Shock index is a simple bedside measure introduced by Allgower and associates  as early as 1967. Shock index is the ratio of heart rate to systolic blood pressure. Normal range of shock index is between 0.5 and 0.7 in healthy adults. Shock index of 1.0 or more indicates a poor prognosis in acute circulatory failure.
Shock index of >0.9 predicts mortality in adult trauma patients. Acker SN and colleagues have developed a pediatric specific shock index: SIPA: Shock index, pediatric age adjusted . SIPA is defined by maximum normal heart rate and minimum normal systolic blood pressure by age. The cut off for children were:
Age 4-6: >1.22
Age 7-12: >1.0
Age 13-16: >0.9
In their retrospective review of around five hundred and fifty children presenting with trauma, 50% had a shock index >0.9, but age adjusted SIPA was above cut off only in 28%. SIPA showed better correlation with injury severity score (ISS), blood transfusion within first 24 hours, grade III liver/spleen laceration requiring blood transfusion and in-hospital mortality.
Allgower M, Buri C. Shock index. Deutsche Medizinische Wodenschrift. 1967;43:1947-50.