Clinical metrics in emergency medicine: the shock index and the probability of hospital admission and inpatient mortality

STUDY OBJECTIVES: 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.