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Acid/Base and Electrolytes > Magnesium Disorders > Flashcards

Magnesium Disorders Flashcards

1
Q

Clinical Practice Review JVECC 2015

A

Magnesium physiology and clinical therapy in veterinary critical care

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2
Q

WHat is the suspected insidence of hypomagnesemia in critically ill canine and feline patients?

A

Dog: 54%
Cat: 50% hypo or hyper (didn’t distinguish)

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3
Q

Where is the majority of magnesium found?

A

Intracellular - 99%

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4
Q

In what forms does serum magnesium take?

A

Protein bound (30-40%), complexed to anions (4-6%), or ionised (55-65%)
Ionised is physiologically active

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5
Q

In what tissue is most magnesium found

A

Bone

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6
Q

What is the normal cytosolic magnesium conc and what are the three mechanisms that maintain it?

A

0.5-1mmol/L
1. Intracellular protein binding, 2. influx and efflux of magnesium, 3. Sequestration

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7
Q

What is the affect of increased cAMP on mg levels in the cell

A

May be increased by catecholamines or by calcium/magnesium sensing receptor –> causes release from organelles, increasing intracellular mg, which then may cross into the ECF via trPM7.

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8
Q

Cellular Functions of MG

A
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9
Q

What are the functions of Mg2+

A

controlling ox phos
Na/K and ca ATPases require Mg as a cofactor
involved in t cell activation
depolarisation of cardiac and neuronal cells
vascular contractility
regulate calcium movement as both often bind to same divalent cation receptors
required for antioxidant synthesis

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10
Q

Mg2+ Absorption and Excretion

A
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11
Q

What is total body magnesium dependent on ?

A

Intestinal and renal absorption and excretion

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12
Q

Through what mechanisms may magnesium be absorbed?

A

Transcellular or paracellular (paracellular is primary)
Transcellular occurs due to divalent cation receptors

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13
Q

By how much can intestinal absorption be increased in times of need?

A

6x

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14
Q

Approximately how much renally filtered mag is resorbed

A

> 95%

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15
Q

Where does most renal absorption of mg occur?

A

Loop of henle - 80%
Proximal tubules 5-15%
DCT 5-10%

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16
Q

What is the more ideal way to measure mg?

A

Ionised however given so much is intracellular while ionised is thought to reflect total body mg status it may not be entirely accurate

17
Q

Mg2+ Disorders

A
18
Q

What are the two most common causes of mg2+ excess

A

iatrogenic and renal failure

19
Q

What Csx may be seen with hypermg

A

Hypotension - due to excess Mg2+ binding to Ca receptors in vascular smooth muscle inhibiting contraction
may also see prolonged P-R interval and bradycardia
Neuro –> decreased deep tendon reflexes, mental depression, flaccid paralysis
GI: V+ and Ileus

20
Q

What are examples of causes of hypomag

A

Decreased intake - anorexia
Decreased GI absorption - V+, D+, IBD, EPI
Body compartment loss - Insulin, catecholamine excess, glucose admin, pancreatits
Renal loss - diuretics, saline
Renal disease - post-obstructive diuresis, dialysis, nephritis or RTA
Endocrine - HyperA, Hypercalm Hyperthyroid,
Drugs - ACEi, citrate, beta agonists, insulin, mannitol
Other - lactation, pregnancy, burns, growth

21
Q

Clinical Signs of hypomagnesemia?

A

Resp - bronchoconstriction
Cardiovascular - vasospasm, hypertension
ECG - VPCs, Vtach, Afib
Neuromuscular - Tetany, muscle spasm, MSK weakness, Seizures,

22
Q

WHy does hypomag result in refractory hypokalaemia?

A

Impaired magnesium-dependent potassium channels result in continuous loss of potassium into the ECF and renal wasting

23
Q

Why is hypomag associated with impaired insulin sensitivity?

A

magnesium serves as a cofactor for insulin release,
also maintains normal cellular response to insulin

24
Q

How may magnesium be involved in analgesia?

A

NMDA antagonism and inhibition of substance P release

25
Q

How may hypomagnesemia affect the immune system?

A

Substance P activation
less antiox
increased inflammatory mediators
TNFa

26
Q

How may hypermagnesemia be treated?

A

Magnesium free IVFT
Calcium gluconate
mannitol or diuretics
Dialysis

27
Q

How may hypomagnesemia be treated?

A

Oral or IV dosing
Dosing is pretty unknown
Recommended at 0.1-0.15mmol/kg (0.2-0.3mEq/kg) for acute
CRI 0.1-0.5mmol/kg/day (0.2-1mEq/kg/day) may be required

28
Q

What fluids are incompatible with mag ?

A

Ca, Bicarb and lactate containing fluids

29
Q

What should be monitored during magnesium infusion in case of hypermagnesemia?

A

GI signs - V+, lethargy, diarrhoea
CV - hypotension, bradycardia, prolonged Q-T, PR prolongation, QRS widening

30
Q

Magnesium as Adjuct to Therapy

A
31
Q

How may magnesium be neuroprotective?

A

Shown to significantly improve survival in people suffering from TBI, modulates several pathologic pathways in secondary brain injury, NMDA antagonism

Acid/Base and Electrolytes (12 decks)

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