Arthur Schultz

Automatic Classification Algorithms of the EEG Monitor Narcotrend for Routinely Recorded EEG Data from General Anaesthesia: a Validation Study

Impacts of hypnotic drugs on brain function are reflected in the EEG. The EEG monitor Narcotrend performs an automatic classification of the EEG using a scale which was proposed by Kugler for visual evaluation of the EEG. In this article the results of a validation study of the automatic classification algorithms implemented in the EEG monitor Narcotrend are presented. Visual and automatic classification of EEG data recorded in routine clinical practice were compared. The correlation between visual and automatic assessment was high (Spearman rank correlation r = 0.90, prediction probability Pk = 0.90) and a sufficient agreement between visual and automatic assessment was achieved for 92% of the analysed EEG epochs. The results of the study suggest that the automatic classification algorithms implemented in the EEG monitor Narcotrend yield a reliable assessment of the depth of hypnosis.

Age-related effects in the EEG during propofol anaesthesia.

Background:  Age‐related differences in the spectral composition of the EEG in induction and emergence times, and in drug consumption during propofol anaesthesia were investigated.

The Narcotrend Index: Classification Algorithm, Correlation with Propofol Effect-Site Concentrations, and Comparison with Spectral Parameters / Der Narcotrend-Index: Klassifikationsalgorithmus, Korrelation mit Propofol-Effekt-Site-Konzentrationen und Vergleich mit Spektralparametern

Abstract A reliable assessment of the depth of hypnosis during sedation and general anaesthesia using the EEG is a subject of current interest. The Narcotrend Index implemented in the latest version 4.0 of the EEG monitor Narcotrend® provides an automatic classification of the EEG on a scale ranging from 100 (awake) to 0 (very deep hypnosis, EEG suppression). The classification algorithms implemented in the EEG monitor Narcotrend are described. In a study the correlation of the propofol effect-site concentration with the Narcotrend Index and with the traditional spectral parameters total power, relative power in the standard frequency bands δ, θ, α, and β, median frequency, 95 % spectral edge frequency, burst-compensated spectral edge frequency, and spectral entropy was investigated. The Narcotrend Index had the highest average correlation with the propofol effect-site concentration and the smallest variability of the individual correlation values. Moreover, the Narcotrend Index was the only parameter which showed a monophasic trend over the whole investigated time period. The Narcotrend monitor can make a significant contribution to the improvement of the quality of anaesthesia by adjusting the dosage of hypnotics to individual patient needs. Die zuverlässige Bewertung der Schlaftiefe während Sedierung und Narkose ist ein Thema von aktuellem Interesse. Der Narcotrend-Index, der in der neusten Version 4.0 des EEG-Monitors Narcotrend® implementiert ist, liefert eine automatische Klassifikation des EEG auf einer Skala von 100 (wach) bis 0 (tiefste Narkose). Die Klassifikationsalgorithmen des Narcotrend-EEG-Monitors werden beschrieben. In einer Studie wurde die Korrelation der Propofol-Effekt-Site-Konzentration mit dem Narcotrend-Index sowie mit den klassischen Spektralparametern Gesamtleistung, relative Leistung in den Standard-Frequenzbändern δ, θ, α und β, Median-Frequenz, 95 % spektrale Eckfrequenz, burst-korrigierte spektrale Eckfrequenz und spektrale Entropie untersucht. Der Narcotrend-Index zeigte die höchste mittlere Korrelation mit der Propofol-Effekt-Site-Konzentration und die geringste Streuung der individuellen Korrelationen. Zudem war der Narcotrend-Index der einzige Parameter, der einen monophasischen Trend über den gesamten untersuchten Zeitverlauf aufwies. Der Narcotrend kann einen wertvollen Beitrag zur Verbesserung der Narkosequalität durch eine individuell auf den einzelnen Patienten abgestimmte Hypnotika-Dosierung leisten.

