- 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