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Printed on 6/29/2026
For informational purposes only. This is not medical advice.
The Shock Index (SI) is a simple bedside tool calculated as heart rate divided by systolic blood pressure. A normal SI is 0.5–0.7 in healthy adults. An SI ≥ 1.0 indicates hemodynamic compromise and is associated with increased mortality, need for massive transfusion, and ICU admission. The Shock Index can detect occult shock even when individual vital signs appear normal, making it particularly useful in trauma, postpartum hemorrhage, and early sepsis where compensatory mechanisms may mask hypovolemia. Complement with [MAP Calculator](/tools/map-calculator) for organ perfusion assessment. For sepsis screening, use [qSOFA Score](/tools/qsofa) and [SIRS Criteria](/tools/sirs-criteria). Assess overall ICU severity with [SOFA Score](/tools/sofa-score) and [APACHE II](/tools/apache-ii). In GI hemorrhage, combine with [Rockall Score](/tools/rockall-score).
Formula: Shock Index = Heart Rate / Systolic Blood Pressure
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Obtain heart rate (beats/min) and systolic blood pressure (mmHg) simultaneously — ideally from the same assessment. Ensure the BP cuff is appropriately sized and the patient has been sitting or lying still for at least 2 minutes. In the pre-hospital or trauma setting, use the most recent available values. Both measurements should be from the same time point to ensure the ratio reflects real-time hemodynamic status.
Divide heart rate by systolic blood pressure. Example: HR 110 bpm, SBP 90 mmHg → SI = 110/90 = 1.22. For Modified Shock Index (MSI), use HR / MAP (mean arterial pressure) instead. MSI may have slightly better predictive performance in some studies.
Normal SI 0.5–0.7: stable hemodynamics. Borderline SI 0.8–0.9: clinical vigilance. SI ≥1.0: significant hemorrhagic shock — consider massive transfusion protocol (MTP) activation in trauma, urgent IV access, fluids, and source control. SI ≥1.4: severe shock requiring immediate intervention. Serial SI is more valuable than a single measurement — a rising SI despite resuscitation indicates ongoing hemorrhage. Trending SI every 15–30 minutes during active hemorrhage guides treatment.
Emergency physicians, trauma surgeons, paramedics
The Shock Index is a core component of trauma assessment. SI ≥1.0 in a trauma patient predicts need for massive transfusion, emergent surgery, and ICU admission with 2× higher mortality versus normal SI. Use alongside the [Glasgow Coma Scale](/tools/glasgow-coma-scale) and [Revised Trauma Score](/tools/revised-trauma-score) for comprehensive trauma triage. Activate massive transfusion protocol (MTP) when SI ≥1.0 in the setting of significant trauma mechanism.
Obstetricians, midwives, labor and delivery nurses
SI ≥0.9 predicts major postpartum hemorrhage (PPH) requiring intervention (Le Bas et al., BJOG 2017). SI ≥1.0 in PPH indicates significant hemodynamic instability requiring immediate uterotonic therapy, uterine massage or compression, and consideration of surgical intervention or interventional radiology. Serial SI during active PPH guides transfusion decisions and response to treatment.
Emergency physicians, gastroenterologists
In GI bleeding, SI ≥1.0 predicts need for blood transfusion and urgent endoscopy. SI supplements clinical assessment and [Rockall Score](/tools/rockall-score) for risk stratification in upper GI bleeding. Use SI as a rapid hemodynamic gauge while obtaining detailed history and initiating workup. Rising SI during observation indicates ongoing bleeding requiring urgent intervention.
Emergency nurses, triage physicians
In emergency triage, SI provides immediate hemodynamic risk stratification from just two measurements. A patient with HR 95 and SBP 95 (SI = 1.0) is more hemodynamically compromised than either vital sign alone suggests. Use SI to identify occult shock in patients presenting with chest pain, abdominal pain, or syncope where hemorrhage is in the differential.
Paramedics, emergency medical technicians
Pre-hospital providers can calculate SI in seconds without any equipment beyond a blood pressure cuff and pulse oximeter. SI ≥1.0 in the field predicts need for trauma center care and activates pre-hospital massive transfusion protocols in systems that have them. Pre-alert the receiving trauma center with the SI value for faster in-hospital resource activation.
ICU teams, trauma surgeons, resuscitation specialists
Serial SI measurement every 15–30 minutes during active resuscitation tracks response to treatment. A falling SI toward 0.7 indicates successful hemostasis and fluid resuscitation. A SI that fails to improve or worsens despite resuscitation indicates ongoing hemorrhage, inadequate source control, or distributive shock component. Pair with serial lactate and [SOFA Score](/tools/sofa-score) for comprehensive monitoring.
A patient with HR 95 and SBP 95 (SI = 1.0) is at significant risk despite both individual vital signs appearing 'borderline normal.' This is the key clinical value of SI — it captures the relationship between the two vital signs that compensatory mechanisms try to maintain. Always calculate SI when both HR and SBP are in borderline ranges.
Beta-blockers blunt the tachycardic response to hemorrhage, producing a falsely reassuring (low) SI despite significant blood loss. An elderly patient on metoprolol with SI 0.8 may be in significant shock. Similarly, pacemaker-dependent patients cannot mount tachycardia. Always inquire about beta-blocker use and cardiac devices when interpreting SI in suspected hemorrhage.
Mutschler et al. (Crit Care 2013) showed SI 0.9–1.0 carries 2× mortality vs normal; SI 1.0–1.4 carries 4× mortality; SI ≥1.4 carries 6× mortality in 21,853 trauma patients. Most trauma centers use SI ≥1.0 as a trigger to activate the MTP and initiate early balanced blood product resuscitation (1:1:1 ratio of PRBC:FFP:platelets).
