Shock Index

How to use it

1. 1

   Measure HR and SBP simultaneously. Use non-invasive cuff measurement. Ideally arterial line in critically ill.

2. 2

   Calculate HR ÷ SBP. Normal SI = 0.5–0.7. SI > 1.0 indicates the heart is working harder than pressure generated — early compensated shock.

3. 3

   Act on elevated SI. SI >1.0: IV access × 2, fluid challenge, blood cultures, consider early vasopressors.

When to use it

Rapid triage in ED or pre-hospital

Identifies haemodynamic instability faster than BP alone, especially in compensated shock where SBP is preserved.

Trauma

SI > 1.0 predicts massive transfusion protocol activation with good sensitivity.

Sepsis screening

SI > 1.0 with suspected infection supports early goal-directed therapy. Pairs well with qSOFA.