EEG variables as measures of arousal during propofol anaesthesia for general surgery in children: rational selection and age dependence

BACKGROUND: Clinical benefits of measuring processed EEG during anaesthesia in adults, such as improved recovery and reduced risk of awareness, may also be valid in children. This study evaluated a rational selection of EEG variables as measures of arousal during surgical anaesthesia in children. METHODS: Sixty children undergoing surgical anaesthesia with propofol and remifentanil were enrolled. The performance of 33 single EEG variables and bispectral index (BIS) was assessed by simultaneous analysis of prediction probability (Pk) of Children's Hospital of Wisconsin Sedation Scores and their signal-to-noise ratio (SNR). Variables performing best in Pk and SNR analysis were selected as potential measures of arousal. Their performance was investigated in five age groups, 0-1, 1-2, 2-5, 5-8, and 8-13 yr. RESULTS: Single EEG variables such as relative power from frequency bands 13-20 and 20-26 Hz, SEF95, and approximate entropy performed best with Pk>0.59 and SNR>5.50. The Pk and SNR of BIS were 0.71 and 15.76, respectively. Their performance was significantly better in children aged 1-13 yr than in 0-1 yr. CONCLUSIONS: BIS may provide a measure of arousal during propofol anaesthesia in children, but its accuracy is less in infants younger than 12 months. Single EEG variables such as high-frequency components of EEG, SEF95, and approximate entropy may be of limited value to detect arousal in the individual paediatric patient.     

Performance of entropy and Bispectral Index as measures of anaesthesia effect in children of different ages

Background. Entropy and Bispectral Index^TM (BIS^TM) have beenpromoted as EEG-based anaesthesia depth monitors. The EEG changeswith brain maturation, but there are limited published datadescribing the characteristics of entropy in children, and somedata suggest that BIS is less reliable in young children. Theaim of this study was to compare the performance of entropyas a measure of anaesthetic effect in different age groups.The performance of entropy was compared with BIS. Methods. Fifty-four children receiving a standard sevofluraneanaesthetic for cardiac catheter studies were enrolled. Theentropy and BIS were recorded pre-awakening and at 1.5%, 2%and 2.5% steady-state end-tidal sevoflurane concentrations.For analysis children were divided into four age groups: 0–1yr, 1–2 yr, 2–4 yr and 4–12 yr. Results. The pre-awakening values were obtained in 46 children.The median pre-awakening values for entropy and BIS varied significantlyacross ages with the values being lowest in the 0–1 yrage group (response entropy: 45 vs 84, 87 and 89, P=0.003; stateentropy: 36 vs 78, 74 and 77, P=0.009; BIS: 56 vs 78, 76.5 and72, P=0.02). Values were recorded at all three sevoflurane concentrationsin 48 children. Compared with older groups, the 0–1 yrage group had the least significant difference in BIS and entropywhen compared among different sevoflurane concentrations. Thecalculated sevoflurane concentrations to achieve mid-scale valuesof entropy and BIS were highest in the 1–2 yr age group,lower in the 0–1 yr age group and progressively lowerin the 2–4 and 4–12 yr age groups. Conclusions. For both entropy and BIS the measure of anaestheticeffect was significantly different for children aged <1 yrcompared with older children. There was no difference in performanceof entropy and BIS. Both should be used cautiously in smallchildren.      

