most widely studied, but at this stage there is no evidence to suggest any one device is substantially superior to any other. There may be a role emerging for their use in older children, but their use in infants cannot be supported.

Inhalation agents in pediatric anaesthesia – an update

PURPOSE OF REVIEW

To present the most recent publications on inhaled agents in children and their implications for clinical care.

RECENT FINDINGS

The roles of clonidine, dexmedetomidine, ketamine and nalbuphine in the treatment of emergence delirium after sevoflurane and desflurane are discussed. Bispectral index monitoring has generated several curious findings in children. Halothane consistently produced higher Bispectral index readings than equi-minimum-alveolar-concentration multiples of ether anesthetics. Bispectral index readings increased as the sevoflurane concentration increased beyond 3%. Inhalation agents may cause two serious complications when administered to children with Duchenne's muscular dystrophy: hyperkalemia in younger children and myocardial depression in adolescents. Recovery after desflurane anesthesia is more rapid than with the other ether anesthetics in infants and children. Single-breath inductions are of interest in children >6 years for rapid anesthesia induction.

SUMMARY

Sevoflurane and desflurane continue to challenge our abilities to anesthetize children safely and efficiently. Although transient emergence delirium after insoluble agents is a problem, several medications may be used to attenuate it. Inhaled agents must be used with caution in children with Duchenne's muscular dystrophy as hyperkalemia may occur in young males and myocardial depression in adolescents. Rapid recovery after desflurane and single-breath inductions with sevoflurane continue to fascinate clinicians.

[Awareness: a problem in paediatric anaesthesia?]

Intraoperative awareness has been reported to occur in 0.8-5.0% of paediatric patients undergoing anaesthesia and, therefore, seems to be more common than in adults (incidence 0.1-0.2%). In adult patients, the consequences of intraoperative awareness are well known and can be severe, in children, however, they have not yet been adequately studied. The causes for intraoperative awareness can be divided into three broad categories: First, no or only a light anaesthetic is given on purpose, second, an insufficient dose of an anaesthetic is given inadvertently, third, there is equipment malfunction or the anaesthesiologist makes an error. Unfortunately, especially in young children, painful interventions are still performed without adequate analgesia, e.g. awake intubation or fracture manipulation under midazolam sedation alone. The key issue is, however, that pharmacokinetics and pharmacodynamics change enormously from the 500 g preterm baby to the adolescent patient. Adequate dosing is much more difficult in paediatric patients compared to standard adult surgical patients. Solid knowledge of the pharmacokinetic and pharmacodynamic characteristics of commonly used drugs in different paediatric age groups, as well as aiming for perfection in daily care will help to reduce the incidence of awareness. Methods for monitoring the depth of hypnosis, e.g. the bispectral index, will be used increasingly, at least in children above 1 year of age. In addition to clinical parameters, they will hopefully help to further reduce the incidence of intraoperative awareness.