EEG Monitoring - Narcotrend - EEG-Monitor für Narkose und Sedierung

Information for patients

Why is it useful to monitor the EEG during anesthesia?

Advantages and benefits of computer-based EEG monitoring

What is an EEG?

EEG is the abbreviation for “electroencephalogram”. An electroencephalogram records the electrical activity of the brain. To make an EEG recording, special electrodes are attached to the scalp. They transfer the electrical brain signals to an electroencephalograph, which displays the EEG in form of waves, and can analyze and store it. Such EEG waves are used to evaluate brain function.

What are the advantages of EEG monitoring in anesthesia?

Drugs affect the brain function in a characteristic way. This can be observed as accompanying changes in the patient’s EEG. Therefore, it is useful to record the EEG and to analyze it with computer-based methods. The benefits include:

Adjusting the depth of hypnosis (sleep):
Monitoring the EEG continuously helps to assess the patient’s depth of hypnosis (sleep). This supports the individualized dosing of anesthetics. Unnecessarily long stays in the recovery room or in the intensive care unit for prolonged ventilation can be avoided.
Early detection of adverse conditions:
Adverse conditions which might affect the patient, such as a lack of oxygen supply to the brain or the presence of epileptiform potentials, can be detected at an early stage thanks to EEG monitoring.

What patients benefit most from EEG monitoring?

Particularly children and older people benefit from the gentle anesthesia provided by EEG monitoring. Finding the optimum dosage of anesthetics in children is difficult. Many drugs have no or only limited approval for use in children. Often, scaled-down adult doses are used. Therefore, the risk of inadequate dosing is increased. In many older patients, the dose requirements are reduced; many suffer from concomitant disorders and are in a frail physical condition.

Nevertheless, EEG monitoring is beneficial in patients of any age, because there is wide interindividual variability in the dose requirements of anesthetic drugs. Computer-based EEG monitoring helps find the optimum dose and contributes to patient safety.

EEG Basics

The purpose of this page is to provide knowledge about EEG basics. This is necessary to achieve optimum signal quality when recording and to confidently assess the signals. As numerous different factors may affect the EEG, it is very important that the EEG only be assessed with the patient’s overall clinical condition in mind.

EEG Monitoring Basics in Anesthesia and Intensive Care

The EEG is a diagnostic method based on cerebral function. It allows assessing the current condition of the brain function. The potentials measured in the EEG are generated in the cerebral cortex. The process is influenced by neuronal interactions on the cortical and subcortical levels.

The amplitudes of the EEG signals are very small - in the microvolt range. This makes it necessary to be very careful when recording EEGs and prioritize avoiding disturbances.

When assessing an EEG, various aspects must be considered. These include the frequency composition of the signal, the topographic configuration of EEG patterns across the skull and the presence of specific forms of potentials.

In most cases, a depressant effect on cerebral function is associated with a slowing of the EEG. The frequency composition of the EEG can therefore be used as a basis to assess the severity of cerebral dysfunction. For the visual analysis of EEG waves, it is common practice to differentiate between four frequency ranges:

Delta (0.5 - 3.5 Hz)
Theta (3.5 - 7.5 Hz)
Alpha (7.5 - 12.5 Hz)
Beta (> 12.5 Hz)

A general distinction can be made between generalized and focal EEG changes. Generalized EEG changes are characterized by being very similar across all skull regions. Typical examples are EEG effects caused by narcotics, sedatives, hypothermia, hypoglycemia and global hypoxia. Focal EEG changes are limited to specific regions of the skull and can be caused by, e.g., tumors, bleeding or locally limited hypoxia.

Specific forms of potentials that can be commonly seen in EEG monitoring during anesthesia and in intensive care are, for instance, epileptiform potentials.

