Shock Index Calculator
Calculate the shock index and age-adjusted shock index from heart rate and systolic blood pressure — a simple bedside marker of haemodynamic compromise.
❤️ Clinical Score📐 Shock index = heart rate / systolic blood pressure🏥 Health
Heart rate (bpm)
Systolic BP (mmHg)
Age (years, for age-adjusted index)
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Shock Index Calculator | — | Shock index = heart rate / systolic blood pressure | ratio |
Step-by-Step Examples
Example 1
Normal Haemodynamics
HR 72, SBP 124.
- SI = 72 / 124
- SI = 0.58
- Within the normal 0.5–0.7 range
✓ Shock index 0.58 — normal
Example 2
Compensated Shock
HR 118, SBP 98, age 45.
- SI = 118 / 98 = 1.20
- Elevated, suggesting haemodynamic compromise
- Age-adjusted = 45 × 1.20 = 54.2
✓ Shock index 1.20 — elevated
Example 3
Occult Hypoperfusion in an Older Patient
HR 96, SBP 118, age 78.
- SI = 96 / 118 = 0.81 — only mildly elevated
- Age-adjusted = 78 × 0.81 = 63.5
- The age-adjusted value flags risk the raw index understates
✓ Age-adjusted SI 63.5 — above threshold
Real-World Applications
Trauma Triage
Shock index outperforms heart rate or blood pressure alone at identifying patients who will need massive transfusion.
Occult Hypoperfusion
Younger patients compensate well and can maintain normal blood pressure despite substantial blood loss — the ratio detects this earlier.
Obstetric Haemorrhage
Modified shock index thresholds are used in obstetric early warning systems for postpartum haemorrhage.
Geriatric Trauma
Age-adjusted shock index addresses the tendency of standard thresholds to miss compromise in older patients.
Common Mistakes to Avoid
⚠️
Applying adult thresholds to children
Normal heart rate and blood pressure vary enormously across paediatric age groups, so adult shock index cutoffs do not transfer.
⚠️
Ignoring rate-controlling medications
Beta blockers blunt the tachycardic response, so a patient on them can be substantially hypovolaemic with a deceptively normal shock index.
⚠️
Treating a normal index as reassurance
Shock index is a marker, not a rule-out. Significant haemorrhage can occur with a normal ratio, particularly early and in young patients.
Frequently Asked Questions
What is the shock index? ▾
Heart rate divided by systolic blood pressure — a ratio that captures haemodynamic compromise better than either value considered alone.
What is a normal shock index? ▾
Approximately 0.5 to 0.7 in healthy adults. Values above 0.9 are commonly treated as concerning.
What is the age-adjusted shock index? ▾
Age multiplied by shock index, developed because older patients tolerate hypoperfusion poorly. Values above roughly 50 have been associated with worse trauma outcomes.
Why is shock index better than blood pressure alone? ▾
Blood pressure is a late sign. Young healthy patients maintain it through compensatory vasoconstriction and tachycardia until decompensation is imminent.
Can shock index be used outside trauma? ▾
It has been studied in sepsis, gastrointestinal bleeding, pulmonary embolism, and obstetric haemorrhage, though thresholds and validation vary by setting.