013: EPICC Review Week 7 - Shock Index for Improved Trauma Care by Prehospital Resuscitationists

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.

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), 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.

Correlation of shock index and modified shock index with the outcome of adult trauma patients: a prospective study of 9860 patients.

Evaluation of preintubation shock index and modified shock index as predictors of postintubation hypotension and other short-term outcomes

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.

Elevated modified shock index in early sepsis is associated with myocardial dysfunction and mortality.

Age Shock Index is Superior to Shock Index and Modified Shock Index for Predicting Long-Term Prognosis in Acute Myocardial Infarction





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