modified shock index as a predictor of admission and in-hospital mortality in emergency departments; an analysis of a us national database

Introduction: the modified shock index (msi) is the ratio of heart rate to mean arterial pressure. it is used as a predictive and prognostic marker in a variety of disease states. this study aimed to derive the optimal msi cut-off that is associated with increased likelihood (likelihood ratio, lr) of admission and in-hospital mortality in patients presenting to emergency department (ed). methods: we retrospectively reviewed data from the national hospital ambulatory medical care survey between 2005 and 2010. adults>18 years of age were included regardless of chief complaint. basic patient demographics, initial vital signs, and outcomes were recorded for each patient. then the optimal msi cut-off for prediction of admission and in-hospital mortality in ed was calculated. lr ≥ 5 was considered clinically significant. results: 567,994,402 distinct weighted adult ed patient visits were included in the analysis. 15.7% and 2.4% resulted in admissions and in-hospital mortality, respectively. msi > 1.7 was associated with a moderate increase in the likelihood of 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 significant for admission (+lr = 1.07) or in-hospital mortality (lr = 0.75). conclusion: in this largest retrospective study, to date, on msi in the undifferentiated ed population, we demonstrated that an msi >1.7 on presentation is predictive of admission and in-hospital mortality. the use of msi could help guide accurate acuity designation, resource allocation, and disposition.