Sodium Balance

Question 1

What is the most common electrolyte imbalance in hospital?

Answer 1

Hyponatraemia

Question 2

What is the boundary for hyponatraemia?

Answer 2

<135mmol/L

Question 3

What is the underlying pathogenesis of hyponatraemia?

Answer 3

Increased extracellular water

Question 4

Which hormone controls water balance?

Answer 4

ADH (vasopressin) water retention via AQ2

Question 5

What do V1 and V2 receptors do?

Answer 5

V1: AQ2 in CD
V2: Vasc. smooth muscle, vasoconstriction

Question 6

What are the two main stimuli for ADH secretion?

Answer 6

High Serum osmolality (hypothalamic osmoreceptors)

Low Blood volume/ pressure (Mediated by baroceptors in carotids/ atria/ aorta)

Question 7

What is the effect of increased ADH secretion on serum sodium?

Answer 7

Hyponatraemia

Question 8

What does increased water reabsorption cause?

Answer 8

Reduced sodium concentration in the blood

Question 9

What is the first step in the clinical assessment of a patient with hyponatraemia?

Answer 9

Assess volume status: Hypo/ Eu/ Hypervolaemic

Question 10

What are the clinical signs of hypovolaemia?

Answer 10

Tachycardia
Postural hypotension
Dry mucous membranes
Reduced skin turgor
Confusion/drowsiness
Reduced urine output
Low urine Na+ (<20) (most reliable)

Question 11

What are the clinical signs hypervolaemia?

Answer 11

Raised JVP
Bibasal crackles (on chest examination)
Peripheral oedema

Question 12

What are the causes of hypovolaemic hyponatraemia?

Answer 12

GI/renal loss:
Diarrhoea
Vomiting
Diuretics
Salt losing nephropathy

Question 13

What are the causes of euvolaemic hyponatraemia?

Answer 13

Endocrine:
Hypothyroidism
Adrenal insufficiency
SIADH

Question 14

What are the causes of hypervolaemic hyponatraemia?

Answer 14

Failures:
Cardiac Failure
Cirrhosis
Nephrotic syndrome

Question 15

What are the causes of SIADH?

Answer 15

CNS pathology

Lung pathology

Drugs (SSRI, TCA, opiates, PPIs, carbamazepine)

Tumours

Surgery

Question 16

How might you investigate the euvolaemic causes of hyponatraemia?

Answer 16

Thyroid: TFTs
Renal insufficiency: Short Synacthen test
SIADH: Plasma & urine osmolality (low plasma & high urine osmolality)

Question 17

How do you diagnosis SIADH?

Answer 17

No Hypovolaemia
No Hypothyroidism
No Adrenal insufficiency
Reduced plasma osmolality AND
Increased urine osmolality (>100)

Question 18

How would you manage a hypovolaemic patient with hyponatraemia?

Answer 18

Volume replacement with 0.9% saline

Question 19

How would you manage a hypervolaemic patient with hyponatraemia?

Answer 19

Fluid restriction 500ml-1hr/24 hr

Treat the underlying cause

Question 20

How would you manage a euvolaemic patient with hyponatraemia?

Answer 20

Fluid restriction 500ml-1hr/24 hr

Treat the underlying cause

Question 21

What happens/ how do you manage in severe hyponatraemia?

Answer 21

Reduced GCS
Seizures
Seek expert help (Treat with Hypertonic 2.75-3% saline)

Question 22

What is the most important point to remember while correcting hyponatraemia?

Answer 22

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

Risk of osmotic demyelination (central pontine myelinolysis)
quadriplegia, dysarthria, dysphagia, seizures, coma, death

Question 23

How do you treat SIADH (With drugs)?

Answer 23

Demeclocycline

Tolvaptan

Question 24

How does Demeclocycline work?

Answer 24

Reduces responsiveness of collecting tubule cells to ADH

Monitor U&Es (risk of nephrotoxicity)

Question 25

How does Tolvaptan work?

Answer 25

V2 receptor antagonist

Question 26

What is the boundary for hypernatraemia?

Answer 26

>145 mmol/L

Question 27

What are the main causes of hypernatraemia?

Answer 27

Unreplaced water loss (GI loss/ renal loss, sweat, DI) Cannot control water intake (child/ elderly)

Question 28

What investigations would you order in a patient with suspected diabetes insipidus?

Answer 28

Serum glucose (exclude diabetes mellitus) Serum potassium (exclude hypokalaemia) - causes ADH resistance Serum calcium (exclude hypercalcaemia) - causes ADH resistance Plasma high & urine low osmolality Water deprivation test

Question 29

How would you treat hypernatraemia?

Answer 29

``` Fluid replacement (dextrose) Treat the underlying cause ```

Question 30

How do you manage hypernatraemia in hypovolaemic patients?

Answer 30

5% dextrose (correct water deficit) 0.9% saline (correct EC fluid volume depletion) Measure Na every 4-6 hours

Question 31

What are the effects of diabetes mellitus on serum sodium?

Answer 31

Variable

Question 32

What may happen in DM which changes serum sodium?

Answer 32

Hyperglycaemia draws water out of the cells leading to hyponatraemia Osmotic diuresis in uncontrolled diabetes leads to loss of water and hypernatraemia

Question 33

What does increased osmolality cause other than a release of ADH?

Answer 33

Thirst

Question 34

Why does vomiting cause hyponatraemia?

Answer 34

Vomiting causes blood volume drop which stimulates water retention which dilutes sodium in the blood

Question 35

What is the most reliable clinical sign of hypovolaemia?

Answer 35

Low urine sodium (<20)- needs to be assessed ASAP

Question 36

Is urine sodium low in hypervolaemia?

Answer 36

Yes- hyperaldosteronism caused by HF etc. causes sodium retention

Question 37

Why does hypothyroidism cause hyponatraemia?

Answer 37

Reduced BP (contractility/ HR) causes more ADH

Question 38

How long does it take for symptoms to arise in central myelinolysis?

Answer 38

A few days- if they look fine after a day and the sodium has jumped up by 20 mmol/L in one day- THEY ARE NOT FINE and you MUST bring it back down

Question 39

When does central myelinolysis happen?

Answer 39

When sodium jumps up more than 8-10 mmol/L

Question 40

How often should sodium be checked?

Answer 40

Every 2-4 hours

Question 41

How does SIADH have high sodium in urine?

Answer 41

SIADH causes expansion of atria which releases natriuretic peptides This causes natriuresis (loss of sodium into the urine)

Question 42

What is water?

Answer 42

'5% dextrose is water' ????

Question 43

What is pseudohyponatraemia?

Answer 43

Low Na, normal osmolality and caused by change in proteins/ lipids )e.g. paraproteinaemia)