Generalized EEG Changes due to Anesthetics

The illustration shows characteristic EEG changes during barbiturate-induced anesthesia with increasing depth of anesthesia. During relaxed waking state, the EEG of most adults is characterized by alpha activity. During the induction of anesthesia, amplitudes initially decrease, and wakeful activity is then fully suppressed. Rapid frequencies are observed, at first with underlying slow waves (theta and delta range) as anesthesia depth increases. Later on, high-amplitude delta activity is dominant amongst the waves. Frequency and amplitude of the delta-range waves decrease while uptake of the anesthetic increases. Flat to isoelectric parts of waves interrupted by individual periodic groups, the so-called “bursts”, are typical of very deep or even too deep anesthesia. If even the bursts are suppressed, the result is an isoelectric course of the wave. When the anesthesia wears off, the described EEG patterns are seen in reverse.

As early as in 1959, Martin et al. divided anesthesia into six electro-physiological levels based on these uniform wave patterns, occurring in generalized manner across the entire cortex. Kugler (1981) suggested an even more differentiated division into stages. From waking state to very deep anesthesia, he differentiates between stages A through F, including sub-stages.

It is known that the waking EEG changes with age. In children, age-dependent particularities of anesthesia stages commonly include very large amplitudes, while the signal amplitudes in the elderly are often quite small.

Although some substances have a specific impact on the EEG, e.g., by strengthening particular frequency components, progressive slowing of the EEG is typical of increasing hypnotic effect. As these are generalized EEG changes, one EEG channel is sufficient to represent them.

Other Causes of Generalized EEG Changes

Generalized EEG changes may also be caused by factors that impact the metabolism or energy supply of the brain, thereby altering cellular function. Such factors include hypoxia, ischemia, hypothermia, hypocapnia/hypercapnia and hypoglycemia.

The stated factors may result in EEG changes very similar to drug-induced EEG effects. It is not rare to observe mixed patterns reflecting EEG effects due to different factors, e.g., drug effects in combination with acute hypoxia. It must therefore be emphasized that EEG registrations may only be interpreted in conjunction with the clinical picture and in consideration of any additional information.

The fact that the EEG is subject to changes not only due to drugs, but also other factors, is clinically beneficial, as this can, for instance, indicate situations that might damage the brain and allows monitoring the brain function of coma patients over the course of their condition.

EEG Monitoring of Focal EEG Changes

Focal EEG changes are detected by comparing EEG signals from both hemispheres. A two-channel recording allows screening for the presence of a focal EEG change. An indication is EEG monitoring during surgeries on the carotid artery.

An abnormal focal process often manifests as slowing on the affected side. However, focal signs may, e.g., also be seizure potentials, focal flattening of waves and even EEG waves speeding up. The subject is comprehensively addressed in the stated literature.

With multi-channel recordings, it is particularly important to ensure symmetric placement of the electrodes to avoid ostensible differences between the sides although there are in fact none.

Not in every case can side differences be demonstrated by way of a two-channel recording. If necessary, a conventional multi-channel EEG must be performed.

In patients with known defined EEG changes or a medical history suggesting the possibility of defined cerebral function changes, the EEG of the unaffected hemisphere should be used to assess drug effects

Special Forms of EEG Potentials

A particular value of EEGs is that epileptiform potentials (also referred to as epileptiform discharges/activity, spike-wave discharges) can be detected, thereby monitoring the effect of antiepileptic therapy. Epileptiform potentials usually feature very sharp and spiky parts.

Epileptiform potentials, e.g., spikes, sharp waves, spike-and-wave complexes etc., are of great clinical relevance. It is recommended that, using literature, practitioners familiarize themselves with these potentials and also other potentials with similar shapes.

Computed Processing of the EEG

It is not sufficient for EEG monitoring to solely represent the original signal. Constant observation of the monitor is not practical and would distract from other tasks. It is necessary to compress the flood of information provided by the EEG in a suitable manner to be able to read trends.

A standard method for analyzing EEGs is spectral analysis. It separates the EEG signal into its underlying frequency components for a defined epoch. The results of the spectral analysis can be shown as a graphical representation, e.g., in form of a power spectrum, and then be used as the basis for further calculations. The spectral analysis can only represent frequency components; the form and temporary sequence of the EEG waves are not taken into account. Specific potential patterns are separated into their frequency components and no longer recognizable as patterns. Short-term EEG changes are often hard to detect in continuous spectral analysis.

