# What is the shock index?

Divides the heart rate by the systolic blood pressure to give the shock index, and shows where it sits against the 0.5 to 0.7 normal range and the 1.0 mark.

- Page: https://www.acalculator.org/health/shock-index-calculator
- JSON spec: https://www.acalculator.org/health/shock-index-calculator.json
- Version: 63a8f96da343

## Default answer

Example with the default inputs (Heart rate (beats per minute) 80, Systolic, top number (mmHg) 120): A heart rate of 80 beats per minute and a systolic pressure of 120 mmHg give a shock index of 0.67.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| hr | Heart rate (beats per minute) | The pulse, 20 to 300 beats per minute. |
| sbp | Systolic, top number (mmHg) | The systolic blood pressure, 50 to 300 mmHg. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| si | Shock index | Heart rate ÷ systolic pressure, to 2 decimals. |
| range | Range | Where the shock index shown sits: under 0.5, 0.5 to 0.7, over 0.7 up to 1.0, or over 1.0. |

## Method

Shock index = heart rate (beats per minute) ÷ systolic blood pressure (mmHg), rounded once to 2 decimals, halves up; the range reads the rounded value.

## Assumptions

- The heart rate and the systolic pressure are taken at the same time.
- The 0.5 to 0.7 normal range and the 1.0 mark are for adults (Koch 2019); children have their own age-based marks.
- The index is worked from the exact typed values and rounded once to 2 decimals, halves up; the range reads the rounded value.

## Worked examples

1. hr = 80, sbp = 120 gives si = 0.67, range = 0.5 to 0.7 (normal range). Source: Koch 2019: SI = HR ÷ SBP.
2. hr = 120, sbp = 100 gives si = 1.20, range = Over 1.0. Source: Koch 2019: 120 ÷ 100 = 1.20, over 1.0.
3. hr = 100, sbp = 100 gives si = 1.00, range = Over 0.7, up to 1.0. Source: Band edge: 100 ÷ 100 = 1.00 is not over 1.0 (Koch 2019).
4. hr = 105, sbp = 150 gives si = 0.70, range = 0.5 to 0.7 (normal range). Source: Band edge: 105 ÷ 150 = 0.70, the top of the 0.5 to 0.7 range (Koch 2019) ().
5. hr = 141, sbp = 200 gives si = 0.71, range = Over 0.7, up to 1.0.
6. hr = 50, sbp = 125 gives si = 0.40, range = Under 0.5.

## FAQ

### What is the shock index?

The heart rate divided by the systolic (top) blood pressure. It has no unit. A review by Koch and colleagues (2019) explains why it is used: early in shock, the heart rate and the blood pressure can each still look normal, while their ratio has already moved.

### How do I calculate the shock index?

Divide the pulse in beats per minute by the systolic pressure in mmHg. A pulse of 80 with a blood pressure of 120/80 gives 80 ÷ 120 = 0.67. A pulse of 120 with a systolic pressure of 100 gives 120 ÷ 100 = 1.20.

### What is a normal shock index?

Koch 2019 gives 0.5 to 0.7 as the currently accepted normal range for adults, and notes some evidence for values up to 0.9.

### What does a shock index over 1.0 mean?

Koch 2019 reports that a shock index above 1.0 has been widely found to go with a higher risk of death and with other signs of serious illness, such as a need for massive transfusion or intensive care. The review also says the index should never be used on its own to diagnose or rule out a critical illness.

### What is the modified shock index?

The heart rate divided by the mean arterial pressure (MAP) in place of the systolic pressure. Koch 2019 describes it, and an age shock index (age × shock index) for older adults. This page works out the standard shock index only; the mean arterial pressure calculator on this site gives the MAP.

### Does the shock index work for children?

Not with the adult ranges. Children have a faster normal heart rate and a lower blood pressure, so Koch 2019 describes a separate pediatric age-adjusted shock index with its own marks for each age group. The ranges on this page are for adults.

### What can make the shock index misleading?

Koch 2019 names drugs that change the heart rate or the blood pressure, such as beta-blockers, and notes doubts about the index in older adults, people with a fever, and people with long-term conditions. High blood pressure at baseline also changes it.

## Sources

- 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 (abstract and introduction: SI = HR ÷ SBP, unitless, normal 0.5 to 0.7, SI above 1.0 and higher mortality; tables 1 and 2: modified, age and pediatric indices; limitations; conclusion). https://doi.org/10.2147/OAEM.S178358 (full text: https://pmc.ncbi.nlm.nih.gov/articles/PMC6698590/, retrieved 2026-10-19)