Magnesium
Background
- Second most abundant intracellular cation; critical for enzymatic reactions, cardiac stability, and neuromuscular function
- Serum levels reflect only ~1% of total body stores
Normal Values
- Normal: 1.7-2.2 mg/dL
Interpretation
- Hypomagnesemia is common in ED patients (alcoholism, diuretic use, diarrhea, malnutrition)
- Must be corrected for effective potassium repletion
- Can cause refractory hypokalemia and hypocalcemia
- ECG: prolonged QT, torsades de pointes
- Treat: IV magnesium sulfate 2g over 15-60 min
- Hypermagnesemia (>2.2 mg/dL) is rare; usually iatrogenic or from renal failure
- Progression: loss of DTRs (>4), respiratory depression (>6), cardiac arrest (>12)
- Treat with IV calcium and cessation of magnesium