sodium

Question 1

What is the commonest electrolyte abnormality in hospitalized patients?

Answer 1

low na

Question 2

What is the commonest electrolyte abnormality in hospitalized patients?

Answer 2

low na

Question 3

what is hypona

Answer 3

<135

Question 4

common causes of low na

Answer 4

HF
renal failure
hypovolaemia

ie excess extracellular water

Question 5

which hormone controls water balance and how

Answer 5

ADH/vasopressin
act on V2 receptor in collecting duct
-> water retention through aquaporin-2 in distal part of tubule

V1 receptor on vascular smooth muscle -> vasoconstriction (higher conc)

Question 6

What are the two main stimuli for ADH secretion?

Answer 6

Serum osmolality (mediated by hypothalamic osmoreceptors detect the increase in osmolarity = more ADH secreted) – if it increases then you need to hang onto water

Blood volume/pressure (mediated by baroreceptors in carotids, atria, aorta) – BP drop detected by baroreceptors = more ADH release = more water resorption

Question 6

What are the two main stimuli for ADH secretion?

Answer 6

Serum osmolality (mediated by hypothalamic osmoreceptors detect the increase in osmolarity = more ADH secreted) – if it increases then you need to hang onto water

Blood volume/pressure (mediated by baroreceptors in carotids, atria, aorta) – BP drop detected by baroreceptors = more ADH release = more water resorption

Question 7

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

Answer 7

hypoNa

Question 8

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

Answer 8

Clinical assessment of volume status - hypo/er/euvolaemic
* Pulse
* Mucous membranes
* BP – lying and standing
* Tissue turgor – pinch skin
* Urine output
* Confusion

Question 9

What are the clinical signs of hypovolaemia?

Answer 9

Tachycardia
Postural hypotension
Dry mucous membranes
Reduced skin turgor
Confusion/drowsiness
Reduced urine output
Low urine Na+ less than 20 - most useful marker. Kidney best detector of hypovolaemia – hold onto water so less Na in urine and less urine. Note cant interpret if taking diuretics

Question 10

What are the clinical signs hypervolaemia?

Answer 10

Raised JVP
Bibasal crackles (on chest examination)
Peripheral oedema

Question 11

causes of hypoNa

Answer 11

hypovol - loss of na and water -> baroreceptor -> more ADH -> Increased water retention -> more water compared to salt

Question 12

causes of hypoNa in hypervol

Answer 12

Cardiac failure: reduced heatrt contractility – low BP detected by baroreceptor =- more ADH = more water = low Na

Cirrhosis: excess NO = low BP (vasodilator) = baroreceptor = more ADH more water

Renal failure: not excreting excess water

Question 13

What are the causes of hyponatraemia in a euvolaemic patient?

Answer 13

Hypothyroidism – less cardiac contractility, low bp
Adrenal insufficiency – less aldosterone, less cortisol
Syndrome of inappropriate ADH (SIADH) – released by tumour/drug – not a dx

Question 14

causes of SIADH

Answer 14

CNS pathology – tumour stroke
Lung pathology
Drugs (SSRI, TCA, opiates, PPIs, carbamazepine)
Tumours
Surgery

Question 15

ix in euvolaemic hypoNa

Answer 15

? Hypothyroidism: Thyroid function tests
? Adrenal insufficiency: Short Synacthen test or 9am cortisol
? SIADH: Plasma & urine osmolality (low plasma & high urine osmolality)

Question 16

why euvolaemic in SIADH

Answer 16

water redistributed, and don’t have Na resorption. Retain more water – lead to stretch of atria = natriatic peptide released = lose Na in urine

Question 17

dx of SIADH

Answer 17

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

Question 18

How would you manage a hypovolaemic patient with hyponatraemia?

Answer 18

Volume replacement with 0.9% saline (NaCl)
Removes stim for excess ADH – replacing the blood volume
If they have SIADH and give saline – they retain excess water and you make it worse

Question 19

How would you manage a hypervolaemic patient with hyponatraemia?

Answer 19

Fluid restriction
Treat the underlying cause

Question 20

How would you manage a euvolaemic patient with hyponatraemia?

Answer 20

Fluid restriction
Treat the underlying cause

Question 21

how do you treat severe hyponatraemia

Answer 21

med emergency
Reduced GCS
Seizures
Seek expert help (Treat with Hypertonic 3% (2.7%) saline) – only if reduced GCS or fitting because serum Na shouldn’t be corrected quickly

Question 22

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

Answer 22

Na must NOT be corrected > 8-10 mmol/L in the first 24 hours
Risk of osmotic demyelination (central pontine myelionlysis)
quadriplegia, dysarthria, dysphagia, seizures, coma, death
Disrupts blood brain barrier, inflammatory cytokines

Question 23

drugs to treat SIADH if water restriction is insufficient

Answer 23

Demeclocycline
* Reduces responsiveness of collecting tubule cells to ADH
* Monitor U&Es (risk of nephrotoxicity)

Tolvaptan
* V2 receptor antagonist

Question 24

what are the main causes of hypernatraemia

Answer 24

Unreplaced water loss
* Gastrointestinal losses, sweat losses
* Renal losses: osmotic diuresis (uncontrolled dm) , reduced ADH release/action (Diabetes insipidus)

Patient cannot control water intake e.g. children, elderly

Question 25

ix in suspected DI

Answer 25

Serum glucose (exclude diabetes mellitus)
Serum potassium (exclude hypokalaemia)
Serum calcium (exclude hypercalcaemia)
Plasma & urine osmolality
Water deprivation test – will still have dilute urine

Question 26

How would you treat hypernatraemia?

Answer 26

Fluid replacement – 5% dextrose
Treat the underlying cause
Correct extracellular fluid volume depletion – because lost water - 0.9% saline

Serial Na+ measurements - Every 4-6 hours

Question 27

What are the effects of diabetes mellitus on serum sodium?

Answer 27

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