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April 15th, 2020


  • Look For

  • Serum magnesium <0.7 mmol/L.


  • 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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