Calculators · Critical Care · Formula

Shock index and age shock index

Also called SI, age x shock index, age shock index, HR/SBP

Heart rate ÷ systolic BP, and age × shock index for older injured patients.

/min
years

Fill 2 more fields to see the result.

Formula and scoring

SI = heart rate ÷ systolic BP. Age SI = age (years) × SI.

Exam and ward pearls

  • Zarzaur 2008 (16 077 blunt-trauma patients): AUC for 48-h mortality 0.812 for SI and 0.831 for age × SI vs 0.716 for HR and 0.753 for SBP.

When not to rely on it

  • No universal cut-off was set in the cited derivation study; thresholds vary by population (trauma, obstetrics, sepsis, children).

Source

  1. Zarzaur BL, et al. New vitals after injury: shock index for the young and age x shock index for the old. J Surg Res. 2008;147(2):229-36. doi:10.1016/j.jss.2008.03.025 · PMID 18498875
  2. Matsumura K, Yamamoto R, Namiki J, Takemura R, Sasaki J. Cushing Index based on Cushing signs to predict in-hospital death and early intervention for minor head injury. J Neurotrauma. 2023;40(19-20):2110-7 (defines SI as HR ÷ SBP; its inverse is the Cushing index). doi:10.1089/neu.2022.0424 · PMID 37288749

Formula and cut-offs checked against these sources on 8 Nov 2026. Educational tool for clinicians; it does not replace clinical judgement.

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