π¨ Shock Index Calculator
Heart rate over systolic pressure: hidden shock detector.
For informational purposes only, not medical advice. Consult a healthcare professional.
The shock index divides heart rate by systolic blood pressure, catching the compensated phase of shock when tachycardia outruns a still-normal pressure. A patient with a heart rate of 110 and systolic of 90 scores 1.22, frankly abnormal, while either vital alone might get a shrug. Emergency and trauma literature uses 0.9 as the concern threshold: above it, occult bleeding, transfusion need, and mortality all rise. This calculator computes it with the standard bands for triage teaching and reference.
How to Use This Calculator
Enter the heart rate and systolic blood pressure from the same set of vitals. The ratio flags compensated shock before pressure alone looks alarming.
Take heart rate and systolic pressure together. The index compares the two, so mismatched timing corrupts it.
Read the index. Under 0.7 is normal; 0.9 and above is the classic concern threshold.
Trend it. A rising shock index across serial vitals warns earlier than either vital alone.
How the Math Works
Divide heart rate by systolic blood pressure. Normal resting adults sit around 0.5 to 0.7: a heart rate of 70 over 120 gives 0.58. The 0.9 threshold emerged from trauma and obstetric studies as the point where adverse outcomes climb; above 1.0 to 1.3 marks overt shock physiology. The modified shock index substitutes mean arterial pressure for systolic, but the classic version dominates practice. The power is in the ratio: tachycardia with borderline pressure multiplies into an abnormal number while each component sits near its own normal range.
Worked Example
A heart rate of 110 with systolic pressure 90 gives a shock index of 1.22, which the calculator flags as Concerning: possible occult shock. Neither vital alone screams: 110 is fast but common in pain, 90 systolic is low but not collapsing. The ratio exposes what the individual numbers hide, which is exactly why trauma teams track it: compensated shock is invisible until it is not.
Reading Your Result
Under 0.7 is reassuring in a stable patient. The 0.7 to 0.9 band is borderline and worth watching with repeat vitals. At 0.9 and above, take occult shock seriously: look for bleeding, check lactate and hemoglobin, and reassess frequently. Above 1.3 is critical physiology needing immediate resuscitation. The index supplements, never replaces, the exam: a sick-looking patient with a normal index is still sick.
| Shock index | Band | Action |
|---|---|---|
| Under 0.7 | Normal | Routine |
| 0.7-0.9 | Borderline | Repeat vitals |
| 0.9-1.3 | Concerning | Work up occult shock |
| Above 1.3 | Critical | Immediate resuscitation |
Limitations
Beta-blockers blunt the heart rate response and falsely lower the index; pain, anxiety, and fever raise it without shock. It was validated in specific populations and performs less cleanly in the elderly and in chronic hypertension. Single values mislead; trends and the clinical picture decide. It is a triage aid, not a diagnosis.
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Related tools: qSOFA sepsis score sepsis risk screener revised trauma score calculator.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is shock index?
Heart rate divided by systolic blood pressure. It detects compensated shock, where tachycardia rises before blood pressure falls. Normal is 0.5 to 0.7; 0.9 and above signals concern. Used in emergency, trauma, and obstetric triage.
What is a normal shock index?
About 0.5 to 0.7 in resting adults. Athletes run lower; anxious or febrile patients run higher without shock. The number needs its context like every vital sign.
Why is 0.9 the cutoff?
It emerged empirically from trauma and hemorrhage studies as the threshold where transfusion need, ICU admission, and mortality climb. It is a validated warning line, not a biological constant, and trends matter as much as crossings.
What is modified shock index?
Heart rate divided by mean arterial pressure instead of systolic. Some studies find it slightly more predictive. The classic systolic version remains far more used at the bedside.
Can shock index predict bleeding?
It correlates with transfusion need and occult hemorrhage in trauma cohorts, which is its main practical use: flagging the patient who looks okay but is compensating. Lactate and hemoglobin trend confirm what it suspects.
Does it work in pregnancy?
With adjusted expectations. Pregnancy raises heart rate and lowers blood pressure physiologically, shifting the baseline up. Obstetric studies still find it useful for hemorrhage with pregnancy-specific thresholds.
Why can the index mislead?
Beta-blockers and calcium-channel blockers blunt tachycardia; pacemakers fix the rate; chronic hypertension resets the pressure baseline. Pain and fever raise it innocently. Know the medications before trusting the number.
Should I trend shock index?
Yes, that is its best use. A climbing index across serial vitals warns of developing shock earlier than any single reading. Many electronic records now graph it automatically for this reason.
Is shock index used in sepsis?
Increasingly, as an early warning alongside qSOFA and lactate. Tachycardia with softening pressure is the classic early sepsis pattern the index captures. It prompts the workup; it does not diagnose.
What do I do with a high shock index?
Assess perfusion: mental status, skin, urine output, lactate. Look for bleeding or sepsis sources. Resuscitate with fluids or blood as indicated and reassess. The number starts the workup; the patient directs it.