Hypomagnesaemia is more common than hypermagnesemia. Defined by serum Mg levels <1.0 mmol/L
Causes of hypomagnesaemia
- Increased magnesium loss
- GI losses (Pancreatitis, diarrhoea, bowel resection)
- Renal
- Volume expansion and osmotic diuresis
- ATN, obstructive uropathy, Gitelman’s
- Drugs
- Alcohol is commonest
- Diuretics, gentamicin, digoxin, amphotericin, cisplatin
- Reduced magnesium intake and absorption
- Starvation, alcoholics, malnutrition
- Metabolic
- Hypocalcaemia
- Hypokalaemia
- Hypophosphataemia
- Metabolic alkalosis
- Endocrine
- Hyperthyroid, Hyperparathyroidism, DKA
- Other
- Burns, sepsis, lactation, hypothermia
Clinical manifestations
Non-specific and often mimic hypokalaemia and hypocalcaemia
- Muscle weakness, paraesthesia, fasciculations and tetany
- Decreased mental awareness, vertigo, seizures, confusion
- Cerebellar dysfunction
Complication
Cardiac Arrhythmia and ECG changes
- ECG changes are similar to hypocalcaemia and hypokalaemia
- Prolonged QTc and PR
- ST depression
- T wave inversion and P wave inversion
- Wide QRS…Torsades de Pointe
- Worsening digoxin toxicity
- Treatment resistant VF
Correction
Dependent on severity of symptoms
- IV Magnesium Sulfate
- 1-2 G of MgSO4 over 10 minutes if cardiac arrhythmia, torsades, seizures
- 1 G of MgSO4 in 100mL Normal Saline over 30 minutes for slow replacement
- NOTE: If too rapid then exceeds renal threshold with magnesium wasting
- Calcium gluconate 1 G to replenish Calcium (normally go hand in hand)
- Replace cautiously if renal failure to prevent hypermagnesemia
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