Study objectives The shock index (SI), defined as the ratio of the heart rate (HR) to the systolic blood pressure (BP), is used as a prognostic tool in trauma and in specific disease states. However, there is scarcity of data about the utility of the SI in the general emergency department (ED)population. Our goal was to use a large national database of EDs in the United States (US) to determine whether the likelihood of inpatient mortality and hospital admission was associated with initial SI at presentation.

Methods Data from the National Hospital Ambulatory Medical Care Survey were retrospectively reviewed to obtain a weighted sample of all US ED visits between 2005 and 2010. All adults >18 years old who survived the ED visit were included, regardless of their chief complaint. Likelihood ratios (LR) were calculated for a range of SI values, in order to determine SI thresholds most predictive of hospital admission and inpatient mortality. +LRs >5 were considered to be clinically significant.

Results A total of 526 455 251 adult patient encounters were included in the analysis. 56.9% were women, 73.9% were white and 53.2% were between the ages of 18 and 44 years. 88 326 638 (15.7%) unique ED visits resulted in hospital admission and 1 927 235 (2.6%) visits resulted in inpatient mortality. SI>1.3 was associated with a clinically significant increase in both the likelihood of hospital admission (+LR=6.64) and inpatient mortality (+LR=5.67). SI>0.7 and >0.9, the traditional cited cut-offs, were only associated with marginal increases (+LR= 1.13; 1.54 for SI>0.7 and +LR=1.95; 2.59 for SI>0.9 for hospital admission and inpatient mortality, respectively).

Conclusions In this largest retrospective study to date on SI in the general ED population, we demonstrated that initial SI at presentation to the ED could potentially be useful in predicting the likelihood of hospital admission and inpatient mortality, which could help guide rapid and accurate acuity designation, resource allocation and disposition.