Hyponatraemia

Question 1

Roughly what percentage of the healthy population have results within reference ranges?

Answer 1

~95%

Question 2

What two main reasons may a patient have hyponatraemia?

Answer 2

• Low serum sodium (Too little sodium)
• Fluid overload (Too much water!)

Depletional or Dilutional hyponatraemia

Question 3

What is a calculation for estimating serum osmolality?

Answer 3

Serum osmolality (mmol/kg) = 2 x serum [sodium] +[urea] + [glucose] (mmol/L)

Question 4

What is the best guide to whole body sodium status?

Answer 4

Lying/Standing Blood Pressure

Question 5

What are the two main ways someone may experience depletional hyponatraemia?

Answer 5

• Sodium loss in gut

- Sodium loss in kidneys

Question 6

What may a urine sodium sample tell you in hyponatraemia?

Answer 6

Whether low sodium is from losses in the gut or the kidneys

If sodium is loss from the gut, urine sodium will be low (RAAS system tries to preserve sodium

Question 7

In a hyponatraemic patient, give some potential causes that would explain a high urine sodium?

Answer 7

• Diuretics
• Adrenal insufficiency
• CSWS
• Salt-wasting nephropathy

Question 8

What conditions may have hyponatraemia and a high ECF volume?

Answer 8

CCF
Liver Failure
Nephrotic Syndrome

Question 9

What conditions may have hyponatraemia and be euvolaemic?

Answer 9

SIADH

Water intoxication

Question 10

In a euvolaemic patient with hyponatraemia, what would be a sign of SIADH?

Answer 10

Urine Osmolarity High (Very concentrated)

Question 11

List criteria for diagnosis of SIADH

Answer 11

• Hyponatraemia with hyo-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

Question 12

List some causes of SIADH

Answer 12

Neoplasia (Bronchial carcinoma, Lymphoma, Pancreatic cancer, Mesothelioma)

Respiratory (Pneumonia, tuberculosis, lung abscess)

Neurological (Head injury, Meningitis, Subdural haematoma, Subarachnoid haemorrhage, Neurosurgery)

Drugs (Carbamazepine, Cyclophos[hamide Ecstasy, NSAIDs, TCAs, Phenothiazines, SSRIs)

Question 13

What is the management of SIADH?

Answer 13

• Treat underlying cause
• If asymptomatic - Fluid restriction to 1L a day
• Can consider tolvaptan in certain cases

If symptomatic and Na<115
-Can consider hypertonic saline with frusemide to prevent circulatory overload, but need to avoid raising sodium too rapidly in view of risk of central pontine myelinolysis

Question 14

What is hydrocortisone used as a treatment to replace in adrenal insufficiency?

Answer 14

Cortisol

Question 15

What is fludrocortisone used as a treatment to replace in adrenal insufficiency?

Answer 15

Aldesterone