Correlation of Narcotrend Index, entropy measures, and spectral parameters with calculated propofol effect-site concentrations during induction of propofol–remifentanil anaesthesia

Objective. The aim of this study was to compare the EEG parameter Narcotrend Index with the spectral and entropy-based EEG parameters median frequency, 95% spectral edge frequency, burst-compensated 95% spectral edge frequency, spectral entropy, amplitude entropy, and approximate entropy with regard to their ability to describe cerebral anaesthetic drug effects during induction of propofol–remifentanil anaesthesia. Methods. Three induction schemes were studied with 10 patients each receiving 2 mg propofol/kg/60s (group 1), 4 mg/kg/120s (group 2), and 4 mg/kg/240s (group 3). The EEG was recorded with the EEG monitor Narcotrend®. To analyse the relation between drug effect and EEG parameters, Spearman rank correlation of the different EEG parameters with the calculated propofol effect-site concentration was computed. Results. In all groups Narcotrend Index showed the highest correlation with the propofol effect-site concentration and the lowest variability of individual correlation values. Furthermore, only the Narcotrend Index showed a monophasic behaviour over the entire time period analysed. In the group of entropy parameters approximate entropy yielded the best results. Among the spectral parameters the burst-compensated 95% spectral edge frequency had the highest correlation with the propofol effect-site concentration. It was markedly higher than for the standard spectral edge frequency. The correlations of median frequency and amplitude entropy with propofol effect-site concentration were the lowest. Conclusions. Changes in the propofol effect-site concentration during induction of anaesthesia were best described by the multivariate Narcotrend Index compared to conventional spectral EEG parameters and different entropy measures.

Intraoperative Electrically Elicited Stapedius Reflex Threshold is Related to the Dosage of Hypnotic Drugs in General Anesthesia

Today cochlear implantation is a widely used means of treatment in deafness and severe hearing disorders in adults, children, and infants. Postoperative fitting of the externally worn speech processor is very important for successful use of the cochlear implant. However, especially in infants and young children, this fitting process can be difficult because of limited communication capabilities. The use of intraoperatively obtained stapedius reflex thresholds has been proposed for postoperative speech processor fitting, but the influence of anesthetics on threshold values needs to be taken into account. In a retrospective study with 20 patients between 3 and 43 years of age, a highly significant correlation between the dosage of methohexital and the mean stapedius reflex threshold value could be shown (r = 0.65, p = .002). We conclude that more reliable threshold values can be obtained by reducing the dosage of hypnotics to achieve a lighter level of hypnosis during stapedius reflex measurement. To achieve a light, but still sufficient level of hypnosis, electroencephalographic monitoring including automatic interpretation of the complex raw signal should be used.

Women need more propofol than men during EEG-monitored total intravenous anaesthesia / Frauen benötigen mehr Propofol als Männer während EEG-überwachter total-intravenöser Anästhesie.

Abstract Gender-related differences in the pharmacology of drugs used in anaesthesiology have been reported by different authors. The aim of this study was to compare propofol dosages in a greater number of male and female patients who had received electroencephalogram (EEG) monitoring to maintain a defined depth of anaesthesia. Data from an EEG-controlled study were analysed with regard to gender differences in the consumption of the short-acting hypnotic propofol during maintenance of total intravenous anaesthesia and with regard to recovery times. The 656 patients (239 male, 417 female) were 15 to 97 years old, underwent different surgical procedures, and received propofol in combination with remifentanil, a short-acting opioid. During the steady-state of anaesthesia the EEG stage D2/E0, which corresponds to deep hypnosis, was the target level (EEG monitor: Narcotrend®). Propofol dosages were calculated as mg/kg body weight/h and as mg/kg lean body mass/h. Significantly higher propofol dosages were observed in female patients compared to male patients, especially with lean body mass as a reference parameter. The dosages were characterised by a high interindividual variability. The time from stop of propofol until extubation was significantly shorter in women than in men. The propofol dosage for maintenance of anaesthesia at the EEG level D2/E0 decreased with increasing age. Zusammenfassung Über geschlechtsspezifische pharmakologische Unterschiede von Anästhetika ist von verschiedenen Autoren berichtet worden. Das Ziel dieser Studie war es, an einer größeren Zahl männlicher und weiblicher Patienten die Propofoldosierungen zu vergleichen, die zur Aufrechterhaltung einer anhand des EEG definierten Hypnosetiefe benötigt wurden. Daten aus einer EEG-kontrollierten Studie wurden hinsichtlich geschlechtsspezifischer Unterschiede im Verbrauch des kurzwirksamen Hypnotikums Propofol bei total-intravenöser Anästhesie und hinsichtlich der Aufwachzeiten analysiert. Die 656 Patienten (239 männlich, 417 weiblich) im Alter von 15 bis 97 Jahren unterzogen sich unterschiedlichen operativen Eingriffen in Anästhesie mit Propofol und dem kurzwirksamen Opioid Remifentanil. Die Steuerung der Narkosetiefe erfolgte mit Hilfe des EEG-Monitors Narcotrend, wobei zur Narkoseaufrechterhaltung das EEG-Stadium D2/E0 angestrebt wurde, welches einem tiefen Schlafstadium entspricht. Propofoldosierungen wurden in mg/kg Körpergewicht/h sowie in mg/kg lean body mass/h errechnet. Im Vergleich zu den Männern war der Verbrauch an Propofol bei den Frauen signifikant höher, besonders wenn in Bezug auf lean body mass verglichen wurde. Dabei gab es große interindividuelle Unterschiede. Die Zeit vom Stopp der Infusion bis zur Extubation war bei den Frauen signifikant kürzer. Der Bedarf an Propofol zur Aufrechterhaltung der Narkose im Stadium D2/E0 sank mit zunehmendem Alter.

