hyponatraemia W2 Flashcards

1
Q

hyponatraemia - 3 important facts!

A

commonest electrolyte imbalance (20-30%)
it can kill!!!
may be caused by sodium loss OR water gain

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2
Q

salt and water?

A

where salt goes, water follows

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3
Q

cations in the different compartments?

A

(cation = positively charged ion)

K+ in intracellular compartment
Na+ in the extracellular compartment

balance each-other out.

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4
Q

hydrostatic vs osmotic pressure?

A

hydrostatic - pressure that pushes
osmotic - forces that pull

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5
Q

hydrostatic pressure and osmotic forces for water moving in/out a cell?

A

to move water into a cell:
external hydrostatic pressure
internal osmotic pressure

to move water out of a cell:
internal hydrostatic pressure
external osmotic pressure

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6
Q

what happens if you add salt to the extracellular compartment

A

sodium doesn’t move into intracellular compartment.
sodium draws water from intra to extracellular compartment.
extracellular = expanded
intracellular = depleted

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7
Q

what happens if you add water to the extracellular compartment

A

all compartments are equally expanded
sodium is diluted - patient is hyponatraemic

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8
Q

names for different volume statuses? what do they mean?

A

hypovolaemic
euvolaemic/normovolaemic
hypervolaemic

different names for volume status (water AND salt)

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9
Q

how is volume status associated with hyponatraemia

A

3 different types of hyponatraemia depending on volume status:

hypovolaemic hyponatraemia
norvolaemic hyponatraemia
hypervolaemic hyponatraemia

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10
Q

when are clinical signs in hyponatraemia generated?

A

when the relationship between extra and intracellular compartments change (no difference seen if compartments change at same ratio)

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11
Q

what happens if you deplete the volume of the extracellular reservoir (done by depleting salt).
symptoms?

A

hypovolaemia
dry mouth, cracked tongues, inelastic skin, low bp, thirsty

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12
Q

what happens if you expand the extracellular reservoir (give water and salt)

A

hypervolaemia
swollen, oedematous, breathless

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13
Q

in simple terms of salt and water movement?

A

lose salt -> lose water (hypovolaemia)
gain salt -> gain water (hypervolaemia)
lose water -> concentrate Na (hypernatraemia)
gain water -> dilute Na (hyponatraemia)

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14
Q

clinical scenarios of fluid loss? - disease

A

haemorrhage
vomiting
diarrhoea
burns
diuretic states
sequestration
misc renal diseases

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15
Q

clinical scenarios of fluid loss? - iatrogenic

A

diuretics
stomas/fistulae
gastric aspiration
surgical drains

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16
Q

diseases creating diuretic states? (causing fluid loss)

A

diabetes
hypercalcaemia

17
Q

clinical scenarios of fluid gain? - disease

A

heart/liver/renal failure
hypothyroidism
psychogenic
ADH excess (SIADH)

18
Q

clinical scenarios of fluid gain? - iatrogenic

A

IV fluids
supplemental nutrition

19
Q

how can hyponatraemia occur in terms of salt and water gains and losses?

A

pure water gain
water gain > Na+ gain
Na+ loss > water loss
(pure Na+ loss?)
Na+ loss and water gain

20
Q

hyponatraemia and volume state?

A

pure water gain = normovolaemic/mild hypervolaemia

Na+ & water gain = interstitial oedema/hypervolaemia

Na+ & water loss = hypovolaemia

21
Q

causes of normovolaemic/hypervolaemic hyponatraemia? (pure water gain)

A

SIADH
hypothyroidism
iatrogenic

22
Q

what is hypovolaemic hyponatraemia?

A

any case where salt and water loss occur, but water loss is insufficient to concentrate the sodium

23
Q

what is hypervolaemic hyponatraemia?

A

water gains exceed sodium gains

24
Q

3 classic cases of hypervolaemic hyponatraemia?

A

heart failure
liver failure
nephrotic syndrome

25
reduced cardiac output? (cardiac failure)
reduced effective circulating volume reduced organ perfusion physiological correcting mechanisms kick in hypervolaemia wins over tonicity RAAS stimulation ADH stimulation
26
which does our body prioritise - baroreceptors or osmoreceptors?
baroreceptors! pressure wins over osmolarity.
27
what do correcting mechanisms in cardiac failure result in
sodium retention (aldosterone) water retention (aldosterone, ADH) hyponatraemia results from dilution fluid overload worsens LV function hypovolaemia continues to win over hyponatraemia vicious cycle worsens