title: Evoked EEG patterns during burst suppression with propofol.
abstract: BACKGROUND
  During EEG suppression with isoflurane or sevoflurane anaesthesia, median nerve stimulation causes cortical responses of two kinds: an N20 wave with a latency of 20 ms and an EEG burst with a latency of 200 ms. We tested the possibility that median nerve stimulation during EEG suppression with propofol would cause an EEG response that was consistent enough to be of use for neuromonitoring.
  
  
  METHODS
  Eight patients were anaesthetized with propofol to allow burst suppression. Electrical stimulation of the median nerve was applied during general anaesthesia and the EEG was measured.
  
  
  RESULTS
  The EEG response to a painful stimulus had four successive components: (i) N20 and P22 potentials, reflecting activation of fast somatosensory pathways; (ii) a high-amplitude negative wave, possibly reflecting activation of the somatosensory cortex SII bilaterally; (iii) a burst (i.e. a negative slow wave with superimposed 10 Hz activity, probably reflecting an arousal mechanism); and (iv) a 13-15 Hz spindle, probably originating from the thalamus, similar to sleep spindles. These could be seen separately and in different combinations. Bursts and spindles during burst suppression were also seen without stimulation. In deepening propofol anaesthesia, spindles were seen in the continuous EEG before burst suppression was achieved. In deep anaesthesia, spindles were seen when bursts had ceased, and painful stimuli evoked sharp waves without subsequent bursts.
  
  
  CONCLUSIONS
  In addition to SSEP (somatosensory evoked potentials), three different evoked responses are noted that could be useful for clinical monitoring.
authors.affiliation: Department of Anaesthesiology, and Department of Clinical Neurophysiology, Oulu University Hospital, Oulu, Finland. ari-matti.huotari@nic.fi
authors.forename: A-M
authors.initials: AM
authors.lastname: Huotari
authors.forename: M
authors.initials: M
authors.lastname: Koskinen
authors.forename: K
authors.initials: K
authors.lastname: Suominen
authors.forename: S
authors.initials: S
authors.lastname: Alahuhta
authors.forename: R
authors.initials: R
authors.lastname: Remes
authors.forename: K M
authors.initials: KM
authors.lastname: Hartikainen
authors.forename: V
authors.initials: V
authors.lastname: Jäntti
mesh_terms: D000328:Adult; D000768:Anesthesia, General; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D004558:Electric Stimulation; D004569:Electroencephalography / Q000187:drug effects*; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D015742:Propofol / Q000494:pharmacology*; D011930:Reaction Time / Q000187:drug effects; D012815:Signal Processing, Computer-Assisted
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol