Plasma calcium < 2.2 mmol/L

Normal values: Total calcium 2.25-2.60 mmol/L; ionised calcium 1.12-1.32 mmol/L

HYPOCALCAEMIA CAUSES:

• Decreased parathyroid hormone

• Decreased Vitamin D activity (e.g. intestinal malabsorption, liver disease, CRF)

• Increased calcium loss (e.g. chelating agents, calcification of soft tissues)

• Decreased ionised calcium (e.g. alkalosis)

• Tumour Lysis Syndrome
• Diarrhoea, vomiting, and nasogastric suction can cause hypomagnesaemia with secondary hypocalcaemia (HSH)

CLINICAL FEATURES:

• Tetany
• Seizures
• Emotional instability/agitation/anxiety
• Myopathy

ECG:

• QTc prolongation by prolonging the ST segment

• Torsades de pointes and atrial fibrillation in severe cases

NB: The corrected QT interval (QTc) is taken as the time between the beginning of the QRS complex and the end of the T wave, it is less than 440 ms in men and 460 ms in women. Severe hypocalcaemia (less than 1.9 mmol/L) may cause a prolongation of the QTc. A QTc greater than 500 ms is associated with an increased risk of Torsades de Pointes.

TREATMENT:

• Ca2+ 0.5mL/kg (max 20mL) of 10% calcium gluconate OR 0.2mL/kg of 10% calcium chloride
• Administer by slow IV (max 2 mL/min), repeat if necessary.
• Calcium can precipitate or exacerbate digitalis toxicity therefore IV calcium must be given very slowly in patients on digoxin and the ECG must be monitored continuously