How this calculator works
Shock index divides heart rate by systolic pressure. Modified shock index uses mean pressure instead. The age variant multiplies the original ratio by age in years. All pressure values are converted to mmHg before forming the indices. The usual MAP estimate can differ from a measured mean pressure. The result is an estimate for information only and is not medical advice.
Formula
SI = HR/SBP. MSI = HR/MAP. Age SI = age x SI. Estimated MAP = (SBP + 2DBP)/3. HR is beats/min, pressure mmHg and age years.
Worked example
At age 40 with heart rate 80 and pressure 120/60, estimated MAP is 80 mmHg. SI is 0.6667, MSI is 1 and age SI is 26.6667. Heart rate 120 and pressure 100/70 at age 60 give MAP 80, SI 1.2, MSI 1.5 and age SI 72.
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Frequently asked questions
Why convert kPa before dividing?
These published indices use pressure in mmHg. Dividing directly by a kPa number would give a different result.
Is there one diagnostic threshold?
No universal threshold is applied here. Age, medicines, pregnancy and clinical setting affect interpretation.
Can normal indices exclude shock?
No. These ratios are supplementary observations and do not replace perfusion assessment or clinical judgement.