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Chemical Pathology > Y Lecture 4: Sodium and Fluid Balance > Flashcards

Y Lecture 4: Sodium and Fluid Balance Flashcards

1
Q

What is the definition of hyponatraemia?

A

Serum sodium <135

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2
Q

Upon which receptors does ADH act?

A

V1 (collecting duct) and V2 (on VSMCs)

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3
Q

What are the 2 stimuli for ADH secretion?

A

Serum osmolality (detected by hypothalamic osmoreceptors)

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

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4
Q

What are the clinical signs of hypovolaemia?

A 
Tachycardia
Postural hypotension
Dry mucous membranes
Reduce skin turgor
Confusion/drowsiness
Reduced urine output
KEY: LOW URINE Na+ (<120)
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5
Q

Recall 4 causes of hypovolaemic hyponatraemia

A

Diarrhoea
Vomiting
Diuretics
Salt losing nephropathy

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6
Q

Recall 3 causes of euvolaemic hyponatraemia

A

Hypothyroidism
Adrenal insufficiency
SIADH

(Euvolaemic = Endocrine - 2 ‘E’s)

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7
Q

Recall 3 causes of hypervolaemic hyponatraemia

A

Cardiac failure
Cirrhosis
Nephrotic syndrome

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8
Q

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

A

Patients on diuretics

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9
Q

How does hypothyroidism cause euvolaemic hyponatraemia?

A

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

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10
Q

How does adrenal insufficiency cause euvolaemic hyponatraemia?

A

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

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11
Q

What are the 5 main causes of SIADH?

A 
CNS pathology
Lung pathology
Drugs (SSRI, PPI, opiates)
Tumours
Surgery
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12
Q

What 3 tests should be done in euvolaemic hyponatraemia?

A

TFTs for hypothyroidism Short SynACTHen test for adrenal insufficiency Plasma and urine osmolality for SIADH

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13
Q

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

A

Hyperaldosteronism –> retention of sodium

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14
Q

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

A

Plasma = low (because it’s hyponatraemia!) Urine = high (>100)

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15
Q

What will urine sodium be in cardiac failure?

A

low

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16
Q

Why do you get hyperaldosteronism in cardiac failure?

A

Activation of RAAS

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17
Q

How do you manage a patient with hypovolaemic hyponatraemia?

A

Fluid replacement with 0.9% saline

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18
Q

How do you manage a patient with hypervolaemic hyponatraemia?

A

Fluid restriction

Treat the underlying cause

19
Q

How do you manage a patient with euvolaemic hyponatraemia?

A

Fluid restriction
Treat the underlying cause

If you give fluids, this will exacerbate the hyponatraemia

20
Q

What are the symptoms of SEVERE hyponatraemia?

A

Reduced GCS

Seizures

21
Q

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

A

No more that 8-10mmol/L in 1st 24 hoursRisk of osmotic demyelination (central pontine myelinolysis)

22
Q

How is SIADH treated?

A

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
Q

Why does SIADH cause euvolaemia?

A

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
Q

What are the main causes of hypernatraemia?

A

Unreplaced water loss

Due to GI losses or renal losses (eg diabetes insipidus)

25
Q

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

A

Serum glucose (exclude DM)

Serum K+ (exclude hypokalaemia)

Serum Ca (exclude hypercalcaemia)

Plasma and urine osmolality

Water deprivation test

26
Q

How would you manage hypernatraemia?

A

Fluid replacement with 5% DEXTROSE (NOT saline)

Treat underlying cause

27
Q

How does diabetes mellitus affect serum Na?

A 
Hyperglycaemia --> water drawn out of cells --> hyponatraemia
Osmotic diuresis (polyuria) --> loss of water --> hypernatraemia
28
Q

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

A

Clinically asses volume status

29
Q

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

A

Seek expert help and use 2.7% hypertonic saline

30
Q

Does ADH cause water loss or retention?

A

Retention (ADH ADds H2o)

31
Q

Is hyponatraemia primarily due to excess water or insufficient salt?

A

Excess water

32
Q

What is the expected urine sodium in a hypovolaemic hyponatraemic patient?

A

<20mmol/L

33
Q

What is the expected urine sodium in euvolaemic hyponatraemia?

A

High

34
Q

What are the clinical signs of hypervolaemia?

A

Peripheral oedema
Bibasal crackles
Raised JVP

35
Q

What is the expected urine sodium in hypervolaemic hyponatraemia?

A

Low

36
Q

Does hypervolaeic hyponatraemia cause nephrotic or nephritic syndrome?

A

Nephrotic

37
Q

What is the definition of hypernatraemia?

A

Na > 145 mmol/L

38
Q

Is hypernatraemia primarily a problem of excess salt or insuffucuent water?

A

Insufficient water

39
Q

What are the units of osmolality vs osmolarity?

A

Osmolality = mmol/kg

Osmolarity = mmol/L

40
Q

At what concentration of sodium should the sodium be treated (rather than just treating the cause)?

A

<125mmol/L and symptomatic

41
Q

How does TURP syndrome cause hyponatraemia?

A

Hyponatraemia from irrigation absorbed through damaged prostate

42
Q

How can hyponatraemia and pseudohyponatraemia be differentiated?

A

Pseudohyponatraemia has an increased protein/ lipid volume

Can be differentiated using serum osmolality - in true hyponatraemia, the serum osmolality is LOW

43
Q

How can renal vs non-renal causes of hyponatraemia be differentiated in both hypovolaemic and hypervolaemic patients?

A

If urine sodium >20 = renal

If urine sodium <20 = non-renal

Chemical Pathology (10 decks)

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