Spectral entropy as a measure of hypnosis in children

BACKGROUND: The Datex-Ohmeda S/5 Entropy Module (Datex-Ohmeda Division, Instrumentarium Corp., Helsinki, Finland), using time-frequency balanced Spectral Entropy, is a novel tool for monitoring the hypnotic state during anesthesia. The Entropy Module produces two values, State Entropy (SE) and Response Entropy (RE), and in adults, it has been shown to measure reliably the hypnotic effects of various drugs. In children, Spectral Entropy has been only preliminary studied. The authors' aim was to study Spectral Entropy as a marker of hypnotic state during general anesthesia in infants and children. METHODS: Twenty infants (aged 1 month-1 yr) and 40 children (aged 1-15 yr) were anesthetized for surgery using standardized sevoflurane-nitrous oxide-based anesthesia. The relationships between SE, RE, or Bispectral Index (BIS) and (1) a modified Observer's Assessment of Alertness/Sedation Scale, (2) non-steady state end-tidal concentration of sevoflurane, (3) steady state end-tidal concentration of sevoflurane, and (4) hemodynamic values were calculated using prediction probability, nonlinear regression, and correlation coefficients, as appropriate. The performances of SE, RE, and BIS were compared. RESULTS: The prediction probability values (+/- SEM) of SE, RE, and BIS versus the modified Observer's Assessment of Alertness/Sedation Scale in the induction phase were 0.83 +/- 0.06, 0.88 +/- 0.06, and 0.87 +/- 0.08 for children and 0.76 +/- 0.08,0.79 +/- 0.08, and 0.73 +/- 0.10 for infants; values in the emergence phase were 0.68 +/- 0.05, 0.74 +/- 0.04, and 0.64 +/- 0.05 for children and 0.64 +/- 0.07, 0.69 +/- 0.06, and 0.72 +/- 0.06 for infants, respectively. SE, RE, and BIS values were inversely proportionally related to the end-tidal concentration of sevoflurane for children, but for infants, the correlation was much less clear. No significant correlations were found between SE, RE, or BIS values and the hemodynamic values. CONCLUSIONS: Spectral Entropy may be a useful tool for measuring the level of hypnosis in anesthetized children and seems to perform as well as BIS. In infants, the clinical usefulness of both these electroencephalogram-derived methods must be evaluated in further controlled studies.     

BIS and Entropy in the elderly

The interaction of many poorly defined, physiological, pharmacological, and pathological factors make titration of general anaesthesia in the elderly difficult. There may be a potential clinical benefit using the processed electroencephalogram (EEG) to monitor hypnotic level in this population. We prospectively studied 16 patients aged over 65 years having hip fractures repaired under general anaesthesia by experienced anaesthetists blinded to Bispectral Index (BIS(XP)) and Entropy values. Pre-induction EEG indices did not correlate with age or mini-mental state examination (MMSE). During maintenance of anaesthesia, BIS(XP) and Response Entropy (RE) values were within the recommended range of 40-60, 45% and 32% of the total time, respectively. BIS(XP) and Response Entropy (RE) values were above 60 for 11% and 13% of the total time, respectively, and below 40 for 44% and 55% of the total time, respectively. BIS(XP) correlated well with RE in 12 patients, but in the other four patients there was a difference of more than 20 points between BIS(XP) and RE.     

Spectral Entropy as a Measure of Hypnosis in Children

Background: The Datex-Ohmeda S/5 Entropy Module (Datex-Ohmeda Division, Instrumentarium Corp., Helsinki, Finland), using time-frequency balanced Spectral Entropy, is a novel tool for monitoring the hypnotic state during anesthesia. The Entropy Module produces two values, State Entropy (SE) and Response Entropy (RE), and in adults, it has been shown to measure reliably the hypnotic effects of various drugs. In children, Spectral Entropy has been only preliminary studied. The authors' aim was to study Spectral Entropy as a marker of hypnotic state during general anesthesia in infants and children.

Methods: Twenty infants (aged 1 month-1 yr) and 40 children (aged 1-15 yr) were anesthetized for surgery using standardized sevoflurane-nitrous oxide-based anesthesia. The relationships between SE, RE, or Bispectral Index (BIS) and (1) a modified Observer's Assessment of Alertness/Sedation Scale, (2) non-steady state end-tidal concentration of sevoflurane, (3) steady state end-tidal concentration of sevoflurane, and (4) hemodynamic values were calculated using prediction probability, nonlinear regression, and correlation coefficients, as appropriate. The performances of SE, RE, and BIS were compared.

Results: The prediction probability values (+/- SEM) of SE, RE, and BIS versus the modified Observer's Assessment of Alertness/Sedation Scale in the induction phase were 0.83 +/- 0.06, 0.88 +/- 0.06, and 0.87 +/- 0.08 for children and 0.76 +/- 0.08,0.79 +/- 0.08, and 0.73 +/- 0.10 for infants; values in the emergence phase were 0.68 +/- 0.05, 0.74 +/- 0.04, and 0.64 +/- 0.05 for children and 0.64 +/- 0.07, 0.69 +/- 0.06, and 0.72 +/- 0.06 for infants, respectively. SE, RE, and BIS values were inversely proportionally related to the end-tidal concentration of sevoflurane for children, but for infants, the correlation was much less clear. No significant correlations were found between SE, RE, or BIS values and the hemodynamic values.     

