Tibial nerve somatosensory evoked potentials during EEG suppression in sevoflurane anaesthesia.
OBJECTIVE
Cortical tibial nerve somatosensory evoked potentials (TSEPs) were recorded from 10 subjects in sevoflurane anaesthesia in order to study TSEP during EEG suppression.


RESULTS
With a stimulation frequency less than one per second the major component was a positive wave which had maximal amplitude parietally ipsilaterally to stimulus and mean latency of 46.1 ms. It probably corresponds to the P40 wave. It was preceded by a widespread smaller positive wave, which corresponds to the subcortical P30 wave. In two patients a high amplitude negative wave, a couple of milliseconds before the positive wave, and maximal parietally contralateral to stimulus, was seen. All later waves were absent.


CONCLUSIONS
The results are in agreement with our previous results from median nerve SEPs showing that the first cortical response from primary somatosensory cortex is enhanced, and later waves are suppressed. Hence, recording TSEPs during EEG suppression provides a way to record the activity of the primary somatosensory cortex accurately and rapidly due to the very good signal to noise ratio, so that even single responses to stimuli can be seen without averaging. Our results suggest that new cortical generators, which are not recordable awake, may be discovered in some patients.
Rytky
S
S
Department of Clinical Neurophysiology, Oulu University Hospital, Finland. seppo.rytky@oulu.fi
Huotari
A M
AM
Alahuhta
S
S
Remes
R
R
Suominen
K
K
Jäntti
V
V
D000328:Adult; D018685:Anesthetics, Inhalation; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D004558:Electric Stimulation; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008738:Methyl Ethers; D008875:Middle Aged; D000077149:Sevoflurane; D013979:Tibial Nerve / Q000502:physiology*
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane