Magnesium Abnormalities In ICU

40–60% of ICU patients have hypomagnesaemia.

Hypomagnesaemia:

Clinical effects of hypomagnesaemia:

• Electrolyte abnormalities:
  • Hypokalaemia
  • Hypocalcaemia
  • Hypophosphataemia
• Arrhythmias:
  • Prolonged QT interval.
  • Polymorphic VT – Torsade de pointes.
• Neurologic:
  • Altered mentation, generalized seizures, tremors, hyper-reflexia, weakness.

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Magnesium supplementation:

IV: Ampoules of 2 g in 1 mL (50% magnesium sulphate solution).

Replacement dose: 

• Magnesium sulphate, 25–50 mg/kg, IV.
  • Maximum rate of IV administration: 1 g/7 minutes.

Life threatening hypomagnesaemia – Torsade de pointes:

1. Infuse 50 mg/kg MgSO4, IV, over 2 to 5 minutes.
2. Follow with 25–50 mg/kg MgSO4 in 250–500 mL N/S over the next 6 hours (maximum 5 g).
3. Continue with 25–50 mg/kg MgSO4 every 12 hourly for 5 days (Note – to replenish total body stores).

Hypermagnesaemia:

• Serum magnesium > 2 mEq/L.
• Usually in patients with renal insufficiency and haemolysis, closely associated with increased potassium and low calcium.

Clinical effects of hypermagnesaemia:

Serious effects of hypomagnesaemia are due to calcium antagonism in the cardiovascular system:

• Weakness/hyporeflexia/paralysis > 4 mEq/L.
• 1^st degree AV block > 5 mEq/L.
• Complete heart block > 10 mEq/L.
• Cardiac arrest > 13 mEq/L.

Treatment of hypermagnesaemia:

• Stop extra oral/IV intake.
• In patients with normal renal function, will correct once supplemental intake is stopped. 
  • IV calcium gluconate (0.6 mL/kg over 2–3 minutes) can be used for hypotension and respiratory depression (only transient effect).
• Haemodialysis for severe cases with significant cardiac signs.

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Standard Treatment Guidelines And Essential Medicines List For South Africa, Hospital Level, Paediatrics, 2023 Edition

Chapter 23: Paediatric Intensive Care,  23.6 Electrolyte Abnormalities,  23.6.3 Magnesium Abnormalities In ICU