Sodium and Fluid Balance

Question 1

What is normal sodium?

Answer 1

135-145 mEq/L

Question 2

How is water retained?

Answer 2

ADH upregulates aquaporin-2

Question 3

What are stimuli for ADH release?

Answer 3

Increased osmolality

Decreased pressure on the baroreceptors

Question 4

What is the difference between V1 and V2 receptors?

Answer 4

V2 are on the collecting duct

V1 is on smooth muscle

Question 5

What do you examine in a fluid exam?

Answer 5

Hands

Neck

Peripheral oedema

Question 6

What are some clinical signs of hypovolaemia

Answer 6

Tachycardia

Postural hypotension

Dry mucous membranes

Reduced skin turgor

Confusion/drowsiness

Reduced urine output

Low urine Na+ (<20)

Question 7

How long do you need to wait before measuring urine Na+ for a patient who is on diuretics?

Answer 7

48 hours after stopping the diuretics

Question 8

What are some clinical signs of hypervolaemia?

Answer 8

Raised JVP

Bibasal crackles

Peripheral oedema

Question 9

What are causes of hyponatraemia in a hypovolaemic patient?

Answer 9

Renal: Drugs (within weeks not years), Salt losing neuropathy

Extra-renal: diarrhoea, vomiting (losing water and salt but ADH absorbs water and not sodium)

Question 10

What are causes of hyponatraemia in a hypervolaemic patient?

Answer 10

Cardiac failure: Excess ADH, reduced CO, low blood volume, ADH secretion

Cirrhosis: Low blood volume stimulates vasodilation, less BP

Nephrotic syndrome/renal failure

Question 11

What are causes of hyponatraemia in a euvolaemic patient?

Answer 11

Hypothyroidism

Adrenal insufficiency

SIADH

Question 12

What are causes of SIADH?

Answer 12

CNS pathology - Stroke, tumour, abscess

Lung pathology - Penumonia, lung cancer, pneumothorax

Drugs - SSRI, TCA, opiates, PPIs, carbamazepine

Tumours

Surgery

Question 13

What is the management for hypovolaemic hyponatraemia?

Answer 13

Volume replacement with 0.9% saline

Remove stimulus for ADH secretion

Question 14

What is the management for euvolaemic hyponatraemia?

Answer 14

Fluid restriction

Treat underlying cause e.g. test for SIADH, breast exam etc.

Question 15

What is the management for hypervolaemic hyponatraemia?

Answer 15

Fluid restriction

Treat the underlying cause (HF)

Question 16

What are symptoms of extreme hypovolaemia?

Answer 16

Reduced GCS

Seizures

Seek expert help (hypertonic 3% saline given as a bolus)

Question 17

Why must sodium be corrected slowly?

Answer 17

Serum Na+ must not be corrected >8-10 mmol/L in the first 24 hours

Risk of osmotic demyelination (central pontine myelinolysis) if too rapid

Question 18

What are the symptoms of increasing sodium too quickly?

Answer 18

Quadriplegia, dysarthria, dysphagia, seizures, coma, death

Question 19

What drugs can be used to treat SIADH?

Answer 19

Demeclocycline - reduces responsiveness of collecting tubule cells to ADH (risk of nephrotoxicity so monitor U+Es)

Tolvaptan - V2 receptor antagonist

Combination of salt and loop diuretic

Question 20

What are the main causes of hypernatraemia?

Answer 20

Unreplaced water loss

• Gastrointestinal losses, sweat losses (only if you don’t drink)
• Renal losses, osmotic diuresis, diabetes insipidus

Patient is not drinking

Question 21

What are tests for diabetes insipidus?

Answer 21

Serum glucose
Serum potassium
Serum calcium
Plasma + urine osmolality
Water deprivation test

Question 22

What are treatments for hypernatraemia?

Answer 22

Fluid replacement (water)
Treat the underlying cause