It is therefore useful to have available a concurrent registration of the original EEG along with the spectral analysis representations, in the case of long-term measurements at least in form of samples.

Various individual parameters can be calculated from the power spectrum. Such spectral parameters are, e.g., absolute or relative power in frequency bands. In the EEG range, the 50% and 90% or 95% quantile of the power spectrum are common descriptors. Trends in the EEG can often be displayed clearly using spectral parameters.

However, it must be considered that individual spectral parameters, just like the spectrum, do not provide any information about specific patterns in the EEG.

For instance, the burst-suppression EEG (stage F0), which is characterized by very flat lines and mixed-frequency waves appearing in turns, cannot be recognized based on spectral parameters. Even with pure suppression sections (stage F1), spectral parameters are not helpful. Therefore, the spectrum and the relative band activities / power are shown grayed out on the screen for these EEG images.

Special algorithms are used to recognize the F range. To automatically classify the other stages, multivariate methods are employed. They ensure a more reliable assessment of the EEG as compared to individual parameters. With the multivariate approach, a large number of parameters is determined from one EEG epoch. It is then checked whether these parameters are present in a composition typical of a stage. If this is the case, this stage is displayed as the current assessment on the screen. If the probability for a correct classification is too low, or too many artifacts have been detected, no assessment is displayed.

In the cerebrogram, all automatic classifications are shown over the course of time, clearly displaying the trends over the course of the anesthesia/sedation.

References

Ebe, M., Homma, I.
Leitfaden für die EEG-Praxis
Stuttgart Jena New York: Fischer, 2002

Freye, E.
Cerebral Monitoring in the OR and ICU.
Dordrecht: Springer, 2005

Kugler, J.
Elektroenzephalographie in Klinik und Praxis, 3. Aufl.
Stuttgart New York: Thieme, 1981

Neundörfer, B.
EEG-Fibel, 5. Aufl.
Stuttgart New York: Fischer, 2002

Zschocke, S., Hansen, H.-C.
Klinische Elektroenzephalographie, 3. Aufl.
Berlin Heidelberg: Springer, 2012

Recommendations

Recommendations for standards of monitoring during anaesthesia and recovery 2021: Guideline from the Association of Anaesthetists

(Consensus document produced by members of a Working Party established by the Association of Anaesthetists of Great Britain and Ireland)

„Processed electroencephalogram (pEEG) ‘depth of anaesthesia’ monitoring provides an indication of the effect of the most commonly used general anaesthetic drugs (including propofol and the inhalational anaesthetic drugs) on the electrical activity of the frontal cerebral cortex. It may aid the anaesthetist in adjusting the dose of anaesthetic drug being given to an individual patient and reduce the incidence of adverse effects resulting from an inadequate or excessive anaesthetic dose. Processed EEG monitoring may reduce the risk of AAGA [accidental awareness during general anaesthesia], improve early recovery times and reduce the incidence of postoperative delirium and postoperative cognitive dysfunction.“

„Processed EEG monitoring should, …, be used when TIVA [total intravenous anaesthesia] is administered together with neuromuscular blockade and should be considered when TIVA is used alone. Monitoring should start before induction and continue at least until full recovery from the effects of the NMB [neuromuscular blocking] drug has been conﬁrmed.“

Recommendations for Electroencephalography Monitoring in Neurocritical Care Units

Neurocritical Care Committee of the Chinese Society of Neurology (NCC/CSN)
(2017 Chinese Medical Journal)

“EEG can provide useful information for the diagnosis, treatment and prognostic evaluation of diseases.”

