Hypomagnesemia

Hypomagnesemia
Magnesium
ICD-10	E83.4
ICD-9	275.2
DiseasesDB	6469
MedlinePlus	000315

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Synonyms and keywords: Hypomagnesaemia; magnesium levels low (plasma or serum)

Investigations

The diagnosis can be made by finding a plasma magnesium concentration of less than 0.7mmol/l. Since most magnesium is intracellular, a body deficit can be present with a normal plasma concentration. In addition to hypomagnesemia, up to 40% cases will also have hypocalcemia while in up to 60% of cases, hypokalemia will also be present. The ECG shows a prolonged QT interval.

Treatment

Treatment of hypomagnesemia depends on the degree of deficiency and the clinical effects. Oral replacement is appropriate for patients with mild symptoms, while intravenous replacement is indicated for patients with severe clinical effects. Intravenous magnesium sulphate (MgSO₄) can be given in the following conditions:

Arrhythmia

Magnesium is needed for the adequate function of the Na⁺/K⁺-ATPase pumps in the cells of the heart. A lack of it depolarises and results in tachyarrythmia. Magnesium inhibits release of potassium, a lack of magnesium increases loss of potassium. Intracellular levels of potassium decrease and the cells depolarise. Digoxin increases this effect. Both digoxin and hypomagnesemia inhibit the Na-K-pump resulting in decreased intracellular potassium.

Magnesium intravenously helps in refractory arrhythmia, most notably torsade de pointes. Others are ventricular tachycardia, supraventricular tachycardia and atrial fibrillation.

The effect is based upon decreased excitability by depolarisation and the slowing down of electric signals in the AV-node. Magnesium is a negative inotrope as a result of decrease calcium influx and calcium release from intracellular storage. It is just as effective as verapamil. In myocardial infarction there is a functional lack of magnesium, suppletion will decrease mortality.

Obstetric

Most importantly pre-eclampsia. It has an indirect antithrombotic effect upon thrombocytes and the endothelial functions (increase in prostaglandin, decrease in thromboxane, decrease in angiotensin II), microvascular leakage and vasospasm through its function similar to calcium channel blockers.

Convulsions are the result of cerebral vasospasm. The vasodilatatory effect of magnesium seems to be the major mechanism.

Electrolyte disturbances

• Hypokalemia: 42% of patients with hypokalemia also have hypomagnesemia, not responding to potassium supplementation. Magnesium is needed for the ATPase, Na-K-pump.
• Hypocalcemia is present in 33% of patients in the intensive care unit, not responding to calcium supplementation. This is because of decreased function of the calcium pump, but also because of a decreased release of calcium by inhibition of parathyroid hormone release.

Pulmonary

Acute asthma, here there is a bronchodilatatory effect, probably by antagonizing a calcium-mediated constriction. Also, adrenergic stimulation, i.e. sympatheticomimetics used for treatment of asthma, might lower serum levels of magnesium, which must therefore be supplemented.

Sedation and anxiolytics may help in decreasing bronchoconstriction.

References

1. Cecil Textbook of Medicine
2. Harrison's Principles of Internal Medicine
3. Intensive Care Medicine by Irwin and Rippe
4. The ICU Book by Marino
5. The Oxford Textbook of Medicine
6. Saeed M.G. Al-Ghamdi, Eugene C. Cameron, MD and Roger A.L. Sutton, "Magnesium Deficiency: Pathophysiology And Clinical Overview", American Journal Of Kidney Diseases, 1994; 24 (5), 737-752.
7. Delhumeau, J.C. Granry, J.P. Monrigal, F. Costerousse, "Indications Du Magnésium En Anesthésie-Réanimation", Annales Francaises D'Anesthésie Et De Réanimation, 1995; 14, 406-416.
8. J. Durlach, V. Durlach, P. Bac, M. Bara and A. Gulet-Bara, "Magnesium And Therapeutics", Magnesium Research 1994; 7 (3-4), 313-328.
9. Mark D. Faber, Warren L. Kupin, Charles W. Heilig and Robert G. Narins, "Common Fluid-Electrolyte and Acid-Base Problems In The Intensive Care Unit: Selected Issues", Seminars In Nephrology 1994; 14 (1), 8-22.
10. Lee Goldman, J. Claude Bennett, Cecil's Textbook of Medicine, 21st Edition, 2000, 1137-1139.
11. Paul L. Marino, The ICU Book, Second Edition 1998, Chapter 42, 660-672.
12. A.E. Meinders, Professor of Internal Medicine at Leids Universitair Medisch Centrum, "Magnesium", Bij Intensive Care Patiënten
13. R. Mills, M. Leadbeater and A. Ravalia, "Case Report: Intravenous Magnesium Sulphate In The Management Of Refractory Bronchospasm In A Ventilated Asthmatic", Anaesthesia, 1997; 52, 782-785.
14. Michael A. Olerich, MD; Robert K. Rude, MD, "Should We Supplement Magnesium In Critically Ill Patients?", New Horizons, 1994; 2 (2),186-192.
15. James G. Ramsay, MD, "Cardiac Management In The ICU", Chest, 1999; 115: 138S-144S.
16. Richard A. Reinhart, MD, "Magnesium Deficiency: Recognition And Treatment In The Emergency Medicine Setting", American Journal Of Emergency Medicine, 1992; 10 (1), 76-83.
17. Richard A. Reinhart, MD; Norman A. Desbiens, MD, "Hypomagnesemia In Patients Entering The ICU", Critical Care Medicine, 1985; 13 (6), 506-507.
18. Elisabeth Ryzen, MD; Park W. Wagers, MD; Frederick R. Singer, MD; Robert K. Rude, MD, "Magnesium Deficiency In A Medical ICU Population", Critical Care Medicine, 1985; 13 (1), 19-21.
19. Elisabeth Ryzen, MD, "Magnesium Homeostasis In Critically Ill Patients", Magnesium, 1998; 8, 201-212.
20. Robert Whang, Edward M. Hampton and David D. Whang, "Magnesium Homeostasis And Clinical Disorders Of Magnesium Deficiency", The Annals Of Pharmacotherapy, 1994; 28, 220-226.
21. Selenium deficiency as a cause of overload of iron and unbalanced distribution of other minerals

Related Chapters

• Hypermagnesemia
• Hypomagnesemia with secondary hypocalcemia

External links

• Magnesium
• WebElements.com – Magnesium
• Magnesium Deficiency
• Lack Energy? Maybe It's Your Magnesium Level
• Dietary Reference Intake