title: Redefining hypotension in traumatic brain injury.
abstract: BACKGROUND
  Systemic hypotension is a well documented predictor of increased mortality following traumatic brain injury (TBI). Hypotension is traditionally defined as systolic blood pressure (SBP)<90 mmHg. Recent evidence defines hypotension by a higher SBP in injured (non-TBI) trauma patients. We hypothesize that hypotension threshold requires a higher SBP in isolated moderate to severe TBI.
  
  
  METHODS
  A retrospective database review of all adults (≥ 15 years) with isolated moderate to severe TBI (head abbreviated injury score (AIS)≥ 3, all other AIS ≤ 3), admitted from five Level I and eight Level II trauma centres (Los Angeles County), between 1998 and 2005. Several fit statistic analyses were performed for each admission SBP from 60 to 180 mmHg to identify the model that most accurately defined hypotension for three age groups: 15-49 years, 50-69 years, and ≥ 70 years. The main outcome variable was mortality, and the optimal definition of hypotension for each group was determined from the best fit model. Adjusted odds ratios (AOR) were then calculated to determine increased odds in mortality for the defined optimal SBP within each age group.
  
  
  RESULTS
  A total of 15,733 patients were analysed. The optimal threshold of hypotension according to the best fit model was SBP of 110 mmHg for patients 15-49 years (AOR 1.98, CI 1.65-2.39, p<0.0001), 100 mmHg for patients 50-69 years (AOR 2.20, CI 1.46-3.31, p=0.0002), and 110 mmHg for patients ≥ 70 years (AOR 1.92, CI 1.35-2.74, p=0.0003).
  
  
  CONCLUSIONS
  Patients with isolated moderate to severe TBI should be considered hypotensive for SBP<110 mmHg. Further research should confirm this new definition of hypotension by correlation with indices of perfusion.
authors.affiliation: Department of Surgery, Division of Trauma and Critical Care, Cedars-Sinai Medical Center, Los Angeles, CA 90048, United States.
authors.forename: Cherisse
authors.initials: C
authors.lastname: Berry
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Ley
authors.forename: Marko
authors.initials: M
authors.lastname: Bukur
authors.forename: Darren
authors.initials: D
authors.lastname: Malinoski
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Margulies
authors.forename: James
authors.initials: J
authors.lastname: Mirocha
authors.forename: Ali
authors.initials: A
authors.lastname: Salim
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D001794:Blood Pressure; D001930:Brain Injuries / Q000175:diagnosis* / Q000401:mortality / Q000503:physiopathology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007022:Hypotension / Q000175:diagnosis* / Q000401:mortality / Q000503:physiopathology; D015601:Injury Severity Score; D015141:Los Angeles / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D011379:Prognosis; D012042:Registries / Q000706:statistics & numerical data; D012189:Retrospective Studies; D014193:Trauma Centers / Q000706:statistics & numerical data*; D055815:Young Adult