AEP-monitor/2 derived, composite auditory evoked potential index (AAI-1.6) and bispectral index as predictors of sevoflurane concentration in children

BACKGROUND: Level of anesthesia may be predicted with the auditory evoked potential or with passive processed electroencephalogram (EEG) parameters. Some previous reports suggest the passive EEG does not reliably predict level of anesthesia in infants. The AAI-1.6 is a relatively new index derived from the AEP/2 monitor. It combines auditory evoked potentials and passive EEG parameters into a single index. This study aimed to assess the AAI-1.6 as a predictor of level of anesthesia in infants and children. METHODS: Four infants aged less than 1 year, and five older children aged between 2 and 11 years were enrolled. They all had uniform sevoflurane anesthesia for cardiac catheterization. The AAI-1.6 and bispectral index (BIS) were recorded after achieving equilibrium at 1.5%, 2% and 2.5% sevoflurane, and immediately prior to awakening. The prediction coefficient (Pk) for BIS and AAI-1.6 was calculated and compared within each age group. RESULTS: The Pk for the AAI-1.6 was low in both 0-1 and 2-11 years age groups. In the 2-12 years group, the Pk for BIS was significantly higher than the Pk for the AAI-1.6 (Pk for BIS: 0.89, Pk for AAI-1.6: 0.53, P < 0.01). In contrast in the 0-1 year age group there was no evidence for a difference between the Pk for BIS and the Pk for the AAI-1.6 (Pk for BIS: 0.74, Pk for AAI-1.6: 0.53, P = 0.25). CONCLUSIONS: This preliminary study suggests AAI-1.6 is a poor predictor of sevoflurane concentration in infants and children.     

The correlation between bispectral index and airway reflexes with sevoflurane and halothane anaesthesia

Background: Unwanted airway reflexes such as laryngospasm are a frequent cause for concern in paediatric anaesthesia. They are more active during light anaesthesia. Bispectral index (BIS) is a recognized measure of anaesthetic effect. Ensuring adequate depth with the BIS may prevent these reflexes. This study investigates the relationship between BIS and a defined measure of airway reactivity. Methods: Sixty‐two children scheduled for direct laryngoscopy and bronchoscopy were enrolled in this prospective nonrandomized blinded study. They were induced and maintained with either sevoflurane or halothane. When depth of anaesthesia was judged deep enough on clinical grounds, the cords were sprayed with 2% lidocaine. Using an A2000 monitor, the BIS was recorded at the moment of spraying the cords. The anaesthetist was blinded to the BIS and noted whether or not spraying resulted in complete closure of the cords. Breath holding, desaturation and coughing were also recorded as secondary endpoints. Results: Using logistic regression there was a significant correlation between BIS and cord closure for halothane but not for sevoflurane (halothane Pseudo r² = 0.5, P = 0.003; sevoflurane Pseudo r² = 0.0004, P = 0.9). Although the study was not specifically designed to test for it, no difference was detected between agents in the incidence of cord closure (halothane 38%, sevoflurane 36%), or secondary endpoints (halothane 29%, sevoflurane 29%). Conclusions: The BIS may be useful to help prevent unwanted airway reflexes when using halothane but not with sevoflurane. The differing sites of anaesthetic action for sevoflurane and halothane may explain this result.     

The correlation of bispectral index with endtidal sevoflurane concentration and haemodynamic parameters in preschoolers

BACKGROUND: Bispectral index (BIS) is a signal processing device that potentially is a pharmacodynamic measure of the effects of anaesthesia on the central nervous system. METHODS: In this prospective blinded study, we investigated the pharmacodynamic relationship between BIS, haemodynamic changes during anaesthesia and endtidal nonsteady state concentrations of sevoflurane in 30 children, mean age 3.3 +/- 1.1 years, who were undergoing tonsillectomy and adenoidectomy. A standardized anaesthetic technique was used and included induction and maintenance with sevoflurane, nitrous oxide and oxygen. BIS, heart rate, mean arterial pressure (MAP) and endtidal sevoflurane (ETsevo) concentrations were continuously recorded and specifically noted at the time of intubation, placement of Dingman gag, incision of adenoid, adenoid out, incision of tonsil, tonsil one out, tonsil two out, last agent off, first spontaneous movement, first eye opening and extubation. The anaesthetist was blinded to BIS throughout the procedure. RESULTS: Using a Spearman correlation analysis, there was significant negative correlation between BIS and ETsevo concentrations (r=- 0.888, P < 0.01) and a pharmacodynamic relationship with EC50 (ETsevo at which BIS=50) of 1.48% (95% confidence interval 0.84-2.11). There was a weak negative correlation between sevoflurane and MAP (r=- 0.391, P < 0.01) but no significant correlation between sevoflurane and heart rate. CONCLUSIONS: In preschool children undergoing sevoflurane anaesthesia for tonsillectomy and adenoidectomy, endtidal sevoflurane concentrations are more closely correlated with BIS than with MAP or heart rate.     

