About

The Shock Index (SI), also known as the Allgöwer Index, is a rapid bedside assessment tool used to gauge the severity of hypovolemic shock and hemodynamic stability in trauma patients. It is defined as the Heart Rate (HR) divided by Systolic Blood Pressure (SBP). The SI is more sensitive than vital signs alone in detecting occult shock/early hemorrhage.

This tool is designed for high-stress environments with large, clear typography. It instantly categorizes the patient's status into Normal, Elevated, or Critical ranges. It also includes interpretation logic for Pediatric patients, whose baseline heart rates are naturally higher, altering the normal SI thresholds.

Formulas

The formula is a simple ratio:

SI = HR (bpm)SBP (mmHg)

For Pediatric patients (Ages 4-12), the Normal SI is higher, typically up to 1.2, due to naturally higher heart rates. Ages < 4 may have normal SI up to 1.6.

Reference Data

SI Value	Classification	Clinical Implication
0.5 - 0.7	Normal Range	Physiological stability.
0.7 - 0.9	Elevated	Mild shock or compensation. Monitor closely.
> 0.9	Critical	Significant risk of requiring massive transfusion or admission to ICU.
> 1.0	Severe Shock	High mortality risk. Immediate intervention required.

Frequently Asked Questions

Compensatory mechanisms can maintain Blood Pressure even after significant blood loss. Heart rate increases to compensate. The Shock Index captures this divergence (rising HR, stable/dropping BP) earlier than BP alone.

While primarily for trauma, SI has been studied in sepsis, pulmonary embolism, and ectopic pregnancy to predict mortality and admission needs, though thresholds may vary.