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Narcotrend

 Barbara Schultz, Hanover Medical School, Hanover, Germany

Introduction

The EEG monitor Narcotrend was developed by an interdisciplinary research group at Hanover Medical School. The monitor performs an automatic classification of the electroencephalogram (EEG) recorded during anaesthesia and intensive care. The automatic classification was developed using visually classified EEG epochs as a basis [6, 7]. The main purpose of the Narcotrend is to support the assessment of the patients` hypnotic state.

Main features

The Narcotrend consists of a small preamplifier and a compact monitor for display of the EEG data. Some of the main features are:

·         1-channel-recordings (assessment of depth of sleep during anaesthesia and sedation) and 2-channel-recordings (comparison of EEG signals from both hemispheres) possible

·         Electrodes: self-adhesive, pregelled disposable ECG electrodes (standard), other electrode types possible, e.g. needle electrodes

·         Standard electrode positions for 1-channel recordings: forehead, other positions possible

·         Clear representation of the raw EEG on the Narcotrend screen facilitating visual assessment

·         Automatic EEG analysis every 5 seconds (epoch length 20 seconds, output: Narcotrend stages (A = awake to F = very deep hypnosis, 15 substages) and as further refinement the Narcotrend Index (100 = awake to 0 = very deep hypnosis)

·         Continuous testing of impedances and electrode potentials

·         Marker, filter, replay, and report functions are available

Validation

The Narcotrend classification uses parameters from the time domain and from the frequency domain. It consists of three major parts: artefact detection, classification of stages A to E by multivariate statistical algorithms, and burst suppression detection. Various validation studies have been published showing a high agreement between visual and automatic classification [7], a high correlation between propofol effect-site concentration and Narcotrend Index [3, 6], and also a reliable differentiation between awake versus steady state anaesthesia [5]. The prediction probability for clinical levels of sedation and for different target concentrations of propofol was high [1]. Furthermore, a close correlation between hypnotic depth and Narcotrend classification was shown in clinical studies using PET [2] and implicit memory testing [4].

Clinical application

In a large multicenter study including over 4600 patients clinical benefits of EEG monitoring could be demonstrated. Propofol consumption was significantly reduced and emergence times were significantly shortened [10]. Recent studies advocate the use of the Narcotrend in paediatric anaesthesia [8, 9].

Conclusions

Important information about the hypnotic state of the patient is made available by means of EEG monitoring. By use of the Narcotrend Stage and Index the dosage of hypnotics can be adjusted to the individual patient`s needs to improve the quality of anaesthesia.

References

1.       Bauerle K et al. Br J Anaesth 2004; 92: 841-845

2.       Beger FA et al. Eur J Anaesthesiol 2003; 20 (Suppl 30): A-328

3.       Grouven U et al. J Clin Monit Comput 2004; 18 : 231-241

4.       Münte S et al. Anesth Analg 2003; 97: 132-138

5.       Schmidt GN et al. Anesthesiology 2003; 99: 1072-1077

6.       Schultz A et al. Biomed Tech 2004; 49: 38-42

7.       Schultz B et al. Biomed Tech 2002; 47: 9-13

8.       Weber F et al. Paediatr Anaesth 2005; 15: 727-732

9.       Weber F et al. Eur J Anaesthesiol 2005; 22: 741-747

10. Wilhelm W et al. Anaesthesist 2002; 51: 980-988