Write a short note on hypomagnesaemia.
A common electrolyte abnormality in the ICU:
Mg primary intracellular cation and plays a major·role in the transfer, storage and utilization of energy.
Causes: diarrhoea, NG suction, TPN, RTA, alcoholism, malabsorption
Drugs-amphotericin B, Aminoglycosides, Carbenicillins, diuretics.
Pathophysiology: Mg deficiency leads to a drop in ICF potassium and a rise in ICF Na., leading to an elevation in the resting membrane potential. This leads to a rise in the inward Ca current and hence the enhanced neurological and cardiac irritability.
Effects: Confusion, injtability, delirium, tremors, tachyanhytbmias, Torsade,
refractory hypokalemia and hypocalcemia.
Treatment: IV MgS04 in doses of 5-10 mmol/L, given slow IV. Repeated doses may
be required. Rapid administration can lead to hypotension.
There are few fellowship questions in this exam which ask the candidate to write a short note about anything. Understandably, somebody who was waiting to critically evaluate something or to discuss your management would have been taken aback by such a question. How does one structure a response?
Using this article, I have attempted a coherent answer.
Causes of hypomagnesaemia
- NG suction
- Renal tubular acidosis
Consequences of hypomagnesaemia
- hypokalemia and hypocalcemia
- tetany, muscle cramps
- vertigo, nystagmus
- ventricular arrhythmias, particularly Torsades de points
- increased sensitivity to digoxin toxicity
Pathophysiology of cardiac consequences
- Magnesium is required for the function of Na+/K+ ATPase.
- Na+/K+ ATPase maintains the Na+ and K+ concentration gradients
- If intracellular K+ concentration decreases, the cell membrane potential becomes less negative which increases its vulnerability to cardiac arrhythmias.
Management of hypomagnesaemia
- Magnesium replacement
- Amelioration of the aetiology of magnesium loss
- Careful monitoring of rising levels
In greater detail, from the hypomagnesemia chapter:
A better way to organise the list of causes would be by pathophysiological disturbance, as below.
Sequestration and chelation
Unclear association with low magnesium
Associated biochemical abnormalities
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SHILS, MAURICE E. "Experimental human magnesium depletion." Medicine 48.1 (1969): 61.
Grubbs, Robert D., and Michael E. Maguire. "Magnesium as a regulatory cation: criteria and evaluation." Magnesium 6.3 (1986): 113-127.
Martin, Kevin J., Esther A. González, and Eduardo Slatopolsky. "Clinical consequences and management of hypomagnesemia." Journal of the American Society of Nephrology 20.11 (2009): 2291-2295.
Chakraborti, Sajal, et al. "Protective role of magnesium in cardiovascular diseases: a review." Molecular and cellular biochemistry 238.1-2 (2002): 163-179.