Emergency Medicine
Shock Index
Heart rate divided by systolic BP.
Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.
Background
The shock index is a simple bedside ratio of heart rate to systolic blood pressure, used as a quick marker of haemodynamic compromise. It was originally described as an indicator of circulatory shock and is applied in settings such as haemorrhage, sepsis and trauma. Because it combines two readily available vital signs, a rising index can reveal occult shock before blood pressure alone falls, as compensatory tachycardia precedes overt hypotension. It is dimensionless and easily recalculated as observations change.
Interpreting the result
A normal shock index is approximately 0.5–0.7. Values of about 0.7–0.9 are borderline and warrant closer monitoring, while values of 1.0 or above suggest significant haemodynamic compromise and should prompt urgent assessment and resuscitation. Because it integrates heart rate and blood pressure, the trend over time is often more informative than a single reading, and a rising index is an early warning even when individual vital signs still look acceptable.
Worked example
A patient with a heart rate of 120/min and a systolic blood pressure of 100 mmHg has a shock index of 120 / 100 = 1.2. This is elevated, suggesting significant haemodynamic compromise that warrants urgent assessment and resuscitation.
Pearls / pitfalls
- It can be misleading in patients who are on rate-controlling medication (e.g. beta-blockers), in whom tachycardia may be blunted despite shock.
- Baseline-adjusted or age-specific thresholds may be needed, as normal vital signs differ in children, older adults and pregnancy.
- A single value is less useful than the trend — a rising index over serial observations is the key warning sign.
- It is a screening adjunct, not a diagnosis; always interpret alongside the full clinical assessment and other markers of perfusion.
Evidence & validation
The shock index was first described by Allgöwer and Burri as a marker of circulatory shock and has since been studied in haemorrhage, sepsis and trauma cohorts as an early indicator of compromise and a predictor of the need for intervention.
Frequently asked questions
What is a normal shock index?
A normal shock index is roughly 0.5–0.7. Values around 0.7–0.9 are borderline and warrant closer monitoring, while a value of 1.0 or above suggests significant haemodynamic compromise.
Why can the shock index detect shock before blood pressure falls?
In early shock, compensatory tachycardia raises the heart rate before the blood pressure drops. Because the index combines both, it can rise and flag occult compromise while the systolic blood pressure still appears acceptable.
When can the shock index be misleading?
It can be unreliable in patients taking rate-limiting drugs such as beta-blockers, who may not mount a tachycardia, and at the extremes of age or in pregnancy, where normal vital-sign ranges differ. In these situations interpret it with caution.
Should I act on a single elevated value?
An elevated value should prompt urgent reassessment, but the trend is often more informative than one reading. A rising shock index over serial observations is a particularly important early warning of deterioration.
References
- Allgöwer M, Burri C. Shock index. Dtsch Med Wochenschr. 1967;92(43):1947–1950.
- Rady MY, Smithline HA, Blake H, et al. A comparison of the shock index and conventional vital signs to identify acute, critical illness. Ann Emerg Med. 1994;24(4):685–690.
Related calculators
Need a calculator we don't have — or a custom tool?
We build evidence-led clinical calculators, dashboards and reference tools for teams.