title: Monitoring cerebral autoregulation after head injury. Which component of transcranial Doppler flow velocity is optimal?
abstract: BACKGROUND
  Cerebral autoregulation assessed using transcranial Doppler (TCD) mean flow velocity (FV) in response to various physiological challenges is predictive of outcome after traumatic brain injury (TBI). Systolic and diastolic FV have been explored in other diseases. This study aims to evaluate the systolic, mean and diastolic FV for monitoring autoregulation and predicting outcome after TBI.
  
  
  METHODS
  300 head-injured patients with blood pressure (ABP), intracranial pressure (ICP), cerebral perfusion pressure (CPP), and FV recordings were studied. Autoregulation was calculated as a correlation of slow changes in diastolic, mean and systolic components of FV with CPP (Dx, Mx, Sx, respectively) and ABP (Dxa, Mxa, Sxa, respectively) from 30 consecutive 10 s averaged values. The relationship with age, severity of injury, and dichotomized 6 months outcome was examined.
  
  
  RESULTS
  Association with outcome was significant for Mx and Sx. For favorable/unfavorable and death/survival outcomes Sx showed the strongest association (F = 20.11; P = 0.00001 and F = 13.10; P = 0.0003, respectively). Similarly, indices derived from ABP demonstrated the highest discriminatory value when systolic FV was used (F = 12.49; P = 0.0005 and F = 5.32; P = 0.02, respectively). Indices derived from diastolic FV demonstrated significant differences (when calculated using CPP) only when comparing between fatal and non-fatal outcome.
  
  
  CONCLUSIONS
  Systolic flow indices (Sx and Sxa) demonstrated a stronger association with outcome than the mean flow indices (Mx and Mxa), irrespective of whether CPP or ABP was used for calculation.
authors.affiliation: Division of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke's Hospital, University of Cambridge, Hills Road, Cambridge CB2 0QQ, UK. kpb26@cam.ac.uk
authors.forename: Karol P
authors.initials: KP
authors.lastname: Budohoski
authors.forename: Matthias
authors.initials: M
authors.lastname: Reinhard
authors.forename: Marcel J H
authors.initials: MJ
authors.lastname: Aries
authors.forename: Zofia
authors.initials: Z
authors.lastname: Czosnyka
authors.forename: Peter
authors.initials: P
authors.lastname: Smielewski
authors.forename: John D
authors.initials: JD
authors.lastname: Pickard
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Kirkpatrick
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D001794:Blood Pressure; D001921:Brain / Q000098:blood supply* / Q000503:physiopathology; D001930:Brain Injuries / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D004453:Echoencephalography; D005260:Female; D015600:Glasgow Coma Scale; D006706:Homeostasis; D006801:Humans; D007427:Intracranial Pressure; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012189:Retrospective Studies; D017585:Ultrasonography, Doppler, Transcranial