Shock Index & Modified Shock Index

Methodology

Shock index (Allgöwer 1967)

SI = HR ÷ SBP; MSI = HR ÷ MAP

A rising shock index can reveal hidden blood loss or shock before blood pressure falls.

Who it is for

Adults.

Version

1.0.1

How this calculator works

Where the formula comes from

• The shock index is heart rate divided by systolic blood pressure, first described in 1967; its normal range is accepted as 0.5–0.7, with some evidence that up to 0.9 is acceptable.^[1]
• A shock index above 1.0 has been widely found to predict higher mortality and other markers such as massive transfusion and ICU admission.^[1]

The inputs

• Heart rate and systolic pressure often look normal in the compensated phase of shock and can be confounded by medicines such as antihypertensives and beta-agonists.^[1]

Versions and alternatives

• A paediatric age-adjusted shock index (SIPA) was developed because adult cut-offs are less reliable in children.^[1]

Where accuracy falls (published evidence)

• A 2023 trauma meta-analysis (35 studies) found sensitivity 0.68 and specificity 0.84 for massive transfusion, and poor accuracy for mortality (AUC 0.553).^[2]
• In 8,111 blunt trauma patients, a prehospital index above 0.7 to 0.9 carried no added transfusion risk over 0.5–0.7, while risk rose steadily above 0.9.^[3]
• In maternal haemorrhage and sepsis, a shock index below 0.9 performed well as a rule-out test, and 0.9–1.69 and 1.7 or more indicated increased risk.^[4]

What guidelines say

• A 2019 review found no consensus on when, where or whether the shock index has a role in the emergency department.^[1]

Sources

1. Koch E, Lovett S, Nghiem T, Riggs RA, Rech MA. Shock index in the emergency department: utility and limitations. Open Access Emerg Med. 2019;11:179–199. doi:10.2147/OAEM.S178358
2. Carsetti A, Antolini R, Casarotta E, et al. Shock index as predictor of massive transfusion and mortality in patients with trauma: a systematic review and meta-analysis. Crit Care. 2023;27(1):85. doi:10.1186/s13054-023-04386-w
3. Vandromme MJ, Griffin RL, Kerby JD, et al. Identifying risk for massive transfusion in the relatively normotensive patient: utility of the prehospital shock index. J Trauma. 2011;70(2):384–388. doi:10.1097/TA.0b013e3182095a0a
4. Nathan HL, Seed PT, Hezelgrave NL, et al. Shock index thresholds to predict adverse outcomes in maternal hemorrhage and sepsis: a prospective cohort study. Acta Obstet Gynecol Scand. 2019;98(9):1178–1186. doi:10.1111/aogs.13626

Compiled from the published sources above. Every statement was agreed independently by three AI research tools (Claude, ChatGPT, DeepSeek) and its source verified in PubMed or Crossref by the Hakeemly editorial team. Not reviewed by a doctor unless stated. Agreed on 2026-10-12

Worked example: how to calculate shock index

An illustration with sample values, worked out with the same method the tool above uses.

Limitations

• Medicines such as antihypertensives and beta-agonists can confound heart rate and systolic blood pressure (Koch 2019). In a study of maternal haemorrhage and sepsis, a shock index below 0.9 performed well as a rule-out test, while 0.9–1.69 and 1.7 or more indicated increased risk (Nathan 2019). Children need age-adjusted interpretation.

References

1. Allgöwer M, Burri C. 'Schockindex'. Dtsch Med Wochenschr. 1967;92(43):1947–1950. doi:10.1055/s-0028-1106070
2. Koch E, Lovett S, Nghiem T, Riggs RA, Rech MA. Shock index in the emergency department: utility and limitations. Open Access Emerg Med. 2019;11:179–199. doi:10.2147/OAEM.S178358
3. Nathan HL, Seed PT, Hezelgrave NL, et al. Shock index thresholds to predict adverse outcomes in maternal hemorrhage and sepsis: a prospective cohort study. Acta Obstet Gynecol Scand. 2019;98(9):1178–1186. doi:10.1111/aogs.13626