SIADH Flashcards
define SIADH?
characterised by continued secretion of ADH, characterised by hyponatraemia secondary to the dilutional effects of excessive water retention
what are causes of SIADH?
Malignancy • small cell lung cancer • also: pancreas, prostate Neurological • stroke • subarachnoid haemorrhage • subdural haemorrhage • meningitis/encephalitis/abscess Infections • tuberculosis • pneumonia Drugs • sulfonylureas* • SSRIs, tricyclics • carbamazepine • vincristine • cyclophosphamide Other causes • positive end-expiratory pressure (PEEP) • porphyrias • alcohol withdrawl
summarise the epidemiology of SIADH?
• Hyponatraemia is the MOST COMMON electrolyte imbalance seen in hospital
what are the presenting symptoms of SIADH?
- Mild hyponatraemia may be ASYMPTOMATIC
- Headache
- Nausea/vomiting
- Muscle cramp/weakness
- Irritability
- Confusion
- Drowsiness
- Convulsions
- Coma
- Symptoms of underlying cause
signs of SIADH on physical examination?
• MILD hyponatraemia - no signs
• SEVERE hyponatraemia:
o Reduced reflexes
o Extensor plantar reflexes
what investigations should be undertaken for SIADH?
o Low serum sodium
o Creatinine (check renal function)
o Glucose, serum protein and lipids
what is pseudohyponatraemia?
when the sodium concentration is actually normal but is erroneously reported as being low because of the presence of either hyperlipidaemia or hyperproteinaemia
what investigation results will confirm SIADH?
o Low plasma osmolality
o Low serum Na+ concentration
o High urine osmolality
o High urine Na+
management plan for SIADH?
- Fluid restriction
- Vasopressin receptor antagonists
- In SEVERE cases - slow IV hypertonic saline and furosemide with close monitoring
when does central pontine myelinolysis occur ?
occurs with rapid correction of hyponatraemia
what is central pontine myelinolysis characterised by?
- Quadriparesis
- Respiratory arrest
- Fits
prognosis for SIADH?
- Depends on the CAUSE
- Na+< 110 mmol/L is associated with a HIGH MORBIDITY and MORTALITY
- 50% mortality with central pontine myelinolysis