Hypocalcaemia
Description
- Corrected calcium <2.10 mmol/L; ionised calcium is what matters
- `Corrected Ca = measured Ca + 0.02 x (40 - albumin)`
- *Alkalosis increases protein binding -> ionised calcium falls with a normal total* - the mechanism of hyperventilation tetany
Clinical - neuromuscular irritability
- Perioral and acral paraesthesia -> cramps, carpopedal spasm, tetany -> laryngospasm, bronchospasm, seizures
- Chvostek sign - tap over the facial nerve anterior to the ear -> ipsilateral facial twitch (present in ~10-25% of normal people - poorly specific)
- Trousseau sign - BP cuff above systolic for 3 minutes -> carpopedal spasm: wrist and MCP flexion, IP extension, thumb adduction (more specific)
- Cardiac: prolonged QT, hypotension, heart failure (reversible cardiomyopathy)
- Chronic: cataract, basal ganglia calcification, papilloedema, dry skin, brittle nails, enamel hypoplasia, extrapyramidal features, anxiety/depression
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