title: Presenting blood pressure in traumatic brain injury: a bimodal distribution of death.
abstract: BACKGROUND
  Recent research explores the relationship between vital signs on arrival to the emergency department and early outcomes. This work has not included traumatic brain injury (TBI). We aimed to evaluate the relationship of the initial emergency department systolic blood pressure (EDSBP) with outcome.
  
  
  METHODS
  By using the National Trauma Data Bank (v7), we analyzed patients older than 16 years with isolated moderate to severe blunt TBI. TBI was defined by International Classification of Diseases--9th Rev diagnosis codes and Abbreviated Injury Scale scores. We determined mortality rates while controlling for age, gender, race, payment type, and injury severity using logistic regression. Survival analysis was performed to determine 3-day survival rates. Scores and rates were plotted against EDSBP.
  
  
  RESULTS
  A total of 7,238 patients were included in the analysis. Plots of adverse outcomes versus EDSBP demonstrated bimodal distributions. The mortality curve had one inflection point at EDSBP 120 mm Hg, indicating higher mortality when blood pressures were lower than this threshold. Another inflection began at EDSBP 140 mm Hg. The mortality rate was 21% when EDSBP was <120 mm Hg, 9% when it was between 120 mm Hg and 140 mm Hg, and 19% when EDSBP was ≥140 mm Hg. Multivariate analysis demonstrated that patients presenting with an EDSBP of <120 mm Hg and ≥140 mm Hg were 2.7 (95% confidence interval =2.13,3.48) and 1.6 (95% confidence interval =1.32,1.96) times more likely to die, respectively, than those who presented with a EDSBP of 120 mm Hg to 140 mm Hg.
  
  
  CONCLUSIONS
  Mortality in moderate to severe TBI has a bimodal distribution. Like hypotension, hypertension at hospital admission seems to be associated with increased mortality in TBI, even after controlling for other factors.
authors.affiliation: Harvard School of Public Health, Boston Massachusetts, USA.
authors.forename: Syed Nabeel
authors.initials: SN
authors.lastname: Zafar
authors.forename: Frederick H
authors.initials: FH
authors.lastname: Millham
authors.forename: Yuchiao
authors.initials: Y
authors.lastname: Chang
authors.forename: Karim
authors.initials: K
authors.lastname: Fikry
authors.forename: Hasan B
authors.initials: HB
authors.lastname: Alam
authors.forename: David R
authors.initials: DR
authors.lastname: King
authors.forename: George C
authors.initials: GC
authors.lastname: Velmahos
authors.forename: Marc A
authors.initials: MA
authors.lastname: de Moya
mesh_terms: D015998:Abbreviated Injury Scale; D000293:Adolescent; D000328:Adult; D000368:Aged; D001795:Blood Pressure Determination; D001930:Brain Injuries / Q000401:mortality* / Q000503:physiopathology*; D016009:Chi-Square Distribution; D004636:Emergency Service, Hospital; D005260:Female; D006801:Humans; D019458:Insurance Coverage; D007902:Length of Stay / Q000706:statistics & numerical data; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012372:ROC Curve; D012121:Respiration, Artificial / Q000706:statistics & numerical data; D016019:Survival Analysis; D013599:Systole; D014481:United States / Q000453:epidemiology; D055986:Vital Signs; D014949:Wounds, Nonpenetrating / Q000401:mortality* / Q000503:physiopathology*