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Hypocalcaemia - Fluid and electrolyte balance

A serum calcium level of <2.2 mmol/L. - Definition, Incidence, Age, Sex, Aetiology, Pathophysiology, Clinical features, Complications, Investigations, Management, Prognosis.

Hypocalcaemia

 

Definition

 

A serum calcium level of <2.2 mmol/L.

 

 

Aetiology

 

Hypocalcaemia may be caused by

 

·        vitamin D deficiency,

 

·        hypoparathyroidism (after parathyroidectomy, thyroid or other neck surgery),

 

·        pseudohypoparathyroidism,

 

·        magnesium depletion by inducing end-organ PTH resistance or deficiency (causes include diuretics, alcoholism and malnutrition),

 

·        hyperphosphataemia,

 

·        acute pancreatitis and severe sepsis,

 

 

·        acute respiratory alkalosis,

 

·        drugs, e.g. chemotherapy especially cisplatin, bispho-sphonates and

 

·        calcium chelators, e.g. citrate following large transfusions of blood.

 

 

Pathophysiology

 

Hypocalcaemia causes increased membrane potentials, which means that cells are more easily depolarised and therefore causes prolongation of the Q–T interval, which predisposes to cardiac arrhythmias. It may also cause refractory hypotension and neuromuscular problems include tetany, seizures and emotional lability or depression.

 

Clinical features

 

The condition may be asymptomatic and diagnosed incidentally on calcium measurement.

 

Neuromuscular manifestations

 

Early symptoms include circumoral numbness, paraesthesiae of the extremities and muscle cramps. Common but less specific symptoms include fatigue, irritability, confusion and depression. Myopathy with muscle weak-ness and wasting may be present. Carpopedal spasm and seizures are signs of severe hypocalcaemia. Elicitation of Trousseau’s sign and Chvostek’s signs should be attempted, although it can be negative even in severe hypocalcaemia:

 

·        Trousseau’s sign: Carpal spasm induced by inflation of a sphygmomanometer above systolic BP for 3 minutes.

 

·        Chvostek’s sign: Contraction of the ipsilateral facial muscles (including the eye, nose and corner of the mouth) after tapping the facial nerve anterior to the ear.

 

The BP may be low despite fluids or inotropes. Cardiac failure may occur.

 

Other findings may include papilloedema and in chronic cases cataracts, dry puffy coarse skin with brittle and thinned hair and nails.

 

Investigations

 

These are aimed at assessing the severity of hypocalcaemia to guide management and to look for the under-lying cause. The serum calcium should be checked and corrected for serum albumin. Blood should also be sent for magnesium, phosphate, U&Es and for PTH level. An ECG should be done to look for ECG changes (increased QT interval, cardiac arrhythmias). Other investigations depend on the suspected cause.

 

Management

 

This depends on the severity, whether acute or chronic and the underlying cause. Mild hypocalcaemia is treated with oral supplements of calcium and magnesium where appropriate. Severe hypocalcaemia may be life-threatening and the first priority is resuscitation as needed (e.g. management of seizures or cardiac arrhythmias), followed by the administration of intravenous calcium. Calcium gluconate contains only a third of the amount of calcium as calcium chloride but is less irritating to the peripheral veins.

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