A doctor might give bicarbonate (HCO₃¯) to a patient who is breathing very rapidly. What is the doctor assuming about the patient’s blood chemistry? The answer is: The doctor is assuming that the rapid breathing is the body’s response to low blood pH. (Source: Campbell Biology) But this answer doesn't make sense. Why would the doctor give the patient even more CO2 if the patient is already suffering from an excess of CO2 that is causing the low body pH?

Bicarbonate is not carbon dioxide. In acidic conditions, bicarbonate will be protonated to form carbonic acid which in turn decomposes into carbon dioxide and water. The overall result is the removal of a proton (ie increase in pH) and formation of carbon dioxide (which accounts for the rapid breathing). The idea behind giving bicarbonate is that it will replenish the buffer.