Sodium Imbalance

Question 1

Normal sodium range?

Answer 1

135-145 mmol/L

Question 2

What is hyponatraemia and what is it caused by?

Answer 2

Water problem of decreased sodium

Caused by too much ADH - either by physiological response or inappropriate secretion

Question 3

3 areas of cause of hyponatraemia?

Answer 3

Hypovolaemia
Euvolaemia
Hypervolaemia

Question 4

Signs of hypovolaemia (dry patient)?

Answer 4

Postural hypotension
Dry mucous membranes
Tachycardic
- reduced turgor (skin goes back to normal more slowly after being pulled, this is a late sign)

Question 5

Signs of hypervolaemia (wet patient)?

Answer 5

Peripheral oedema
Raised JVP
(fluid overload signs)

Question 6

If signs of hypo/hypervolaemia are absent, what can you assume about the volume status of the patient?

Answer 6

They are euvolaemic

Question 7

Mechanism for hypovolaemia to cause hyponatraemia?

Answer 7

Drop in BP detected by the hypothalamus - causes more ADH to be secreted in order to absorb more water (remember that blood sodium is measured as a concentration thus when more water is absorbed without associated sodium reabsorption, the total sodium concentration goes down and causes hyponatraemia)

Question 8

Causes of hypovolaemia (and thus hypovolaemic hyponatraemia)?

Answer 8

Diarrhoea
Vomiting
Diuretics

Question 9

Investigation findings in hypovolaemia?

Answer 9

Clinically hypovolaemic
Low urine sodium (decreased volume will cause kidneys to retain sodium)
- measure with patient off diuretics if they’re on them (low urine Na off diuretics = hypovolaemia)

Question 10

Euvolaemic causes of hyponatraemia?

Answer 10

Hypothyroidism
Hypoadrenalism
SIADH (pneumonia/cancer)

Question 11

Investigations for cause(s) in euvolaemic hyponatraemia?

Answer 11

TFTs
Short synACTHen test
Drug review, breast examination, CXR, brain MRI

Question 12

Hypervolaemic causes of hyponatraemia?

Answer 12

Heart failure
Cirrhosis
Nephrotic syndrome

Question 13

Investigations for cause(s) in hypervolaemic hyponatraemia?

Answer 13

Urine sodium low

- will cause increased aldosterone secretion to try to retain Na

Question 14

Mechanism of hypervolaemic cause of hyponatraemia?

Answer 14

Total body salt goes up, but total body water/fluid content goes disproportionately up, such that (again, remember that sodium measured by concentration) blood becomes diluted = hyponatraemia

Question 15

Euvolaemic hyponatraemia investigation pathway?

Answer 15

1 - TFTs
2 - Short synACTHen for adrenal insufficiency
3 - SIADH (drugs causing it, breast exam, CXR for lung pathology, brain MRI for CNS pathology)

Question 16

Management of hyponatraemia?

Answer 16

Treatment of the cause - different if severe (separate card)

Question 17

Symptoms of severe hyponatraemia?

Answer 17

Seizures

Loss of/decreased consciousness

Question 18

Management of severe hyponatraemia and specific complication?

Answer 18

Slow hypertonic saline

• must NOT exceed 10mmol/L in the first 24 hours
• risks central pontine myelinolysis

Question 19

Causes of hypernatraemia?

Answer 19

- water loss or excess retention not matched by increased water intake
Vomiting
Diarrhoea
Diabetes insipidus
Primary aldosteronism

Question 20

Presentation of hypernatraemia?

Answer 20

Lethargy
Irritability
Thirst
Signs of dehydration
Confusion
Coma
Fits

Question 21

Management of hypernatraemia?

Answer 21

Replace water loss

Question 22

Absolutely CRITICAL principle about hyponatraemia?

Answer 22

EUVOLAEMIC hyponatraemia = ENDOCRINE cause

hypothyroid, hypoadrenal, SIADH