Shock Index (SI)

Shock Index (SI) is a quick bedside marker used to assess the severity of shock and early hemodynamic compromise.

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Definition

Shock Index = Heart Rate (HR) ÷ Systolic Blood Pressure (SBP)

Example:

HR 120 bpm / SBP 100 mmHg → SI = 1.2

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Normal Value

Normal SI: 0.5 – 0.7

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Abnormal (Suggestive of Shock)

SI ≥ 0.9 → Early indicator of circulatory failure, even when BP is still “normal.”

SI ≥ 1.0 → Strong predictor of significant shock, need for urgent intervention.

SI ≥ 1.3 → Associated with high risk of mortality, ICU admission, transfusion, and severe shock.

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Why It’s Useful

Very sensitive for early shock detection (trauma, sepsis, hemorrhage, cardiogenic shock).

Better than systolic BP alone, particularly in young or compensated patients.

Helpful in triage and predicting need for massive transfusion in trauma.

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Clinical Interpretation

Shock Index Interpretation

0.5–0.7 Normal

0.7–0.9 Mild concern / compensated shock

≥ 0.9 Significant shock risk → acts earlier than BP drop

≥ 1.3 Severe shock / high mortality risk

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Variations

Modified Shock Index (MSI) = HR ÷ MAP

Better in sepsis and cardiogenic shock.

Age Shock Index (ASI) = SI × Age

Improves prediction in elderly.

pSI / sSI: Pediatric versions adapted for age.