Hyponatraemia Flashcards
What is the definition of hyponatraemia?
Serum Na <135meq/L
Commonly result of intake and retention of water
Name some causes of hyponatraemia with high ADH
Hypovolaemia - Burns, D+V, thiazide diuretics
Hypervolaemia - liver cirrhosis, heart failure (hypertonic fluid leaks out)
SIADH, MDMA, Hypothyroid, Pregnancy
Name some causes of hyponatraemia with appropriate suppression of ADH (→ADH low)
Renal Failure
Primary polydipsia
Name some causes of hyponatraemia with high/normal serum osmolality
Renal failure - uraemic solutes compensate
Mannitol therapy (osmotic sugar - to reduce raised ICP)
Marked hyperglycaemia, DKA
Pseudohyponatraemia - Severe hyperlipidaemia, para-proteinaemia
What is exercised induced hyponatraemia?
Increased water intake, ADH stimulation by exercise - decreased osmolality not be enough to suppress ADH secretion
What are the clinical manifestations of hyponatraemia?
Nausea and confusion,
Headache and lethargy
Convulstions and coma
Severity reflects cerebral oedema
What investigations would be done for hyponatraemia?
Serum osmolality - Low in most patients, but can be normal/high
Urine osmolality - usually high, low in polydipsia/beer drinkers
Urinary Na concentration - normally low, high in SIADH
What is a cause for dilutional hyponatraemia?
Excessive release of ADH in SIADH
How is SIADH diagnosed?
Low serum osmolality, low serum Na
Low blood urea
High urine osmolality, high urinary Na
normal acid/base balance
normal adrenal and thyroid function
How is hyponatraemia managed?
Treat underlying cause
Fluid restriction - below level of urine output
Salt replacement - oral tablets, isotonic saline (only in volume depletion), hypertonic saline in SIADH
Loop diuretics
Tolvaptam - Vasopressin R Antagonist
What are the choices of therapy for the following:
Mild hyponatraemia
Moderate hyponatraemia
Severe hyponatraemia
Mild → Asymptomatic = Fluid restriction
Moderate → Confusion, forgetfulness, drowsiness = Fluid restriction + Salt replacement
Severe → convulsions = +hypertonic saline + vasopressin antagonist
Why must the use of Tolvaptam need to be carefully monitored?
Tolvaptam is a vasopressin receptor antagonist, rapid correction of hyponatraemia can → osmotic demyelination syndrome
12-20mmol/L of Na/day
What is osmotic demyelination syndrome?
Develops with rapid correction of severe hyponatraemia
Paralysis, dysphagia, dysarthria etc.
Rapid correction → Hypertonic ECF → fluid leaks out
When is it safe to correct hyponatraemia?
Acute hyponatraemia - <48 hours
