Hyponatraemia

Question 1

What is the definition of hyponatraemia?

Answer 1

Serum sodium <130mmol/L

Question 2

The causes of hyponatraemia can be divided into 4 classes. Name them.

Answer 2

1) Factitious ‘pseudohyponatraemia’; 2) Hypovolaemic; 3) Normovolaemia; 4) Hypervolaemic

Question 3

What conditions are associated with pseudohyponataemia?

Answer 3

Hyperglycaemia, hyperlipidaemia, hyperproteinaemia

Question 4

How do you correct the sodium for hyperglycaemia?

Answer 4

Adjust the serum sodium up by 1mmol/L for every 3 mmol/L elevation in blood sugar

Question 5

Name some causes of hypovolaemic hyponatraemia if the urinary sodium is >20 mmol/L

Answer 5

Renal causes including diuretics, Addison’s disease, salt-losing nephropathy, glycosuria, ketonuria

Question 6

Name some causes of hypovolaemic hyponatraemia if the urinary sodium <20 mmol/L

Answer 6

Extra renal losses such as vomiting, diarrhoea, burns, pancreatitis

Question 7

Name some causes of normovolaemic hyponatraemia if the urine osmolality > serum osmolality

Answer 7

SIADH d/t head injury, CVA, pneumonia, COPD, neoplasa, HIV infection, drugs inc. carbamazepine, NSAIDs and antidepressants; positive-pressure ventilation, porphyria

Question 8

Name some causes of normovolaemic hyponatraemia where the urine osmolality is less than the serum osmolality

Answer 8

Hypotonic post-operative fluids such as 5% dextrose or 4% dextrose 1/5 normal saline, TURP irrigation fluid, psychogenic polydipsia, ‘tea and toast diet’

Question 9

Name some causes of hypervolaemic hyponatraemia if the urinary sodium <20 mmol/L

Answer 9

Congestive cardiac failure, cirrhosis, nephrotic syndrome, hypoalbuminaemia, hepatorenal syndrome

Question 10

Name some causes of hypervolaemia hyponatraemia is the urinary sodium is > 20 mmol/L

Answer 10

Steroids, cerebral salt wasting , chronic renal failure, hypothyroidism

Question 11

Describe symptoms of hyponatraemia at different levels

Answer 11

Na > 125 mmol/L Usually asymptomatic
Na 115-125 mmol/L Lethargy, weakness, ataxia, vomiting
Na < 115 mmol/L Confusion, headache, convulsions, coma

Question 12

What is the first thing you do when assessing hyponatraemia?

Answer 12

Assess the volume status. Lok at skin turgor, JVP, measure lying and siting BP, listen for basal crackles

Question 13

What investigations would you like?

Answer 13

Bloods: FBC, U&E, LFTs, TFTs, serum osmolality. Urine: Sodium and osmolality. Other: ECG, CXR

Question 14

Describe management fo hyponatraemia

Answer 14

1. Commence high-flow oxygen by face mask
2. Asymptomatic pts: (i) Discontinue implicated drugs and treat underlying medical condition; (ii) Restrict fluid intake to 50% of estimated maintenance fluid requirements in SIADH (ie. around 750mls/day) (iii) Aim to increase the serum sodium gradually by 0.5 mmol/L per hour, to a maximum rate of 12 mmol/L per 24 h
   3) Get help is the pt has neurological signs: Administer 3% hypertonic saline to raise serum sodium by 1 mmol/hr. If pt develops seizures or coma, give 20% hypertonic saline 10-20ml by rapid IV infusion

Question 15

What can result if you replenish sodium levels too quickly?

Answer 15

Coma associated with osmotic demyelination syndrome or central pontine demyelinosis