The Shock Index Calculator turns two routine vital signs — heart rate and systolic blood pressure — into a single ratio that detects early circulatory compromise. Because the body compensates for blood loss by speeding the heart before pressure falls, the shock index often signals trouble while the blood pressure still looks reassuringly normal.
How it works
The shock index is a simple ratio:
Shock index = heart rate (bpm) ÷ systolic blood pressure (mmHg)
A patient with a heart rate of 80 and a systolic of 120 has a shock index of
80 ÷ 120 ≈ 0.67, which is normal. As bleeding progresses, heart rate climbs
and systolic pressure starts to drop, pushing the ratio upward — a heart rate of
120 over a systolic of 90 gives 1.33, a clear danger signal.
The risk bands used here are: < 0.7 normal, 0.7–0.9 borderline, and ≥ 1.0 high risk (significant haemodynamic instability, higher likelihood of massive transfusion and critical-care admission).
Uses and notes
The shock index is widely applied in trauma, sepsis, and obstetric haemorrhage triage. In postpartum haemorrhage an index around 0.9–1.0 is a common escalation trigger because pregnant patients mask blood loss particularly well.
The index is a screening tool, not a diagnosis. Beta-blockers, pacemakers, pre-existing hypertension, and athletic baselines can all shift it, so always combine it with the full clinical picture and trend it over time rather than relying on a single reading.