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chemical pathology > Sodium > Flashcards

Sodium Flashcards

1
Q

What is the normal range of sodium in the blood?

A

135-145mmol/l

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2
Q

What percentage of body sodium is freely exchangeable? Where is the rest?

A

70%

Rest is complexed in bone

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3
Q

Below what value should hyponatraemia be treated

A

125mmol/l and symptomatic

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4
Q

What are the symptoms of hyponatraemia?

A

Nausea, vomiting, confusion
< 125mmol/l seizures, non-cardiogenic pulmonary oedema
<117mmol/l coma and eventual death

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5
Q

What causes apparent hyponatraemia with high osmolality?

A

High glucose, mannitol infusion

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6
Q

What causes apparent hyponatraemia with normal osmolality?

A

Hyperlipidaemia, paraproteinaemia, sample taken from arm receiving IV fluids

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7
Q

What is a true hyponatraemia?

A

Hyponatraemia with low osmolality

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8
Q

Name three causes of hypervolaemic hyponatraemia

A

Heart failure, liver failure, kidney failure

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9
Q

How is hypervolaemic hyponatraemia treated?

A

Fluid restriction, correct cause

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10
Q

Name three causes of euvolaemic hyponatraemia

A

Hypothyroidism, glucocorticoid insufficiency, SIADH, primary polydipsia

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11
Q

What investigations are required with euvolaemic hyponatraemia?

A

TFTs, short synACTHen test, paired urine and serum osmolality

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12
Q

How is hypovolaemic hyponatraemia managed?

A

Fluid restoration with 5% dextrose.

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13
Q

Name three causes of hypovolaemic hyponatraemia with >20mmol/l urinary sodium

A

Diuretics, Addison’s disease, salt-wasting nephropathies

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14
Q

Name three causes of hypovolaemic hyponatraemia with <20mmol/l urinary sodium

A

Vomiting, diarrhoea, excess sweating, ascites, burns

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15
Q

How does cirrhosis cause hyponatraemia?

A

Poor breakdown of vasodilators (e.g. nitric oxide) leads to hypotension, stimulating ADH release and causing water retention and dilution of serum sodium

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16
Q

What is the danger of correcting hyponatraemia too fast?

A

Central pontine myelinolysis

17
Q

What is the biggest risk factor for central pontine myelinolysis?

A

Alcoholism

18
Q

What are the features of central pontine myelinolysis?

A

Pseudobulbar palsy, paraparesis, locked-in syndrome

19
Q

State the laboratory criteria for diagnosing SIADH

A

True hyponatraemia (low serum osmolality), euvolaemia, inappropriately high urine osmolality, increased renal sodium excretion >20mmol/l, normal 9am cortisol and TFTs

20
Q

State at least 5 causes of SIADH

A

Malignancy, meningoencephalitis, CNS abscess, CNS haemorrhage, TB, pneumonia, lung abscess, drugs

21
Q

State at least 3 drug classes which can cause SIADH

A

Opiates, SSRIs, carbamazepine, proton pump inhibitors

22
Q

Which malignancy most commonly causes SIADH?

A

Small cell lung cancer

23
Q

State at least 3 causes of hypovolaemic hypernatraemia

A

Diarrhoea, vomiting, excessive sweating, burns, loop diuretics, osmotic diuresis following initial hyponatraemia

24
Q

State at least 3 causes of euvolaemic hypernatraemia

A

Tachypnoea, sweating, fever, diabetes insipidus

25
Q

State 2 causes of hypervolaemic hypernatraemia

A

Mineralocorticoid excess (Conn’s syndrome), inappropriate IV saline

26
Q

How is hypernatraemia managed?

A

Slow fluids - oral if possible, if not IV dextrose or Hartmann’s

27
Q

What are the clinical features of diabetes insipidus?

A

Polyuria, polydipsia, lethargy, thirst, irritability, coma, seizures

28
Q

What is the urine: plasma osmolality in diabetes insipidus?

A

<2

29
Q

State 3 causes of cranial diabetes insipidus

A

Brain surgery, head trauma, brain tumours

30
Q

State 3 causes of nephrogenic diabetes insipidus

A

Inherited channelopathies, lithium, demeclocycline, hypercalcaemia

31
Q

What is a normal response in an 8h fluid deprivation test?

A

Urine concentration increases to >600mOsmol/kg

32
Q

What result in an 8h fluid deprivation test suggests primary polydipsia?

A

Urine concentration increases to <400-600mOsmol/kg

33
Q

What result in an 8h fluid deprivation test suggests cranial diabetes insipidus?

A

Urine concentrates only after giving desmopressin

34
Q

What result in an 8h fluid deprivation test suggests nephrogenic diabetes insipidus?

A

Low concentration urine even after desmopressin

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