Hypomegnesemia

Hypomegnesemia

David Ray Velez, MD

Definition: Magnesium (Mg) < 1.4 mEq/L (1.7 mg/dL)

Causes

  • Massive Diuresis
  • Chronic TPN without Magnesium Replacement
  • Alcohol Abuse
  • Uncontrolled Diabetes
  • Chronic PPI Therapy

Presentation

  • Weakness
  • Tremor
  • Tetany and Seizures
  • Nystagmus
  • Coma

Subsequent Electrolyte Deficiencies

  • Hypokalemia
    • From Renal Potassium Wasting – K Secreted by Potassium (ROMK) Channels That are Normally Inhibited by Magnesium
    • Relatively Refractory to Potassium Supplementation Until Magnesium is Corrected
  • Hypocalcemia
    • Blocks PTH Release (Hypoparathyroidism)
    • End-Organ PTH-Resistance
    • Vitamin D Deficiency

EKG Changes

  • Widened QRS
  • Prolonged QT Interval
  • Prolonged PR Interval
  • Polymorphic Ventricular Tachycardia

Treatment

  • Primary Treatment: Magnesium Replacement
  • Magnesium Sulfate (MgSO4)
    • Correction: Every 1 g will Increase Serum Mg 0.2 mg/dL
    • IV Replacement is Preferred – Enteral Absorption Has Highly Variable Bioavailability
    • Goal is to Achieve the Middle of the Normal Range, Not the Lower Limit of Normal, to Allow for Ongoing Losses
  • Rechecking After Replacement:
    • Wait 8-12 Hours to Allow Gradual Redistribution to Tissues
  • Correct Any Underlying Hypokalemia or Hypocalcemia as Well