hyponatraemia

Question 1

causes of hypovolaemic hypotonic hyponatraemia

Answer 1

renal causes:
- acute or chronic renal failure with high urine output
- diuretics
- mineralocorticoid deficiency (Addison’s disease)
- recovery of acute tubular necrosis
- cerebral salt wasting syndrome

extrarenal causes
- diarrhoea
- vomiting
dermal fluid loss eg. burns, sweating
- third space fluid loss
- bleeding

Question 2

causes of euvolaemic hypotonic hyponatraemia

Answer 2

renal causes:
- SIADH
- medication use
- exercise associated hyponatraemia
- acute or chronic renal failure
- glucocorticoid deficiency
- severe hypothyroidism

extrarenal causes
- decreased salt intake
- water intoxication (dilution hyponatraemia)
by excessive hypotonic infusion, primary polydipsia, beer potomania

Question 3

causes of hypervolaemic hypotonic hyponatraemia

Answer 3

acute or chronic renal failure with low urine output

extrarenal causes:
- CHF
- liver cirrhosis
- severe hyperproteinaemia

Question 4

causes of hypertonic hyponatraemia

Answer 4

low Na but with high serum osmolality

caused by
hyperglycaemia: glucose is osmotically active and pulls water into the intravascular space
IV mannitol
radio contract use

Question 5

causes of isotonic hyponatraemia

Answer 5

low measured Na but normal serum osmolality

TURP syndrome
pseudohyponatraemia due to hyperlipidaemia, multiple myeloma

Question 6

clinical picture of hyponatraemia

Answer 6

severely symptomatic: confusion, seizures, ataxia, respiratory failure
mild symptoms: forgetfulness, gait disturbances, malaise, headache, dizziness, fatigue, Nausea and vomiting

Question 7

diagnostic approach to hyponatraemia

Answer 7

reconfirm: repeat UECs
exclude hyperglycaemia
check serum osmolality

consider, based on suspected cause:
TSH for hypothyroidism
serum cortisol and ACTH
urine drug screen for MDMA
BNP to evaluate for CHF

Question 8

management of hyponatraemia

Answer 8

for severely symptomatic: use IV hypertonic saline followed by cause specific treatment
for nonsecure symptoms: slow correction with cause specific treatment
stop all medications that may be contributing to avoid sodium overcorrection to minimise risk of ODS

Question 9

how to minimise risk of ODS

Answer 9

carefully monitor sodium levels and urine output
follow the recommended sodium correction rates
provide management of sodium overcorrection if needed
potassium supplementation also increases sodium levels

Question 10

Rapid correction of chronic hyponatremia can cause

Answer 10

osmotic demyelination syndrome!

Question 11

osmotic demyelination syndrome

Answer 11

Damage to the myelin sheath of nerves in the CNS caused by a sudden rise in the osmolarity of blood. Most commonly caused by rapid correction of chronic hyponatremia.
Clinical symptoms appear 2–6 days after correction of hyponatremia and include an altered level of consciousness, coma, locked-in syndrome, dysarthria, dysphagia, diplopia, and/or worsening quadriparesis.

Question 12

why do initially severe symtpoms require aggressive treatment with IV hypertonic saline

Answer 12

Severe or moderately severe symptoms require initial aggressive treatment with IV hypertonic saline to reverse neurological symptoms and prevent brain herniation.

Question 13

emergency treatment with hypertonic saline

Answer 13

Severe symptoms: hypertonic saline bolus e.g., 3% NaCl
conduct serial serum sodium measurement
monitor urine output