Shock Index Calculator — HR / Systolic BP
Calculate the Shock Index (SI = heart rate ÷ systolic blood pressure) to rapidly screen for haemodynamic compromise. A normal SI is 0.5–0.7; values above 1.0 indicate probable significant shock requiring urgent evaluation.
bpm
mmHg
Normal — haemodynamically stable
- 1
Heart rate
80 - 2
Systolic blood pressure
120 - 3
Shock Index (HR ÷ SBP)
80 ÷ 120 = 0.67Normal range is 0.5–0.7; values above 1.0 indicate probable haemodynamic compromise.
How does this calculator work?
Shock Index = Heart Rate ÷ Systolic BP. Normal range: 0.5–0.7 in healthy adults. SI > 0.9 signals possible haemodynamic instability; SI > 1.0 indicates probable significant shock requiring urgent assessment. It is a screening tool only — always integrate with clinical findings.
Formula
How this is calculated
The Shock Index was described by Allgöwer and Burri in 1967 as a simple, bedside-calculable ratio of heart rate to systolic blood pressure. In a healthy adult, the heart rate is usually lower than the systolic blood pressure, so the ratio sits between 0.5 and 0.7. When circulatory volume is lost — from haemorrhage, dehydration, sepsis or other causes — the heart rate rises and blood pressure falls, pushing SI upward. Studies have associated an SI > 0.9 with significant haemodynamic compromise and an SI > 1.0–1.2 with high in-hospital mortality and the need for blood transfusion in trauma.
SI is widely used in trauma and emergency medicine because it detects instability before either heart rate or blood pressure has crossed individual normal thresholds. A patient with HR 100 and SBP 100 may look "borderline" individually but has SI = 1.0, flagging probable shock. Conversely, an athletic individual might have a resting SI < 0.5 — not pathological, but worth noting.
Limitations: SI is a screening aid, not a definitive diagnosis. It does not account for age, medication (beta-blockers artificially lower HR), or baseline hypertension (where SBP 90 mmHg is critically low even though SI may appear unremarkable). Always integrate the result with the full clinical picture, examination findings, and trend monitoring. Paediatric normal values differ from adult thresholds.
Frequently asked questions
A normal Shock Index in a resting healthy adult is 0.5–0.7. Values of 0.7–1.0 indicate an elevated index worth monitoring; above 1.0 suggests probable haemodynamic compromise; above 1.3 is associated with severe shock and high mortality risk.
The Modified Shock Index (MSI) divides heart rate by mean arterial pressure (MAP) rather than systolic BP. MSI is considered by some studies to be more sensitive for detecting early shock, but it requires knowing the diastolic blood pressure to compute MAP. SI is simpler and still clinically useful when only the systolic pressure is available.
Adult thresholds do not apply to children, who have higher resting heart rates and lower blood pressures by age. Paediatric normal SI values are higher and age-specific. Consult paediatric-specific reference ranges (e.g., 2019 Shock Index paediatric adjusted guidelines) for patients under 16.
TG we-Calculate Editorial Team. (2026). Shock Index Calculator — HR / Systolic BP [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/shock-index-calculator
TG we-Calculate Editorial Team. "Shock Index Calculator — HR / Systolic BP." TG we-Calculate. 2026. https://we-calculate.com/calculator/shock-index-calculator.
TG we-Calculate Editorial Team, "Shock Index Calculator — HR / Systolic BP," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/shock-index-calculator
@misc{wecalculate_shock_index_calculator, title = {Shock Index Calculator — HR / Systolic BP}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/shock-index-calculator}}, year = {2026}, note = {TG we-Calculate} }
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