Hyponatraemia

Question 1

Normal sodium range

Answer 1

136 - 145 mol/l

Question 2

Symptoms of hyponatraemia

Answer 2

Asymptomatic 
Lethargy 
Headaches 
Dizziness 
Postural hypotension 
Ataxia 
Severe changes(confusion, seizures, comas)

Question 3

What is osmolality

Answer 3

Osmoles of solute in kg of solvent

Question 4

What is osmolarity

Answer 4

Osmoles of solute in litre of solution

Question 5

Causes of dehydration leading to low sodium

Answer 5

Diuretics 
Adrenal insufficiency 
Sweating 
Diarrhoea 
Vomiting 
Burns

Question 6

Causes of euvolaemic hyponatraemia

Answer 6

SIADH

H2O intoxication

Question 7

Causes of oedematous hyponatraemia

Answer 7

CCF

Hypoalbuminaemia secondary to liver disease, nephrotic syndrome, inflammation

Question 8

Causes of SIADH

Answer 8

Small cell lung cancer causing release of ADH
Atypical pneumonia(legionella)
Brain damage(meningitis/SAH)
Drugs(Carbamazepine/SSRIs)

Question 9

Management of SIADH

Answer 9

Restrict fluid intake
Treat underlying cause of SIADH such as pneumonia
Captains(tolvaptan) - competitive ADH receptor antagonists

Question 10

What is central pontine myelinolysis

Answer 10

Occurs when sodium is corrected too quickly which causes demyelination of nerve cells

Question 11

Presentation of central pontine myelinolysis

Answer 11

Acute paralysis
Speech problems
Swallowing problems

Question 12

Definition of acute hyponatraemia

Answer 12

develops over a period of < 48 hours

Question 13

Definition of chronic hyponatraemia

Answer 13

develops over a period > 48 hours

Question 14

Def of mild hypontraemia

Answer 14

mild: 130-134 mmol/L

Question 15

Def of moderate hyponatraemia

Answer 15

moderate: 120-129 mmol/L

Question 16

Def of severe hyponatraemia

Answer 16

severe: < 120 mmol/L

Question 17

Initial steps in management of all cases of hyponatremia

Answer 17

exclude a spurious result (e.g. blood taken from a drip arm)

review medications that may cause hyponatraemia

Question 18

Management of chronic hyponatraemia if a hypovolemic cause is suspected

Answer 18

isotonic, saline (0.9% NaCl)
this may sometimes be given as a trial

if the serum sodium rises this supports a diagnosis of hypovolemic hyponatraemia
if the serum sodium falls an alternative diagnosis such as SIADH is likely

Question 19

Management of hyponatremia if a euvolemic cause is suspected

Answer 19

fluid restrict to 500–1000 mL/day
consider medications:
demeclocycline
vaptans

Question 20

Management of hyponatraemia if a hypervolemic cause is suspected

Answer 20

fluid restrict to 500–1000 mL/day
consider loop diuretics
consider vaptans

Question 21

Management of acute hypontraemia with severe symptoms

Answer 21

Hypertonic saline (typically 3% NaCl)

Question 22

How does vasopressin work in SIADH

Answer 22

act primarily on V2 receptors - antagonism of V2 receptors results in selective water diuresis, sparing the electrolytes

Question 23

In which patients should vasopressin be avoided in

Answer 23

Hypovolemic hyponatremia

Can also be hepatotoxic so should be avoided in patients with underlying liver disease