Trending SI over time during resuscitation distinguishes responders from non-responders. A SI that falls from 1.2 to 0.7 with resuscitation confirms successful hemostasis. A SI that remains ≥1.0 despite 2L crystalloid + 2 units PRBC suggests ongoing hemorrhage requiring surgical or interventional control. Measure SI every 15–30 minutes during active resuscitation.
The Modified Shock Index (HR/MAP) incorporates diastolic blood pressure information and may have slightly better performance in some populations (Rady et al., Ann Emerg Med 1994). A normal MSI is 0.7–1.3. MSI ≥1.3 suggests hemodynamic compromise. Consider MSI when MAP is available and you want additional precision beyond the basic SI.
In obstetric settings, SI ≥0.9 predicts major PPH requiring blood transfusion and/or surgical intervention (Le Bas et al., BJOG 2017). PPH is the leading cause of maternal mortality in low-income settings, and SI provides an earlier warning than blood pressure drop alone. Maternity wards should have SI thresholds built into PPH protocols.
The trajectory of SI matters as much as the absolute value. A patient with SI 0.9 that is stable over 2 hours with a clear diagnosis (e.g., known GI bleed being scoped) is less urgent than a patient with SI 0.8 that rises to 1.0 to 1.2 over 30 minutes. Rising SI despite resuscitation is a sign of ongoing, uncontrolled hemorrhage requiring source control.
Children normally have higher heart rates and lower blood pressure than adults, resulting in SI values above the adult normal range even when hemodynamically stable. Do not apply adult SI thresholds to pediatric patients. Use age-adjusted vital sign targets and pediatric-specific shock assessment criteria for patients under 16 years of age.
Anxiety, pain, and fever can elevate heart rate and cause SI to rise above 0.9 without hemodynamic compromise. Always correlate SI with clinical context: mechanism of injury or illness, skin perfusion (color, cap refill, mottling), mental status, and urine output. A patient in severe pain with SI 0.9 who has warm, well-perfused extremities and intact mentation is less concerning than the number alone suggests.
Shock Index introduced by Allgöwer and Burri (Langenbecks Arch Chir 1967). SI >1.0 associated with in-hospital mortality: Mutschler et al. (Crit Care 2013) in 21,853 trauma patients (SI 0.9–1.0 = 2× mortality vs normal; SI >1.4 = 6× mortality). Postpartum hemorrhage: Le Bas et al. (BJOG 2017) validated SI ≥0.9 predicts major PPH. Modified Shock Index (HR/MAP): Rady et al. (Ann Emerg Med 1994). ATLS guidelines reference SI as a screening tool for hemorrhagic shock classification.
Your Shock Index (SI) is the ratio of heart rate to systolic blood pressure and provides a rapid assessment of hemodynamic status. A normal SI of 0.5 to 0.7 suggests stable hemodynamics. An SI between 0.7 and 1.0 may be normal in some individuals but warrants clinical correlation, as it can represent early or compensated hemodynamic compromise.
An SI of 1.0 or greater is elevated and indicates hemodynamic instability that may not be apparent from individual vital signs alone. For example, a patient with a heart rate of 110 bpm and systolic blood pressure of 100 mmHg has an SI of 1.1 — both values might individually appear only mildly abnormal, but the ratio reveals meaningful cardiovascular stress. An SI of 1.0 or above in trauma is associated with increased need for massive transfusion, emergent intervention, and ICU admission.
An SI of 1.4 or greater indicates severe hemodynamic compromise and is associated with significantly increased mortality. These patients typically require immediate resuscitation with fluids and blood products, urgent identification and treatment of the underlying cause (hemorrhage, sepsis, cardiac dysfunction), and close hemodynamic monitoring.
The Shock Index is most valuable in the initial assessment of trauma patients, where it can identify occult hemorrhagic shock before traditional vital sign thresholds are met. Compensatory mechanisms — particularly in young, healthy patients — can maintain systolic blood pressure in the normal range despite significant blood loss, making individual vital signs unreliable early indicators of shock.
This tool is also useful in the evaluation of postpartum hemorrhage, ruptured ectopic pregnancy, gastrointestinal bleeding, early sepsis, and any clinical scenario where hemorrhage or hemodynamic compromise is suspected. It can be calculated at the bedside in seconds, making it practical for triage and rapid assessment in the emergency department or pre-hospital setting.
The Shock Index may be unreliable in patients taking beta-blockers or other heart rate-limiting medications, as the blunted heart rate response will produce a falsely reassuring (low) SI despite hemodynamic compromise. Patients with baseline bradycardia (athletes) or baseline tachycardia (anxiety, pain, fever, hyperthyroidism) will also have altered baseline SI values.
Pregnant patients normally have a higher resting heart rate and lower blood pressure, resulting in a physiologically elevated SI that does not indicate pathology. Age-adjusted and pregnancy-adjusted SI values have been proposed but are not yet widely standardized. Children also have different normal heart rate and blood pressure ranges that affect SI interpretation.
The SI is a screening tool and does not replace comprehensive hemodynamic assessment. A normal SI does not rule out significant pathology, and an elevated SI does not specify the underlying cause. It should be used in conjunction with clinical assessment, trending of vital signs, lactate levels, and focused evaluation for the source of hemodynamic instability.
For related assessments, see MAP Calculator, qSOFA Score and SOFA Score.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
April 21, 2026 · trust-baseline
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