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Shock Index: What's In a Quotient?


Source: Edwards Lifesciences


This may be controversial for some, but all prehospital providers diagnose in the field. I unapologetically said what I said. To reach a diagnosis or to compile a list of potential differential diagnoses before we transfer care, we rely heavily on our patient assessment skills and lots of cutting-edge diagnostic equipment. Most of this equipment gives rise to numbers that help guide our decision making and reinforce a sick or not sick clinical picture. This blog will be centered on some numbers that come straight from our heart monitors/stethoscopes/pulse oximeters. These generated numbers - including how we interpret them and how we act afterward are "vital" to a successful patient outcome..... see what I did there!!


The shock index (SI) was first introduced in the late 1960's and it is simply derived by dividing the patient's heart rate by their systolic blood pressure. A normal healthy patient should have a SI of around 0.5-0.7. -- and as it climbs to > 1.0 moderate shock is setting in and direct correlations to mortality can be made. SI is very sensitive and can be used to identify patients needing a higher level of care despite vital signs that may not appear strikingly abnormal. (It's also important to note that since pediatrics patient's vitals vary based on age, a separate "adjusted" tool exist for children) + (The SI may also underestimate shock in the elderly as they can have an elevated baseline SBP - use/interpret with caution).


At first pass, the name would imply that this index is only applicable to trauma, but that's not the case at all. Shock comes in many forms/varieties and medical origins aren't going to be left out. Myocardial infarctions, pulmonary embolism, and sepsis can all affect the SI, just like a life-threatening hemorrhage. Many clinicals also utilize the shock index in trauma, especially as an indicator for blood administration, but it can also be applied to help predict post intubation hypotension.


For reasons mentioned above, the SI is not a perfect tool, but the benefit is that it can be computed quickly in an emergent setting. More recently this index has been improved upon in the literature and the modified shock index as well as the respiratory adjusted shock index have begun to show up. Those calculations are below (all of them are valuable bedside tools - as you do your best to filter out + triage your most high-risk patients): Elementary math for the win.


Source: Edwards Lifesciences


Regardless of the tool you use on the streets or in a hospital setting -- TIMELY INTERVENTION IN SHOCK IS KEY!! The biggest takeaway here is that blood pressure and heart rate when used individually fail to predict the severity of hypovolemia and shock in major trauma. Their utility, however, is increased when they are used together to help tell a bigger story. Happy computing, and don't forget to carry the one!!


August 21, 2023

Author: Joshua Ishmael, MBA, MLS(ASCP)CM, NRP

Pass with PASS, LLC.

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