title: Correlation Between Cerebral Autoregulation and Carbon Dioxide Reactivity in Patients with Traumatic Brain Injury.
abstract: Cerebral blood flow autoregulation is commonly impaired in patients with traumatic brain injury (TBI). This study was to investigate correlations between cerebral autoregulation and CO2 reactivity in patients with TBI during transient mild hypocapnia.
  
  
  
  Patients with TBI who were on mechanical ventilation were hyperventilated for approximately 60 min. Indices of autoregulation, based on a model of the relationship between arterial blood pressure and blood flow velocity (FV) (ARIabp) and, separately, between cerebral perfusion pressure and FV (ARIcpp), were calculated. Mean flow index (Mx) was also calculated.
  
  
  
  We investigated 31 consecutive patients. At baseline, median PaCO2 was 5.09 kPa (range 4.30-5.67 kPa); during hyperventilation, median PaCO2 was 4.38 kPa (range 3.72-4.96 kPa). ARI was associated with Mx (ARIabp vs. Mx: r = -0.39, p = 0.04; ARIcpp vs Mx: r = -0.67, p < 0.001). CO2 reactivity showed significant correlation with ARIcpp (r = 0.41, p = 0.04) and Mx (r = -0.37, p = 0.04). ARI after hyperventilation was significantly higher than ARI at baseline (ARIcpp: p = 0.02; ARIabp: p < 0.001).
  
  
  
  Cerebral autoregulation seemed to be well linked to CO2 reactivity during transient hyperventilation. ARIcpp had a stronger correlation with CO2 reactivity than ARIabp. ARI indicated improvement of autoregulation during hyperventilation. Cerebral autoregulation indices (ARI, Mx) were associated with each other.
authors.affiliation: Department of Neurosurgery, University of Cambridge, Cambridge, UK. eveyizhang@msn.com.|Department of Neurology, University of Rochester Medical Center, 601 Elmwood Avenue, 673, Rochester, NY, 14642, USA. eveyizhang@msn.com.|Department of Neurology, Saint Louis University, Saint Louis, MO, USA. eveyizhang@msn.com.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Neurosurgery, University of Cambridge, Cambridge, UK.
authors.forename: Xiuyun
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Neurosurgery, University of Cambridge, Cambridge, UK.|Department of Anesthesiology, University Hospital in Basel, Basel, Switzerland.
authors.forename: Luzius
authors.initials: L
authors.lastname: Steiner
authors.affiliation: Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Smielewski
authors.affiliation: Department of Neurology, Saint Louis University, Saint Louis, MO, USA.
authors.forename: Eli
authors.initials: E
authors.lastname: Feen
authors.affiliation: Department of Neurosurgery, University of Cambridge, Cambridge, UK.
authors.forename: John D
authors.initials: JD
authors.lastname: Pickard
authors.affiliation: Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
mesh_terms: D000328:Adult; D062186:Arterial Pressure; D001783:Blood Flow Velocity; D000070642:Brain Injuries, Traumatic / Q000378:metabolism / Q000503:physiopathology*; D002245:Carbon Dioxide / Q000378:metabolism; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D016857:Hypocapnia / Q000378:metabolism / Q000503:physiopathology*; D007427:Intracranial Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D012121:Respiration, Artificial; D017585:Ultrasonography, Doppler, Transcranial
chemical_list: D002245:Carbon Dioxide
keywords: Carbon dioxide reactivity; Cerebral autoregulation; Hypocapnia; Traumatic brain injury