Shock Index

A more sensitive quotient for circulatory shock than vital signs alone


The Shock Index was proposed by Allgower et al. in 1967 as a quotient designed to improve detection of severe circulatory collapse in the setting of hypovolemic medical patients. It has since been validated with large retrospective studies to show that as compared to standard vital signs in isolation, it is more sensitive in the prediction of developing hypotension, the need for massive transfusion, and rates of post-intubation hypotension.

Criticism of the Shock Index has been that there are no prospective trials validating its use in clinical practice, limiting definitive conclusions that can be reached based on the current level of evidence. The role of the Shock Index continues to function as another tool in the resuscitation of sick medical and trauma patients despite its current limitations.

Variable & Associated Points

Shock Index (SI) is calculated from a simple equation relating heart rate and systolic blood pressure

SI = HR / Systolic BP (mmHg)

Normal shock index is 0.5-0.7, whereas higher values are more sensitive in the detection of occult shock, transfusion requirements, and post-intubation hypotension than either vital sign in isolation.


Allgower M, Burri C.

Deutsche Medizinische Wochenschrift 1967 October 27, 92 (43): 1947-50

Rady MY, Smithline HA, Blake H, Nowak R, Rivers E.

Annals of Emergency Medicine 1994, 24 (4): 685-90

Mutchler M, Nienaber U, Munzberg M, et al.

Critical Care: the Official Journal of the Critical Care Forum 2013 August 12, 17 (4): R172

Heffner A, Swords D, Nussbaum M, Kline J, Jones A.

Journal of Critical Care 2012, 27 (6): 587-93

The Shock Index calculator is created by QxMD.

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