Sodium Flashcards
What percentage of inpatients have a low sodium?
3%
Define the five classifications of hyponatraemia
- Spurious
- Pseudo
- Hypovolaemic hyponatraemia
- Hypervolaemia hyponatraemia
- Normovolaemic hyponatraemia
Classify Hypovolaemic hyponatraemia into causes (2) and give examples
Renal [diuretics, adrenal failure, salt wasting] and non renal [GI, burns, haemorrhage])
Classify Hypervolaemia Hypernatraemia into causes (2) and give examples
Oedmatous [CCF, ALF, CLF, Nephrotic] or without [acute or chronic renal disease
Classify Normovolaemic hyponatraemia into causes (2) and give examples (there are many examples)
Acute dilutional [iatrogenic, psychogenic, drowning, TURP syndrome] or chronic dilutional [chest tumours, GI cancer, myeloproliferative, infectional, ashthma, PPV, any CNS tumour, GBS, MS, cerebral atrophy, DDAVP, oxytocin i.e. AVP analogues, stimulants of AVP release e.g. nicotine, trycyclics, idiopathic, low osmotic load, gain of function mutation in AVPR2
Outline what element of the sample high protein and lipids alters to cause pseudohyponatraemia
The plasma water fraction is markedly decreased in these cases.
Outline the four responses to a hypertonic saline infusion
A) random B) reset osmostat C) slow leak of AVP irrespective of the osmolality D) Appropriate (Ectopic)
Describe what is happening in reset osmostat. What conditions does this occur?
reset osmostat (i.e. AVP release is triggered at far lower blood osmolality than would be appropriate – felt to be mechanism behind hyponatraemia in tumours and neurological disease
What is the cause of slow low level release of AVP usually, despite hyponatraemia?
Usually pituitary trauma e.g. surgery
What gene is mutated that can lead to type D AVP release following hypertonic saline infusion?
AVPR2 gain of function
Define the 7 criteria for SIADH
hyponatraemia with hypoosmolality, renal excretion of sodium, absence of fluid overload, urine not maximally dilute i.e. osmolality greater than appropriate for the osmolality of serum, normal renal, adrenal and thyroid
What is the sick cell syndrome? (2 possibilities)
Simply, that cells leak sodium into themselves, causing hyponatraemia. Also, osmoreceptors in the brain fail to synthesise enough osmolytes (happens if patients are generally unwell) so the point they start to swell and release AVP is reduced.
Beer potomonia results in low osmotic load hyponatraemia how?
There is a minimum concentration of urine about 40-80mOsm/kg of water. If the beer has a low mineral content this may be exceeded if large amounts are drunk and no intact of other salts.
Explain the mechanisms behind the tea and toast diet found in elderly hyponatraemia
Patient usually on a thiazide (blocks sodium and chloride resorption), combined with high intake of tea and low mineral diet. Hence, maximally dilute urine cannot be made (a form of beer potomania).
What is cerebral salt wasting?
the result of natriuretic peptide release
