SIADH Flashcards
What does SIADH stand for?
Syndrome of inappropriate ADH
What is SIADH?
Inappropriately large amounts of ADH secreted/released
water reabsorbed in CD, Dilute euvolemia
SIADH is the over diagnosed cause of?
Hyponatremia
Why does SIADH cause hyponatremia?
Excess ADH = more water retention = compensatory Na+ excretion to maintain euvolemia
Main 3 Causes of SIADH?
Tumour (sclc)
Trauma to head
Infection: TB, Pneumonia, Meningitis
Other causes of ‘SIADH’
SCLC
Infection/immunosuppressed
Abscesses
Drugs - SSRIs, carbamazepine, sulfonylureas
Head trauma
Pathology of SIADH
Increased ADH independent of RAAS,
vessel vasoconstriction (high BP)
APoII Expression of CD so high Blood volume by water retention
Excess H20 retained means more dilute blood and more Na+ loss
Sx of SIADH
Hyponatremia (similar to dehydration Sx)
Vomiting, low GCS, muscle weakness
Low Na+ = Seizures, neurological complications, BRAIN STEM HERNIATION
How can brain stem herniation occur?
Low Na+ means compensatory H20 enters skull and increases ICP
Causes hyponatremia encephalopathy
Risk of brain stem herniating through foramen magnum (tentorial herniation)
Dx of SIADH?
Low Na+ and NORMAL K+
High urine osm as concentrated urine and diluted blood
What is a Ddx?
Na+ depletion (salt)
What would you give as a Tx for Na+ depletion?
0.9% saline
What would be seen after Tx if it was Na depletion or SIADH?
Na+ = Serum will normalise
SIADH = Serum fails to normalise
Tx?
Fluid restriction + hypertonic saline (concentrate blood)
Treat underlying cause (eg, tumour excision may fix SIADH)
What drugs to give for chronic cases?
Furosemide
Vasopressin (ADH) antagonist - Tolvaptan
Demeclocycline (treat infections)
