Shock Index – Another Way To Avoid Missing Shock

The Shock Index is helpful in the early recognition of shock in both trauma patients (Reference 1) and patients with septic shock (Reference 2).

For a brief, complete, and current discussion of definition and diagnosis of sepsis, see (Reference 3).

The following is the excellent post, Shock Index – A Better Vital Sign in Trauma, Jan 8, 2012, from The Short Coat blog:

The gist: Don’t rely on a trauma patient’s normal vital signs to assume they’re hemodynamically stable. Rather, use the shock index (HR/SBP) to predict a patient’s need for massive transfusion.Normal SI = 0.5-0.7

  • SI > 0.9 then approach the patient as though they are actively bleeding
  • SI increases more than 0.3 at any point in care (prehospital to ED), then treat this as though the patient is actively exsanguinating
  • Don’t rule out bleeding if SI is within normal limits
  • Elderly patient multiply their age by the SI (Age x SI)

The Vandromme, et al paper* in the Journal of Trauma in 2011 posited that the following holds true…

  • SI > 0.9 predicts twice the risk of massive transfusion
  • SI > 1.1 predicts four times the risk of massive transfusion
  • SI > 1.3 predicts nine times the risk of massive transfusion!

So, in trauma patients who come in with normal appearing vital signs, calculate the SI (and hopefully get a lactate and base deficit) before determining the patient is stable.

*Identifying risk for massive transfusion in the relatively normotensive patient: utility of the prehospital shock index [PubMed Abstract]. J Trauma. 2011 Feb;70(2):384-8; discussion 388-90.


(1) Shock index as a mortality predictor in patients with acute polytrauma  [Full Text HTML] [Full Text PDF]. Journal of Acute Disease Volume 4, Issue 3, August 2015, Pages 202–204

Objective: To evaluate whether the shock index (SI), given by the formula SI = heart rate/systolic blood pressure (HR/SBP), is useful for predicting mortality at 24 h in trauma
patients admitted to the emergency department of a university hospital in Colombia.
Methods: A database of trauma patients admitted between January 2013 and December 2013 was constructed; the result according to the shock index was determined, generating
a dichotomous variable with two groups: Group A (SI < 0.9) and Group B (SI > 0.9).
Univariate analysis was performed.
Results: A total of 666 patients were analyzed, 83.3% (555) had SI < 0.9, and 16.7% (111) SI > 0.9. The mean age for Groups A and B was 32.4 and 35.4 respectively. The average injury severity score for both groups was 9.6 and 17.6 respectively. Mortality at 24 h after injury for both groups was 3.1% (P = 0.032) and 59.5% (P = 0.027) respectively.
Conclusions: An initial shock index greater than 0.9 implies a worse prognosis 24 h after injury. The shock index predicts mortality in multiple trauma patients in the emergency
department, and is also a quick and applicable in all hospital.

(2) Shock Index and Early Recognition of Sepsis in the Emergency Department: Pilot Study [PubMed Abstract] [Full Text HTML] [Full Text PDF]. West J Emerg Med. 2013 Mar; 14(2): 168–174.

Screening for severe sepsis in adult emergency department (ED) patients may involve potential delays while waiting for laboratory testing, leading to postponed identification or over-utilization of resources. The systemic inflammatory response syndrome (SIRS) criteria are inaccurate at predicting clinical outcomes in sepsis. Shock index (SI), defined as heart rate / systolic blood pressure, has previously been shown to identify high risk septic patients. Our objective was to compare the ability of SI, individual vital signs, and the systemic inflammatory response syndrome (SIRS) criteria to predict the primary outcome of hyperlactatemia (serum lactate ≥ 4.0 mmol/L) as a surrogate for disease severity, and the secondary outcome of 28-day mortality.
We performed a retrospective analysis of a cohort of adult ED patients at an academic community trauma center with 95,000 annual visits, from February 1st, 2007 to May 28th, 2008. Adult patients presenting to the ED with a suspected infection were screened for severe sepsis using a standardized institutional electronic order set, which included triage vital signs, basic laboratory tests and an initial serum lactate level. Test characteristics were calculated for two outcomes: hyperlactatemia (marker for morbidity) and 28-day mortality. We considered the following covariates in our analysis: heart rate >90 beats/min; mean arterial pressure < 65 mmHg; respiratory rate > 20 breaths/min; ≥ 2 SIRS with vital signs only; ≥2 SIRS including white blood cell count; SI ≥ 0.7; and SI ≥ 1.0. We report sensitivities, specificities, and positive and negative predictive values for the primary and secondary outcomes.
2524 patients (89.4%) had complete records and were included in the analysis. 290 (11.5%) patients presented with hyperlactatemia and 361 (14%) patients died within 28 days. Subjects with an abnormal SI of 0.7 or greater (15.8%) were three times more likely to present with hyperlactatemia than those with a normal SI (4.9%). The negative predictive value (NPV) of a SI ≥ 0.7 was 95%, identical to the NPV of SIRS.
In this cohort, SI ≥ 0.7 performed as well as SIRS in NPV and was the most sensitive screening test for hyperlactatemia and 28-day mortality. SI ≥ 1.0 was the most specific predictor of both outcomes. Future research should focus on multi-site validation, with implications for early identification of at-risk patients and resource utilization.

(3) Sepsis Definitions and Diagnosis  blog post reviewed and revised 24 February 2016 from Life In The Fast Lane.

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