Guideline on monitoring during anaesthesia

(Australian and New Zealand College of Anaesthetists, 2017)

„When clinically indicated, equipment to monitor other physiological variables (for example the electroencephalogram, central venous pressure, cerebral oximetry, transoesophageal echocardiogram, cardiac output or respiratory mechanics) should be available.“

S3 Guideline Analgesia, Sedation and Delirium Management in Intensive Care

DSA Guideline 2020, as of March 31, 2021

“EEG based monitoring procedures, however, constitute an important option in patients with deep sedation. The aim should be to optionally use them from a RASS <-3 to avoid oversedation. The duration of burst suppression in the processed EEG was relevant to delirium after deep sedation."
“In patients with unclear disturbances of consciousness (for example, hypoactive delirium), EEGs are a valuable differential-diagnosis procedure to rule out a non-convulsive status, which is often underestimated in differential diagnosis. In intensive-care patients, an incidence of approximately 20% has been described. In patients treated with electrosuppressive medication for non-convulsive status, (EEG-based) machine monitoring of the sedation depth should also be employed.”

References

Georgevici AI, Kyprianou T, Herzog-Niescery J, Procopiuc L, Loganathan S, Weber TP, Bellgardt M.
Negative drift of sedation depth in critically ill patients receiving constant minimum alveolar concentration of isoflurane, sevoflurane, or desflurane: a randomized controlled trial.
Crit Care 2021; 25(1): 141.
Free PMC article

Mulvey DA, Klepsch P.
Use of Processed Electroencephalography in the Clinical Setting.
Curr Anesthesiol Rep 2020: 1-8.
Free PMC article

Li RY, Lin M, Jiang HY, Wen SH, Shen JT, Huang WQ, Zhang XY.
Impact of Anxiety or Depression Symptoms on Propofol Requirements for Sedation in Females: A Prospective Cohort Study.
J Clin Pharmacol 2020;60(10): 1376-1384.

Villa EK, Villa D, Bundoc RC.
Narcotrend-guided intraoperative care of a Trisomy 21 paediatric patient who underwent occipitocervical fusion.
BMJ Case Rep 2020; 13(2): e231276.

de Heer IJ, Warmenhoven AT, Weber F.
Electroencephalographic density spectral array monitoring during propofol sedation in teenagers, using the narcotrend electroencephalographic monitor.
Minerva Anestesiol 2020; 86(6): 601-607.

Sponholz C, Schuwirth C, Koenig L, Hoyer H, Coldewey SM, Schelenz C, Doenst T, Kortgen A, Bauer M.
Intraoperative reduction of vasopressors using processed electroencephalographic monitoring in patients undergoing elective cardiac surgery: a randomized clinical trial.
J Clin Monit Comput 2020; 34(1): 71-80.

Berger-Estilita J, Steck K, Vetter C, Seidel K, Krejci V, Hight D, Kaiser H.
A case report of several intraoperative convulsions while using the Narcotrend monitor: Significance and predictive use.
Medicine (Baltimore) 2019; 98(47): e18004.
Free PMC article.

Hou BJ, Du Y, Gu SX, Fan J, Wang R, Deng H, Guo DX, Wang L, Wang YY.
General anesthesia combined with epidural anesthesia maintaining appropriate anesthesia depth may protect excessive production of inflammatory cytokines and stress hormones in colon cancer patients during and after surgery.
Medicine (Baltimore) 2019; 98(30): e16610.
Free PMC article.

Niu K, Guo C, Han C, Teng S.
Equipment failure of intravenous syringe pump detected by increase in Narcotrend stage: A case report.
Medicine (Baltimore) 2018 ; 97(47): e13174.
Free PMC article.

Weber F, Prasser C.
Investigating propofol-sufentanil interaction using clinical endpoints and processed electroencephalography: a prospective randomized controlled trial.
Minerva Anestesiol 2019; 85(3): 271-278.

Weber F, Walhout LC, Escher JC.
The impact of Narcotrend™ EEG-guided propofol administration on the speed of recovery from pediatric procedural sedation-A randomized controlled trial.
Paediatr Anaesth 2018; 28(5): 443-449.

Dennhardt N, Arndt S, Beck C, Boethig D, Heiderich S, Schultz B, Weber F, Sümpelmann R.
Effect of age on Narcotrend Index monitoring during sevoflurane anesthesia in children below 2 years of age.
Paediatr Anaesth 2018; 28(2): 112-119.

