From the Guidelines
The shock index is a critical clinical tool calculated by dividing heart rate by systolic blood pressure, with values above 0.9 suggesting early shock and hemodynamic instability, and values exceeding 1.0 indicating significant shock requiring immediate intervention. This calculation is based on the principle that as patients lose blood volume or develop vasodilation, the body compensates with tachycardia before hypotension becomes evident, making this ratio change more sensitive than either parameter alone 1. The shock index is particularly valuable in emergency settings for identifying patients with occult shock, as traditional vital signs like blood pressure may remain normal during early compensatory mechanisms.
Key Points to Consider
- The shock index helps clinicians quickly identify patients who may be compensating for blood or fluid loss before obvious hypotension develops
- It is especially useful in trauma, sepsis, and hemorrhage cases where early recognition of shock is critical for timely intervention
- While not a standalone diagnostic tool, the shock index provides valuable information that complements other clinical assessments in critically ill patients
- The TASH score, which uses seven parameters to predict the probability of mass transfusion, has been validated as a useful tool in predicting the individual probability of massive transfusion and ongoing life-threatening hemorrhage 1
Clinical Application
The shock index is easy to calculate and can be used in a variety of clinical settings to quickly assess patients for potential shock. By using this simple calculation, clinicians can identify patients who require closer monitoring and potential intervention, even if their traditional vital signs appear normal. This can help improve patient outcomes by allowing for earlier recognition and treatment of shock. As noted by Paladino et al., the shock index may be useful in drawing attention to abnormal values, but it is too insensitive to rule out disease and should not lower the suspicion of major injury 1.
From the Research
Definition of Shock Index
- The shock index (SI) is defined as the heart rate (HR) divided by systolic blood pressure (SBP) 2, 3, 4, 5.
- It is used as a prognostic tool in trauma and specific disease states, such as hemorrhage, myocardial infarction, pulmonary embolism, sepsis, and ruptured ectopic pregnancy 2.
Calculation and Interpretation of Shock Index
- The SI is calculated by dividing the heart rate by the systolic blood pressure (SI = HR/SBP) 2, 3, 4, 5.
- A SI > 1.0 has been widely found to predict increased risk of mortality and other markers of morbidity, such as need for massive transfusion protocol activation and admission to intensive care units 2.
- A SI ≥ 1 has been shown to be a predictive factor of hospital mortality at 7 days and one month in severe trauma patients 3.
- A SI > 1.3 has been associated with a clinically significant increase in both the likelihood of hospital admission and inpatient mortality in the general emergency department population 4.
Clinical Applications of Shock Index
- The SI can be used as a simple tool in the triage and orientation of severe trauma patients to trauma centers 3.
- It can help guide rapid and accurate acuity designation, resource allocation, and disposition in the emergency department 4.
- The SI has been shown to be a useful marker for significant injury in trauma patients, with an optimal threshold of 0.83 for predicting poor outcomes 5.