013: EPICC Review Week 7 - Shock Index for Improved Trauma Care by Prehospital Providers
Background: For year EMS providers have relied on certain clinical signs and symptoms to predict clinically unstable trauma patients and the need for emergent transport for definitive surgical care. Commonly EMS providers have used HR>120, systolic BP<90mmHg, and MAP’s <60mmHg as benchmarks for clinically unstable patients. However, these indicators can frequently be misleading if not carefully evaluated in the context of a patient’s overall clinical presentation leading prehospital providers to underestimate the severity of our patient's injuries or illness.
Shock Index
First showed up in the literature in the late 60’s and early 70’s as a marker for instability in hypovolemic patients (1), and and patients experiencing acute myocardial infarctions (2).
SI = HR/SBP (Normal 0.5-0.7)
Example of normal:
HR = 60
SBP = 100
DBP = 70
MAP = 85
SI = 60/100 = 0.6
Example of abnormal:
HR = 115
SBP = 100
DBP = 70
MAP = 85
SI = 115/100= 1.15
SI > 0.7 ~ 75% accurate at predicting badness.
SI > 0.9 is considered cut point for most studies for identifying critical patients
SI >1 = Sensitivity 68 and Specificity 81 for predicting need for MTP.
Higher SI scores better at predicting need for more aggressive resuscitation.
Like most other things, this seems to be better if trended over time.
Balhara KS, Hsieh Y, Hamade B, et al. Clinical metrics in emergency medicine: the shock index and the probability of hospital admission and inpatient mortality. Emerg Med J 2017;34:89-94.
Problems: Independent factors, HR and SBP, are not great in the prehospital or transport environment. Subject to significant fluctuations independent of patients hemodynamic status.
Improperly sized cuffs
Inexperienced providers
Temperature
Pain
Vibration
etc.
Ongoing efforts to find better objective indicator for predicted outcomes and need for aggressive resuscitation.
REMEMBER THIS!
HR should be less than SBP
SBP ≤ HR = BAD NEWS!
Modified Shock Index
MSI = HR/MAP (0.7 - 1.3)
We know that trending MAP’s gives us a better clinical picture of our patients status vs. just looking at SBP.
MSI < 0.7 or > 1.3 indicates greater mortality
Example of normal:
HR 60
SBP 100
DBP 70
MAP 85
MSI = 60/85 = 0.71
Example of abnormal:
HR 115
SBP 100
DBP 70
MAP 85
MSI = 115/85 = 1.35
Shown in multiple studies to be statistically more accurate at predicting patients requiring MTP in the ED.
MSI > 1.3 ≈ 94% chance of requiring MTP
Many studies show equal sensitivity.
My Conclusion: Prehospital Emergency Care has evolved since the days of 3-lead ECG’s, calling for an order to administer oxygen, or waiting until a patient arrives at the ED before someone active the cath team. More and more “Prehospital Resuscitationists” are being asked to use a combination of technology (POCUS and iSTAT), evidence, higher education, and experience to make life changing decisions from the field with limited information. It is essential that we develop, and incorporate into our clinical practice, all available knowledge and tools so that we can make the best decisions possible for our trauma patients, and while neither the SI or the MSI are a perfect tool for predicting a patients need for aggressive resuscitation or hospital mortality, I believe either are good tools for increasing our index of suspicion and should be added to our proverbial “Bag of Tricks.”
References
(1) Arterial pressure, pulse, "shock index" and central venous pressure in 30 hypovolemic patients. Langenbecks Arch Chir. 1968;320(1):1-7.
(2) Acute myocardial infarct. VII. Prognostic significance of a new shock index. Bleifeld W, Mathey D, Hanrath P, Effert S. Dtsch Med Wochenschr. 1973 Jul;98(28):1355-7.
Balhara KS, Hsieh Y, Hamade B, et al. Clinical metrics in emergency medicine: the shock index and the probability of hospital admission and inpatient mortality. Emerg Med J 2017;34:89-94.
Modified shock index and mortality rate of emergency patients
Accuracy of shock index versus ABC score to predict need for massive transfusion in trauma patients
Prediction of massive bleeding. Shock index and modified shock index.
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Sean
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