title: Lower head of the bed position does not change blood flow velocity in subarachnoid hemorrhage.
abstract: BACKGROUND
  Transcranial Doppler (TCD) is commonly used to monitor for vasospasm in patients with aneurysmal subarachnoid hemorrhage (aSAH). Changes in head of the bed (HOB) positions alter blood flow velocities measured by TCD in patients with ischemic stroke. However, the effects of HOB position on the velocities of the cerebral blood flow have not been studied in aSAH patients.
  
  
  METHODS
  We measured the middle cerebral artery (MCA) mean flow velocity (MFV) in consecutive patients with aSAH using TCD with the HOB positioned at 30°-45° and then at 0°-15°. We also collected information on intracranial pressure (ICP) and arterial blood pressure at the time of the TCD studies. Our aim was to determine if changes in HOB position affect MFV in patients with aSAH.
  
  
  RESULTS
  We analyzed 35 TCD studies in 19 patients (mean age 53 ± 13 years). Thirteen studies (37%) showed ultrasonographic evidence of vasospasm. Systolic arterial blood pressure, heart rate, and ICP were not significantly affected by HOB position. The mean MFV of the MCA was 101.0 ± 47.3 cm/s with 0°-15° HOB position versus 100.1 ± 46.8 cm/s with 30°-45° HOB position (P = 0.77 on paired t test). HOB position did not have a significant influence on MFV regardless of the presence of vasospasm.
  
  
  CONCLUSIONS
  HOB position did not significantly affect MFV in our patients with aSAH.
authors.affiliation: Department of Neurology, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Alejandro A
authors.initials: AA
authors.lastname: Rabinstein
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001513:Beds; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003422:Critical Care / Q000379:methods / Q000592:standards; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000502:physiology; D015203:Reproducibility of Results; D013345:Subarachnoid Hemorrhage / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D016683:Supine Position; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods* / Q000592:standards*; D020301:Vasospasm, Intracranial / Q000000981:diagnostic imaging / Q000503:physiopathology