The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Monitoring Depth of Anesthesia with Electroencephalogram: Methods and Performance Evaluation

Mika Särkelä

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium TU1 at Helsinki University of Technology (Espoo, Finland) on the 18th of April, 2008, at 12 noon.

Overview in PDF format (ISBN 978-951-22-9289-9)   [1290 KB]
Dissertation is also available in print (ISBN 978-951-22-9288-2)

Abstract

In monitoring depth of anesthesia, use of electroencephalogram (EEG) signal data helps to prevent intraoperative awareness and reduces the costs of anesthesia. Modern depth-of-anesthesia monitors use frontal EEG signal to derive an index value, which decreases monotonically with increasing anesthetic drug levels. In this study, electroencephalogram signal processing methods for depth-of-anesthesia monitoring were developed.

The first aim was to develop a method for burst suppression detection and integrate it into the anesthetic depth monitor. Accurate detection of burst suppression improves the accuracy of depth-of-anesthesia monitoring at deep levels of anesthesia. The method developed utilizes a nonlinear energy operator and is based on adaptive segmentation. The developed monitor has been proven accurate in several scientific studies.

A second aim was to develop a depth-of-anesthesia monitor that utilizes both cortical and subcortical information and is applicable with most commonly used anesthetics. The method developed is based on the spectral entropy of EEG and facial electromyogram (EMG) signals. In the method, two spectral entropy variables are derived, aiming to differentiate the cortical state of the patient and subcortical responses during surgery. The concept has been confirmed in the scientific studies conducted during surgery.

Another aim was to develop a method for monitoring epileptiform activity during anesthesia. The method developed is based on a novel EEG-derived quantity, wavelet subband entropy (WSE), which followed the time evolution of epileptiform activity in anesthesia with prediction probability of 0.8 and recognized misleading readings of the depth-of-anesthesia monitor during epileptiform activity with event-sensitivity of 97%.

The fourth aim was to investigate the monitoring technique developed, called Entropy, in S-ketamine anesthesia and in dexmedetomidine sedation. In S-ketamine anesthesia, high-frequency EEG oscillations turned out to be the reason for the high entropy values seen despite deep anesthesia. In dexmedetomidine sedation, Entropy proved a rapid indicator of transition phases from conscious and unconscious states.

This thesis consists of an overview and of the following 5 publications:

  1. M. Särkelä, S. Mustola, T. Seppänen, M. Koskinen, P. Lepola, K. Suominen, T. Juvonen, H. Tolvanen-Laakso, V. Jäntti. 2002. Automatic analysis and monitoring of burst suppression in anesthesia. Journal of Clinical Monitoring and Computing 17, no. 2, pages 125-134.
  2. H. Viertiö-Oja, V. Maja, M. Särkelä, P. Talja, N. Tenkanen, H. Tolvanen-Laakso, M. Paloheimo, A. Vakkuri, A. Yli-Hankala, P. Meriläinen. 2004. Description of the Entropy™ algorithm as applied in the Datex-Ohmeda S/5™ Entropy module. Acta Anaesthesiologica Scandinavica 48, no. 2, pages 154-161. © 2004 Blackwell Publishing. By permission.
  3. M.O.K. Särkelä, M.J. Ermes, M.J. van Gils, A.M. Yli-Hankala, V.H. Jäntti, A.P. Vakkuri. 2007. Quantification of epileptiform electroencephalographic activity during sevoflurane mask induction. Anesthesiology 107, no. 6, pages 928-938. © 2007 Lippincott Williams & Wilkins. By permission.
  4. A. Maksimow, M. Särkelä, J.W. Långsjö, E. Salmi, K.K. Kaisti, A. Yli-Hankala, S. Hinkka-Yli-Salomäki, H. Scheinin, S.K. Jääskeläinen. 2006. Increase in high frequency EEG activity explains the poor performance of EEG spectral entropy monitor during S-ketamine anesthesia. Clinical Neurophysiology 117, no. 8, pages 1660-1668. © 2006 Elsevier Science. By permission.
  5. A. Maksimow, A. Snapir, M. Särkelä, E. Kentala, J. Koskenvuo, J. Posti, S.K. Jääskeläinen, S. Hinkka-Yli-Salomäki, M. Scheinin, H. Scheinin. 2007. Assessing the depth of dexmedetomidine-induced sedation with electroencephalogram (EEG)-based spectral entropy. Acta Anaesthesiologica Scandinavica 51, no. 1, pages 22-31. © 2007 Blackwell Publishing. By permission.

Keywords: anesthesia, burst suppression, EEG, entropy, wavelet

This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

© 2008 Helsinki University of Technology

Last update 2011-05-26