Magnesium is one of the body's major electrolytes. As the second most common intracellular cation, it plays a vital role in many cellular metabolic pathways.[1] Magnesium is required for deoxyribonucleic acid (DNA) and protein synthesis. It is a necessary cofactor 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 g. The magnesium is distributed in bone (67%), intracellularly (31%), and extracellularly (a mere 1%).[2] 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% is complexed, and the remaining 50-60% is ionized.
Magnesium is absorbed in the ileum and excreted in stool and urine. The minimum daily requirement of magnesium is 300-350 mg, or 15 mmol; this amount is easily obtainable with a normal daily intake of fruits, seeds, and vegetables because magnesium is a component of chlorophyll and is present in high concentrations in all green plants.
The kidney is the main regulator of magnesium concentrations. Absorption occurs primarily in the proximal tubule and thick ascending limb of the loop of Henle.
Hypermagnesemia is a rare electrolyte abnormality because the kidney is very effective in excreting excess magnesium.[3]
Magnesium excess affects the CNS, neuromuscular, and cardiac organ systems. It most commonly is observed in renal insufficiency and in patients receiving intravenous (IV) magnesium for treatment of a medical condition.[4]
A study by Haider et al that screened 5,339 patients with plasma magnesium concentrations reported that 36.9% of the 151 patients with hypermagnesemia died and that hypermagnesemia was a strong independent risk factor for mortality.[5]
Common causes of hypermagnesemia include renal failure and iatrogenic manipulations.[6] However, other diseases may result in increased magnesium; the degree of elevation determines the symptoms. Acute elevations of magnesium usually are more symptomatic than slow rises.
Magnesium levels of 2-4 mEq/L are associated with the following:
Nausea
Vomiting
Skin flushing
Weakness
Lightheadedness
High magnesium levels are associated with depressed levels of consciousness, respiratory depression, and cardiac arrest.
Most cases of hypermagnesemia are due to iatrogenic interventions and administration,[1] especially errors in calculating appropriate infusions. Additional causes include the following:
Ingestion of magnesium-containing substances such as vitamins, antacids, or cathartics by patients with chronic renal failure
Acute renal failure (in the absence of dialysis)
Excessive intravenous infusions of magnesium in patients being treated for eclampsia, asthma, torsade de pointes, or other cardiac arrhythmias
In neonates, treatment of maternal eclampsia with magnesium, which passes through the placental circulation
Decreased GI elimination and increased GI absorption of magnesium due to intestinal hypomotility from any cause
GI medications that decrease motility, including narcotics and anticholinergics
Hypomotility disorders such as bowel obstruction and chronic constipation
Tumor lysis syndrome, by releasing massive amounts of intracellular magnesium
Adrenal insufficiency (secondary hypermagnesemia)
Rhabdomyolysis, like tumor lysis syndrome, by releasing significant amounts of intracellular magnesium
Milk-alkali syndrome
Hypothyroidism
Hypoparathyroidism
Neoplasm with skeletal muscle involvement
Lithium intoxication
Extracellular volume contraction, as in diabetic ketoacidosis (DKA)
Electrolytes, including potassium, magnesium, and calcium levels[7, 8]
A test for ionized magnesium is clinically available. However, it is used most often for monitoring magnesium infusions. The serum magnesium level is often used as an initial study in the ED.
Elevation in magnesium level is usually not found as an isolated electrolyte abnormality.
Hyperkalemia and hypercalcemia are often present concurrently.
BUN and creatinine levels
Obtain renal function tests and calculate creatinine clearance to assess the ability of the kidney to excrete magnesium.
Serum magnesium levels rise when creatinine clearance is less than 30 mL/min.
Check serum creatine phosphokinase (CPK) level or urine myoglobin level in patients in whom rhabdomyolysis is suspected.
Arterial blood gases (ABG) may reveal a respiratory acidosis.
Thyroid function tests
Hypothyroidism is a rare cause of hypermagnesemia.
Check these tests in the absence of any other good explanation.
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, when life-threatening symptoms are present, or in patients with poor renal function.
Assess the patient's ABCs and stabilize.
Intubate if necessary.
Treat hypotension with fluids.
Treat arrhythmia as per advanced cardiac life support (ACLS) protocol or with treatment outlined below, if hypermagnesemia is known.
Obtain appropriate studies as discussed in Workup.
Treatment depends upon the level of magnesium and the presence of symptoms. In patients with mildly increased levels, simply stop the source of magnesium. In patients with higher concentrations or severe symptoms, other treatments are necessary. Calcium should be reserved for patients with life-threatening symptoms, such as arrhythmia or severe respiratory depression.
Clinical Context:
Both fluids are essentially isotonic, and, while some of their metabolic effects differ, the differences are clinically irrelevant for the purpose of promoting diuresis.
Intravenous fluids work by dilution of the extracellular magnesium. Fluids are used with diuretics to promote increased excretion of magnesium by the kidney.
Clinical Context:
Directly antagonizes neuromuscular and cardiovascular effects of magnesium. The 10% IV solution provides 100 mg/mL of calcium gluconate that equals 9 mg/mL (0.46 mEq/mL) of elemental calcium. One 10 mL ampule contains 93 mg of elemental calcium.
Complications of magnesium administration seen in the ED often are a function of the rate and/or concentration of delivery rather than the total amount administered.
Nona P Novello, MD, Chief Medical Information Officer, MedStar Franklin Square Medical Center
Disclosure: Nothing to disclose.
Specialty Editors
Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Jeffrey L Arnold, MD, FACEP, Chairman, Department of Emergency Medicine, Santa Clara Valley Medical Center
Disclosure: Nothing to disclose.
Chief Editor
Erik D Schraga, MD, Staff Physician, Department of Emergency Medicine, Mills-Peninsula Emergency Medical Associates
Disclosure: Nothing to disclose.
Additional Contributors
Joseph J Sachter, MD, FACEP, Consulting Staff, Department of Emergency Medicine, Muhlenberg Regional Medical Center
Disclosure: Nothing to disclose.
Acknowledgements
Howard A Blumstein, MD, FAAEM Assistant Professor of Surgery, Medical Director, Department of Emergency Medicine, Wake Forest University School of Medicine
Howard A Blumstein, MD, FAAEM is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, Emergency Medicine Residents Association, and Society for Academic Emergency Medicine