Dennhardt N, Beck C, Boethig D, Heiderich S, Horke A, Tiedge S, Boehne M, Sümpelmann R.
Impact of temperature on the Narcotrend Index during hypothermic cardiopulmonary bypass in children with sevoflurane anesthesia.
Perfusion 2018; 33(4): 303-309.

Dennhardt N, Boethig D, Beck C, Heiderich S, Boehne M, Leffler A, Schultz B, Sümpelmann R.
Optimization of initial propofol bolus dose for EEG Narcotrend Index-guided transition from sevoflurane induction to intravenous anesthesia in children.
Paediatr Anaesth 2017; 27(4): 425-432.

Kreuzer I, Osthaus WA, Schultz A, Schultz B.
Influence of the sevoflurane concentration on the occurrence of epileptiform EEG patterns.
PLoS One 2014; 9(2): e89191.
Free PMC article.

Schultz B, Schultz A.
Neuromonitoring bei Kindern: Wie tief schläft mein Patient?
Anästhesiol Intensivmed Notfallmed Schmerzther 2014; 49:84-90.

Rinösl H, Fleck T, Dworschak M.
Brain ischemia instantaneously tracked by the Narcotrend EEG device. J Cardiothorac Vasc Anesth 2013 Apr;27(2):e13-4.

Schultz B, Otto C, Schultz A, Osthaus WA, Krauss T, Dieck T, Sander B, Rahe-Meyer N, Raymondos K.
Incidence of epileptiform EEG activity in children during mask induction of anaesthesia with brief administration of 8% sevoflurane.
PLoS One 2012;7(7):e40903. doi: 10.1371/journal.pone.0040903.

Linde HJ van der, Van Deuren B, Somers Y, Teisman A, Drinkenburg WH, Gallacher DJ.
EEG in the FEAB model: measurement of electroencephalographical burst suppression and seizure liability in safety pharmacology. J Pharmacol Toxicol Methods 2011; 63(1): 96-101.

Büttner N, Schultz B, Grouven U, Schultz A.
EEG-adaptierte "target-controlled infusion" - Propofolzielkonzentration bei unterschiedlichen Remifentanildosierungen.
Anaesthesist 2010; 59: 126-134.
Abstract

Stuttmann R, Schultz A, Kneif T, Krauß T, Schultz B.
Assessing the depth of hypnosis of xenon anaesthesia with the EEG.
Biomed Tech 2010; 55: 77-82.
Abstract

Willig M, Schultz B, Kneif T, Schultz A.
Einfluss des EEG-Monitorings auf das Dosierverhalten bei intravenöser Anästhesie - Eine multizentrische Analyse.
Klin Neurophysiol 2010; 41: 28-32.
Abstract

Haensch K, Schultz A, Krauß T, Grouven U, Schultz B.
Women need more propofol than men during EEG-monitored total intravenous anaesthesia.
Biomed Tech 2009; 54: 76-82.
Abstract

Schultz A, Siedenberg M, Grouven U, Kneif T, Schultz B.
Comparison of Narcotrend Index, Bispectral Index, spectral and entropy parameters during induction of propofol-remifentanil anaesthesia.
J Clin Monit Comput 2008; 22: 103-111.

Schultz B, Schleppers A, Kneif T, Scheinichen D, Schultz A.
Einfluss von EEG-Monitoring, Alter und Geschlecht auf den Propofolbedarf während neurochirurgischer Eingriffe.
Klin Neurophysiol 2008; 39: 189-193.

Weber F, Hollnberger H, Weber J.
Electroencephalographic Narcotrend Index monitoring during procedural sedation and analgesia in children.
Pediatr Anesth 2008; 18: 823-830.

Panousis P, Heller AR, Burghardt M, Bleyl JU, Koch T.
The effects of electromyographic activity on the accuracy of the Narcotrend monitor compared with the Bispectral Index during combined anaesthesia.
Anesthesia 2007; 62: 868-874.

