Hyponatraemia

Question 1

What are the two main reasons for hyponatraemia?

Answer 1

Sodium depletion
excess water

Question 2

What often causes a pseudohyponatraemia?

Answer 2

hyperlipidaemia (increase in serum volume)

OR taking blood from a drip arm

Question 3

If urine sodium is >20 and a patient is thought to be hypovolaemic, what could be repsonsible for the hyponatraemia?

Answer 3

• diuretics: thiazides, loop
• Addison’s disease
• diuretic stage of renal failure

Question 4

If urine sodium is >20 and a patient is thought to be euvolaemic, what could be repsonsible for the hyponatraemia?

Answer 4

• SIADH (urine osmolality > 500 mmol/kg)
• hypothyroidism

Question 5

If urine sodium is <20 what could be causing the hyponatraemia?

Answer 5

Na loss via:
- diarrhoea/vomiting/sweating/ burns

Water excess (hypervolaemia)
- secondary hyperaldosteronism
- nephrotic syndrome
- IV dextrose
- psychogenic polydipsia

Question 6

After what time period is a hyponatraemia defined as “Chronic”?

Answer 6

48 hours

Question 7

How do we treat a hyponatraemia?

Answer 7

If hypovolaemic
- IV saline

If euvolaemic
- fluid restrict
- consider “vaptan” medications

If hypervolaemic
- fluid restrict
- consider “vaptans”/loop diuretics

Question 8

What is the mechanism of action of “vaptans”?

Answer 8

V2 receptor antagonists
=> causes selective water diuresis but spares electrolytes.

Question 9

What severe complication can occur if hyponatraemia is corrected too quickly?

Answer 9

Osmotic demyelination syndrome (central pontine myelinolysis)

(MAX increase 4 to 6 mmol/l in a 24-hours)

Question 10

How long does it take for sypmtoms of central pontine myelinolysis to appear? And hw long do they last?

Answer 10

• 2 days
• symptoms usually irreversible

Question 11

Describe the symptoms experienced in central pontine myelinolysis

Answer 11

dysarthria
dysphagia
paraparesis or quadriparesis
seizures
confusion
coma