REVIEW/ Journal of Intensive Care (2018) 6:21


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Hypomagnesemia in critically ill patients

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Magnesium (Mg) is essential for life and plays a crucial role in several biochemical and physiological processes in the human body.

 

Distribution (Human Adult):

Total = 25 g or 1000 mmol

60% stores in bones

20% in muscles

20% in soft tissues

0.5% in erythrocytes, and

0.3% in serum

 

 

Mg is a crucial co-factor in several enzyme systems.

 

Defining magnesium status: Normal serum concentration of Mg is 1.5 to 1.9 mEq/L

 

A normal serum level does not exclude magnesium deficiency.

 

Mg tolerance test are most widely used.

 

The serum Mg is easily available but may not adequately reflect the body Mg stores because of the physiological distribution of Mg. Notably, normal serum levels may be found even if a patient is intracellularly Mg depleted because intracellular stores are recruited to keep the serum levels within its range.

 

Hypocalcemia: Mg deficiency inhibit the release of parathyroid hormone (PTH) leading to hypocalcemia. Patients with Mg deficiency and hypocalcemia also present low levels of calcitriol (1.25-dihydroxyvitamin D) and together with impaired PTH secretion a reduced conversion of 25-hydroxyvitamin D to 1.25-dihydroxyvitamin D in the kidneys is suspected.

 

Clinical manifestations of hypomagnesemia:

Cardiovascular: Widening of the QRS complex and peaking of T waves are described in moderate Mg deficiency whereas prolongation of the PR interval, progressive widening of the QRS complex, and diminution of the T wave are seen in severe Mg depletion.

 

Neurovascular

Asthma

Preeclampsia

 

Magnesium therapy:

Patients with suspected Mg deficiency should be given Mg despite of normal Serum value. Don’t wait for Serum Mg to fall. About half of the patients with clinically potassium deficiency also have Mg depletion. The magnitude of Mg deficiency is hard to predict but may be 1–2 mEq/kg of body weight. In general, mild hypomagnesemia with no or only mild symptoms can be treated with per oral supplement whereas parenteral Mg supplementation is indicated if Mg concentration is < 0.5 mmol/L or if the patient presents with significant symptoms.

 

Severe hypomagnesemia may require treatment with doses until 1.5 mEq/kg; doses < 6 g MgSO4 can be given over a period of 8–12 h whereas higher doses should be administrated over a time period > 25 h. The slow distribution of Mg in tissues and the rapidly renal excretion makes the infusion time crucial.

 

Patients with renal failure are at risk of developing hypermagnesemia and Mg treatment is therefore generally not recommended for these patients.

 

 

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