Jump to content

Hypomagnesemia

Add links
From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by Sinharaja2002 (talk | contribs) at 13:00, 15 October 2008. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Hypomagnesemia

The prefix hypo- means low (contrast with hyper-, meaning high). The middle magnes refers to magnesium. The end portion of the word, -emia, means 'in the blood' (note, however, that hypomagnesemia is usually indicative of a systemic magnesium deficit). Thus, Hypomagnesemia is an electrolyte disturbance in which there is an abnormally low level of magnesium in the blood. Usually a serum level less than 0.7 mmol/l is used as reference. It must be noted that hypomagnesemia is not equal to magnesium deficiency. Hypomagnesemia can be present without magnesium deficiency and vice versa.

It may result from a number of conditions including inadequate intake of magnesium, chronic diarrhea, malabsorption, alcoholism, chronic stress, diuretic use and other disorders.

Homeostasis

The body contains 21-28 grams of magnesium (1 mmol=2mEq=12.0 mg). Of this, 53% is located in bone, 19% in non-muscular tissue, and 1% in extracellular fluid. For this reason, blood levels of magnesium are not an adequate means of establishing the total amount of available magnesium. Most of the serum magnesium is bound to chelators, (i.e. ATP, ADP, proteins and citrate). Roughly 33% is bound to proteins, and 5-10% is not bound. This "free" magnesium is essential in regulating intracellular magnesium. Normal plasma Mg is 1.7-2.3 mg/dl (0.69-0.94 mmol/l). Of this 60% is free, 33% is bound to proteins, and less than 7% is bound to citrate, bicarbonate and phosphate.

Magnesium is abundant in nature. It can be found in green vegetables, chlorophyll, cocoa-derivatives, nuts, wheat, seafood, and meat. It is resorbed through the small intestine, and to a lesser degree in the colon. The rectum and sigmoid colon can absorb magnesium. Hypermagnesemia has been reported after enemas containing magnesium. Forty percent of dietary magnesium is absorbed. Hypomagnesemia stimulates and hypermagnesemia inhibits this absorption.

The kidneys regulate the serum magnesium. About 2400 mg of magnesium passes through the kidneys, of which 5% (120 mg) is excreted through urine. The loop of Henle is the major site for Mg-homeostasis and 60% is resorbed.

Magnesium homeostasis comprises three systems: kidney, small intestine, and bone. In the acute phase of magnesium deficiency there is an increase in absorption in the distal small intestine and tubular resorption in the kidneys. When this condition persists serum magnesium drops and is corrected with magnesium from bone tissue. The level of intracellular magnesium is controlled through the reservoir in bone tissue.

Metabolism

Magnesium is a cofactor in more than 300 enzyme regulated reactions. Most importantly forming and using ATP, i.e. kinase. There is a direct effect on sodium- (Na), potassium- (K) and calcium (Ca)channels. It has several effects:

  • Potassium channels are inhibited by magnesium. Hypomagnesemia results in increased efflux of intracellular K. The cell loses potassium which then is excreted by the kidneys, resulting in hypokalemia.
  • Release of calcium from the sarcoplasmic reticulum is inhibited by magnesium. Low levels of magnesium stimulate the release of calcium and thereby an intracellular level of calcium. This effect similar to calcium inhibitors makes it "nature's calcium inhibitor." Lack of magnesium inhibits the release of parathyroid hormone, which can result in hypoparathyroidism and hypocalcemia. Furthermore, it makes skeletal and muscle receptors less sensitive to parathyroid hormone.
  • Through relaxation of bronchial smooth muscle it causes bronchodilation.
  • The neurological effects are:
    • reducing electrical excitation
    • blocking release of acetylcholine
    • blocking N-methyl-D-aspartate, an excitatory neurotransmitter of the central nervous system.

Causes

Magnesium deficiency is not uncommon in hospitalized patients. Elevated levels of magnesium (hypermagnesemia), however, are nearly always iatrogenic. 10-20% of all hospital patients, and 60-65% of patient in the intensive care unit (ICU) have hypomagnesemia. Hypomagnesiemia is underdiagnosed, as testing for serum magnesium levels is not routine. Hypomagnesemia results in increased mortality.

Low levels of magnesium in your blood may mean either there is not enough magnesium in the diet, the intestines are not absorbing enough magnesium or the kidneys are excreting too much magnesium. Deficiencies may be due to the following conditions:

  • alcoholism. Hypomagnesemia occurs in 30% of alcohol abuse and 85% in delirium tremens, due to malnutrition and chronic diarrhea. Alcohol stimulates renal excretion of magnesium, which is also increased because of alcoholic and diabetic ketoacidosis, hypophosphatemia and hyperaldosteronism resulting from liver disease. Also hypomagnesemia is related to thiamine deficiency because magnesium is needed for transforming thiamine into thiamine pyrophosphate.
  • diuretic use (the most common cause of hypomagnesemia)(loop and thiazides)
  • antibiotics (i.e. aminoglycosides, amphotericin, pentamidine, gentamicin, tobramycin, viomycin) block resorption in the loop of Henle. 30% of patients using these antibiotics have hypomagnesemia,
  • other drugs
    • digitalis, displaces magnesium into the cell. Digitalis causes an increased intracellular concentration of sodium, which in turn increases intracellular calcium by passively decreasing the action of the sodium-calcium exchanger in the sarcolemma. The increased intracellular calcium gives a positive inotropic effect.
    • adrenergics, displace magnesium into the cell
    • cisplatin, stimulates renal excretion
    • ciclosporin, stimulates renal excretion
  • excess calcium
  • increased levels of stress
  • excess saturated fats
  • excess coffee or tea intake
  • excess phosphoric or carbonic acids (soda pop)
  • insufficient water consumption
  • excess salt
  • excess sugar intake
  • insufficient selenium
  • insufficient vitamin D or sunlight exposure
  • insufficient vitamin B6
  • gastrointestinal causes: the distal tractus digestivus secretes high levels of magnesium. Therefore, secretory diarrhoea can cause hypomagnesemia. Thus, Crohn's disease, ulcerative colitis, Whipple's disease and coeliac sprue can all cause hypomagnesemia.
  • renal magnesium loss in Bartter's syndrome, postobstructive diuresis, diuretic phase of acute tubular necrosis (ATN) and kidney transplant
  • diabetes mellitus: 38% of diabetic outpatient clinic visits involve hypomagnesemia, probably through renal loss because of glycosuria or ketoaciduria.
  • acute myocardial infarction: within the first 48 hours after a heart-attack 80% of patients have hypomagnesemia. This could be the result of an intracellular shift because of an increase in catecholamines.
  • malabsorption
  • milk diet in infants
  • acute pancreatitis
  • hydrogen fluoride poisoning
  • Gittleman Syndrome.
  • Bartter Syndome.

Clinical Features

Deficiency of magnesium causes weakness, muscle cramps, cardiac arrhythmia, increased irritability of the nervous system with tremors, athetosis, jerking, nystagmus and an extensor plantar reflex. In addition, there may be confusion, disorientation, hallucinations, depression, epileptic fits, hypertension, tachycardia and tetany.

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 sulfate (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 tachyarrhythmia. 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. al-Ghamdi SM, Cameron EC, Sutton RA (1994). "Magnesium deficiency: pathophysiologic and clinical overview". Am. J. Kidney Dis. 24 (5): 737–52. PMID 7977315.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  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. Durlach J, Durlach V, Bac P, Bara M, Guiet-Bara A (1994). "Magnesium and therapeutics". Magnes Res. 7 (3–4): 313–28. PMID 7786695.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. Faber MD, Kupin WL, Heilig CW, Narins RG (1994). "Common fluid-electrolyte and acid-base problems in the intensive care unit: selected issues". Semin. Nephrol. 14 (1): 8–22. PMID 8140344.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  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. Mills R, Leadbeater M, Ravalia A (1997). "Intravenous magnesium sulphate in the management of refractory bronchospasm in a ventilated asthmatic". Anaesthesia. 52 (8): 782–5. PMID 9291766.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. Ramsay JG (1999). "Cardiac management in the ICU". Chest. 115 (5 Suppl): 138S–144S. PMID 10331347.
  15. Reinhart RA (1992). "Magnesium deficiency: recognition and treatment in the emergency medicine setting". Am J Emerg Med. 10 (1): 78–83. PMID 1736922.
  16. Reinhart RA, Desbiens NA (1985). "Hypomagnesemia in patients entering the ICU". Crit. Care Med. 13 (6): 506–7. PMID 3996005.
  17. Ryzen E, Wagers PW, Singer FR, Rude RK (1985). "Magnesium deficiency in a medical ICU population". Crit. Care Med. 13 (1): 19–21. PMID 3965244.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  18. Ryzen E (1989). "Magnesium homeostasis in critically ill patients". Magnesium. 8 (3–4): 201–12. PMID 2682045.
  19. Whang R, Hampton EM, Whang DD (1994). "Magnesium homeostasis and clinical disorders of magnesium deficiency". Ann Pharmacother. 28 (2): 220–6. PMID 8173141.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  20. Chareonpong-Kawamoto N, Yasumoto K (1995). "Selenium deficiency as a cause of overload of iron and unbalanced distribution of other minerals". Biosci. Biotechnol. Biochem. 59 (2): 302–6. PMID 7766029.

See also

Retrieved from "https://en.wikipedia.org/w/index.php?title=Hypomagnesemia&oldid=245434103"