Resuscitation & trauma
Shock Index (SI)
The shock index (HR ÷ SBP) is a quick bedside marker of physiologic reserve. Elevated values predict higher mortality, occult bleeding, and need for massive transfusion.
Inputs
HR: 98 bpm
SBP: 118 mmHg
Shock Index
0.83
Normal adult reference: 0.5 – 0.7
Shock Index <0.9 generally reflects adequate hemodynamic compensation in adults, but interpret within clinical context.
Consider age-adjusted shock index (HR ÷ SBP × age) or SI variants for pediatrics or obstetrics.
How to Use This Calculator
Measure heart rate and systolic BP
Use simultaneous vital signs for accuracy. Repeat after interventions (fluids, blood products, vasopressors).
Interpret trends, not single values
Rising SI indicates worsening perfusion. Combine with mentation, urine output, lactate, and bedside ultrasound.
Escalate care for SI ≥1.0
Initiate hemorrhage control, sepsis protocols, or cardiogenic shock workup depending on clinical presentation.
Formula
Shock Index = Heart rate (beats/min) ÷ Systolic blood pressure (mmHg).
Normal adult range: 0.5 – 0.7.
Values ≥0.9 predict increased mortality, transfusion requirement, and ICU admission in trauma and sepsis cohorts.
Full Description
Shock Index is a dimensionless ratio reflecting cardiovascular compensation. Tachycardia with hypotension yields higher values, flagging inadequate perfusion before overt vital sign collapse. SI is validated in trauma, obstetrics (postpartum hemorrhage), and sepsis. Age-adjusted variants (SIA, SIPA) improve sensitivity in older adults and pediatrics.
Limitations: Beta blockers, atrial fibrillation, or chronic hypertension may mask changes. Always interpret with the full clinical picture and consider continuous hemodynamic monitoring.
Frequently Asked Questions
What is the Age Shock Index (ASI)?
ASI multiplies SI by patient age. ASI > 50 is associated with increased mortality, especially in geriatric trauma.
How does SI compare to systolic BP alone?
SI detects compensated shock before hypotension occurs. Many trauma patients maintain SBP >90 mmHg despite significant hemorrhage.
Can SI be used in pregnancy?
Yes, but remember baseline SI is higher in pregnancy. Rising SI is still concerning for hemorrhage (e.g., postpartum).
Is SI useful after beta-blocker use?
Use caution. Medications affecting heart rate may blunt SI changes; rely on lactate, mental status, and other perfusion markers.