Hyponatremia COPY Flashcards
How do you rule out psudo-hyponatraemia and what are some causes?
- Measure serum osmolality (mOsm/Kg) and then compare it to calculated osmolarity (mOsm/L). If there are similar then it is a true hyponatraemia. If very different then it is a psudo-hyponatraemia. Causes include hyperlipidaemia or taking bloods from an arm with a drop.
How do you calculate osmolarity?
2xNa + urea = Glucose
What is extracellular hypertonicity?
It is hyponatremia due to the osmotic effects of hyperglycaemia. So often the hyponatraemia does not require treatment
How do you measure the corrected sodium in extracellular hypertonicity?
Glucose/4 + measured sodium.
How do you assess the volume status of a patient?
- pulse
- Postural BP
- Urine output/fluid status,
- JVP,
- Ascites,
- Oedema
What are some causes of hypovolaemic hyponatraemia?
- Burns,
- Sweating,
- Diarrhoea,
- Vomiting,
- Fistula,
- Addison’s disease
What are some causes of Euvolaemic hyponatraemia?
- SIADH
- Hypothyroidism,
What are some causes of hypervolaemic hyponatraemia?
- Renal failure,
- Heart failure,
- Liver failure,
- Nephrotic sundrome
Once the fluid status of a hyponatraemic patient is established, what is the next step?
Measure urine sodium (losing sodium or retaining sodium) and urine osmolality (how concentrated the urine is)
What is the cause of a hypervolaemic hyponatraemic with a urine sodium over 20 and under 20?
If urine Na is > 20 then acute/chronic renal failure.
If urine Na is <20 then hepatic failure or nephrotic syndrome
What are the causes of a euvolaemic hyponatremic patient with urine Na >20?
If osmolality is >100 then SIADH is indicated.
If osmolality is <100 then it suggests H20 intoxication.
- Could also be due to hypothyroidism
What is the cause of a hypovolaemic hyponatraemic with a urine sodium over 20 and under 20?
If urine Na > 20 then renal losses, diuretic excess, mineralocorticoid def (Addison’s) or salt loosing nephropathy.
If urine Na < 20 then extra renal losses eg, vomiting, burns or diarrhoea
What is the difference between osmolarity and osmolality?
Osmolarity is the number of solute particles per liter (changes with temp so osmolality is preferred)
Osmolality is the number of solute particles per Kg.
Describe features of SIADH
- Common cause of low Na but euvolaemia.
- High osmolality and high urine sodium/
- Diagnosis of exclusion of renal disease, thyroid disease, adrenal disease and not on diuretics
What are some causes of SIADH?
- Pulmonary infections and lesions,
- Carcinoma
- CNS disorders,
- AIDS,
- Post op pain/ stress,
- Vomiting
- Drugs eg, amitriptyline and other tricyclic antidepressants or fluoxeine (can include lots others two but these are the most commons)