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Related Subjects: |Calcium Physiology |Magnesium Physiology |Calcitonin |Hypocalcaemia |Hypercalcaemia |Hypomagnesaemia |Hypermagnesaemia |Primary Hyperparathyroidism |Familial hypocalciuric hypercalcaemia (FHH) |Sarcoidosis

High values of serum magnesium can induce cardiorespiratory arrest and coma.

Definition

• Serum Magnesium = 1.05 mmol/L [2.6 mg/dl]
• Symptoms usually develop when the plasma Mg > 2-4 mmol/L
• Treat when Mg > 6 or symptoms

Causes

• Addison's disease, CKD, AKI
• Excessive Magnesium containing laxatives and antacids
• Haemodialysis with high [Mg²⁺] dialysate
• Receiving excess PO or IV Magnesium
• Tumour lysis syndrome, Diabetic ketoacidosis
• Acute renal failure, Hypercalcaemia
• Hyperkalaemia, Hypoparathyroidism
• Hypothyroidism, Lithium toxicity
• Haemolysis, Rhabdomyolysis

Clinical

• Weakness with hyporeflexia proceeding to narcosis
• Respiratory paralysis and cardiac conduction defects
• Cardiac arrest when Mg > 6.0-8.0 mmol/L.

Toxicity

• 2.5-5.0 mmol/L ECG changes (QRS widens)
• 4.0-5.0 mmol/L Reduction in tendon reflexes
• >5.0 mmol/L Loss of deep tendon reflexes
• >7.5 mmol/L Heart block, respiratory paralysis, CNS depression
• >12 mmol/L Cardiac arrest

Investigations

• U&E and reduced eGFR if AKI/CKD
• ECG: increased PR interval, broadened QRS complex or elevated T waves

Management

• ABC. Stop any Mg therapy is usually enough.
• If symptoms or levels > 6 or symptoms then 10-20 mL 10% Calcium Gluconate 10% IV slow over 5 mins if not hypercalcaemic. Monitor serum calcium concentration
• Glucose and Insulin (as for hyperkalaemia) lowers Mg
• IV Furosemide can increase magnesium excretion if renal function normal
• Dialysis may be required in patients with severe kidney disease.

References

• NHS Leeds Teaching Hospital
• Hypermagnesaemia