Shock Index Calculator
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Shock Index = Heart Rate ÷ Systolic BP
beats per minute (bpm)
mmHg
mmHg — for modified SI
Shock Index
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HR/SBP
Modified SI
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HR/MAP
Massive Transfusion
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risk
Shock Index Reference
| Shock Index | Category | Clinical Significance |
|---|---|---|
| <0.6 | Normal | Normal haemodynamics |
| 0.6–1.0 | Normal–Borderline | Mild compensated shock possible |
| 1.0–1.4 | Elevated | Significant haemodynamic compromise — may predict massive transfusion |
| ≥1.4 | Severe | Shock — high mortality, massive transfusion likely needed |
| ≥1.7–2.0 | Critical | Severe shock — immediate intervention required |
Clinical Applications
- Trauma: SI ≥1.0 predicts massive transfusion with ~70% sensitivity. Activate MTP (massive transfusion protocol) at SI ≥1.0–1.4 in context of trauma
- Obstetric haemorrhage: SI ≥1.0 in PPH indicates significant blood loss (>1000 mL), SI ≥1.7 predicts severe maternal morbidity. Valuable because BP may remain deceptively normal in young women
- Sepsis screening: SI ≥1.0 combined with clinical features suggests haemodynamic compromise in sepsis
- Pulmonary embolism: SI ≥1.0 in suspected PE predicts right heart strain and adverse outcomes — consider thrombolysis
- Upper GI bleeding: SI ≥1.0 at presentation predicts adverse outcomes and need for urgent intervention
Why Shock Index Can Be More Sensitive Than BP Alone
A young, healthy patient can maintain systolic BP in the normal range while developing significant hypovolaemia through compensatory tachycardia. A patient with HR 110 and SBP 110 has a normal blood pressure but a shock index of 1.0 — suggesting significant circulatory stress. SI captures the haemodynamic relationship that isolated BP or HR values miss.
Related Calculators
⚠ Medical Disclaimer: Shock index is a triage and screening tool. Haemodynamic assessment requires full clinical evaluation, serial vital signs, and clinical context. Shock index thresholds vary by clinical setting, patient age, and comorbidities. Always treat the patient, not the number.