title: Does stimulus rate matter when performing somatosensory evoked potentials for coma patients?
abstract: BACKGROUND
  It is unclear whether the rate of stimulation for somatosensory evoked potentials (SEPs) can influence the presence or absence of cortical responses to median nerve stimulation in comatose patients. If so, this could affect how SEPs are performed and interpreted for prognostication in coma. Our objective was to determine how frequently our comatose patients had absent median nerve SEP responses at 3 Hz stimulation, but present responses at 1 Hz stimulation, and to report outcomes of these patients.
  
  
  METHODS
  We reviewed SEP recordings in 639 comatose patients over a 9-year period. All had stimulation at 3 Hz and 1 Hz. This is a retrospective review.
  
  
  RESULTS
  There were seven patients who had absent median nerve SEP responses at 3 Hz stimulation bilaterally, but had present responses at 1 Hz on one or both sides. Six of the seven died. One 16-year-old patient with traumatic brain injury awoke, but had moderate disability.
  
  
  CONCLUSIONS
  Stimulation rate is an important determinant of presence or absence of cortical responses in about 1% of comatose patients. It is unclear whether such patients have a different outcome that those with absent responses at both rates of stimulation.
authors.affiliation: Department of Rehabilitation Medicine, University of Washington School of Medicine, P.O. Box 356380, Seattle, WA 98195, USA. lorenzo@u.washington.edu
authors.forename: Lawrence R
authors.initials: LR
authors.lastname: Robinson
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Micklesen
mesh_terms: D000293:Adolescent; D002543:Cerebral Hemorrhage / Q000175:diagnosis / Q000401:mortality / Q000503:physiopathology; D003128:Coma / Q000401:mortality / Q000503:physiopathology*; D003422:Critical Care; D004185:Disability Evaluation; D004558:Electric Stimulation / Q000379:methods*; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D006801:Humans; D020925:Hypoxia-Ischemia, Brain / Q000175:diagnosis / Q000401:mortality / Q000503:physiopathology; D008475:Median Nerve / Q000503:physiopathology*; D011379:Prognosis; D012189:Retrospective Studies; D012815:Signal Processing, Computer-Assisted; D013003:Somatosensory Cortex / Q000503:physiopathology