Electroencephalographic signals during anesthesia recorded from surface and depth electrodes

Abstract

Purpose: Anesthesiologists have increasingly started to use EEG-based indexes to estimate the level and type of unconsciousness. However, the physiology and biophysics are poorly understood in anesthesiological literature.

Methods: EEG was recorded from electrodes on the surface of head, including scalp, as well as DBS (deep brain stimulation) electrodes implanted deep in the brain. Mathematical modeling with a realistic head model was performed to create illustrative images of the sensitivity of electrode montages.

Results: EEG pattern of anesthesia, burst-suppression, is recordable outside of scalp area as well in the depth of brain because the EEG current loops produce recordable voltage gradients in the whole head. The typical electrodes used in anesthesia monitoring are most sensitive to basal surface of frontal lobes as well as frontal and mesial parts of temporal lobes.

Conclusions: EEG currents create closed-loops, which flow from the surface of the cortex and then return to the inside of the hemispheres. In the case of widespread synchronous activity like physiological sleep or anesthesia, the currents recorded with surface and depth electrodes return through the base of brain and skull.

Keywords:

• EEG
• electrode
• montage
• sensitivity
• anesthesia

Disclosure statement

The authors do not report commercial connection.

Additional information

Notes on contributors

Ville Jäntti

Ville Jäntti, MD, received his PhD degree in Clinical Neurophysiology from University of Turku, Finland. He is a senior lecturer in neurophysiological technology at Tampere University of Technology, Tampere, Finland. His research focus is neurophysiological monitoring of anesthesia.

Tuomo Ylinen

Tuomo Ylinen, MD, MSc (tech, engineering physics) is an anesthesiology resident in Tampere University Hospital, Tampere, Finland, currently working on his PhD thesis. His research interest concerns neurophysiological monitoring of anesthesia.

Narayan Puthanmadam Subramaniyam

Dr. Narayan Puthanmadam Subramaniyam received his PhD degree in Biomedical Engineering from Tampere University of Technology. He is currently a postdoctoral researcher in Department of Neuroscience and Biomedical Engineering at Aalto University. His research interests are in statistical signal processing, EEG/MEG inverse problems and brain connectivity analysis.

Kotoe Kamata

Dr. Kotoe Kamata is a staff anesthesiologist at Tokyo Women's Medical University. She received her PhD degree in Medicine from Tokyo Women's Medical University. She studied as a postdoctoral fellow of anesthesia EEG at Tampere University Hospital. Her current research interests are anesthesia EEG, procedural sedation and analgesia outside OR, and neuroanesthesia.

Arvi Yli-Hankala

Dr. Arvi Yli-Hankala, MD, PhD, received his PhD degree in Anesthesiology (EEG monitoring during Anesthesia) from University of Tampere, Finland. He holds the professorship of Anesthesia at the University of Tampere. His main research focus is on the monitoring of adequacy of anesthesia in the clinical setting.

Pasi Kauppinen

Pasi Kauppinen, DSc (Biotechnology), Laboratory Manager in Tampere University of Technology, Tampere, Finland.

Eila Sonkajärvi

Eila Sonkajärvi, MD, PhD, Senior Physician, Specialist in Neuroanesthesiology Department of Anesthesiology, Oulu University Hospital, Oulu, Finland.