hyponatraemia W2 Flashcards
hyponatraemia - 3 important facts!
commonest electrolyte imbalance (20-30%)
it can kill!!!
may be caused by sodium loss OR water gain
salt and water?
where salt goes, water follows
cations in the different compartments?
(cation = positively charged ion)
K+ in intracellular compartment
Na+ in the extracellular compartment
balance each-other out.
hydrostatic vs osmotic pressure?
hydrostatic - pressure that pushes
osmotic - forces that pull
hydrostatic pressure and osmotic forces for water moving in/out a cell?
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
what happens if you add salt to the extracellular compartment
sodium doesn’t move into intracellular compartment.
sodium draws water from intra to extracellular compartment.
extracellular = expanded
intracellular = depleted
what happens if you add water to the extracellular compartment
all compartments are equally expanded
sodium is diluted - patient is hyponatraemic
names for different volume statuses? what do they mean?
hypovolaemic
euvolaemic/normovolaemic
hypervolaemic
different names for volume status (water AND salt)
how is volume status associated with hyponatraemia
3 different types of hyponatraemia depending on volume status:
hypovolaemic hyponatraemia
norvolaemic hyponatraemia
hypervolaemic hyponatraemia
when are clinical signs in hyponatraemia generated?
when the relationship between extra and intracellular compartments change (no difference seen if compartments change at same ratio)
what happens if you deplete the volume of the extracellular reservoir (done by depleting salt).
symptoms?
hypovolaemia
dry mouth, cracked tongues, inelastic skin, low bp, thirsty
what happens if you expand the extracellular reservoir (give water and salt)
hypervolaemia
swollen, oedematous, breathless
in simple terms of salt and water movement?
lose salt -> lose water (hypovolaemia)
gain salt -> gain water (hypervolaemia)
lose water -> concentrate Na (hypernatraemia)
gain water -> dilute Na (hyponatraemia)
clinical scenarios of fluid loss? - disease
haemorrhage
vomiting
diarrhoea
burns
diuretic states
sequestration
misc renal diseases
clinical scenarios of fluid loss? - iatrogenic
diuretics
stomas/fistulae
gastric aspiration
surgical drains
diseases creating diuretic states? (causing fluid loss)
diabetes
hypercalcaemia
clinical scenarios of fluid gain? - disease
heart/liver/renal failure
hypothyroidism
psychogenic
ADH excess (SIADH)
clinical scenarios of fluid gain? - iatrogenic
IV fluids
supplemental nutrition
how can hyponatraemia occur in terms of salt and water gains and losses?
pure water gain
water gain > Na+ gain
Na+ loss > water loss
(pure Na+ loss?)
Na+ loss and water gain
hyponatraemia and volume state?
pure water gain = normovolaemic/mild hypervolaemia
Na+ & water gain = interstitial oedema/hypervolaemia
Na+ & water loss = hypovolaemia
causes of normovolaemic/hypervolaemic hyponatraemia? (pure water gain)
SIADH
hypothyroidism
iatrogenic
what is hypovolaemic hyponatraemia?
any case where salt and water loss occur, but water loss is insufficient to concentrate the sodium
what is hypervolaemic hyponatraemia?
water gains exceed sodium gains
3 classic cases of hypervolaemic hyponatraemia?
heart failure
liver failure
nephrotic syndrome
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
which does our body prioritise - baroreceptors or osmoreceptors?
baroreceptors! pressure wins over osmolarity.
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
