Overview
Look For
- Serum magnesium <0.7 mmol/L.
Aetiology
Causes of Hypomagnesaemia
- Reduced intake - malnutrition, TPN
- Urinary loss - acute tubular necrosis (polyuric phase), postobstructive diuresis, loop / thiazide diuretics, ACE inhibitors, renal tubular acidosis, aminoglycoside toxicity, hypercalcaemia, genetic tubular defects
- GI loss - diarrhoea, laxative abuse, malabsorption, vomiting, NG aspirates, GI fistula, short bowel syndrome, long-term PPI use
- Compartmental shift - refeeding syndrome, hyperparathyroidism, hyperthyroidism, acute pancreatitis, hungry bone syndrome
Clinical Features
Signs and Symptoms
Only occur in the presence of resultant biochemical abnormalities- Hypocalcaemia - hyperreflexia, tetany, seizures, heart failure
- Hypokalaemia - weakness, hypotonicity, depression, constipation, ileus
ECG Changes
- Long QTc → torsade de pointes
- Atrial or ventricular ectopics
- Atrial fibrillation
- Ventricular arrhythmias
- Hypokalaemia - ST depression, prolonged QT interval, T wave flattening or inversion, prominent U wave
Associated Lab Abnormalities
- Hypokalaemia
- Hypocalcaemia
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