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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