Shock Index Calculator
Shock index is a fast bedside marker of haemodynamic instability. Enter heart rate and systolic blood pressure.
Shock index formula
Shock index (SI) = heart rate ÷ systolic blood pressure. It rises early in shock — often before blood pressure falls — making it a useful triage signal.
How to interpret the shock index
| Shock index | Interpretation |
|---|---|
| 0.5–0.7 | Normal |
| 0.7–0.9 | Borderline — watch closely |
| > 0.9–1.0 | Elevated — suggests haemodynamic instability |
Frequently asked questions
What is a normal shock index?
A normal shock index is about 0.5 to 0.7. Values above 0.9–1.0 suggest haemodynamic instability.
How do you calculate shock index?
Divide the heart rate by the systolic blood pressure: SI = HR ÷ SBP.
Why is shock index useful?
It often rises before blood pressure falls, giving an early warning of shock during triage.
Educational tool. These calculators are for study and RCIS exam preparation only — not for clinical decision-making or patient dosing. Always follow institutional protocols and verify with a qualified clinician.