title: New vitals after injury: shock index for the young and age x shock index for the old.
abstract: BACKGROUND
  The traditional view that tachycardia and hypotension accompany hemorrhagic shock following injury has been challenged. This is particularly true at extremes of age. Shock index (SI) may be an alternative indicator of life-threatening bleeding after injury. Because age negatively impacts physiological reserve, we hypothesized that age multiplied by SI (Age x SI) would be a better predictor of 48 h mortality (48 MORT) compared to heart rate (HR), systolic blood pressure (SBP), or SI.
  
  
  METHODS
  A Level I trauma center registry was used to identify victims of blunt injury, aged 18-84 (YOUNG < or =55 and OLD >55) admitted from 1996-2005. Patients with head and spinal cord injury injuries were excluded. The main outcome was 48 MORT. Areas under the receiver operating characteristic curves (AUC) for each predictor were determined.
  
  
  RESULTS
  Sixteen thousand seventy-seven patients were identified. Forty-eight MORT was 1.27% (0.93% in YOUNG and 3.17% in OLD; P < 0.0001). Overall, SI (AUC 0.812) and Age x SI (AUC 0.831) were better predictors of 48 MORT compared to HR (AUC 0.716, P < 0.0001) or SBP (AUC 0.753, P = 0.0004) alone. In OLD patients, AGE x SI (AUC 0.828) was a better predictor of 48 MORT compared to HR (AUC 0.659 P < 0.0001), SBP (AUC 0.762 P = 0.003), or SI (AUC 0.787 P = 0.0005).
  
  
  CONCLUSIONS
  SI and Age x SI are better predictors of 48 MORT in injured patients than HR or SBP alone. SI and Age x SI should be used to identify patients at risk for early mortality following injury.
authors.affiliation: Department of Surgery at The University of Tennessee Health Science Center, Memphis, TN 38163, USA. bzarzaur@utmem.edu
authors.forename: Ben L
authors.initials: BL
authors.lastname: Zarzaur
authors.forename: Martin A
authors.initials: MA
authors.lastname: Croce
authors.forename: Peter E
authors.initials: PE
authors.lastname: Fischer
authors.forename: Louis J
authors.initials: LJ
authors.lastname: Magnotti
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Fabian
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001794:Blood Pressure; D001803:Blood Transfusion / Q000706:statistics & numerical data; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012189:Retrospective Studies; D012769:Shock / Q000175:diagnosis* / Q000401:mortality / Q000503:physiopathology; D013714:Tennessee / Q000453:epidemiology; D015599:Trauma Severity Indices