title: EEG sources of noise in intraoperative somatosensory evoked potential monitoring during propofol anesthesia.
abstract: OBJECTIVE
  It was hypothesized that somato- sensory evoked potentials can be achieved faster by selective averaging during periods of low spontaneous electroen- cephalographic (EEG) activity. We analyzed the components of EEG that decrease the signal-to-noise ratio of somatosensory evoked potential (SEP) recordings during propofol anesthesia.
  
  
  METHODS
  Patient EEGs were recorded with a high sampling frequency during deep anesthesia, when EEGs were in burst suppression. EEGs were segmented visually into bursts, spindles, suppressions, and artifacts. Tibial somatosensory evoked potentials (tSEPs) were averaged offline separately for burst, suppression, and spindle segments using a signal bandwidth of 30-200 Hz. Averages achieved with 2, 4, 8, 16, 64, 128, and 256 responses were compared both visually, and by calculating the signal-to-noise ratios.
  
  
  RESULTS
  During bursts and spindles, the noise levels were similar and significantly higher than during suppressions. Four to eight times more responses had to be averaged during bursts and spindles than during suppressions in order to achieve a similar response quality. Averaging selectively during suppressions can therefore yield reliable tSEPs in approximately one-fifth of the time required during bursts.
  
  
  CONCLUSIONS
  The major source of EEG noise in tSEP recordings is the mixed frequency activity of the slow waves of bursts that occur during propofol anesthesia. Spindles also have frequency components that increase noise levels, but these are less important, as the number of spindles is fewer. The fastest way to obtain reliable tSEPs is by averaging selectively during suppressions.
authors: Department of Biomedical Engineering, Tampere University of Technology, Tampere, Finland. atte.joutsen@tut.fi
authors: Atte
authors: A
authors: Joutsen
authors: Pasi
authors: P
authors: Puumala
authors: Leo-Pekka
authors: LP
authors: Lyytikäinen
authors: Olli
authors: O
authors: Pajulo
authors: Aira
authors: A
authors: Etelämäki
authors: Hannu
authors: H
authors: Eskola
authors: Ville
authors: V
authors: Jäntti
mesh_terms: D000293:Adolescent; D000328:Adult; D000758:Anesthesia; D018686:Anesthetics, Intravenous; D004569:Electroencephalography / Q000379:methods*; D004576:Electromyography / Q000379:methods; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D008991:Monitoring, Physiologic; D015742:Propofol / Q000494:pharmacology; D013977:Tibia / Q000294:innervation
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol