Hypomagnesemia 2-21-06

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HypomagnesemiaGinny Barton, M3

Gyn/Onc PresentationFebruary 2006


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Magnesium

4th most common cation in thebody

2nd most abundant intracellularcation after K+

plays a fundamental role inmany functions of the cell

Involved in regulation of PTHsecretion

Systemically, Mg lowers blood

pressure and alters peripheralvascular resistance


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More on Magnesium

The total body magnesium level of an averageadult is 25 g

Approximately 60% is present in bone, 20% inmuscle, and 20% in soft tissue and the liver

Approximately 99% of the total bodymagnesium is intracellular

Normal plasma magnesium concentration is 1.7-2.1 mg/dL


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Mg Homeostasis

The main determinates are gastrointestinal absorptionand renal excretion

Healthy individuals need to ingest 0.15-0.2 mmol/kg/d to

stay in balance Extracellular magnesium is in equilibrium with that in the

bone, kidneys, intestine, and other soft tissues

There is no hormonal modulation of urinary magnesiumexcretion

Bone, the principal reservoir of magnesium, does notreadily exchange with circulating magnesium in theextracellular fluid space


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Causes of Hypomagnesemia

Malabsorption of Mg in the ileum

GI secretions in large amounts

Malnutrition with low dietary intake of Mg

Renal losses from primary renal disorders orsecondary causes

Extracellular volume expansion

Redistribution of Mg into cells (Insulin) Pregnant women have been found to be Mg

depleted (esp those who experience PTL)


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More on Renal losses of Mg

Primary renal disorders cause hypomagnesemiaby decreased tubular reabsorption of

magnesium by the damaged kidneys Drugs may cause magnesium wasting

Endocrine disorders may causehypomagnesemia

Osmotic diuresis results in magnesium loss inthe kidney


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Evaluation of Hypomagnesemia

History

Physical

Labs

EKG and Cardiac Monitoring

Other tests as needed


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History

Clues to the presence of hypomagnesemiacan be found by obtaining a history of

potential causes Historical complaints related to

hypomagnesemia are nonspecific

Altered mental status may be present insevere cases


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Physical Findings

Neuromuscular irritability

-Hyperactive deep tendon reflexes

-Muscle cramps

-Muscle fibrillation

-Trousseau and Chvostek signs

-Dysarthria and dysphagia fromesophageal dysmotility


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Physical Findings (cont)

CNS hyperexcitability

-Irritability and combativeness

-Disorientation

-Psychosis

-Ataxia, vertigo, nystagmus, and seizures(at levels


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More Physical Findings

Cardiovascular

-Atrial Fibrillation

-Ventricular arrhythmias

-Repolarization Alternans

-Coronary Artery Vasospasm

-Sudden Death


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Neonatal Physical Findings

Apnea

Weakness

Seizures

Jitteriness


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Labs

Serum magnesium, calcium, potassium,and phosphorus levels

BUN and creatinine levels Blood glucose level


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Considerations

Body stores of magnesium may be depleted markedlybefore the serum level drops, so a deficiency of Mg isclearly present if the serum level is low

Because extracellular magnesium is protein bound, thepatient's protein status is an important consideration ininterpreting magnesium levels

Hypocalcemia is caused by magnesium depletion, butthe reason is not known

Hypophosphatemia has been found in patients withhypomagnesemia


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Hypomagnesemia & Hypokalemia

Hypomagnesemia can cause Hypokalemia

Mg is a cofactor for the Na+/K+ATPase

Without Mg, cellular homeostasis cannotbe maintained and K+ loss occurs in thekidneys

*HYPOKALEMIA CANNOT BE CORRECTEDUNLESS HYPOMAGNESEMIA HAS BEENCORRECTED*


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EKG and Cardiac monitoring

Findings in hypomagnesemia are nonspecific

Findings include ST segment depression; tall,

peaked T waves; flat T waves or depressionin the precordium; U waves; loss of voltage;PR prolongation; and widened QRS.


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Treatment of Mild or ChronicHypomagnesemia

Treated with 240mg elemental Mg PO qd-bid

Mg oxide preparations include Mag-Ox 400and Uro-Mag

The major side effect of these is diarrhea

Singer G: Fluid and electrolyte management. In: The Washington Manual of

Therapeutics. Lippencott. 30th edition, 2001. p68-69.


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Treatment of Severe SymptomaticHypomagnesemia

Treated with 1-2g Mg sulfate (4mEq/ml) IV over15 min, followed by infusion of 6g Mg sulfate in1L or more IV fluid over 24hrs

B/c of the need to replenish intracellular stores,the infusion should be continued for 3-7 days

Serum Mg should be measured q24h and theinfusion rate adjusted to maintain a serum Mglevel of


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Considerations with MgReplacement

In pt with normal renal function, excess Mg isreadily excreted, and there is little risk ofcausing hypermagnesemia with recommended

doses. However, Mg must be given withextreme care in renal failure b/c of the riskof hypermagnesemia

Reduced doses and more frequent monitoring

must be used even in mild renal failure Tendon reflexesshould be tested frequently as

hyporeflexia suggests hypermagnesemia


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DONT FORGET

*HYPOKALEMIA CANNOT

BE CORRECTED UNLESSHYPOMAGNESEMIA HAS

BEEN CORRECTED*


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References

Agraharker M, Fahlen M:Hypomagnesemia. www.emedicine.com

Novello N, Blumstein HA:Hypomagnesemia. www.emedicine.com

Singer G: Fluid and electrolytemanagement. In: The Washington Manualof Therapeutics. Lippencott. 30th edition,2001. p68-69.
http://www.emedicine.com/http://www.emedicine.com/http://www.emedicine.com/http://www.emedicine.com/

Hypomagnesemia 2-21-06

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