title: Clinical metrics in emergency medicine: the shock index and the probability of hospital admission and inpatient mortality.
abstract: OBJECTIVE
  The shock index (SI), defined as the ratio of HR to systolic BP, has been studied as an alternative prognostic tool to traditional vital signs in specific disease states and subgroups of patients. However, literature regarding its utility in the general ED population is lacking. Our main objective was to determine the probability of admission and inpatient mortality based on the first measured SI at initial presentation in the general adult ED population in our tertiary care centre.
  
  
  METHODS
  A retrospective chart review of all adult patients (≥18 years old) presenting to the ED at our tertiary care centre over a 12-month period was conducted. Likelihood ratios (LRs) were calculated in order to determine the optimal SI cut-off for predicting hospital admission and inpatient mortality.
  
  
  RESULTS
  We reviewed 58 336 ED patient encounters occurring between 1 October 2012 and 30 September 2013. SI >1.2 was associated with a large increase in the likelihood of hospital admission, with a positive LR (+LR) of 11.69 (95% CI 9.50 to 14.39) and a moderate increase in the likelihood of inpatient mortality with a +LR of 5.82 (95% CI 4.31 to 7.85). SI >0.7 and >0.9, the traditional 'normal' cut-offs cited in the literature, were only associated with minimal to small increases in the likelihood of admission and inpatient mortality.
  
  
  CONCLUSIONS
  In our single-centre study, the initial SI recorded in the ED shows promise as a clinical metric in the general adult ED population, increasing the probability of both hospital admission and inpatient mortality, specifically at a threshold of SI >1.2.
authors.affiliation: Department of Emergency Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas.
authors.forename: Kamna S
authors.initials: KS
authors.lastname: Balhara
authors.affiliation: Department of Emergency Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Yu-Hsiang
authors.initials: YH
authors.lastname: Hsieh
authors.affiliation: Department of Emergency Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Bachar
authors.initials: B
authors.lastname: Hamade
authors.affiliation: Department of Emergency Medicine, Baltimore Washington Medical Center, University of Maryland, Glen Burnie, Maryland, USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Circh
authors.affiliation: Department of Emergency Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Gabor D
authors.initials: GD
authors.lastname: Kelen
authors.affiliation: Department of Emergency Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Jamil D
authors.initials: JD
authors.lastname: Bayram
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D017052:Hospital Mortality; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011336:Probability; D011379:Prognosis; D012189:Retrospective Studies; D012307:Risk Factors; D012720:Severity of Illness Index; D012769:Shock / Q000175:diagnosis* / Q000401:mortality*
keywords: acute care; clinical assessment; emergency department