A normal Shock Index is 0.5–0.7 in healthy adults. Values of 0.7–1.0 may be normal or indicate early hemodynamic changes. An SI ≥ 1.0 is considered elevated and suggests hemodynamic compromise. An SI ≥ 1.4 indicates significant shock requiring immediate intervention.

The Shock Index is most useful in trauma (predicting need for massive transfusion), postpartum hemorrhage, early sepsis, GI bleeding, and ectopic pregnancy. It can identify patients at risk even when traditional vital signs appear normal — a patient with HR 100 and SBP 100 has an SI of 1.0, suggesting possible occult shock.

The SI may be unreliable in patients on beta-blockers (blunted HR response), those with baseline bradycardia or tachycardia, pregnant patients (physiologic tachycardia), and patients with chronic hypertension. It is most validated in trauma and hemorrhagic shock settings.