SIADH Flashcards
What is SIADH?
Syndrome of inappropriate ADH secretion
Continuous secretion of ADH despite plasma being very dilute
What is the pathophys?
Xs release of ADH = higher water reabsorption/retention = dilute blood plasma
Dilute plasma = decrease in aldosterone release = more Na lost in urine = HYPONATRAEMIA
What are the 2 roles of ADH?
Works on distal convoluted tubule and collecting duct = increases aquaporin availability = more water reabsorbed = dilute water
Constricts blood vessels (vasopressin)
What are the causes?
Malignancy:
SCLC ectopic ADH
Neuro:
Stroke, SAH, subdural haemorrhage, meningitis
Infections:
TB, pneumonia
Meds:
Sulfonylureas, SSRIs, TCA, carbamazepine, cyclophosphamide
How does it present?
Presents with sx/signs of hyponatraemia
What are the sx/ signs of hyponatraemia?
Headache, N/V, myalgia, tremor
Cerebral oedema:
Confusion, mood swings
Severe = fits, coma, death
What level of serum Na suggest hyponatraemia?
And what is severe hyponatraemia?
<130 mmol/L
<115 mmol/L
What are urine Na levels?
> 30 mmol/L
How is it dx?
U&E
Urinalysis
Concentrated urine (Na >20mmol/L and osmolality > 100mosmol/kg)
In the presence of hyponatraemia (plasma Na <125mmol/L) and low plasma osmolality (< 260mosmol/kg)
In the absence of hypovolaemia, oedema, or diuretics.
What is important to consider in elderly patients?
Hyponatraemia is common during illness and in frail alderly pts
Difficult to distinguish SIADH from salt and water deprivation
To do so:
Give trial of 1-2L 0.9% saline
Na depletion will respond to this, whereas SIADH won’t
How is it mx?
Slow correction to not precipitate central pontine myelinolysis!!!!
Fluid restriction: 500-1000ml/24h
Hypertonic saline + furosemide
Demeclocycline - reduces the responsiveness of the collecting tubule cells to ADH
TOLVAPTAN - vasopressin receptor antagonist
What does aldosterone do?
Regulates salt + water in body
Increase aldosterone = retention of Na/ water, loss of K in urine
Decrease aldosterone = retention of K, loss of Na/water in urine
