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Hypermagnesaemia

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Anaesthetics and Critical Care

Obstetrics Gynaecology

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Urology

Version Jan 2023

Severe hypermagnesaemia with symptoms
Stop Magnesium infusions or medications 10-20 mls of 10% Calcium gluconate slow IV over 5-10 mins IV Furosemide 80 mg increases Mg excretion if renal function normal IV fluids Normal saline to ensure hydration If ESRF Haemodialysis may be valuable to remove Mg

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

Approximate Serum magnesium concentration (mmol/L)	Features of hypermagnesaemia
2 - 3.5 mmol/L	Flushing, ECG changes, nausea, vomiting
4 - 5 mmol/L	Drowsiness, slurred speech, hypotension, absent deep tendon reflexes, dizziness
>6 mmol/L	Muscle paralysis, respiratory depression, coma
>8 mmol/L	Cardiac arrest

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

PLEASE NOTE LEGAL ADVICE: The contents are under continuing development and improvements and may contain errors of omission or fact. The official launch will be at the end of 2018. Feedback vital and always welcome at drokane at gmail.com. This is not to be used for the assessment, diagnosis or management of patients. It should not be regarded as medical advice. It is only for educational purposes. Please adhere to your local protocols. If you are unwell please seek healthcare advice from your doctor. This does not replace senior or specialist advice. If you do not accept this then please do not use the website. If you need medical advice, please consult a doctor or other appropriate medical professional. If you are a medical professional and you need advice then speak to your senior or colleagues.

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