Syndrome of Inappropriate ADH Flashcards
Where is ADH produced?
Hypothalamus & secreted by posterior pituitary
ADH AKA?
Vasopressin
What does ADH do?
Stimulates water reabsorption from CDs in kidneys
What is SIADH?
Condition where there is inappropriately large amounts of ADH
What does inappropriately large amounts of ADH result in?
XS-ive water reabsorption in CD’s
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Resulting in hyponatraemia, but water not usually enough to cause fluid overload therefore euvolemic hyponatraemia
Urine osmolality and urine sodium of patients with SIADH?
High urine osmolality
High urine sodium
General cause of SIADH?
Result of posterior pituitary secreting too much ADH or ADH may be coming from somewhere else eg sclc
Causes of SIADH?
- Post-operative from major surgery
- Infection (atypical pneumonia/lung abscesses)
- Head injuries
- Meds
- Malignancy
- Meningitis
Meds which can cause SIADH?
Thiazide diuretics Carbamazepine Vincristine Cyclophosphamide Antipsychotics SSRIs NSAIDs
Presnetation of SIADH?
- Headache
- Fatigue
- Muscle aches and cramps
- Confusion
- Severe hyponatraemia leading to seizures
Initial diagnosis of SIADH?
Almost a diagnosis of exclusion
- Clinical exam shows euvolaemia
- U&Es show hyponatraemia
- Urine Na and osmolality will be high
Excluding causes of hyponatraemia by?
- Negative short synacthen test (excludes adrenal insufficiency)
- No history of diuretic use
- No diarrhoea, burns, fistula or XSive sweating
- No XSive water intake
- No CKD or AKI
What does a negative short synacthen test rule out?
Adrenal insufficiency
Establishing cause of SIADH?
CXR= 1st line for pneumonia, abscesses, lung cancer
If malignancy is sus= CT thorax/abdomen & pelvis & MRI brain
Management of SIADH?
Establish and treat cause
- Essential to correct Na slowly to prevent central pontine myelinolysis
- Fluid restriction
- Tolvaptins & ADH receptor blockers
- Demeclocycline
Rules when correcting Na in SIADH?
GO SLOW
-Aim for change in Na <10mmol/L/24Hours
TO PREVENT CENTRAL PONTINE MYELINOLYSIS
Restrict fluids to?
500mls-1Litre
Drugs for SIADH?
Tolvaptins & ADH receptor blockers: RAPID increase in Na
Demeclocycline: Tetracycline AB which inhibits ADH
What is central pontine myelinolysis AKA?
Osmotic demyelination syndrome
What is ODS usually caused by?
Complication f long term severe hyponatraemia (120
What happens as blood Na decreases?
H2O will move by osmosis across BBB to cells to brain, causing brain swelling
How does brain adapt to brain swelling when Blood Na decreases?
Reducing solutes in brain cells
This takes a few days but results in chronic hyponatraemia
Osmolality and Na in CPM?
LOW osmolality
LOW Na
What occurs when Na rapidly rises?
Water shifts out of brain causing 2 phases
1st phase of CPM?
- Due to electrolyte imbalance
- Encephalopathic and confused
- Symptoms - Headache, N/V
2nd phase of CPM?
Due to demyelination of neurones especially in pons
- Few days after rapid Na correction
- May present as spastic quadriparesis, pseudobulbar palsy and cognitive behavioural changes
Prevention of CPM is essential as there isn’t really treatment. True or false?
TRUE
Management = supportive
