SIADH Flashcards
Define SIADH
Plasma vasopressin/ADH concentration is inappropriately high for the existing plasma osmolality
Characterised by hypotonic hyponatraemia, concentrated urine and a euvolemic state. In the absence of stimuli for secretion e.g. raised osmolality or reduced blood volume.
Aetiology of SIADH
Malignancy: small-cell lung, pancreas, prostate, thymus, lymphoma
CNS disorders: Meningoencephalitis, abscess, stroke, SA/SDH, head injury, SLE
Chest disease: TB, pneumonia, abscess, aspergillosis, small-cell lung
Endocrine disease: Hypothyroidism, Addison’s
Drugs: SSRI, TCA, PPI, carbamazepine, opiates, omeprazole
Other: Acute intermittent porphyria, trauma, major abdominal or thoracic surgery, HIV
Symptoms and signs of SIADH
Mild hyponatraemia: asymptomatic
<120: generalised weakness, poor mental function
<110: confusion, coma, death
Nausea and vomiting (brain oedema?)
Altered mental status
Headache
Muscle cramp/weakness
Irritability
Confusion
Drowsiness
Seizure
Coma
Investigations for SIADH
Urinalysis:
- Osmolality raised >100 mOsm/kg H₂O
- Sodium raised >30 mmol/L
Serum osmolality: Reduced <275 mmol/kg (<275 mOsm/kg) H₂O
U&Es: Hyponatraemia, Urea <3.6
TFTs: NORMAL
Short SynACTHen test: NORMAL
CT CAP/head
CXR
What is the criteria for SIADH diagnosis
- Low serum osmolality and sodium
- High urine osmolality and sodium
- Absence of renal failure, hypovolaemia, hypotension, oedema, renal failure
- Absence of Addison’s
- Absence of hypothyroidism
Management of SIADH
- Stop any offending drugs
- Fluid restriction (1L/day)
- Severe: Consider hypertonic saline ± diuretic
a. 3x normal saline followed by second bolus
Treat underlying cause
± vaptans, demeclocycline
Complications of SIADH
Convulsions
Coma
Death
Central pontine myelinolysis (Na corrected >8mmol/L in 24hrs)
Prognosis of SIADH
Depends on underlying cause
High morbidity and mortality if Na+ <110,mol/L
Up to 50% mortality with central pontine myelinolysis
