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Potassium | Sodium | Chloride | Calcium | Phosphorus | Serum CO2

Most magnesium is intracellular bound to ATP. This electrolyte is important in most metabolic processes, including carbohydrate, protein and nucleic acid synthesis. In addition it is a cofactor in many enzymes. In heart patients, low magnesium levels increase cardiac irritability and aggravate dysrhythmias.  hypermagnesemia retards neuromuscular transmission - decreased cardiac conduction, diminished deep tendon reflexes, and respiratory depression.
**Think of magnesium as neuromuscular sedative.

Magnesium, potassium and calcium are closely linked in the body. A decrease in one element, indicates a decrease in the others. Magnesium is especially closely related to calcium. It increases intestinal absorption of calcium and is important in calcium metabolism.

Normal values: Adult          1.4-2.2 mEq/L
                        Newborn   1.4-2.0 mEq/L
                        Child          1.4-1.7 mEq/L

Hypomagnesemia

Signs and symptoms:

• May be difficult to differentiate from hypocalcemia
• Weakness
• irritability
• Tetany
• ECG changes, dysrhythmias
• Delirium
• Convulsions
• Increased risk of digoxin toxicity

Causes:

• Malabsorption syndromes
• Postoperative patients who do not eat for 7 days
• Alcohol abuse - increased excretion in urine
• Diabetes, hypoparathyroidism, hyperthyroidism, hyperaldosteronism
• Toxemia of pregnancy
• Post-cardiac surgery
• Drugs: diuretics, some antibiotics, insulin

Treatment: Replace orally or IV. If IV, need to monitor cardiac rhythm and deep tendon reflexes

Hypermagnesemia

Signs and symptoms:

• Flushed skin
• Lethargy
• Nausea and vomiting
• Slurred speech
• Excessive perspiration
• Sedation
• Decreased deep tendon reflexes
• Cardiac dysrhythmias
• Respiratory depression

Causes:

• Ingestion of magnesium containing antacids
• Chronic renal disease
• Hemolysis of blood during collection
• Drugs: thyroid medication, antacids, laxatives, calcium-containing medications, lithium, loop diuretics, aminoglycoside antibiotics.

Treatment:

Diuretics
Calcium gluconate will antagonize respiratory depression. Use with caution - will increase risk of digoxin toxicity.