title: Physiologic and functional outcome correlates of brain tissue hypoxia in traumatic brain injury.
abstract: OBJECTIVE
  Assess the prevalence of brain tissue hypoxia in patients with severe traumatic brain injuries (TBI), and to characterize the relationship between brain tissue hypoxia and functional outcome.
  
  
  METHODS
  Retrospective review of severe TBI patients.
  
  
  METHODS
  Intensive care unit of a level I trauma center.
  
  
  METHODS
  Twenty-seven patients with severe TBI requiring intracranial pressure (ICP) monitoring. Median age was 22 yrs, and a majority (63%) had traumatic subarachnoid hemorrhage.
  
  
  METHODS
  Hourly assessments of ICP, brain tissue oxygen, mean arterial pressure, fraction of inspired oxygen (FiO2), partial pressure of arterial carbon dioxide (PaCO2), and hemoglobin concentration (hemoglobin) were recorded. Outcome was assessed 6-9 months postinjury.
  
  
  RESULTS
  Mean (SD) ICP and BTpO2 were 13.7 (6.6) cm H2O and 30.8 (13.6) mm Hg. A total of 13.5% (379) of the BTpO2 values recorded were < 20 mm Hg, only 86 of which were associated with ICP > or = 20 cm H2O. This prevalence was comparable with episodes of ICP elevations above 20 cm H2O (14.1%, 397). Hypoxic episodes were more common when cerebral perfusion pressure was below 60 mm Hg (relative risk = 3.0, p < 0.0001). We did not find an association in hypoxic risk and hemoglobin in the range of 7-12 g/dL or PaCO2 in the range of 25-40 mm Hg. Subjects with hourly episodes (epochs) of hypoxia > 20% of the time had poorer scores on outcome measures compared with those with fewer hypoxic epochs.
  
  
  CONCLUSIONS
  Hypoxic episodes are common after severe TBI, and most are independent of ICP elevations. Most episodes of hypoxia occur while cerebral perfusion pressure and mean arterial pressure are within the accepted target range. There is no clear association between PaCO2 and hemoglobin with BTpO2. The young age and high prevalence of traumatic subarachnoid hemorrhage in this cohort may limit its generalizability. Increased frequency of hypoxic episodes is associated with poor functional outcome.
authors.affiliation: Department of Neurology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
authors.forename: Jason J J
authors.initials: JJ
authors.lastname: Chang
authors.forename: Teddy S
authors.initials: TS
authors.lastname: Youn
authors.forename: Dan
authors.initials: D
authors.lastname: Benson
authors.forename: Heather
authors.initials: H
authors.lastname: Mattick
authors.forename: Nicholas
authors.initials: N
authors.lastname: Andrade
authors.forename: Caryn R
authors.initials: CR
authors.lastname: Harper
authors.forename: Carol B
authors.initials: CB
authors.lastname: Moore
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Madden
authors.forename: Ramon R
authors.initials: RR
authors.lastname: Diaz-Arrastia
mesh_terms: D000293:Adolescent; D000328:Adult; D001930:Brain Injuries / Q000150:complications*; D005260:Female; D006801:Humans; D002534:Hypoxia, Brain / Q000453:epidemiology / Q000209:etiology* / Q000503:physiopathology; D015601:Injury Severity Score; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011379:Prognosis; D012189:Retrospective Studies; D055815:Young Adult