Background: Currently for physicians, there are limited parameters to stratify patients at risk for short term cardiovascular collapse (i.e. vasopressor dependence). The shock index (SI, heart rate divided by systolic blood pressure) is a simple formula useful for detecting changes in cardiovascular performance before the onset of systemic hypotension. It is an easily accessible, non-invasive, and non-costly risk stratification tool that may enhance current methods for differentiating severe sepsis patients at risk for imminent cardiovascular collapse