hyponatraemia W2

Question 1

hyponatraemia - 3 important facts!

Answer 1

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

Question 2

salt and water?

Answer 2

where salt goes, water follows

Question 3

cations in the different compartments?

Answer 3

(cation = positively charged ion)

K+ in intracellular compartment
Na+ in the extracellular compartment

balance each-other out.

Question 4

hydrostatic vs osmotic pressure?

Answer 4

hydrostatic - pressure that pushes
osmotic - forces that pull

Question 5

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

Answer 5

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

Question 6

what happens if you add salt to the extracellular compartment

Answer 6

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

Question 7

what happens if you add water to the extracellular compartment

Answer 7

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

Question 8

names for different volume statuses? what do they mean?

Answer 8

hypovolaemic
euvolaemic/normovolaemic
hypervolaemic

different names for volume status (water AND salt)

Question 9

how is volume status associated with hyponatraemia

Answer 9

3 different types of hyponatraemia depending on volume status:

hypovolaemic hyponatraemia
norvolaemic hyponatraemia
hypervolaemic hyponatraemia

Question 10

when are clinical signs in hyponatraemia generated?

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

hypervolaemia
swollen, oedematous, breathless

Question 13

in simple terms of salt and water movement?

Answer 13

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

Question 14

clinical scenarios of fluid loss? - disease

Answer 14

haemorrhage
vomiting
diarrhoea
burns
diuretic states
sequestration
misc renal diseases

Question 15

clinical scenarios of fluid loss? - iatrogenic

Answer 15

diuretics
stomas/fistulae
gastric aspiration
surgical drains

Question 16

diseases creating diuretic states? (causing fluid loss)

Answer 16

diabetes
hypercalcaemia

Question 17

clinical scenarios of fluid gain? - disease

Answer 17

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

Question 18

clinical scenarios of fluid gain? - iatrogenic

Answer 18

IV fluids
supplemental nutrition

Question 19

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

Answer 19

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

Question 20

hyponatraemia and volume state?

Answer 20

pure water gain = normovolaemic/mild hypervolaemia

Na+ & water gain = interstitial oedema/hypervolaemia

Na+ & water loss = hypovolaemia

Question 21

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

Answer 21

SIADH
hypothyroidism
iatrogenic

Question 22

what is hypovolaemic hyponatraemia?

Answer 22

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

Question 23

what is hypervolaemic hyponatraemia?

Answer 23

water gains exceed sodium gains

Question 24

3 classic cases of hypervolaemic hyponatraemia?

Answer 24

heart failure
liver failure
nephrotic syndrome

Question 25

reduced cardiac output? (cardiac failure)

Answer 25

reduced effective circulating volume
reduced organ perfusion
physiological correcting mechanisms kick in
hypervolaemia wins over tonicity
RAAS stimulation
ADH stimulation

Question 26

which does our body prioritise - baroreceptors or osmoreceptors?

Answer 26

baroreceptors! pressure wins over osmolarity.

Question 27

what do correcting mechanisms in cardiac failure result in

Answer 27

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