Hypermagnesaemia

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Hypermagnesaemia is associated with Hyperkalaemia and Hypocalcaemia

Aetiologies

Increased intake
- Magnesium infusion
- Massive oral ingestion
- Unregulated absorption (eg. with peptic ulcer)
- Milk-alkali syndrome
Compartment shift or leak
- Tumour lysis syndrome
- Rhabdomyolysis
- Acidosis (shift out of cells)
Decreased loss
- Renal failure
- Primary Hyperparathyroidism (reabsorption in the tubule)
- Lithium therapy
- Hypoadrenalism
- Familial hypocalciuric hypercalcemia

Can otherwise be classified:

Iatrogenic
- Hyperalimentation
- IV and oral magnesium
- Laxatives, enemas, antacids (especially in elderly and renal failure)
Renal failure
Other
- Perforated viscus with continued oral intake
- Tumour lysis
- Rhabdomyolysis

Clinical Features

Serum Magnesium Level	Physiologic Effects
1.8-2.0 mmol/L	Antiarrhythmic effects Inhibition of parathyroid hormone secretion Hypocalcemia Ileus
2.0-4.0mmol/L	Hyporeflexia Muscle weakness Nausea Flushing Headache Lethargy, somonolence
4.0-6.0mmol/L	Respiratory failure Hypotension Bradycardia Decreased level of consciousness Bladder paralysis
6.0-10.0mmol/L	Apnoea “Pseudocoma” … or actual coma Parasympathetic blockade Complete heart block Cardiac arrest (asystole)
Over 10mmol/L	Limits of the survivable

ECG changes are non-specific and often do not cause ECG changes
- Can prolong QT interval and widen QRS complex

Management

In patients with normal renal function, renal clearance ensures rapid correction
Discontinue magnesium intake
However, in renal failure additional therapies are often required:
- IV calcium
- Insulin and glucose
- Haemodialysis
- Forced diuresis with IV normal saline and frusemide while monitoring for Hypocalcaemia

Sources