Dott. M. M. Ciammaichella
Dirigente Medico

SC Medicina Interna I° per l'Urgenza
(Direttore: Dott. G. Cerqua)
A.C.O. S. Giovanni Addolorata, Roma, Italia


 

_HYPERMAGNESEMIA_

 

KEY-WORDS: Hypermagnesemia

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INTRODUCTION
CLINICAL
WORKUP
TREATMENT
MEDICATION
FOLLOW-UP
MISCELLANEOUS
BIBLIOGRAPHY


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INTRODUCTION

Background: Magnesium is a major electrolyte of the body. As the second most common intracellular cation, it acts as a vital part in many cellular metabolic pathways. Magnesium is required for DNA and protein synthesis as well as necessary for most enzymes in phosphorylation reactions. It is also important for parathyroid hormone synthesis. The total body content of this central cation is 2000 mEq or 24 grams. The distribution of magnesium is 67% in bone, 31% intracellularly and a mere 1% extracellularly. The intracellular concentration is 40 mEq/L, while the normal serum concentration is 1.5-2.0 mEq/L. Of this serum component, 25-30% is protein bound, 10-15% complexed and the remaining 50-60% ionized.
Magnesium is absorbed in the ileum and excreted in stool and urine. The daily requirement of magnesium is 300 -350 mg or 15 mmol, which is easily obtainable with normal daily intake of fruits, seeds and vegetables. This is because magnesium is part of chlorophyll.
The kidney acts as the main regulator of magnesium concentrations. Absorption occurs mainly in the proximal tubule and thick ascending limb of the loop of Henle. Hypermagnesemia is a rare electrolyte abnormality because the kidney is so effective in excreting excess.
Pathophysiology: Magnesium excess affects the CNS, neuromuscular and cardiac organ systems. It is most commonly seen in renal insufficiency.
Frequency:

In the U.S.: Rare

 

 

CLINICALPATHOPHYSIOLOGY

History: Common causes of hypermagnesemia include renal failure and iatrogenic manipulations. However, other diseases may result in an increased magnesium and the degree of elevation will determine the symptoms present. Acute elevations of magnesium will usually be more symptomatic than slow rises.

  • Levels of 2-4 mEq/L
    • Nausea
    • Vomiting
    • Skin flushing
    • Weakness
    • Lightheadedness
  • High Levels:

    Depressed levels of consciousness

Physical: The physical findings are related to the serum magnesium levels.

  • Level of 3.0-4.0 mEq/L:
    • Disappearence of deep tendon reflexes
    • Muscle weakness
  • Level of 5.0-6.0 mEq/L:
    • Hypotension
  • Vasodilatation
  • Level of 8.0-10.0 mEq/L:
  • Arrythmias, including atrial fibrillation
  • Intraventricular conduction delay
  • Levels greater than 10.0 mEq/L:
    • Asystole
    • Heart block
    • Ventilatory failure
    • Stupor or coma
    • Death
  • Elevated levels of magnesium are also associated with delayed thrombin formation and platelet clumping.

Causes: The causes of hypermagnesemia are varied but are usually due to iatrogenic interventions.

  • Patients with chronic renal failure who are taking magnesium containing antacids or cathartics commonly develop hypermagnesemia.
  • Acute renal failure
  • Mothers treated for eclampsia with magnesium infusions
  • Infants born to mothers treated with magnesium infusions
  • Decreased GI elimination caused by hypomotility and subsequent increased magnesium absorption
    • Medications, including narcotics and anticholinergics
    • Hypomotility disorders like bowel obstruction and chronic constipation
  • Tumor lysis syndrome
  • Adrenal insufficiency
  • Rhabdomyolysis
  • Milk-alkali syndrome
  • Hypothyroidism
  • Hypoparathyroidism
  • Neoplasm with skeletal muscle involvement
  • Lithium intoxication

  • Extracellular volume contraction as in DK

 



WORKUP

Lab Studies:

  • Electrolytes, including potassium, magnesium and calcium

    Magnesium is not usually found as an isolated electrolyte abnormality. Hyperkalemia and hypercalcemia are often present concurrently.
  • BUN and Creatinine:
    • Renal function tests should be ordered and creatinine clearance calculated to ascess the ability of the kidney to excrete magnesium.
    • Serum magnesium levels rise when the creatinine clearance is below 30 cc/min.
  • Check serum creatinine phosphokinase (CPK) or urine myoglobin in pateints where rhabdomyolysis is suspected.
  • An arterial blood gas (ABG) may reveal a respiratory acidosis.
    • Hypothyroidism is a rare cause of hypermagnesemia. Check thyroid function tests in the absence of any other good explanation.

Other Tests:

  • Electrocardiogram (ECG):

    An ECG and cardiac monitor may show prolongation of the PR interval or intraventricular conduction delay, which are nonspecific findings.

 


TREATMENT

Emergency Department Care: Although the effectiveness of dialysis in removing divalent cations is debated, some studies have demonstrated removal of a large amount of magnesium using this modality. Dialysis is best used when levels exceed 8 mEq/L, there are life threatening symptoms or in patients with poor renal function.

  • Ascess the patient's ABC's and stabilize them.
  • Intubate if necessary.
  • Treat hypotension with fluids.
  • Treat arrythmias as per ACLS protocol or with treatment outlined below, if hypermagnesemia is known.
  • Obtain appropriate studies as discussed above.

Consultations:

  • A renal consult should be obtained for dialysis if the patient is severely hypermagnesemic.