Implementation of linear and quadratic discriminant analysis incorporating costs of misclassification

Discriminant analysis plays an important role in biological and medical research. In practice, standard linear and quadratic methods are often applied which assume equal costs of misclassification. However, there can be situations where misclassifications between certain groups may be more serious than between other groups. Such considerations can be taken into account by using classification methods which incorporate misclassification costs. The widely applied statistical packages BMDP, SAS, and SPSS do not offer the possibility of using unequal misclassification costs for discriminant analysis with more than two groups. In this paper a menu-driven, user-friendly PC program written in Borland Pascal is introduced which performs linear and quadratic discriminant analysis for g > or = 2 groups allowing for the incorporation of misclassification costs.

Incidence of Epileptiform EEG Activity in Children during Mask Induction of Anaesthesia with Brief Administration of 8% Sevoflurane

Background A high incidence of epileptiform activity in the electroencephalogram (EEG) was reported in children undergoing mask induction of anaesthesia with administration of high doses of sevoflurane for 5 minutes and longer. This study was performed to investigate whether reducing the time of exposure to a high inhaled sevoflurane concentration would affect the incidence of epileptiform EEG activity. It was hypothesized that no epileptiform activity would occur, when the inhaled sevoflurane concentration would be reduced from 8% to 4% immediately after the loss of consciousness. Methodology/Principal Findings 70 children (age 7–96 months, ASA I–II, premedication with midazolam) were anaesthetized with 8% sevoflurane in 100% oxygen via face mask. Immediately after loss of consciousness, the sevoflurane concentration was reduced to 4%. EEGs were recorded continuously and were later analyzed visually with regard to epileptiform EEG patterns. Sevoflurane at a concentration of 8% was given for 1.2±0.4 min (mean ± SD). In 14 children (20%) epileptiform EEG patterns without motor manifestations were observed (delta with spikes (DSP), rhythmic polyspikes (PSR), epileptiform discharges (PED) in 10, 10, 4 children (14%, 14%, 6%)). 38 children (54%) had slow, rhythmic delta waves with high amplitudes (DS) appearing on average before DSP. Conclusions/Significance The hypothesis that no epileptiform potentials would occur during induction of anaesthesia with a reduction of the inspired sevoflurane concentration from 8% to 4% directly after LOC was not proved. Even if 8% sevoflurane is administered only briefly for induction of anaesthesia, epileptiform EEG activity may be observed in children despite premedication with midazolam.

Assessing the depth of hypnosis of xenon anaesthesia with the EEG / Bestimmung der Hypnosetiefe bei Xenon-Narkosen mit dem EEG

