The Shock Index (SI) is the ratio of the heart rate to systolic blood pressure. The index is a sensitive indicator of left ventricular dysfunction and can become elevated following a reduction in left ventricular stroke work. It can be used in the Emergency Department and Intensive Care Unit to identify patients needing a higher level of care despite vital signs that may not appear strikingly abnormal.
shock index =
= (heart rate in beats per minute) / (systolic blood pressure in mm Hg)
• normal: 0.5 to 0.7
• An elevated shock index (> 0.9) was found helpful by Rady et al (1994) to identify patients in the Emergency Department requiring admission and/or intensive care despite apparently stable vital signs.
• Persistent elevation of the SI has been associated with poor outcome in critically ill patients.
Rady MY, Smithline HA, et al. A comparison of the shock index and conventional vital signs to identify acute, critical illness in the Emergency Department. Ann Emerg Med. 1994; 24: 685-690.
Yealy DM, Delbridge TR. The shock index: All that glitters. Ann Emerg Med. 1994; 24: 714-715.