  • Intensive care unit monitoring should be arranged if the symptoms are severe.

 

 

MEDICATION

Treatment depends upon the level of magnesium and the presence of symptoms. In patients with mildly increased levels, the source of magnesium may simply be stopped. In patients with higher concentrations or severe symptoms, other treatments are necessary. Calcium should be reserved for patients with life-threatening symptoms, such as arrythmias or severe respiratory depression.

Drug Category: Intravenous fluids - Dilution of the extracellular magnesium concentration is the rational for intravenous use. Fluids are employed with diuretics to promote diuresis of magnesium by the kidney.


Drug Name

Normal saline or Lactated Ringers - Both fluids are essentially isotonic and while there are some differences between metabolic changes seen with the administration of large quantities of either fluid, for practical purposes and in most situations, the differences are clinically irrelevant for the purpose of promoting diuresis.

Adult Dose

A typical adult dose is 1 L

Pediatric Dose

The initial pediatric dose is 20 mL/kg

Contraindications

Avoid use in patients with poor renal function and inadquate urine output.
The major complication of isotonic fluid resuscitation is interstitial edema. Edema in an extremity is unsightly, but not a significant complication. Edema in the brain or lungs is potentially fatal. The major contraindication to isotonic fluid resuscitation is pulmonary edema in which the added fluid promotes more edema.

Interactions

No significant drug interactions have been reported with this product.

Pregnancy

A - Safe in pregnancy

Precautions

Volume overload may occur in patients with poor renal function.
Fluids should be stopped when the desired magnesium levels are attained or pulmonary edema develops.

Drug Category: Diuretics - These agents increase the excreation of magnesium by the kidney.


Drug Name

Furosemide - It acts at the Loop of Henle to promote loss of magnesium in the urine.

Adult Dose

20-80 mg/dose IV with a maximum single dose of 6 mg/kg

Pediatric Dose

1 mg/kg/dose q6-12h prn

Contraindications

Avoid use in patients with documented hypersensitivity to this drug, sulfonylureas, or related products and those diagnosed with hepatic coma, anuria, or are in a state of severe electrolyte depletion.

Interactions

Metformin decreases furosemide concentrations. Conversely, furosemide interferes with the hypoglycemic effect of antidiabetic agents. It also antagonizes the muscle relaxing effect of tubocurarine.
Auditory toxicity appears to be increased with the concurrent use of aminoglycosides and furosemide. Hearing loss of varying degrees may occur.
The anticoagulant activity of warfarin, plasma lithium levels and toxicity may increase, when these drugs are taken concurrently with furosemide.

Pregnancy

C - Safety for use during pregnancy has not been established.

Precautions

Observe for blood dyscrasias and liver or kidney damage.
Perform frequent serum electrolyte, CO2, glucose, creatinine, uric acid, calcium, and BUN determinations during the first few months of therapy and periodically thereafter.
Loop diuretics may increase the urinary excretion of magnesium and calcium.

Drug Category: Mineral supplements - Calcium directly antagonizes the effects of magnesium.


Drug Name

Calcium Gluconate - It directly antagonizes the neuromuscular and cardiovascular effects of magnesium.

Adult Dose

Administer a 10% solution, 100-200 mg calcium IV; continuous infusion 2-4 mg/kg/h

Pediatric Dose

2 mg/kg of elemental calcium or about 0.2 mg of 10% calcium gluconate/kg.

Contraindications

Do not administer to patients diagnosed with renal calculi, hypercalcemia, hypophosphatemia, renal or cardiac disease, and patients with digitalis toxicity.

Interactions

Calcium may decrease the effects of tetracyclines, atenolol, salicylates, iron salts, and fluoroquinolones. Administered IV, calcium antagonizes the effects of verapamil.
Conversely, large intakes of dietary fiber may decrease calcium absorption and thus levels.

Pregnancy

B - Usually safe but benefits must outweigh the risks.

Precautions

Exercise caution when administering to digitalized patients and those with respiratory failure or acidosis and with severe hyperphosphatemia.


 

 

FOLLOW-UP

Transfer:

  • Consider transfer if a patient with renal failure has a severe elevation of magnesium and no dialysis is available.

Prognosis:

  • Patients do well upon restoration of normal magnesium levels.

Patient Education:

  • Information regarding avoidance of medications that cause hypermagnesemia should be given.

 



MISCELLANEOUS

Medical/Legal Pitfalls:

  • It is not uncommon for the cause of hypermagnesemia to be iatrogenic. Physician education of these problem may help decrease the incidence.

 



BIBLIOGRAPHY

  • Agus ZS, Wasserstein A, Goldfarb S: Disorders of Calcium and Magnesium Homeostasis. American Journal of Medicine 1982; 72: 482.
  • Gigg MA, Wolfson AB, Tayal VS: Electrolyte Disturbances. Emergency Medicine Concepts and Clinical Practice 1998; III: 2445-2448.
  • Knochel JP: Disorders of Magnesium Metabolism. Harrison's Principles of Internal Medicine 1994; II: 2187-2189.
  • Nadler JL, Rude RK: Disorders of Magnesium Metabolism. Clinical Disorders of Fluid and Electrolyte Metabolism 1995; 24: 623-637.
  • Quereshi TI, Melonakos TK: Acute hypermagnesemia after laxative use. Annals of Emergency Medicine 1996; 28: 552.
  • Wilson RF, Barton C: Fluid and Electrolyte Problems. Emergency Medicine Comprehensive Study Guide 1996; 135-137.