Hyponatraemia

Question 1

Causes with hypovolaemia

Answer 1

• Diarrhoea
• Vomiting
• Burns
• Sepsis
• Pancreatitis
• Diuretics
• Addisons

Question 2

Causes with euvolaemia

Answer 2

• SIADH

- Severe hypothyroidism

Question 3

Causes with hypervolaemia

Answer 3

• Cardiac failure
• Renal failure
• Hepatic failure and cirrhosis
• Nephrotic syndrome

Question 4

Investigations (plasma osmolality)

Answer 4

• If normal or raised consider pseudohyponatraemia due to high lipids, proteins or glucose
• If low consider true causes of hyponatraemia

Question 5

Investigations (urine osmolality and urine Na)

Answer 5

• High urine osmolality and urinary Na >30mmol/l consider diuretics, renal failure, addisons and SIADH
• High urine osmolality and urinary Na <30mmol/l consider heart failure, liver cirrhosis, nephrotic syndrome, diarrhoea and vomiting

Question 6

Management

Answer 6

• Address the underlying causes
• Considering stopping any causative medications
• Hypervolaemic and euvolaemic patients - fluid restriction
• Hypocolaemic patients - infusion of 0.9% sodium chloride
• Emergency situations - hypertonic saline may be used

NB - Remember to correct slowly (usually no more than 10mmol/l per day)