Electrolyte disorders are a significant cause of morbidity and mortality for adults in the intensive care unit and hospital. Hypocalcemia occurs in 15% to 88% of hospital admissions. The incidence of ionized hypocalcemia has been reported at 15% to 50% in patients in the intensive care unit. Another 15% of hospitalized adults demonstrate hypercalcemia. The purpose of this column is to explain the actions of calcium on cardiac depolarization and repolarization and explore the manifestations of serum calcium derangements in a 12-lead electrocardiograph (ECG) tracing. We report the diagnosis and management of 2 composite scenarios that illustrate hypocalcemia and hypercalcemia with illustrative ECGs.

M.K., a 50-year-old white woman, presented to the preadmission testing area prior to a scheduled surgery for an elective tonsillectomy for airway obstruction. During the review of systems, she reported feeling “weak and tired,” with new muscle cramps...

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