Hyponatraemia Flashcards
Normal serum sodium range?
133-146mmol/l
What is osmolality?
Measure of overall no. of solute particles in a fluid.
What is the equation to work out serum osmolality?
(2 x serum [sodium]) + [urea] + [glucose]
When someone has hyponatraemia what is the first thing that needs to be calculated to identify cause?
Serum osmolality
What are the potential causes of hyponatraemia with high serum osmolality? (3)
Hypergylcaemia,
Alcohol,
Mannitol
What are the potential causes of hyponatraemia with normal serum osmolality? (1)
Pseudohyponatraemia (lipaemia/ hyperproteinaemia)
What are the potential causes of hyponatraemia with low serum osmolality? (2)
Salt loss or water overload
What to assess and how to assess the cause of hyponatraemia with low serum osmolality?
Assess ECF volume:
Assess this by lying/ standing blood pressure
What to assess when:
Hyponatraemia,
Low serum osmolality,
Low ECF volume
Urine Sodium levels
Cause of hyponatraemia in:
Low serum osmolality,
Low ECF volume,
Low Na urine levels
(2)
(h: due to digestive system)
Diarrhoea,
Vomiting
Cause of hyponatraemia in:
Low serum osmolality,
Low ECF volume,
High Na urine levels
(4)
(h: due to renal excretion)
Diuretics,
Adrenal insufficiency,
Cerebral salt wasting syndrome,
Salt-wasting nephropathy
What to assess when:
Hyponatraemia,
Low serum osmolality,
Normal ECF volume
Urine osmolality
Cause of hyponatraemia in:
Low serum osmolality,
Normal ECF volume,
High urine osmolality
(1)
Syndrome Inappropriate Antidiuretic Hormone (SIADH)
Cause of hyponatraemia in:
Low serum osmolality,
Normal ECF volume,
Low urine osmolality
(1)
Water intoxication
Cause of hyponatraemia in:
Low serum osmolality,
High ECF volume,
(3)
(h: oedema)
CCF,
Liver failure,
Nephrotic syndrome
Criteria for diagnosis of SIADH?
- Hyponatraemia with hypo-osmolality,
- Inappropriate urinary concentration
- Elevated urinary sodium
- Absence of clinical evidence of volume depletion or overload
- Normal renal function
- Absence of hypothyroidism, glucocorticoid deficiency and recent diuretic therapy
Causes of SIADH?
h: 4 classes of causes
Neoplasia:
- Bronchial carcinoma
- Lymphoma
- Pancreatic cancer
- Mesothelioma
Neurological:
- Head injury
- Meningitis
- Subdural haematoma
- Subarrachnoid haemorrhage
- Neurosurgery
Respiratory:
- Pneumonia
- Tuberculosis
- Lung abscess
Drugs:
- Carbamazepine
- Cyclophosphamide
- Ecstasy
- NSAIDs
- TCAs
- Phenothiazines
- SSRIs
Management of SIADH
Treat underlying cause
Fluid restriction if asymptomatic (1L/day)
Tolvaptan
If asymptomatic with Na <115 can consider hypertonic saline with frusemide to prevent circulatory overload
