title: Appropriate time to establish baseline responses for brain stem auditory evoked potentials during microvascular decompression for hemifacial spasm.
abstract: OBJECTIVE
  To evaluate the appropriate time to establish baseline responses for brain stem auditory evoked potentials (BAEPs) during microvascular decompression for hemifacial spasm and its implications on the alarm criteria and outcomes.
  
  
  METHODS
  Overall, 61 patients who had intraoperative monitoring with BAEP during microvascular decompression were retrospectively identified. The latencies and amplitudes of wave V before skin incision and at dura opening (before major manipulation) were compared with the latency and amplitude of wave V at change start (first alarm reported to the surgeon). Also, the results with respect to postoperative outcomes were evaluated.
  
  
  RESULTS
  More alarms would have been communicated to the surgeon when baseline values were set at the beginning of the procedure, when compared with baseline values reset at dura opening (before major manipulation).
  
  
  CONCLUSIONS
  Significant variations in BAEP latency exist before any major manipulations during microvascular decompression. Despite a false-negative case, baselines can be set before any major manipulations (e.g., just before dura opening), with an understanding of the etiology of changes to BAEPs during microvascular decompression.
  
  
  CONCLUSIONS
  This is the first study to establish that during intraoperative BAEP monitoring, baselines that are reset before any significant manipulations are performed, rather than at the beginning of the procedure, have a higher level of sensitivity with regards to hearing outcomes.
authors.affiliation: Departments of *Neurological Surgery, †Neurology, and ‡Neuroscience, University of Pittsburgh, Pittsburgh, Philadelphia, U.S.A.
authors.forename: Santhosh K
authors.initials: SK
authors.lastname: Mohanraj
authors.forename: Parthasarathy D
authors.initials: PD
authors.lastname: Thirumala
authors.forename: Miguel E
authors.initials: ME
authors.lastname: Habeych
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Crammond
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Balzer
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000368:Aged; D004569:Electroencephalography; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D005260:Female; D006309:Hearing; D019569:Hemifacial Spasm / Q000503:physiopathology* / Q000601:surgery*; D006801:Humans; D008297:Male; D061145:Microvascular Decompression Surgery / Q000379:methods*; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D010036:Otolaryngology; D011930:Reaction Time; D012016:Reference Values; D012189:Retrospective Studies; D016896:Treatment Outcome