Modified Shock Index as a Predictor of Admission and In-hospital Mortality in Emergency Departments; an Analysis of a US National Database

The modified shock index (MSI) is the ratio of heart rate to mean arterial pressure. It is used as a pre-dictive and prognostic marker in a variety of disease states. This study aimed to derive the optimal MSI cut-off that isassociated with increased likelihood (likelihood ratio, LR) of admission and in-hospital mortality in patients present-ing to emergency department (ED).

We retrospectively reviewed data from the National Hospital AmbulatoryMedical Care Survey between 2005 and 2010. Adults>18 years of age were included regardless of chief complaint. Basicpatient demographics, initial vital signs, and outcomes were recorded for each patient. Then the optimal MSI cut-offfor prediction of admission and in-hospital mortality in ED was calculated. LR≥5 was considered clinically significant.

567,994,402 distinct weighted adult ED patient visits were included in the analysis. 15.7% and 2.4% resulted inadmissions and in-hospital mortality, respectively. MSI > 1.7 was associated with a moderate increase in the likelihoodof both admission (Positive LR (+LR) = 6.29) and in-hospital mortality (+LR = 5.12). +LR for hospital admission at MSI>1.7 was higher for men (7.13; 95% CI 7.11-7.15) compared to women (5.49; 95% CI 5.47-5.50) and for non-white (7.92;95% CI 7.88-7.95) compared to white patients (5.85; 95% CI 5.84-5.86). For MSI <0.7, the +LRs were not clinically signif-icant for admission (+LR = 1.07) or in-hospital mortality (LR = 0.75).

In this largest retrospective study, todate, on MSI in the undifferentiated ED population, we demonstrated that an MSI >1.7 on presentation is predictive ofadmission and in-hospital mortality. The use of MSI could help guide accurate acuity designation, resource allocation,and disposition.