Evaluation of the efficiency of heat and moisture exchangers during paediatric anaesthesia

This study evaluates the efficiency of heat and moisture exchangers (HMEs) in allowing adequate humidification and warming during anaesthesia in children. Eighteen paediatric patients undergoing anaesthesia were divided into two groups: group A ten patients: infants up to 10 kg-->Hygrobaby HME; group B 8 patients: children above 10 kg-->Hygroboy HME. The following parameters were evaluated: body temperature (bT), room temperature (rT), fresh gas temperature, HME warm-up time, inspired and expired gases temperature and humidity, conserving efficiency, and duration of anaesthesia. Gas temperatures were recorded by means of a recorder fitted with four thermal probes. Humidity values were mathematically derived. The correlation between efficiency and rT, bT, and fresh gas temperature was computed. In both groups the inspired gases temperatures were below 30 degrees C. Inspired absolute humidity was never more than 28 mgH2O.l(-1). The conserving efficiency was good (0.93 in both groups). A positive correlation was found between efficiency and fresh gas temperature. HMEs did not meet the minimum standards for humidity and heating during anaesthesia in children, although their conserving efficiency was found to be satisfactory.     

Time-frequency balanced spectral entropy as a measure of anesthetic drug effect in central nervous system during sevoflurane, propofol, and thiopental anesthesia

BACKGROUND: Time-frequency balanced spectral entropy of electroencephalogram (EEG) and frontal electromyogram (FEMG) is a novel measure of hypnosis during anesthesia. Two Entropy parameters are described: Response entropy (RE) is calculated from EEG and FEMG; and State Entropy (SE) is calculated mainly from EEG. This study was performed to validate their performance during transition from consciousness to unconsciousness under different anesthetic agents. METHODS: Response entropy, SE [S/5 Entropy Module, M-ENTROPY (later in text: Entropy), Datex-Ohmeda Division, Instrumentarium Corp., Helsinki, Finland] and BIS (BIS XP, A-2000, Aspect Medical Systems, Newton, MA) data were collected from 70 patients; 30 anesthetized with propofol 2 mg kg-1, 20 with sevoflurane inhalation, and 20 with thiopental 5 mg kg-1. Loss and regaining of consciousness (LOC, ROC) was tested every 10 s, and sensitivity, specificity, and prediction probability (Pk) were calculated. Behavior of the indices was studied. RESULTS: Sensitivity, specificity, and Pk values for consciousness were high and similar for all indices. During regaining of consciousness after propofol bolus, RE, SE, and BIS values recovered by 81 +/- 22%, 75 +/- 26%, and 59 +/- 18% (mean +/- SD), respectively, from the minimum relative to their baseline. After thiopental bolus, RE, SE, and BIS values recovered by 86+/-21%, 88 +/- 13%, and 63 +/- 14%, respectively. The relative rise was higher in RE and SE compared with BIS (P < 0.01). During deep levels of hypnosis, RE and SE decreased monotonously as a function of burst suppression ratio, while BIS showed biphasic behavior. On average, RE indicated emergence from anesthesia 11 s earlier than SE, and 12.4 s earlier than BIS. CONCLUSIONS: All indices, RE, SE, and BIS, distinguished excellently between conscious and unconscious states during propofol, sevoflurane, and thiopental anesthesia. During burst suppression, Entropy parameters RE and SE, but not BIS, behave monotonously. During regaining of consciousness after a thiopental or propofol bolus, RE and SE values recovered significantly closer to their baseline values than did BIS. Response entropy indicates emergence from anesthesia earlier than SE or BIS.     

