Shock Index
Normal hemodynamic status
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Evidence-based calculations Used in clinical settings worldwide Regular monitoring recommended
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Shock Index
Visual Analysis
Shock Index Gauge
Vital Signs
Risk Profile
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Step-by-Step Calculation
The Shock Index is a simple ratio of heart rate to systolic blood pressure.
Shock Index = Heart Rate / Systolic BP
Shock Index = 80 / 120 = 0.667
Mean Arterial Pressure (MAP) = (SBP + 2×DBP) / 3 = (120 + 2×80) / 3 = 93.3 mmHg
Modified Shock Index = HR / MAP = 80 / 93.3 = 0.857
Pulse Pressure = 120 - 80 = 40 mmHg
Shock Index 0.67 = Normal (0.5-0.7)
Stable cardiovascular function
Shock Index Reference
| SI Range | Classification | Est. Blood Loss | Action |
|---|---|---|---|
| 0.5-0.7 | Normal | Stable cardiovascular function | Standard monitoring |
| Less than 0.5 | Low Normal | May indicate athletic conditioning, medication effect, or elevated BP | Assess for beta-blocker use |
| 0.7-1.0 | Elevated | Subtle hemodynamic instability - may have ~10-20% blood loss | Enhanced monitoring |
| 1.0-1.4 | High | Significant hemodynamic compromise - 20-30% blood loss typical | Urgent fluid resuscitation |
| Greater than 1.4 | Critical | Severe hemodynamic instability - 30-40%+ blood loss | Immediate aggressive resuscitation |
For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
🏥 Health Facts
— WHO
— CDC
❤️ What is the Shock Index?
The Shock Index (SI) is a simple bedside calculation defined as heart rate divided by systolic blood pressure. First described by Allgöwer and Burri in 1967, it has been validated as an early indicator of hemodynamic instability.
The value of SI lies in its ability to detect compensated shock - identifying patients who are hemodynamically unstable even when their blood pressure appears normal. This is because heart rate often increases before blood pressure drops in early shock.
Normal Values
- • Normal SI: 0.5-0.7
- • Elevated SI: 0.7-1.0 (concerning)
- • High SI: 1.0-1.4 (likely shock)
- • Critical SI: greater than 1.4 (severe shock)
📋 How to Use Shock Index
- Measure heart rate: Obtain pulse rate in beats per minute
- Measure blood pressure: Record systolic blood pressure in mmHg
- Calculate SI: Divide heart rate by systolic BP
- Interpret result: Compare to normal range (0.5-0.7)
- Serial monitoring: Track changes over time
Example Calculation
HR = 100 bpm, SBP = 110 mmHg
SI = 100 / 110 = 0.91 (Elevated - early shock)
⏰ When to Use Shock Index
Clinical Applications
- • Trauma assessment
- • GI bleeding evaluation
- • Obstetric hemorrhage
- • Sepsis screening
- • Post-surgical monitoring
- • Ectopic pregnancy
Advantages
- • Simple bedside calculation
- • No equipment needed
- • Detects occult shock
- • Predicts transfusion need
- • Better than BP alone
📐 Shock Index Formula
Shock Index = Heart Rate / Systolic Blood Pressure
SI = HR (bpm) / SBP (mmHg)
Modified Shock Index = HR / MAP
MSI = HR / ((SBP + 2×DBP) / 3)
Blood Loss Correlation
- • SI 0.5-0.7: less than 10% blood volume loss
- • SI 0.7-1.0: ~10-20% blood volume loss
- • SI 1.0-1.4: ~20-30% blood volume loss
- • SI greater than 1.4: greater than 30% blood volume loss
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