What is The Shock Index?

One of the more difficult things to relate to new EMTs who are just cutting their first patient assessment teeth is putting assessment finding in context. Frequently, while teaching a new batch of EMT students patient assessment, I’m peppered with questions like these:

“How fast does the pulse have to be before you consider the possibility of shock?”

“Do you always put someone on oxygen when they have pale skin?”

“How slow does a person have to breathe before we should start breathing for them?”

“So if the blood pressure is low, that means that they are bleeding?”

“If the patient doesn’t have pinpoint pupils, should I still give Narcan?”

“What does the Glasgow need to be before we decide to go emergent?”

All of these questions have a simple desire at their core. The desire to know, with certainty, that a single assessment can give us the answer to our treatment questions. We want patient care to be simple. If then, then this. The less experience we have, the more cook-book we want patient care to be.

The unfortunate truth that our new EMTs are (hopefully) quick to learn is this, patient assessment is never quite that simple. Everything needs to be taken in context. Respiratory rate is inseparably bound to tidal volume. Pallor is dependent on the patients baseline. Some abnormal findings aren’t abnormal for patients with congenital pupil abnormalities or naturally pale skin. The unsatisfying answer to many of these questions is, “It depends.”

One of the more difficult aspects of patient assessment is being able to step back and put it all together. What do all these symptoms, when taken together, mean to me as a caregiver? What does the current constellation of symptoms mean?

To that end, I think it’s useful to understand the shock index. The shock index s a simple calculation, based on the heart rate and the systolic blood pressure, that uses the coloration between those two numbers to try to identify potential shock patients. Understanding the shock index helps us understand how multiple vital signs can be evaluated in combination to increase our index of suspicion for certain occult injuries or disease processes. (In this case, shock.)

Here’s how we calculate the shock index. We take our patients systolic blood pressure and we divide it into the heart rate in beats per minute. Under normal conditions, we will tend to get a number between .5 and .8. (Yes, you can do this on your smart phone if you, like me, are mathematically challenged. As a for-instance, when the classic vital findings of HR = 80BPB and a Blood pressure = 120/80. Our shock index calculates a comfortable .67. When the systolic blood pressure and the pulse become equal (for instance HR = 100BPM, BP = 100/60) our shock index reaches an uncomfortable 1.0. The farther we climb above that number, the higher our index of suspicion for an underlying shock state.

This holds true for all of our shock presentations including those sometimes cryptic presentations like sepsis and occult bleeding. This is where recognizing the concept behind the shock index can be a powerful tool in your physical assessment arsenal.

One of the powerful things about calculating the shock index is that it keys us in to the critical association between vital signs.

Vital signs don’t exist in a vacuum. None of our assessments live in a vacuum. We must consider them in association with the entire clinical picture.

Research suggests that calculating the shock index might help us identify the presence of occult traumatic bleeding even when one of the two vital signs in question remain within a normal range (for any number of reasons). But even more than that, understanding how the shock index works can help us become more in tune to the relationship between all of the vital signs…even when we don’t take the time to calculate it. And that’s where it might prove its real value.

I’m not yet ready to recommend calculating the shock index as part of a standard trauma assessment. While it could be used on the fly in limited clinical presentations, I’d prefer to see EMTs play with it retrospectively and prospectively to better understand how these two vital numbers work in combination to help us identify underlying shock states.

Have fun with it and let me know how it goes.

Now it’s your turn. Have you experimented with the shock index? Did you find it useful? Leave us a comment and let everyone know what you think.


  1. “As a for-instance, when the classic vital findings of HR = 80BPB and a Blood pressure = 120/80. Our shock index calculates a somewhat comfortable .83.”

    120 (systolic) divided by 80 (HR) — wouldn’t that be .67?

  2. administrator says:

    Ahem…yup. Every single time I calculate it. This is why I need to make sure I’m sober when I edit my posts. Thanks Collin. I’ll fix it right now.

  3. Hey guys,

    First of all, great website.

    Trying to understand the calculation. 120/80 is 1.5, not .67.

    Above you state dividing BPM “into” the SBP. This would mean 120/80, leaving us with 1.5. Do you mean dividing the BPM “by” SBP?

    Sorry to get all “semanticy” on you. Just trying to understand.


  4. BPM (80) divided “by” SBP (120) gives us .67

    right? haha, I’m no Mathematician.

  5. administrator says:

    You’re right Tyler. It was confusing the way it was stated. I’ve corrected it. Maybe I should avoid these math type posts all together. Don’t even get me started on my mechanism of injury post. Thanks for helping to make the post better.

  6. No no, please don’t avoid these. I had never heard of this. It’s great food for thought!! Keep it coming!

  7. I like the simplicity of this.

    Another, different way of looking at this in medical pts is the (Modified) Early Warning Score ((M)EWS).

    This takes into account both the individual systemic parameters and the holistic bservations taken. Excellent for sepsis and overall monitoring.


  8. Hey the person in charge of your website needs to give us credit for photos used via Flickr.

    Dept de Prensa Comandos de Salvamento El Salvador.

  9. administrator says:

    Hi Marco, great photo. I love it. Thank you for posting it under a creative commons agreement. We depend on photographers like you for our site appearance. We have credited your photo in two ways. First, we only use photos listed under creative commons agreements (we also upload our photos for use under this same agreement.) and we put a floating caption over the photo with the photographer, name of the photo and source (in this case, Flickr). Hover your mouse over the photo and you’ll see the caption. We also link every photo directly to the original source on flickr. If you click the photo you’ll find it links to your stream on flickr. If these two photo credits are insufficient please let me know and I’ll replace it. Thanks again for your work, Steve.

  10. if you are using a calculator, put in 80 first, then divide, then put in 120 that is how you get .67

  11. Shock index is give me every important information. when my patient is bleeding from esophagus with Varicosis. I find that a shock index by it — Heart rate per one minute divide by Systolic Blood Pressure. it’s normally – 0.5-0.8. If it goes up higher, U need to think about that my patient with shocking. That above example is 80 (heart rate per minute) divide by 120 (systolic blood pressure) then answer is 0.67. It is normal. no shocking.