title: Significance of a reduced cerebral blood flow during the first 12 hours after traumatic brain injury.
abstract: BACKGROUND
  It is controversial whether a low cerebral blood flow (CBF) simply reflects the severity of injury or whether ischemia contributes to the brain's injury. It is also not clear whether posttraumatic cerebral hypoperfusion results from intracranial hypertension or from pathologic changes of the cerebral vasculature. The answers to these questions have important implications for whether and how to treat a low CBF.
  
  
  METHODS
  We performed a retrospective analysis of 77 patients with severe traumatic brain injury who had measurement of CBF within 12 hours of injury. CBF was measured using xenon-enhanced computed tomography (XeCT). Global CBF, physiological parameters at the time of XeCT, and outcome measures were analyzed.
  
  
  RESULTS
  Average global CBF for the 77 patients was 36+/-16 mL/100 g/minutes. Nine patients had an average global CBF<18 (average 12+/-5). The remaining 68 patients had a global CBF of 39+/-15. The initial ICP was >20 mmHg in 90% and >30 mmHg in 80% of patients in the group with CBF<18, compared to 33% and 16%, respectively, in the patients with CBF>or=18. Mortality was 90% at 6 months postinjury in patients with CBF<18. Mortality in the patients with CBF>18 was 19% at 6 months after injury.
  
  
  CONCLUSIONS
  In patients with CBF<18 mL/100 g/minutes, intracranial hypertension plays a major causative role in the reduction in CBF. Treatment would most likely be directed at controlling intracranial pressure, but the early, severe intracranial hypertension also probably indicates a severe brain injury. For levels of CBF between 18 and 40 mL/100 g/minutes, the presence of regional hypoperfusion was a more important factor in reducing the average CBF.
authors.affiliation: Department of Neurosurgery, Baylor College of Medicine, Houston, TX 77030, USA, and Department of Neurosurgery, University Hospital, Charles' University, Hradec Kralove, Czech Republic.
authors.forename: Roman
authors.initials: R
authors.lastname: Hlatky
authors.forename: Charles F
authors.initials: CF
authors.lastname: Contant
authors.forename: Pedro
authors.initials: P
authors.lastname: Diaz-Marchan
authors.forename: Alex B
authors.initials: AB
authors.lastname: Valadka
authors.forename: Claudia S
authors.initials: CS
authors.lastname: Robertson
mesh_terms: D000328:Adult; D001930:Brain Injuries / Q000150:complications / Q000503:physiopathology* / Q000628:therapy; D002545:Brain Ischemia / Q000209:etiology / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D015600:Glasgow Coma Scale; D023261:Glasgow Outcome Scale; D006801:Humans; D019586:Intracranial Hypertension / Q000209:etiology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013997:Time Factors; D016896:Treatment Outcome