Shock Index Calculator — Free Online Calculator
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Shock Index
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About This Calculator
The Shock Index (SI) is a simple bedside calculation defined as the ratio of heart rate to systolic blood pressure. It is used as an early indicator of hemodynamic instability and occult shock, particularly in trauma, hemorrhage, and sepsis. A normal SI is 0.5–0.7. An elevated SI may identify patients at risk before traditional vital sign thresholds are breached.
Formula
Interpretation
| Shock Index | Interpretation |
|---|---|
| 0.5 – 0.7 | Normal |
| 0.7 – 1.0 | Elevated — concern for early shock |
| > 1.0 | Significant shock |
| > 1.5 | Severe shock |
References
Frequently Asked Questions
Why is the Shock Index useful if vital signs are normal?
The Shock Index can detect occult hemodynamic compromise before individual vital signs become overtly abnormal. A patient may have a 'normal' heart rate of 95 bpm and 'normal' SBP of 100 mmHg, but the SI of 0.95 flags concern.
Does the Shock Index work in all populations?
SI may be less reliable in elderly patients (who may have blunted heart rate responses), patients on beta-blockers or calcium channel blockers, pregnant women (physiologically elevated HR), and pediatric patients (age-dependent normal ranges).
What is the Modified Shock Index?
The Modified Shock Index (MSI) = HR / MAP. It may be more sensitive than the traditional SI. An MSI > 1.3 has been associated with increased mortality in trauma and sepsis patients.
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⚠ Medical Disclaimer
This tool is for educational and informational purposes only. It is not intended to replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional for clinical decisions.