CONTENTS

• Diagnosis
• Causes
• Evaluation
• Treatment
• Podcast
• Questions & discussion
• Pitfalls

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diagnosis

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rough correlation between Mg level and symptoms

physical examination

• Hyporeflexia:
  • Presence of reflexes argues against severe hypermagnesemia.
  • Hyporeflexia is nonspecific, however (e.g. some patients have sluggish reflexes at baseline).
• Bradycardia, hypotension.

ECG findings

• Wide QRS and peaked T-waves (can mimic hyperkalemia).
• Heart block.

range of symptoms that may occur

• Cardiac:
  • Hypotension.
  • Bradycardia, complete heart block.
• Neurologic:
  • Muscular weakness (can progress to respiratory failure from diaphragmatic involvement).
  • Delirium, coma.
  • Smooth muscle paralysis: urinary retention, intestinal ileus, pupillary dilation.

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causes

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Renal Failure plus:

• Persistent hypermagnesemia requires renal failure (or, less commonly, and ongoing source of magnesium).
• However, in addition to renal failure, there is usually another source of magnesium.

[1] exogenous magnesium

• Magnesium infusions for pre-eclampsia.
• Magnesium-containing antacids.
• Magnesium-containing laxatives or enemas.

[2] endogenous magnesium from cellular lysis

• Rhabdomyolysis.
• Hemolysis.
• Tumor lysis syndrome.
• Crush injury, severe burns.

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evaluation

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• If the lab is hemolyzed, repeat it (hemolysis may cause pseudo-hypermagnesemia).
• Obtain a complete set of electrolytes including Ca/Mg/Phos (to evaluate for additional concurrent electrolyte abnormalities).
• Consider LDH, creatinine kinase, or uric acid (to evaluate for hemolysis, rhabdomyolysis, or tumor lysis).

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treatment

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Depending on the clinical context, five treatments may be considered: 

[1] membrane stabilization with IV calcium (for severe, symptomatic hypermagnesemia)

• IV calcium can acutely counteract the effects of hypermagnesemia.
• Two grams of calcium gluconate IV over 5-10 minutes (or one gram of calcium chloride).
• May need to repeat.

[2] volume resuscitation if hypovolemic

• Resuscitation with magnesium-free fluid could theoretically have an immediate effect via dilution of serum magnesium levels. However, there is no evidence on this.
• If the patient is hypovolemic, they should certainly be volume resuscitated.
• ⚠️ Avoid any fluids containing magnesium (e.g., plasmalyte, normosol).

[3] specific therapy for an underlying cause

• In some situations, a specific therapeutic strategy may be required to treat the underlying diagnosis. For example:
  • Rhabdomyolysis: discussed further here 📖
  • Tumor lysis syndrome: discussed further here 📖

[4] diuretics to promote renal excretion

• This is similar to the use of diuretics to treat hyperkalemia:
  • [a] Administer a combination of loop diuretic (e.g., furosemide) plus a thiazide diuretic (e.g., IV chlorothiazide or oral metolazone). The doses of these agents will depend on the urgency of the situation and the renal function. Higher doses should be utilized in more urgent situations and for patients with baseline renal dysfunction. When in doubt consider using a high dose of thiazide diuretic plus a moderate furosemide dose, with prompt up-titration of IV furosemide as needed to promote adequate urine output.
  • [b] Replete urine losses with a magnesium-free IV fluid (e.g., lactated ringers). The goal is to maintain a net even fluid balance.
  • [c] Carefully monitor all electrolytes (including Ca/Mg/Phos and perhaps ionized calcium).
• ⚠️ There is no high-level evidence to support this strategy. Magnesium reabsorption by the kidney is predominantly regulated in the thick ascending limb of the loop of Henle and in the distal convoluted tubule. Please note that using a loop diuretic alone may not be sufficient, since the distal convoluted tubule may still be able to reclaim magnesium from the urine (hence the need for dual site nephron blockade). It has been observed that the combination of a loop diuretic plus a thiazide diuretic may cause severe magnesium wasting and hypomagnesemia. (36872194)

[5] dialysis

• For hypermagnesemia in the context of anuric renal failure, dialysis is required.
• Dialysis is highly effective in removal of magnesium.

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podcast

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The segment of this podcast about hypermagnesemia begins at 18:30:

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questions & discussion

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To keep this page small and fast, questions & discussion about this post can be found on another page here.

• Moderate hypermagnesemia (e.g., Mg 5-8 mg/dL) is generally pretty well tolerated. Be careful about attributing severe symptoms to this degree of hypermagnesemia.

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