Chemical Pathology 11 - Sodium and fluid balance Flashcards Preview

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Flashcards in Chemical Pathology 11 - Sodium and fluid balance Deck (43)
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1

What is the definition of hyponatraemia?

Serum sodium <135

2

Upon which receptors does ADH act?

V1 (collecting duct) and V2 (on VSMCs)

3

What are the 2 stimuli for ADH secretion?

Serum osmolality (detected by hypothalamic osmoreceptors)

Blood volume/ pressure (mediated by baroreceptors in carotids, atria and aorta)

4

What are the clinical signs of hypovolaemia?

Tachycardia
Postual hypotension
Dry mucous membranes
Reduce skin turgor
Confusion/drowsiness
Reduced urine output
KEY: LOW URINE Na+ (<20)

5

Recall 4 causes of hypovolaemic hyponatraemia

Diarrhoea
Vomiting
Diuretics
Salt losing nephropathy

6

Recall 3 causes of euvolaemic hyponatraemia

Hypothyroidism
Adrenal insufficiency
SIADH
(Euvolaemic = Endocrine - 2 'E's)

7

Recall 3 causes of hypervolaemic hyponatraemia

Cardiac failure
Cirrhosis
Nephrotic syndrome

8

In which patients can you not use urine sodium as a reliable test result?

Patients on diuretics

9

How does hypothyroidism cause euvolaemic hyponatraemia?

Hypothyroidism --> Reduced cardiac contractility --> detected by baroreceptors --> more ADH --> increased water resorption --> low plasma Osm secondary to dilution --> less water excreted in urine --> high urinary Osm

10

How does adrenal insufficiency cause euvolaemic hyponatraemia?

Adrenal insufficiency --> low aldosterone and cortisol

Aldosterone is necessary for sodium and water resorption, cortisol is necessary for water clearance, therefore you get excess ADH

11

What are the 5 main causes of SIADH?

CNS pathology
Lung pathology
Drugs (SSRI, PPI, opiates)
Tumours
Surgery

12

What 3 tests should be done in euvolaemic hyponatraemia?

TFTs for hypothyroidism

Short SynACTHen test for adrenal insufficiency

Plasma and urine osmolality for SIADH

13

Why is urine sodium low in cardiac failure (hypervolaemic hyponatraemia)

Hyperaldosteronism --> retention of sodium

14

What will be the urine and plasma and urine osmolality in SIADH

Plasma = low (because it's hyponatraemia!)

Urine = high (>100)

15

What will urine sodium be in cardiac failure?

low

16

Why do you get hyperaldosteronism in cardiac failure?

Activation of RAAS

17

How do you manage a patient with hypovolaemic hyponatraemia?

Fluid replacement with 0.9% saline

18

How do you manage a patient with hypervolaemic hyponatraemia?

Fluid restriction
Treat the underlying cause

19

How do you manage a patient with euvolaemic hyponatraemia?

Fluid restriction
Treat the underlying cause
If you give fluids, this will exacerbate the hyponatraemia

20

What are the symptoms of SEVERE hyponatraemia?

Reduced GCS
Seizures

21

What is the max rate of serum Na+ correction in hyponatraemia and why?

No more that 8-10mmol/L in 1st 24 hours

Risk of osmotic demyelination (central pontine myelinolysis)

22

How is SIADH treated?

Water restriction
PLUS (but both used rarely)

1. Demeclocycline (reduces responsiveness of collecting tubule cells to ADH - but caution because nephrotoxic) OR
2. Tolvaptan (V2 receptor agonist)

23

Why does SIADH cause euvolaemia?

SIADH --> hypervolaemia (due to water retention) --> natiuretic peptide released from heart --> increased sodium excretion to try and pull water into urine --> euvolaemia (as you have now lost the water, but have also lost sodium in order to do so)

24

What are the main causes of hypernatraemia?

Unreplaced water loss
Due to GI losses or renal losses (eg diabetes insipidus)

25

What investigations would you order in a pt with suspected Diabetes insipidus?

Serum glucose (exclude DM)
Serum K+ (exclude hypokalaemia)
Serum Ca (exclude hypercalcaemia)
Plasma and urine osmolality
Water deprivation test

26

How would you manage hypernatraemia?

Fluid replacement with 5% DEXTROSE (NOT saline)
Treat underlying cause

27

How does diabetes mellitus affect serum Na?

Hyperglycaemia --> water drawn out of cells --> hyponatraemia

Osmotic diuresis (polyuria) --> loss of water --> hypernatraemia

28

What is the first investigation to do in suspected hyponatraemia/hypernatraemia?

Clinically asses volume status

29

How should severe hyponatraemia (<125mmol/L AND symptomatic) be treated?

Seek expert help and use 2.7% hypertonic saline

30

Does ADH cause water loss or retention?

Retention (ADH ADds H2o)

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