Maintenance requirement of alcuronium in paediatric patients

Seventeen paediatric patients from 0.3 to 19 years old were studied to determine the individual dose-response curves and the maintenance requirements of alcuronium during N2O-O2-opioid anaesthesia. Alcuronium 300 micrograms/kg maintained the mean (SD) neuromuscular block at 90-95% for 62 34 min). This time was longest in patients of less than 1 year of age (92 min). The hourly maintenance requirement of alcuronium was 0.41 (0.12) times the individual ED95 dose. This value was comparable in infants, children and adolescents and indicates similar duration of effect of alcuronium in all paediatric age groups.     

The influence of age on EEG-based anaesthesia indices

Study objectiveIn the upcoming years there will be a growing number of elderly patients requiring general anaesthesia. As age is an independent risk factor for postoperative delirium (POD) the incidence of POD will increase concordantly. One approach to reduce the risk of POD would be to avoid excessively high doses of anaesthetics by using neuromonitoring to guide anaesthesia titration. Therefore, we evaluated the influence of patient's age on various electroencephalogram (EEG)-based anaesthesia indices.Design and patientsWe conducted an analysis of previously published data by replaying single electrode EEG episodes of maintenance of general anaesthesia from 180 patients (18–90 years; ASA I-IV) into the five different commercially available monitoring systems and evaluated their indices. We included the State/Response Entropy, Narcotrend, qCON/qNOX, bispectral index (BIS), and Treaton MGA-06. For a non-commercial comparison, we extracted the spectral edge frequency (SEF) from the BIS. To evaluate the influence of the age we generated linear regression models. We also assessed the correlation between the various indices.Main resultsDuring anaesthetic maintenance the values of the SEF, State/Response Entropy, qCON/qNOX and BIS all significantly increased (0.05 Hz/0.19–0.26 index points per year) with the patient's age (p < 0.001); whereas the Narcotrend did not change significantly with age (0.06 index points per year; p = 0.28). The index values of the Treaton device significantly decreased with age (−0.09 index points per year; p < 0.001). These findings were independent of the administered dose of anaesthetics.ConclusionsAlmost all current neuromonitoring devices are influenced by age, with the potential to result in inappropriately high dosage of anaesthetics. Therefore, anaesthesiologists should be aware of this phenomenon, and the next generation of monitors should correct for these changes.     

Comparative evaluation of Bispectral Index and Narcotrend Index in children below 5 years of age

BACKGROUND: The use of electroencephalogram (EEG) monitoring devices for assessing the depth of hypnosis is most difficult in children under 5 years of age. METHODS: Forty five children aged 0-60 months were included in a prospective observational study. A direct comparison of the processed EEG variables Bispectral Index (BIS, version 3.4) and Narcotrend Index (NI, version 2.0AF) was to be achieved by simultaneous recording. The ability of these parameters to differentiate between various clinical states was evaluated by using the prediction probability (P(k)). Age-related effects on the BIS and NI were analyzed by dividing the children into three age groups: 0-6, 7-18 and 19-60 months. RESULTS: The preanesthesia, conscious children were differentiated from anesthetized patients by the BIS and NI with no overlap (P(k) = 1.0). In the awake period the BIS was superior to the NI (P(k) to differentiate 'end of anesthesia' from 'awakening' was 0.97 vs 0.73 respectively; P = 0.002). Patients aged 7-18 months showed higher BIS and NI values in the course of anesthesia than the younger and older children (P = 0.001). On awakening, children aged 0-6 months showed the lowest mean BIS (n.s.) and NI (P = 0.006) values. CONCLUSIONS: The BIS currently seems to be superior to the NI, but age-related processing algorithms of the raw EEG must be implemented in both BIS and NI in order to be useful in children younger than 5 years of age.     

Effects of mild hypothermic cardiopulmonary bypass on EEG bispectral index

We studied the effect of mild hypothermic cardiopulmonary bypass (30 degrees C) on the EEG Bispectral Index in 10 patients undergoing elective CABG. BIS was recorded at 11 event-related time points during the procedure. After a significant decrease at the induction of anaesthesia, BIS was not further modified during the procedure. BIS was neither affected by surgical stimulation nor by CPB and mild hypothermia. We conclude that we did not find any reason to preclude the use of BIS to assess the hypnotic effects of anaesthetics during normothermic or mild hypothermic CPB.     

