The essentials of calcium, magnesium and phosphate metabolism: part II. Disorders.

OBJECTIVE: To review the components of calcium, phosphate and magnesium metabolism that are relevant to the critically ill patient, in a two-part presentation.

DATA SOURCES: A review of articles reported on calcium, phosphate and magnesium disorders in the critically ill patient.

SUMMARY OF REVIEW: Abnormal calcium metabolism in the critically ill patient often presents with an alteration in plasma ionised calcium. The characteristic clinical features of an acute reduction in ionised plasma calcium include tetany, laryngospasm, paraesthesia, confusion, hallucinations, seizures and, rarely, hypotension all of which resolve with intravenous calcium administration. The clinical features of an acute increase in plasma ionised calcium include anorexia, nausea, vomiting, constipation, polyuria, weakness, lethargy, hypotonia and ectopic calcification and, depending on the aetiology, may require intravenous saline, frusemide, diphosphonate, glucocorticoid or calcitonin. Acute hypophosphataemia may present with paraesthasia, confusion, seizures, weakness, hypotension and heart failure and in the critically ill requires intravenous sodium or potassium phosphate. Hyperphosphataemia is often associated with renal failure and if severe usually presents with the clinical features of the associated hypocalcaemia. The clinical features of hypomagnesaemia include confusion, delerium, seizures, weakness, cramps, tetany and tachyarrhythmias, all of which resolve with intravenous magnesium sulphate. Hypermagnesaemia is usually associated with excess magnesium administration in a patient with renal failure and if severe can cause areflexia, hypotonia, respiratory and cardiac arrest. Intravenous calcium chloride will rapidly reverse the cardiovascular abnormalities.

CONCLUSIONS: Calcium, phosphate and magnesium functions are closely linked with abnormal plasma levels of these compounds often causing similar cardiovascular and neurological features.