Disorders of calcium and magnesium metabolism

Although relatively common, aberrations in divalent cation homeostasis may be overlooked in Emergency Department patients. The intracellular concentration of ionized calcium is the major regulator of cellular function. Patients may present with signs and symptoms of deranged calcium homeostasis that range from the mild and nonspecific to the truly life threatening. Critically ill patients may develop profound, life-threatening hypocalcemia either as a result of their underlying illness or as a complication of resuscitation. Patients with hypercalcemia may present with symptoms that are so vague and nonspecific that the diagnosis may not be considered. An understanding of the pathophysiology of calcium metabolism allows the emergency physician to identify patients at risk for abnormal calcium homeostasis, and to intervene in an appropriate manner. Magnesium is an essential cofactor in a host of important biochemical reactions. Magnesium deficiency is fairly common in certain groups of patients and can cause serious complications. The diagnosis is often difficult to make in the Emergency Department setting. The emergency physician should be aware of clinical situations that predispose to magnesium deficiency and be prepared to institute empiric therapy if indicated. Severe hypermagnesemia is rather uncommonly encountered in the Emergency Department. The magnesium ion is an effective calcium channel blocker, and patients with severe hypermagnesemia develop profound cardiovascular and neuromuscular dysfunction as a result. In pharmacologic doses, magnesium's unique calcium channel antagonism may be clinically useful, and there is growing interest in its potential use as an antiarrhythmic, anticonvulsant, and smooth muscle relaxant.