Shock Index

What This Calculator Measures

Relates heart rate to systolic blood pressure to flag patients whose heart rate is inappropriately high relative to blood pressure, indicating impaired hemodynamic reserve.

How to Use

1. Obtain heart rate (bpm) and systolic blood pressure (mmHg) at the same time.
2. Enter both values.
3. Compare the result against the normal range (approximately 0.5–0.7).
4. Use serial measurements to track trends during resuscitation.

Interpretation Guide

A shock index of 0.5–0.7 is generally considered normal. Values above 0.7 are commonly regarded as elevated and warrant investigation; progressively higher values indicate increasing concern for impaired hemodynamic reserve, particularly in trauma, hemorrhage, and sepsis.

Clinical Significance

The shock index is a simple, inexpensive screening tool that can identify compensated shock before frank hypotension develops, because heart rate often rises before blood pressure falls.

When to Use

• Rapid bedside assessment in trauma and suspected hemorrhage
• Screening for occult hypoperfusion in sepsis and critical illness
• Monitoring response to volume resuscitation
• Emergency triage when hemodynamics are concerning

When Not to Use

• As the sole indicator of shock
• In patients with bradycardia, pacemakers, or arrhythmias where heart rate is not a reliable marker
• In children, where normal values differ by age
• As a replacement for blood pressure, lactate, urine output, or perfusion assessment

Limitations

• Heart rate is affected by rate-control medications, pacemakers, and autonomic dysfunction.
• Does not measure cardiac output, lactate, or tissue perfusion directly.
• Normal reference values differ in children.
• A single normal value does not exclude compensated shock.

Worked Example

A 45-year-old man after a motor vehicle accident has a heart rate of 120 bpm and a systolic blood pressure of 80 mmHg.

Shock Index = 120 / 80 = 1.5. This is well above the normal range (0.5–0.7) and indicates significant hemodynamic compromise requiring urgent evaluation.

Evidence

Source

Emergency Medicine / Critical Care

Reference

Rady MY, Smithline HA, Blake H, et al. A comparison of the shock index and conventional vital signs to identify acute, critical illness in the emergency department. Ann Emerg Med. 1994;24(4):685-690.

Reviewed By

MedCalcHub Clinical Team

Version

1.0

Updated

2026-08

1. Rady MY, et al. Ann Emerg Med. 1994;24(4):685-690.

References

1. Rady MY, Smithline HA, Blake H, et al. A comparison of the shock index and conventional vital signs to identify acute, critical illness in the emergency department. Ann Emerg Med. 1994;24(4):685-690. (Validation Study)