Carbon dioxide elimination in anaesthetized children

Carbon dioxide elimination (VCO2) was measured in 186 anaesthetized, spontaneously breathing infants and children with body weights ranging from 2.8 to 26.5 kg. They all underwent minor paediatric surgical procedures. The influence on VCO2 of age, operation, premedication, caudal anaesthesia, and different volatile anaesthetic agents was investigated. The volume of exhaled gas, during three- to five-minute collection periods, was measured and the fraction of exhaled CO2 was determined by a CO2 meter. Under basal anaesthetic conditions, the average output before operation followed the equation: VCO2 (ml.min-1) = -1.25X + 13.0X2, in which X = lne (body weight, kg). Expressed on a weight basis, the youngest infants (weighing less than 5 kg) had the lowest VCO2. Higher values were measured up to a body weight of 10 kg above which a negative correlation occurred between VCO2 (ml.min-1.kg-1) and body weight. The use of premedication resulted in a more variable VCO2 during operations than when opioid premedication was not used. The combination of a general anaesthetic and caudal anaesthesia stabilized VCO2. Also, children anaesthetized with halothane had a higher VCO2 than those who were anaesthetized with enflurane or isoflurane (P less than 0.05). The variable VCO2 emphasizes the need for increased monitoring of VCO2 during routine anaesthesia and operation in infants and children.     

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

Background. The relationship between end-tidal sevoflurane concentration,bispectral index (BIS) and the EEG bispectrum in children appearsto be age dependent. The aim of this study was to quantify theBIS values at 1 MAC (minimum alveolar concentration) for desfluraneand halothane, and explore the relationship with age for theseanaesthetic agents in children. Methods. ECG, EEG and BIS were recorded continuously in 90 childrenaged 6–170 months requiring anaesthesia for elective surgery.Fifty children were anaesthetized with desflurane, and 40 childrenwith halothane. Recordings were performed through to a steadystate of 2 MAC, and thereafter at 1 and 0.5 MAC, respectively.The bispectrum of the EEG was estimated using MATLAB© software.A multiple correspondence analysis (MCA) was used. Results. At a steady state of 1 MAC, BIS values were significantlyhigher with halothane 62 (43–80) than desflurane 34 (18–64).BIS values were significantly correlated with age in both groups:DES (r²=0.57; P<0.01) and HALO (r²=0.48; P<0.01). Changesin position in the structured model of the MCA (dependent onthe pattern of the EEG bispectrum) were different for the twovolatile anaesthetic agents. Conclusions. In children, BIS values are linked to age irrespectiveof the volatile anaesthetic agent used. The difference in BISvalues for different agents at the same MAC can be explainedby the specific effect on the EEG bispectrum induced by eachanaesthetic agent, bringing into question the ability of theEEG bispectrum to accurately determine the depth of anaesthesia.     

The Narcotrend™– a new EEG monitor designed to measure the depth of anaesthesia A comparison with bispectral index monitoring during propofol-remifentanil-anaesthesia

INTRODUCTION: The Narcotrend is a new EEG monitor designed to measure the depth of anaesthesia based on a 6-letter classification from A (awake) to F (general anaesthesia with increasing burst suppression) and divided into 14 substages (A, B0-2, C0-2, D0-2, E0,1, F0,1). This study was designed to investigate the assessment of the depth of anaesthesia as measured by the Narcotrend in comparison with bispectral index monitoring (BIS). METHODS: Both BIS and Narcotrend EEG electrodes were positioned on the patient's forehead as recommended by the manufacturers. All patients were premedicated with diazepam 0.15 mg/kg orally in the evening and on the morning before surgery. Induction of anaesthesia was started with a remifentanil infusion at 0.4 microgram/kg/min; 5 min later propofol was given for hypnosis using a target-controlled infusion initially started at 3.5 micrograms/ml. After loss of consciousness patients received 1.2 mg/kg of suxamethonium. Immediately after intubation, remifentanil was reduced to 0.2 microgram/kg/min, and the depth of anaesthesia was adjusted according to clinical needs by regulating the propofol target-controlled-infusion. BIS values and Narcotrend stages were recorded as data pairs in intervals of 1 min during anaesthetic induction and emergence, and in intervals of 5 min during maintenance of anaesthesia. RESULTS: Fifty patients undergoing orthopaedic surgery were studied and 2031 data pairs were obtained. An increasing depth of anaesthesia as indicated by the Narcotrend was associated with significantly lower mean BIS values. With BIS values between 100 and 85 (representing awake patients), 95.5% of all data pairs indicated a Narcotrend stage A or B. In case the BIS was found to be 65-40 (representing general anaesthesia) the corresponding Narcotrend stages were measured as D (52.4%) or E (41.1%). No patient complained of intraoperative recall when interviewed on the 1st and 3rd postoperative day. CONCLUSIONS: We could demonstrate that an increase of the hypnotic component of anaesthesia as indicated by BIS is accompanied by corresponding effects as displayed by the Narcotrend during propofol-remifentanil anaesthesia. The Narcotrend stages D or E are assumed equivalent to BIS values between 64 and 40 indicating general anaesthesia.     

