Editing Magnesium

== '''Physiology''' ==

* Essential element for utilisation of energy - needed to release energy from ATP
* Also used to maintain the sodium-potassium exchange pump across cell membranes, and regulating calcium movement into smooth muscle cells
* More than half is found in bone, with <1% in plasma. Therefore serum magnesium is not actually that useful of a measurement.
* 67% of the magnesium in plasma is in the ionised (active) form, and 33% bound to plasma proteins or chelated. The standard assay measures all three.
* Normally, only small amounts of magnesium is secreted in the urine, and this is highly conserved when magnesium intake is deficient.



== '''Hypermagnesaemia''' ==

* '''Aetiology'''
** Almost always iatrogenic in setting of impaired renal function
** Haemolysis
** DKA
** Adrenal insufficiency
** Hyperparathyroidism
** Lithium intoxication
* '''Symptoms'''
** Muscle paralysis
** CNS depression
**
* '''Management'''
** Dialysis
** IV calcium gluconate stabilises the cardiac membrane until dialysis is started
** Aggressive volume infusion and furosemide can work in mild derangements and preserved renal function

== '''Hypomagnesaemia''' ==

* Common in early recovery period after being critically ill - seen in 65% of ICU patients, and the true incidence is probably higher, because we can't exactly measure total body magnesium depletion.
* '''Predisposing factors'''
** Drugs
*** Furosemide - seen in 50% of patients on furosemide
*** Thiazide diuretics
*** Aminoglycosides (seen in 30%), amphotericin, pentamidine
*** Digitalis
*** Cisplatin, cyclosporine
** Diarrhoea (secretory)
** Chronic alcohol abuse - generalised malnutrition, chronic diarrhoea
** Diabetes mellitus
** Acute MI
* '''Clinical findings'''
** Neurologic
*** Altered mentation through to seizures
*** All are uncommon
** Dysrhythmias
*** Torsade de pointes
*** Magnesium deficiency magnify the digitalis effect and promote digitalis cardiotoxicity
** Other electrolytes
*** Hypokalaemia - need to replete mag prior to fixing K
*** Hypophosphataemia - this is a cause of magnesium depletion, not an effect
*** Hypocalcaemia - impaired PTH release
* '''Diagnosis'''
** Urinary magnesium excretion in response to a magnesium load is a more sensitive test for hypomagnesaemia than serum mag level. This test can be useful for determining the end-point of magnesium replacement therapy.
**
* '''Treatment'''
** '''Best done IV in the acute phase''' (oral magnesium salts can cause diarrhoea, and intestinal absorption of magnesium is erratic)
** Chronic therapy can be given orally
** Standard preparation is magnesium sulfate
** Regime as per UTD:
*** <0.7mmol/L: 4-8mmol replacement
*** 0.4-0.6: 8-16mmol
*** <0.4: 16-32mmol
**


[[Category:Nutrition]]
[[Category:Intern education]]