Hypermagnesaemia

• Definition: Serum Mg above normal range of 1.3-2.2 mEq/L
• Toxic: Mg > 4mEq/L
• Incidence Rare and usually iatrogenic
• Note ↑Magnesium is closely associated with ↑K and ↓Ca

Causes of hypermagnesaemia

1)    Iatrogenic

• Hyperalimentation
• IV and oral magnesium
• Laxatives, enemas, antacids (especially in elderly and renal failure)

2)    Renal Failure

3)    Other

• Perforated viscus with continued oral intake
• Tumour lysis (Increased K, Mg, PO4 and decreased Ca)
• Rhabdomyolysis

Clinical manifestations

• Often asymptomatic
• Serum level >4
  • Muscle weakness, hyporeflexia
  • Nausea and vomiting
  • Hypotension secondary to vasodilation
• Serum level >10
  • Coma
  • Hypoventilation
  • Neuromuscular Paralysis
  • Cardiac arrhythmias, bradycardia and death

Complications

Cardiac arrhythmia and ECG changes

• ECG (as for hyperkalaemia)
  • Increase PR and QTc
  • Prolonged QRS
  • Peaked T waves and flattened p waves
  • Complete AV block and asystole

Correction

• Discontinue magnesium intake
• Antagonising Mg with Calcium
• Removing Magnesium from serum

1. Dialysis – Treatment of choice
2. Calcium chloride 10% in 5-10ml repeated
   • Treats life threatening arrhythmia
3. Forced diuresis
   • IV normal saline and Frusemide
   • Watch for hypocalcemia which can make symptoms worse

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