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An effective correlation dimension and burst suppression ratio of the EEG in rat. Correlation with sevoflurane induced anaesthetic depth

Published online by Cambridge University Press:  10 February 2006

P. L. C. van den Broek ,
C. M. van Rijn ,
J. van Egmond ,
A. M. L. Coenen  and
L. H. D. J. Booij
P. L. C. van den Broek
Affiliation:
Radboud University Nijmegen, NICI Department of Psychology, Nijmegen, The Netherlands Radboud University Nijmegen, Department of Anaesthesiology, Nijmegen, The Netherlands
C. M. van Rijn
Affiliation:
Radboud University Nijmegen, NICI Department of Psychology, Nijmegen, The Netherlands
J. van Egmond
Affiliation:
Radboud University Nijmegen, Department of Anaesthesiology, Nijmegen, The Netherlands
A. M. L. Coenen
Affiliation:
Radboud University Nijmegen, NICI Department of Psychology, Nijmegen, The Netherlands
L. H. D. J. Booij
Affiliation:
Radboud University Nijmegen, Department of Anaesthesiology, Nijmegen, The Netherlands
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Abstract

Summary

Background and objective: Anaesthesiologists need parameters that measure the depth of anaesthesia. In the context of this need, the present study investigated in rats how two variables from the electroencephalogram, the burst suppression ratio and effective correlation dimension correlated with a measure of anaesthetic depth as measured in the strength of a noxious withdrawal reflex. Methods: Eight rats were exposed to different inspiratory concentrations of sevoflurane, each rat in two separate experiments. In the first experiment, spontaneously breathing animals could move freely and no painful stimuli were applied. In the second experiment, in mechanically ventilated restrained anaesthetized rats, the withdrawal reflex was measured every 80 s. In both experiments the electroencephalogram was continuously recorded. The concentration in the effector compartment was estimated using a first order two compartment model. Correlation dimension was computed following the Grassberger/Procaccia/Takens approach with optimized parameter settings to achieve maximum sensitivity to anaesthetic drug effects and enable real-time computation. The Hill, equation was fitted to the data, describing the effect as a function of sevoflurane concentration. Results: Good correlations of Depth of Anaesthesia with correlation dimension as well as burst suppression ratio were established in both types of experiments. Arousal by noxious stimuli decreased burst suppression ratio and increased correlation dimension. The effective sevoflurane concentration associated with 50% of the maximum effect (C50) was higher in experiment II (stimulation) than in experiment I (no stimulation): i.e. for correlation dimension 2.18% vs. 0.60% and for burst suppression ratio 3.07% vs. 1.73%. The slope factors were: γCD = 4.15 vs. γCD = 1.73 and γBSR = 5.2 vs. γBSR = 5.4. Correlation dimension and burst suppression ratio both correlated with the strength of the withdrawal reflex with correlation coefficients of 0.46 and 0.66 respectively (P < 0.001). Conclusions: Both correlation dimension and burst suppression ratio are related to anaesthetic depth and are affected by noxious stimuli. The relationship between anaesthetic depth and burst suppression ratio is confirmed and the potential of correlation dimension is demonstrated.

Keywords

ANAESTHETICS, INHALATION, sevofluraneELECTROENCEPHALOGRAPHY, methodsNON-LINEAR DYNAMICSRATANAESTHESIA GENERAL, measurement of depth of anaesthesia
Type
Original Article
Information
European Journal of Anaesthesiology , Volume 23 , Issue 5 , May 2006 , pp. 391 - 402
Copyright
2006 European Society of Anaesthesiology

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