The formula for calculating the shock index, often expressed as pulse rate divided by systolic blood pressure, can help determine the presence or absence of shock and the degree of severity. An index of 0.5 indicates the absence of shock. An index greater than 1.0-1.5 is indicative of the presence of shock. If the index is greater than 2.0, it indicates the presence of severe shock. Patients in shock may have apathetic expression, clammy and cold skin, irritability, and decreased blood pressure. There are many diseases that lead to shock, such as severe infection, massive blood loss, severe heart failure, massive burns, and severe allergic reactions. It is important to actively identify the cause of shock and resuscitate while treating for the cause.