Shock Index is calculated as which of the following?

• A. Heart Rate Divided by Diastolic Blood Pressure
• B. Systolic Blood Pressure Divided by Heart Rate
• C. Heart Rate Divided by Systolic Blood Pressure
• D. Mean Arterial Pressure Divided by Heart Rate

Answer: (C)

Shock Index equals heart rate divided by systolic blood pressure. This simple ratio reflects how the heart’s response to blood loss or injury (rising heart rate) is matched against the peak arterial pressure driving organ perfusion (systolic pressure). In early shock from hemorrhage or trauma, SBP can drop while HR increases, causing the SI to rise. A higher SI indicates greater hemodynamic compromise and helps flag patients at risk for decompensation.

Using SBP as the denominator is key because it directly relates to the pressure propelling blood during the heartbeat; alternatives like using diastolic pressure or mean arterial pressure with heart rate don’t track this same rapid-hemodynamic shift as reliably. Thus, heart rate divided by systolic blood pressure is the established calculation.