Calcium is an important element in many of the physiological functions inside the body. There is a great interaction between calcium and the anesthetic and analgesic drugs, making the ionized serum calcium level of great importance to the anesthetist. During anesthesia, there are many special situations that are related to calcium. These situations include ischemia-reperfusion injury, massive blood transfusion, acid-base balance, cardiopulmonary bypass and malignant hyperthermia.