An observational study exploring amplitude-integrated electroencephalogram and spectral edge frequency during paediatric anaesthesia

Processed electroencephalography is used in adults to guide anaesthesia, but the algorithms used may not apply to infants. Knowledge of infants' electroencephalogram (EEG) responses to anaesthetics is fragmentary. An earlier pilot study suggested amplitude-integrated EEG (aEEG) may be a useful measure of anaesthetic effect. The aim of this study was to determine how aEEG changes between awake and anaesthetised children of varying ages and to compare the response to that seen with Spectral Edge Frequency 90% (SEF90). A prospective observational study of children receiving a general anaesthetic was conducted. Anaesthetic regimen remained at the discretion of the treating anaesthetist. EEG data were collected using the BrainZ ReBrim(TM) monitor using forehead and biparietal montages. SEF90 and aEEG were compared across age groups, EEG montage and between awake and anaesthetised states. A total of 178 children (aged 24 days to 14 years) were recruited. All aEEGs were greater during anaesthesia compared to when awake and this difference varied with age. Only children older than two years showed lower SEF90 while anaesthetised compared to when awake. SEF90 from children younger than six months was higher during anaesthesia compared to when awake. Analysis of parietal and forehead EEG montages revealed age-related differences. These findings suggest that SEF90 and aEEG can discriminate between awake and anaesthetised states in older children. In younger children aEEG changes are less pronounced and SEF90 either cannot discriminate between states or responds paradoxically. The aEEG may be marginally better than other EEG parameters in measuring anaesthetic depth in children.     

Automatic analysis of electroencephalogram: what is its value in the year 2000 for monitoring anesthesia depth?]

Spontaneous EEG has been proposed for monitoring depth of anaesthesia and adjusting anesthetic drugs doses. This review describes the main features of spontaneous EEG, the principles of EEG signal analysis used in anaesthesia, and the EEG effects of the different anesthetic drugs in adults and children. Then, the correlations between EEG parameters changes and clinical signs of anesthesia (loss of consciousness and memory, lack of movement and haemodynamic stability despite noxious stimulations) are analyzed. The best signal analysis technique available today for routine use seems to be bispectral analysis, which returns, in the available monitors, a single number called bispectral index or BIS. Based upon the recent literature, clinical uses, performances and limits of use of BIS are described and discussed.     

BIS does not predict dreams reported after anaesthesia

Background: In earlier studies, between 1% and 57% of patients have been reported to dream during anaesthesia. Thus, dreaming is much more common than definite memories of real events. We wanted to examine whether dreaming during anaesthesia is related to insufficient hypnotic action, as indicated by BIS levels and, thus, may constitute a risk for awareness.
Methods: After IRB approval, 2653 consecutive surgical patients were included. BIS registrations were recorded continuously during the anaesthetic procedure. The patients were interviewed on three occasions after anaesthesia. Standard questions, according to Brice, to evaluate awareness and dreaming during anaesthesia were asked. The dreams were categorized as either pleasant/neutral or unpleasant without any further evaluation of the dream content. Episodes with a mean BIS below 40, above 60 and above 70 were identified and subdivided according to duration (1, 2, 4 and 6 min, respectively). The total time as well as number and duration of episodes for the three BIS-levels were used to analyze any relation to reported dreaming. The mean BIS was also analyzed.
Results: Dreaming during anaesthesia was reported by 211 of patients (8.0%) on at least one of the post-operative interviews. BIS data did not show any significant correlation with dreaming, and neither did any of the tested case-specific parameters (gender, age, ASA group, BMI, use of relaxants, induction agent, maintenance agent, length of procedure, omitting N₂O and concomitant regional anaesthesia).
Conclusion: Dreaming during anaesthesia seems to be a separate phenomenon, not in general related to insufficient anaesthesia as indicated by high BIS levels.