Schultz A, Kneif T, Grouven U, Schultz B.
EEG-Monitoring zur Sedierungsüberwachung: Verkürzung der intensivstationären Behandlungsdauer. Klin Neurophysiol 2007; 38: 198-202.
St. Louis, E. K., Frey, L. C. (Eds.)
Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants
Chicago: American Epilepsy Society; 2016.
https://www.ncbi.nlm.nih.gov/books/NBK390354/

Kreuer S, Wilhelm W.
Der Narcotrend-Monitor. In: Wilhelm W, Bruhn J, Kreuer S (Hrsg.). Überwachung der Narkosetiefe (2. Auflage).
Deutscher Ärzte-Verlag, Köln 2006, 108-132.

Schultz B.
EEG-Monitoring auf der Intensivstation.
In: Wilhelm W, Bruhn J, Kreuer S (Hrsg.). Überwachung der Narkosetiefe (2. Auflage).
Deutscher Ärzteverlag, Köln 2004, 300-317.

Schultz B, Büttner NA, Schönberg G, Bezler C, Schultz A.
EEG-gestützte Narkoseüberwachung: Untersuchung hinsichtlich einer EEG-adaptierten Propofoldosierung.
Klin Neurophysiol 2006; 37: 1-5.

Grouven U, Beger F, Schultz B, Schultz A.
Correlation of Narcotrend Index, entropy measures, and spectral parameters with calculated propofol effect-site concentrations during induction of propofol-remifentanil anaesthesia.
J Clin Monit Comput 2005; 18: 231-240.

Kreuer S, Schreiber JU, Bruhn J, Wilhelm W.
Impact of patient age on propofol consumption during propofol-remifentanil anaesthesia.
Eur J Anaesthesiol. 2005; 22: 123-128.

Kreuer S, Schreiber JU, Bruhn J, Wilhelm W.
Impact of patient age on propofol consumption during propofol-remifentanil anaesthesia.
Eur J Anaesthesiol. 2005; 22: 123-128.

Kreuer S, Bruhn J, Stracke C, Aniset L, Silomon M, Larsen R, Wlhelm W.
Narcotrend or Bispectral Index monitoring during desflurane-remifentanil anaesthesia: a comparison with a standard practice protocol.
Anesth Analg 2005;101: 427-434.

Weber F, Hollnberger H, Gruber M, Frank B, Taeger K.
The correlation of the Narcotrend Index with endtidal sevoflurane concentrations and hemodynamic parameters in children.
Paediatr Anaesth 2005; 15: 727-732.

Wilhelm W, Buchinger H, Biedler A, Altmann S, Larsen R, Kreuer S.
Einfluss des Geschlechts auf Propofolverbrauch und Aufwachzeiten bei standardisierter Anästhesietiefe.
Anaesthesist 2005; 54: 567-574.

Bauerle K, Greim CA, Schroth M, Geisselbrecht M, Kobler A, Roewer N.
Prediction of depth of sedation and anaesthesia by the Narcotrend EEG monitor.
Br J Anaesth 2004; 92: 841-845.

Kreuer S, Wilhelm W, Grundmann U, Larsen R, Bruhn J.
Narcotrend index versus bispectral index as EEG measures of anesthetic drug effect during propofol anesthesia.
Anesth Analg 2004; 98: 692-697.

Schultz A, Grouven U, Beger FA, Schultz B.
The Narcotrend Index: classification algorithm, correlation with propofol effect-site concentrations, and comparison with spectral parameters.
Biomed Tech 2004; 49: 38-42.

Schultz A, Grouven U, Zander I, Beger FA, Siedenberg M, Schultz B.
Age-related Effects in the EEG during Propofol Anaesthesia.
Acta Anaesthesiol Scand 2004; 48: 27-34.

Grouven U, Beger FA, Schultz A, Schultz B.
Vergleich von Spektral- und Komplexitätsparametern zur Beschreibung von Medikamentenwirkungen im Narkose-EEG.
Inform Biom Epidemiol Med Biol 2003; 34(3): 192-193.

Kreuer S, Biedler A, Larsen R, Altmann S, Wilhelm W.
Narcotrend monitoring allows faster emergence and a reduction of drug consumption in propofol-remifentanil anesthesia.
Anesthesiology 2003; 99: 34-41.

