Hypermagnesemia

Question 1

Clinical Manifestations of Hypermagnesemia

Answer 1

Signs/symptoms: Muscular weakness, paralysis, ataxia, drowsiness, confusion, paralytic ileus, bladder paralysis, nausea/vomiting, hypotension, bradycardia, absent tendon reflexes, hypoventilation (everything slows down)

Associated electrolyte changes: hypocalcemia (due to suppressed PTH secretion and possible Mg2+ binding and activation of CaSR)

Question 2

Clinical Manifestations of Hypermagnesemia

Answer 2

ECG changes:

Increased PR and QT

Increased QRS duration

Variable decrease in P-wave voltage

Variable degree of T-wave peaking

Complete AV block

Asystole

Question 3

Clinical Manifestations of Hypermagnesemia

Answer 3

Other effects: hypoparathyroidism, vascular relaxation, interference with platelet adhesiveness, thrombin-generation time and clotting time.

NOTE: Hyperkalemia may occur due to suppression of K+ secretion. This is possibly due to Mg2+-gate keeping function in ROMK: Mg2+ normally keeps ROMK closed and limits K+ wasting.

Question 4

Causes of Hypermagnesemia

Answer 4

Kidney failure, rhabdomyolysis, tumor lysis

Question 5

Causes of Hypermagnesemia

Answer 5

Excessive intake: oral, infusion, magnesium-containing enemas, Dead Sea water drowning (very high content of both calcium and magnesium), parenteral, urethral irrigation; common Mg2+-containing medications: laxatives (milk of magnesia), antacids (extra-strength Rolaids)

Question 6

Causes of Hypermagnesemia

Answer 6

Redistribution: acute acidosis

Others: familial hypocalciuric hypercalemia, diabetic ketoacidosis, lithium, milk-alkali syndrome, theophylline toxicity, adrenal insufficiency, hypothyroidism

Question 7

Treatment of Hypermagnesemia

Answer 7

Antagonizing magnesium:

Calcium: ~100 to 200 mg elemental Ca2+ infused over 5 to 10 minutes

One 10 mL ampule of Ca2+ gluconate contains 90 mg of elemental calcium

One 10 mL ampule of Ca2+ chloride contains 272 mg of elemental calcium

Question 8

Treatment of Hypermagnesemia

Answer 8

Removal of magnesium:

• Dialysis
• Use of loop diuretics (NOTE: loop diuretics can lower Ca2+ and facilitate development of arrhythmias in patients with hypermagnesemia!!! Calcium is a natural antagonist of Mg2+.)

Cardiopulmonary support

Question 9

Treatment of Hypermagnesemia

Answer 9

NOTE
Magnesium can potentiate the hypotensive effect of calcium channel blockers (CCB) and can cause severe hypotension in preeclamptic/eclamptic patients treated with both. Treatment: calcium gluconate

Both hypo- and hypermagnesemia can reduce PTH secretion.