Shock Index Calculator
The shock index is a quick bedside ratio — heart rate divided by systolic blood pressure — that can reveal circulatory compromise earlier than either vital sign alone, because a rising pulse and a falling pressure move it in the same direction. It is used to flag occult shock in trauma, sepsis and obstetric bleeding. Enter the heart rate and systolic blood pressure to get the shock index and its interpretation.
About the shock index
The shock index detects circulatory compromise earlier than heart rate or blood pressure alone. Source: Allgöwer M, Burri C, “Schockindex,” Deutsche Medizinische Wochenschrift 1967.
Frequently asked questions
What is the shock index?
Shock index = heart rate (beats per minute) ÷ systolic blood pressure (mmHg). A normal value is about 0.5 to 0.7. Because it combines both numbers, it can rise into an abnormal range while the heart rate and blood pressure are each still within their own “normal” limits, giving an earlier warning of circulatory stress.
What value is concerning?
A shock index above about 0.9 is widely used as a threshold suggesting haemodynamic compromise and a higher risk of needing resuscitation, transfusion or critical care. Values of 1.0 or more indicate more significant compromise. It is a red flag prompting closer assessment, not a diagnosis of shock by itself.
Where is it used?
The shock index is used in trauma (to predict the need for massive transfusion), in sepsis and in obstetric haemorrhage, where a modified version against mean arterial pressure is also used. It is popular precisely because it needs only two routine observations and no calculation aids at the bedside. Both numbers are recorded at triage anyway, so the index can be applied retrospectively to an existing set of observations without any extra test. A pulse of 110 with a systolic of 105 mmHg gives 1.05, above the 0.9 threshold, even though neither figure on its own would normally trigger an alert.
What are its limitations?
The shock index has real limitations, chiefly wherever the heart rate is an unreliable signal. It can mislead when the rate is controlled by medication (such as beta-blockers), in atrial fibrillation, in pregnancy (where baseline values differ) and in people with a paced rhythm. It also does not capture the cause of the problem. Always interpret it alongside the full clinical picture and trend it over time.
How does it differ from the modified shock index?
The modified shock index divides the heart rate by the mean arterial pressure (MAP) instead of the systolic pressure, which some studies find slightly more predictive. This calculator uses the classic shock index (heart rate ÷ systolic pressure). This is an educational reference, not medical advice.
This is a reference tool, not a diagnosis or medical advice. Results depend on the laboratory, assay and clinical context, and reference intervals vary between labs and by age and sex — always read your result against the range printed on your own report and discuss it with a qualified healthcare professional.
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