title: Intraoperative somatosensory evoked potential monitoring decreases EEG burst suppression ratio during deep general anesthesia.
abstract: OBJECTIVE
  The burst suppression (BS) EEG patterns induced by general anesthesia can react to somatosensory stimuli. We investigated this reactivity by studying the effect of peripheral nerve stimulation used for routine intraoperative spinal cord monitoring by somatosensory evoked potentials on BS patterns.
  
  
  METHODS
  The relative time spent in suppression expressed as BS ratio (BSR) and mean burst duration were measured before (BSR(Pre)), during (BSR(Stim)), and after (BSR(Post)) a 60-second repetitive electrical ulnar nerve stimulation in nine patients under total intravenous general anesthesia with propofol. The BS reactivity was measured as BSR(Pre)-BSR(Stim).
  
  
  RESULTS
  Overall, 27 trials were included with BSR(Pre) up to 77%, indistinguishable from BSR(Post). During stimulation, the mean BSR transiently decreased from 42% to 35%. For each 1% increase in BSR(Pre), the BS reactivity increased with 0.6%, whereas the burst duration remained approximately 3 seconds. For BSR(Pre) below 30%, the BS reactivity was negligible.
  
  
  CONCLUSIONS
  Data from this study show that somatosensory input can evoke bursts, altering the "spontaneous" deep BS patterns (BSR(Pre) >30%). Further studies are necessary to objectively assess the clinical relevance of stimulus-induced BS reactivity during deep general anesthesia.
authors.affiliation: *Division of Physiology and Fundamental Neurosciences, Department for Functional Sciences, Carol Davila University of Medicine and Pharmacy, Bucharest, Romania; †Intraoperative Neurophysiology Unit, Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, U.S.A.; ‡Department of Neurology, Case Western Reserve University, Cleveland, Ohio, U.S.A.; and §Department of Neuroscience and Pharmacology, Panum Institute, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Călin
authors.forename: Vishakhadatta M
authors.initials: VM
authors.lastname: Kumaraswamy
authors.forename: Diana
authors.initials: D
authors.lastname: Braver
authors.forename: Dinesh G
authors.initials: DG
authors.lastname: Nair
authors.forename: Mihai
authors.initials: M
authors.lastname: Moldovan
authors.forename: Mirela V
authors.initials: MV
authors.lastname: Simon
mesh_terms: D000328:Adult; D000368:Aged; D000768:Anesthesia, General / Q000379:methods*; D004558:Electric Stimulation; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects* / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D011930:Reaction Time; D013118:Spinal Cord Diseases / Q000601:surgery; D055815:Young Adult