Circulatory shock, commonly known as shock, is a life-threatening medical condition of low blood perfusion to tissues resulting in cellular injury and inadequate tissue function. The typical signs of shock are low blood pressure, rapid heart rate, signs of poor end-organ perfusion (i.e.: low urine output, confusion, or loss of consciousness), and weak pulses.
The shock index (SI), defined as heart rate divided by systolic blood pressure, is an accurate diagnostic measure that is more useful than hypotension and tachycardia in isolation. Under normal conditions, a number between 0.5 and 0.8 is typically seen. Should that number increase, so does suspicion of an underlying state of shock. Blood pressure alone may not be a reliable sign for shock, as there are times when a person is in circulatory shock but has a stable blood pressure