- Enter the heart rate (bpm) and systolic blood pressure (mm Hg). The Shock Index (HR ÷ SBP) updates automatically.
- Optionally add the diastolic blood pressure (mm Hg) to compute the mean arterial pressure (MAP) and the Modified Shock Index (HR ÷ MAP).
- Optionally add the patient's age (years) to compute the Age Shock Index (SI × age).
- The result box is colour-coded by the Shock Index band: green if < 0.7, amber 0.7–< 0.9, red ≥ 0.9 (occult shock / hemodynamic compromise).
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When to Use
Use the Shock Index at the bedside whenever you need a fast, vitals-only read on perfusion — at triage, on a deteriorating ward patient, or during resuscitation. Because the heart rate often climbs while the systolic pressure is still "normal," the Shock Index can flag occult or compensated shock earlier than systolic blood pressure alone. An elevated index has been shown to predict massive transfusion, ICU admission, and mortality across trauma, sepsis, gastrointestinal bleeding, pulmonary embolism, and postpartum hemorrhage.
Appropriate use
Any adult being triaged or resuscitated for possible hypovolemia or shock: trauma, sepsis, major GI bleed, suspected PE, obstetric (postpartum) hemorrhage, and undifferentiated hypotension. Best used as a trend — a rising index over serial vitals is more informative than one snapshot.
When NOT to rely on it
The Shock Index is confounded when the heart-rate response is blunted — beta-blockers, calcium-channel blockers, or a paced rhythm — which can mask hypoperfusion. Chronic hypertension raises the baseline systolic pressure and lowers the apparent index, while pain, anxiety, fever, or stimulants drive tachycardia and inflate it without true shock. A single value is only a snapshot: always interpret alongside lactate, perfusion pressure, and the full clinical picture.
Pearls & Pitfalls
It moves before the pressure drops
Normal Shock Index is roughly 0.5–0.7. Because tachycardia is an early compensatory response, the index rises while the systolic pressure is still preserved — making it a sensitive early flag for occult shock. A value ≥ 0.9 (some use > 1.0) signals hemodynamic compromise and correlates with the need for transfusion, ICU care, and higher mortality.
Modified and Age Shock Index
The Modified Shock Index (HR ÷ MAP) folds in the diastolic pressure and reflects systemic vascular tone: a normal MSI is roughly 0.7–1.3, with > 1.3 suggesting a hyperdynamic, low-SVR state and < 0.7 a low-output state. The Age Shock Index (SI × age) improves risk stratification in older patients, in whom a "normal-looking" index can still mask significant compromise.
Pitfalls
(1) Beta-blockers, calcium-channel blockers, and paced rhythms blunt the tachycardic response and can produce a falsely reassuring index. (2) Chronic hypertension raises the baseline systolic pressure, lowering the apparent index for a given degree of hypovolemia. (3) Pain, anxiety, fever, and stimulants drive tachycardia and inflate the index without true shock. (4) A single value is a snapshot — trend serial measurements, and never let a "normal" index override clinical judgment, lactate, or perfusion pressure.
Why Use It
The Shock Index turns two numbers everyone already measures — heart rate and systolic blood pressure — into an early, objective marker of hypoperfusion. A patient whose systolic pressure still reads "normal" may already be in compensated shock, and the rising index catches that before the pressure crashes. For the nephrologist this matters because sustained hypoperfusion drives acute kidney injury: poor renal blood flow from hypovolemia or distributive shock is a leading cause of AKI, so an elevated Shock Index should prompt early attention to volume status, mean arterial (perfusion) pressure, and lactate. First described by Allgöwer and Burri in 1967, the index — and its modified and age-adjusted forms — is now widely used to triage and risk-stratify across trauma, sepsis, hemorrhage, and PE.
Shock Index, Modified SI & Age SI
Enter the heart rate and systolic blood pressure to get the Shock Index. Add the diastolic pressure for the Modified Shock Index (HR ÷ MAP) and the age for the Age Shock Index. The result box is colour-coded by the Shock Index band.
⚕ Allgöwer M, Burri C. Dtsch Med Wochenschr. 1967. The Shock Index is a triage and risk-stratification aid, not a diagnosis. It is confounded by beta-blockade, pacing, chronic hypertension, and pain/anxiety, and a single value is a snapshot — trend it and pair with lactate and perfusion pressure. For licensed clinicians; not a substitute for individualized assessment.
Next Steps
Use the Shock Index band to triage and direct the next move — and trend it on serial vitals.
- SI < 0.7 (green): hemodynamics within normal range by this marker. Continue to monitor, especially if the patient is on rate-limiting drugs or chronically hypertensive (which can mask compromise).
- SI 0.7–< 0.9 (amber): borderline. Reassess perfusion, repeat vitals, and check a lactate; look for an early source of hypovolemia or distributive shock.
- SI ≥ 0.9 (red): hemodynamic compromise / occult shock. Begin resuscitation, identify the source (hemorrhage, sepsis, PE, postpartum hemorrhage), prioritize perfusion pressure, and escalate care — an elevated index predicts transfusion, ICU admission, and mortality.
- Because sustained hypoperfusion drives acute kidney injury, protect the kidneys early: support the mean arterial (perfusion) pressure and integrate with severity scores such as qSOFA / SOFA.
Evidence & References
Formulas
| Quantity | Formula |
|---|---|
| Shock Index (SI) | Heart rate ÷ Systolic BP |
| Mean arterial pressure (MAP) | DBP + (SBP − DBP) ÷ 3 |
| Modified Shock Index (MSI) | Heart rate ÷ MAP |
| Age Shock Index | SI × age (years) |
Interpretation
| Value | Interpretation |
|---|---|
| SI 0.5–0.7 | Normal hemodynamics |
| SI 0.7–< 0.9 | Borderline — reassess, trend, check lactate |
| SI ≥ 0.9 (some use > 1.0) | Hemodynamic compromise / occult shock — predicts transfusion, ICU, mortality |
| MSI 0.7–1.3 | Normal; > 1.3 hyperdynamic / low SVR, < 0.7 low output |
The Shock Index often rises before the systolic pressure falls, making it a sensitive early marker of hypoperfusion across trauma, sepsis, GI bleeding, pulmonary embolism, and postpartum hemorrhage. Interpret cautiously in patients on beta-blockers or with chronic hypertension, and trend rather than relying on a single value.
References
- Allgöwer M, Burri C. Schockindex [Shock index]. Dtsch Med Wochenschr. 1967;92(43):1947–1950. doi:10.1055/s-0028-1106070.
- Berger T, Green J, Horeczko T, et al. Shock index and early recognition of sepsis in the emergency department. West J Emerg Med. 2013;14(2):168–174. doi:10.5811/westjem.2012.8.11546.
- Liu YC, Liu JH, Fang ZA, et al. Modified shock index and mortality rate of emergency patients. World J Emerg Med. 2012;3(2):114–117. doi:10.5847/wjem.j.issn.1920-8642.2012.02.006.