Münte S, Münte TF, Grotkamp J, Haeseler G, Raymondos K, Piepenbrock S, Kraus G.
Implicit memory varies as a function of hypnotic electroencephalogram stage in surgical patients.
Anesth Analg 2003; 97: 132-138.

Schmidt GN, Bischoff P, Standl T, Jensen K, Voigt M, Schulte am Esch J.
Narcotrend® and Bispectral Index Monitor Are Superior to Classic Electroencephalographic Parameters for the Assessment of Anesthetic States during Propofol-Remifentanil Anesthesia.
Anesthesiology 2003; 99:1072-1077.

Schultz A, Beger FA, Weber BP, Grouven U, Niclaus O, Lüllwitz E, Schultz B.
The intraoperative electrically elicited Stapedius Reflex Threshold is related to the dosage of hypnotic drugs in general anaesthesia.
Ann Oto Rhinol Laryn 2003; 112: 1050-1055.

Schultz B, Beger FA, Weber BP, Niclaus O, Lüllwitz E, Grouven U, Schultz A.
Influence of EEG Monitoring on Intraoperative Stapedius Reflex Threshold Values in Cochlear Implantation in Children.
Paediatr Anaesth 2003; 13: 790-796.

Schultz B, Kreuer S, Wilhelm W, Grouven U, Schultz A.
Der Narcotrend®-Monitor: Entwicklung und Interpretationsalgorithmus.
Anaesthesist 2003; 52: 1143-1148.

Kreuer S, Molter G, Biedler A, Larsen R, Schoth S, Wilhelm W.
Narcotrend-Stadien und endexspiratorische Desflurankonzentrationen - Eine Untersuchung bei Ausleitung von Desfluran-Remifentanil-Anästhesie.
Anaesthesist 2002; 51: 800-804.

Schmidt GN, Bischoff P, Standl T, Voigt M, Papavero L, Schulte am Esch J.
Narcotrend, Bispectral Index, and Classical Electroencephalogram Variables During Emergence from Propofol/Remifentanil Anesthesia.
Anest Analg 2002; 95: 1324-1330.

Schultz B, Grouven U, Schultz A.
Automatic classification algorithms of the EEG monitor Narcotrend for routinely recorded EEG data from general anaesthesia: a validation study.
Biomed Tech 2002; 47: 9-13.

Schultz B, Schultz A.
EEG monitoring improves quality and safety of TIVA.
Anaesth Intensive Care 2002; 30: 817-818.

Wehrmann T, Grotkamp J, Stergiou N, Riphaus A, Kluge A, Lembcke B, Schultz A.
EEG-monitoring facilitates propofol sedation for routine ERCP. A randomized, controlled trial.
Gastrointest Endosc 2002; 56: 817-824.

Wilhelm W, Kreuer S, Larsen R und die Narcotrend-Studiengruppe.
Narcotrend-EEG-Monitoring bei total intravenöser Anästhesie.
Anaesthesist 2002; 51: 980-988.

Kreuer S, Biedler A, Larsen R, Schoth S, Altman S,. Wilhelm W.
The Narcotrend - a new EEG monitor designed to measure the depth of anaesthesia.
Anaesthesist 2001; 50: 921-925.

Schultz A, Schultz B, Grouven U, Beger FA, Korsch G.
Sharp transients in the EEGs of non-epileptic adult patients receiving sevoflurane.
Pharmacy World & Science 2001; 23: 82-85.

Schultz, A., Schultz, B., Grouven, U., Korsch, G.
Epileptiform activity in the EEGs of two nonepileptic children under sevoflurane anesthesia.
Anaesth Intensive Care 2000; 28: 205-207.

Schultz B, Beger FA, Grouven U, Hausdörfer J, Rohde U, Schultz A.
Epilepsietypische EEG-Potentiale unter Sevofluran bei Erwachsenen - zwei Kasuistiken.
Anästhesiol Intensivmed 2000; 41:427.