1: Hyponatraemia Flashcards
What is hypotonic hyponatraemia
- Hypernatraemia
- Low serum osmolality
How can causes of hypotonic hyponatraemia be divided
- Hypovolaemia
- Euvolaemia
- Hypervolaemia
What is hypovolaemic hyponatraemia
There is large loss of sodium with associated small loss of water
What are the renal causes of hypovolaemic hypontraemia
- Diuretics
- Osmotic Diuresis
What are the extra-renal causes of hypovolaemic hyponatraemia
Diarrhoea
Vomitting
Burns
Cerebral salt-wasting
What is cerebral salt wasting syndrome
Low sodium and dehydration in response to head trauma or tumour
What is euvolaemic hyponatraemia
When serum sodium remains the same, however there is an increase in total body water. However, as water is increased in vascular and not interstitial space, it does not cause oedema
How can euvolaemic hyponatraemia be divided
- Increase urine osmolality (concentration)
- Decrease urine osmolality (concentration)
What causes euvolaemic hyponatraemia with concentrated urine (high urine osmolality)
- SIADH
= increase water reabsorption leaves concentrated urine and dilute plasma
What causes euvolaemic hyponatraemia with dilute urine (low urine osmolality)
- Psychogenic polydipsia
- Pottomania
- Hypothyroidism
What is potomania
Excess beer intake
What is hypervolaemia hyponatraemia
Excess water, with relatively small increase in sodium
What causes hypervolaemic hyponatraemia
CHF
Liver cirrhosis
Nephrotic syndrome
What is isotonic hyponatraemia
Same serum osmolality
What causes isotonic hyponatraemia
Pseudohyponatraemia
Paraproteinaemia
What is Pseudohyponatrarmia
Increase in lipids and proteins - interferes with measurement of sodium
What causes paraproteinaemia
Myeloma
What is hypertonic hyponatraemia
Increase serum osmolality
What causes hypertonic hyponatraemia
Hyperglycaemia
Cushing’s Disease
What are the symptoms of hyponatraemia
N+V
Weakness
What does severe hyponatraemia cause
Cerebral Oedema
How does cerebral oedema present
Confusion
Seizures
Death
What are the two mechanisms of hyponatraemia
- Loose more sodium than water
2. Gain more water than sodium
What is first-line investigation for hyponatraemia
U+E
How will U+Es present in hyponatraemia
Low sodium
What is second-line for investigating hyponatraemia
Serum osmolality
How is serum osmolality calculated
2Na + Glucose + Urea
If serum osmolality is low, what does it indicate
True hyponatraemia.
= Loss of sodium will cause a low serum osmolality
what is a ‘true’ hyponatraemia also known as and why
Hypotonic hyponatraemia
= Low sodium causes reduction in serum osmolality and therefore hypotonic
what does a normal serum osmolality indicate and why
Pseudohyponatraemia.
There is no loss of osmotic particles which contribute to serum osmolality measurement. However there is a gain of lipids and protein which disrupt sodium measurement in U+E
what does a high serum osmolality indicate and why
Raised glucose
after working out serum osmolality, what is calculated
urine osmolality
what urine osmolality indicates concentrated urine
> 500
what does a high urine osmolality and hyponatraemia indicate and why
SIADH
- Increase ADH causing water reabsorption. This means more concentrated urine (high osmolality).
- Increase water dilutes sodium causing hyponatraemia
how is hyponatraemia managed
- Treat cause
- Hypertonic saline
explain correction of hyponatraemia
Needs to be corrected slowly at a rate of 4-6mmol/L in 24h
why is hyponatraemia corrected at 4-6mmol/L in 24h
Too rapid correction causes cerebral pontine myelinolysis
when do symptoms of hyponatraemia present
Days-after
what are symptoms of cerebral pontine myelinolysis
Presents as ‘locked-in’ syndrome patients are awake but:
- Quadraplegia
- Paraparesis
- Dysarthria
- Dysphagia
- Seizures
is cerebral pontine myelinolysis reversible
Yes
