Shock Index (HR / SBP), Modified Shock Index (HR / MAP) & Age Shock Index

Ratios derived from supplied vital signs

Shock index is heart rate in beats/min divided by systolic pressure in mmHg. Modified shock index divides heart rate by mean arterial pressure; here MAP is approximated as (SBP+2*DBP)/3. Age shock index multiplies SI by age in years.

These indices have been studied in particular emergency and trauma populations. Cutoffs and predictive accuracy vary; they do not independently diagnose shock, rule it out, determine transfusion need or produce an individual mortality probability. Age and medicines that affect heart rate can change interpretation.

The MAP formula is an approximation, not a direct measurement of perfusion or vascular tone, and can be less suitable at unusual heart rates or rhythms. Use readings from the same assessment with correct units. This adult teaching example requires positive pressures and heart rate, DBP below SBP for MSI, and age at least18 for the age-weighted result.

Shock index: HR divided by systolic pressure

Report the numeric ratio without turning it into a normal-versus-shock diagnosis.

=IF(COUNT(B2:B3)<>2,"Invalid inputs",IF(OR(B2<=0,B3<=0),"Invalid inputs",ROUND(B2 / B3, 2)))

Modified shock index using estimated MAP

The pressures must be positive and diastolic pressure below systolic pressure. This input consistency check does not validate a measurement clinically.

=IF(COUNT(B2:B4)<>3,"Invalid inputs",IF(OR(B2<=0,B3<=0,B4<=0,B4>=B3),"Invalid inputs",ROUND(B2 / ((B3 + 2 * B4) / 3), 2)))

Age shock index in this adult example

Multiply by the unrounded SI rather than its two-decimal display. This does not select a universal age-specific intervention threshold.

=IF(COUNT(B2:B3,B5)<>3,"Invalid inputs",IF(OR(B2<=0,B3<=0,B5<18),"Invalid inputs",ROUND(B5*(B2/B3),1)))

Further reading

• Microsoft Support — ROUND function
• Primary study — shock, modified shock and age shock indices in a district emergency centre