Modified Shock Index Calculator

About this calculator

The Modified Shock Index (MSI) is heart rate divided by mean arterial pressure (MAP), where MAP itself is calculated as diastolic pressure plus one-third of the pulse pressure (systolic minus diastolic). A normal MSI sits around 0.5 to 0.7; values climbing above roughly 0.7–1.0 can signal early hemodynamic instability before a patient's blood pressure alone would raise alarm.

Because MSI reacts to blood loss and shock sooner than standard vital-sign thresholds, it's used by emergency physicians, trauma teams, and paramedics for rapid triage — for instance in trauma, sepsis, or postpartum hemorrhage — to flag patients who look stable on paper but are compensating for significant blood loss. This tool is for reference and education only, not medical advice.