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clinical chemistry > Hyponatraemia > Flashcards

Hyponatraemia Flashcards

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1
Q

what is hyponatraemia?

A

serum Na+ <135 mmol/L

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2
Q

what are the different categories of hyponatraemia?

A
  1. hypovolaemic
  2. euvolaemic
  3. hypervolaemic
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3
Q

what are some causes of hypovolaemic hyponatraemia?

A
  • burns
  • sweating
  • diarrhoea
  • vomiting
  • fistulae
  • addison’s disease
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4
Q

what are some of the causes of euvolaemic hyponatraemia?

A
  • syndrome of inappropriate ADH release (SIADH)
  • hypothyroidism
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5
Q

what are some of the causes of hypervolaemic hyponatraemia?

A
  • renal failure
  • heart failure
  • liver failure
  • nephrotic syndrome
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6
Q

what investigations should be carried out in hyponatraemia of unknown cause?

A
  • U&Es
  • urine and plasma osmolalities
  • urine sodium
  • urine dip - to screen for infection and glomerular pathology
  • TSH and cortisol - to exclude hypothyroidism and addison’s disease
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7
Q

what is the management of hypovolaemic hyponatraemia?

A
  • IV normal saline (0.9% NaCl)
  • treat underlying cause
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8
Q

what is the management of euvolaemic hyponatraemia caused by SIADH?

A
  • fluid restriction = 500-1000 mL/day
  • ADH receptor antagonists (e.g. tolvaptan, deomeclocycline)
  • oral sodium and furosemide
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9
Q

what is the management of euvolaemic hyponatraemia caused by hypothyroidism?

A

levothyroxine

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10
Q

what is the management of hypervolaemic hyponatraemia?

A
  • fluid restriction = 500-100mL/day
  • consider loop diuretics
  • consider vaptans
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11
Q

what is mild hyponatraemia?

A

serum sodium 130-134 mmol/L

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12
Q

what is moderate hyponatraemia?

A

serum sodium 120-129 mmol/L

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13
Q

what is severe hyponatraemia?

A

serum sodium <120 mmol/L

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14
Q

what are the early symptoms of hyponatraemia?

A
  • headache
  • lethargy
  • nausea
  • vomiting
  • dizziness
  • confusion
  • muscle cramps
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15
Q

what are the late symptoms of hyponatraemia?

A
  • seizure
  • coma
  • respiratory arrest

causes cerebral oedema which can lead to brain herniation

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16
Q

how is severe hyponatraemia treated?

A

150ml of hypertonic (3%) saline over 20 minutes

17
Q

what is the risk of correcting sodium too quickly?

A

central pontine myelinosis

correcting sodium faster than 12mmol/L per day leads to risk of central pontine myelinosis because of fluid shifts

18
Q

what is the differential diagnosis of a urinary sodium of >20 mmol/L indicate?

A

sodium depletion, renal loss (hypovolaemic)
* diuretics
* addison’s disease
* diuretic stage of renal failure

euvolaemic
* SIADH
* hypothyroidism

19
Q

what is the differential diagnosis of a urinary sodium of <20 mmol/L indicate?

A

sodium depletion, extra-renal loss
* diarrhoea, vomiting, sweating
* burns
* adenoma of rectum

water excess (hypervolaemic and oedematous)
* secondary hyperaldosteronism - heart failure, liver cirrhosis
* nephrotic syndrome
* IV dextrose
* psychogenic polydipsia

20
Q

what is a contraindication to aggressive 3% sodium chloride management of hyponatraemia?

A

duration of hyponatraemia is >48hours due to risk of central pontine myelinosis

21
Q

what should be checked following sodium correction with IV saline?

A

urine output to montior fluid restriction

22
Q

what mechanism leads to demyelination in treatment of hyponatraemia?

A
  1. hypovolaemic patient -> ADH production in large amonuts
  2. prevents water loss via urine
  3. restoration of IV volume blocks ADH release
  4. causes free water diuresis
  5. leads to acute rise in serum sodium
  6. rapid overcorrection
  7. osmotic demyelination syndrome and possible HYPERnatraemia
23
Q

what is diruesis?

A

when your body makes extra urine to get rid of a substance

24
Q

what is the mechanism of action of vaptans?

vasopressin/ADH receptor antagonists

A
  1. act primarily on V2 receptors
  2. antagonism of V2 receptors results in selective water diuresis
  3. spares the electrolytes

stimulate the thirst receptors leading to desire to drink free water

25
Q

when should vaptans (vasopressin/ADH receptor antagonists) NOT be given?

A
  • hypovolaemic hyponatraemia
  • liver disease - excessive drinking of water can be hepatotoxic
26
Q

what are the symptoms of central pontine myelinolysis?

A
  • dysarthria
  • dysphagia
  • paraparesis or quadriparesis
  • seizures
  • confusion
  • coma
  • “locked-in” syndrome
27
Q

what causes pseudohyponatraemia?

A
  • hyperlipidaemia
  • paraproteinaemia (seen in multiple myeloma)
  • high blood glucose levels
  • use of mannitol or glycine
28
Q

what does postural hypotension indicate when assessing hyponatraemia?

A

hypovolaemic state

29
Q

what formula is used to estimate serum osmolality?

A

2(sodium + potassium) + glucose + urea

example = 2(124 + 4.5) + 6.5 + 7.5 -> 271mOsm/kg

clinical chemistry (4 decks)

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