How this instrument works
Shock index divides pulse rate by systolic blood pressure. A healthy resting adult typically lands somewhere around 0.5 to 0.7, meaning the pulse sits comfortably below the systolic reading in the usual proportion. Early blood loss or another circulatory strain can nudge heart rate up and blood pressure down together, in a compensated phase where neither number crosses an alarming line by itself — the ratio can surface that pattern before either vital sign does on its own.
Allgöwer and Burri described the index in a 1967 German-language paper, and it saw a widely cited modern re-evaluation by Rady and colleagues in 1994, who tested it specifically in patients with acute circulatory failure. Emergency medicine research on trauma and sepsis has kept refining the working threshold since, generally converging on roughly 0.9 as a more sensitive line than the 1.0 cutoff sometimes quoted from older sources.
This is a triage aid, not a diagnosis. Pain, anxiety, physical conditioning, pregnancy, and rate-limiting medications such as beta-blockers can all shift heart rate or blood pressure independent of blood volume, so a single elevated reading is a prompt for closer clinical assessment rather than a verdict read off one division.
- Enter Heart rate in beats per minute.
- Enter Systolic blood pressure in mmHg.
- Read Shock Index; compare against the roughly 0.5–0.7 normal band and the approximately 0.9 threshold flagged in validation studies.
Worked example — three readings across the normal line
A pulse of 80 beats per minute against a systolic reading of 120 mmHg: 80 ÷ 120 = 0.667, squarely inside the commonly cited normal band of roughly 0.5 to 0.7. Slow the pulse to 70 against a higher systolic of 140 and the ratio falls to 70 ÷ 140 = 0.5, the low end of that same band.
Now raise the pulse to 110 while the systolic reading drops to 100: 110 ÷ 100 = 1.1, well past the roughly 0.9 line that modern validation studies in trauma and sepsis literature associate with a meaningfully higher chance of circulatory compromise — a pattern worth flagging even though neither number alone, a pulse of 110 or a systolic of 100, would necessarily raise concern by itself.
Questions
What is a normal shock index?
Roughly 0.5 to 0.7 for a healthy resting adult, reflecting a pulse comfortably below systolic blood pressure in the usual proportion — for example, 70 beats per minute against 140 mmHg gives exactly 0.5. Values in that band generally describe stable hemodynamics rather than any particular concern.
What shock index value indicates a problem?
Most modern validation research in emergency medicine treats a value at or above roughly 0.9 as the threshold worth acting on, a lower and more sensitive line than the 1.0 cutoff sometimes quoted from older sources. A reading of 1.1 — a pulse of 110 against a systolic pressure of 100 — sits clearly past that mark and has been associated in trauma and sepsis studies with a materially higher chance of hemodynamic compromise.
Why use a ratio instead of watching pulse and blood pressure separately?
Because early blood loss or shock can raise pulse and lower blood pressure together before either value individually looks alarming on a standard vital-signs chart. A systolic reading of 100 mmHg alone doesn't necessarily worry a clinician, and neither does a pulse of 110 by itself — but the ratio of the two together can surface a pattern that reading each number in isolation misses.
Can medications affect the shock index reading?
Yes, and this is one of the index's real limitations. Beta-blockers and other rate-limiting drugs blunt the pulse response the ratio depends on, so someone taking one can be in genuine circulatory trouble while their heart rate stays artificially low and the ratio understates the risk. Pain, anxiety, fitness level, and pregnancy can shift the numbers the other way. Read the ratio alongside the fuller clinical picture, not in isolation.
Is shock index a diagnosis?
No — it's a triage and screening aid, not a diagnosis. A raised shock index flags a pattern worth a closer clinical look, whether the cause is ongoing blood loss, sepsis, or another source of circulatory strain, but confirming and treating the underlying problem depends on full clinical assessment, not one ratio built from two vital signs.
Who first described the shock index?
Max Allgöwer and Charles Burri described it in a 1967 German-language paper, and it saw a widely cited modern re-evaluation by Rady and colleagues in 1994, who tested it specifically in patients with acute circulatory failure. Emergency medicine literature on trauma and sepsis has continued validating and refining the threshold since.
References
- Allgöwer & Burri 1967, Dtsch Med Wochenschr — original description
- Rady et al. 1994, Resuscitation — re-evaluation in acute circulatory failure (PubMed)
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.