Heart rate often rises before blood pressure falls, so their ratio picks up early shock. A shock index of 1.0 or more is associated with a need for transfusion and higher mortality in trauma and sepsis. In older adults the age shock index (above 50) performs better.
How to use the Shock Index Calculator
- Heart rate
- Systolic blood pressure
- Diastolic blood pressure
- Age
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter heart rate and blood pressure, and age.
Inputs explained
| Field | What to enter |
|---|---|
| Heart rate | In bpm |
| Systolic blood pressure | In mmHg |
| Diastolic blood pressure | In mmHg |
| Age | In years |
What each result means
- Shock index = [Heart rate]÷[Systolic blood pressure]
- Modified shock index = [Heart rate]÷([Diastolic blood pressure] + ([Systolic blood pressure] – [Diastolic blood pressure])÷3)
- Age shock index = [Age]×[Shock index]
Example values
How the main result changes when Heart rate changes and everything else stays at the example values above:
| Heart rate (bpm) | Shock index |
|---|---|
| 47.5 | 0.43 |
| 71.25 | 0.65 |
| 95 | 0.86 |
| 118.75 | 1.08 |
| 142.5 | 1.3 |
| 190 | 1.73 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Shock index = heart rate ÷ systolic blood pressure
Modified shock index = heart rate ÷ mean arterial pressure
Age shock index = age × shock index
Worked example
Inputs: Heart rate: 95 bpm; Systolic blood pressure: 110 mmHg; Diastolic blood pressure: 70 mmHg; Age: 45 years.
Results: Shock index = 0.86; Modified shock index = 1.14; Age shock index = 39.
Key terms
- MSI
- Modified shock index.
Frequently asked questions
What is a normal shock index?
About 0.5–0.7 in healthy adults.
What shock index is worrying?
0.9–1.0 or more suggests shock or significant blood loss.
Is it used in children?
Age-adjusted cut-offs are used because normal heart rates differ.