Abstract Xenon was approved as an inhaled anaesthetic in Germany in 2005 and in other countries of the European Union in 2007. Owing to its low blood/gas partition coefficient, xenons effects on the central nervous system show a fast onset and offset and, even after long xenon anaesthetics, the wake-up times are very short. The aim of this study was to examine which electroencephalogram (EEG) stages are reached during xenon application and whether these stages can be identified by an automatic EEG classification. Therefore, EEG recordings were performed during xenon anaesthetics (EEG monitor: Narcotrend®). A total of 300 EEG epochs were assessed visually with regard to the EEG stages. These epochs were also classified automatically by the EEG monitor Narcotrend® using multivariate algorithms. There was a high correlation between visual and automatic classification (Spearmans rank correlation coefficient r=0.957, prediction probability Pk=0.949). Furthermore, it was observed that very deep stages of hypnosis were reached which are characterised by EEG activity in the low frequency range (delta waves). The burst suppression pattern was not seen. In deep hypnosis, in contrast to the xenon EEG, the propofol EEG was characterised by a marked superimposed higher frequency activity. To ensure an optimised dosage for the single patient, anaesthetic machines for xenon should be combined with EEG monitoring. To date, only a few anaesthetic machines for xenon are available. Because of the high price of xenon, new and further developments of machines focus on optimizing xenon consumption. Zusammenfassung Xenon wurde im Jahr 2005 in Deutschland und 2007 auch in anderen Ländern der Europäischen Union als Inhalationsanästhetikum zugelassen. Aufgrund seines niedrigen Blut-Gas-Verteilungskoeffizienten flutet Xenon sehr schnell an und ab, daher ist die Aufwachzeit auch nach langen Xenon-Narkosen sehr kurz. In einer Untersuchung sollte geprüft werden, welche Stadien unter Xenon im Elektroenzephalogramm (EEG) erreicht und ob diese mittels einer automatischen EEG-Klassifikation erkannt werden. Aus diesem Grund erfolgten EEG-Registrierungen während Xenon-Narkosen (EEG-Monitor Narcotrend®). 300 EEG-Abschnitte wurden visuell hinsichtlich der EEG-Stadien bewertet. Zum Vergleich wurden die EEG-Abschnitte durch den EEG-Monitor Narcotrend® über multivariate Algorithmen klassifiziert. Es gab eine hohe Übereinstimmung zwischen visueller und automatischer Klassifikation (Spearmanscher Rangkorrelationskoeffizient r=0,957, Pk=0,949). Zudem zeigte sich, dass auch sehr tiefe Hypnosestadien erreicht wurden, bei denen das EEG durch langsame Deltaaktivität geprägt war. Das Burst-Suppression-Muster war nicht vorhanden. Das Propofol-EEG zeigte in tiefer Hypnose im Gegensatz zum Xenon-EEG eine ausgeprägte überlagernde höherfrequente Aktivität. Um für den einzelnen Patienten eine Dosisoptimierung zu gewährleisten, sollten Narkosegeräte für Xenon mit einem EEG-Monitoring kombiniert werden. Bisher stehen nur wenige Typen von xenontauglichen Narkosegeräten zur Verfügung. Im Hinblick auf den hohen Xenon-Preis liegt ein Schwerpunkt bei Neu- bzw. Weiterentwicklungen von Geräten in der Optimierung des Xenonverbrauchs.

Reduktion der Anzahl von EEG-Ableitungen für ein routinemäßiges Monitoring auf der Intensivstation - Electroencephalographic Monitoring in the ICU - Reduction of the Number of Recorded Channels

Monitoring patients in the intensive care unit with the aid of the conventional electroencephalogram employing a large number of recording channels is rather difficult, and can be laborious. This imposes limits on the routine application of this method. To investigate the possibility of developing a new monitoring device for easier application in the ICU, we aimed to establish whether the relevant information provided by a multi-channel EEG could be found in a subgroup of channels, thus reducing the number of channels required. Preferably those channels should be identified for use which are least contaminated by artefacts under routine conditions in the ICU. A total of 150 EEG recordings from the intensive care unit were inspected visually for the presence of artefacts. The derivations C3-P3 and C4-P4 proved to be least contaminated, at 35% and 39%, respectively. In these derivations visual assessment of the EEG was found to be impossible due to artefacts in only 4 and 5%, of all cases, respectively. A data set comprising 52 EEG segments with the fewest possible artefacts, was analysed using time series methods. On the basis of multivariate autoregressive processes, a measure was derived which describes the loss of information associated with a reduction in the number of EEG channels. The computation of the information loss for several channel combinations revealed that the derivations F3-C3, C3-P3 and A1-Cz represent a good compromise between information content, number of channels and frequency of artefacts. Practical experience shows that, at least for the control of sedation, a further reduction to a single channel should be possible.(ABSTRACT TRUNCATED AT 250 WORDS)