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Pathology by week > W5 - Sodium and fluid balance > Flashcards

W5 - Sodium and fluid balance Flashcards

1
Q

What is the commonest electrolyte abnormality in hospitalized patients?

A

hyponatraemia

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2
Q

Hyponatraemia serum Na+ range?

A

< 135 mmol/L

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3
Q

What is the underlying pathogenesis of hyponatraemia?

A

Increased extracellular water aka fluid overload

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4
Q

Which hormone controls water balance?​ How does it exert its effect?

A

ADH (vasopressin)

  1. acts on V2 receptors in collecting duct = insertion of aquaporin-2 channels = water reabsorption
  2. acts on V1 receptors in vascular SM = vasoconstriction = bring BP up
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5
Q

What are the two main stimuli for ADH secretion?​ How are they sensed?

A
  1. Raised serum osmolality = hypothalamic osmoreceptors
  2. reduced blood volume/pressure = baroreceptors in carotids/atria/aorta
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6
Q

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

A

Hyponatraemia

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7
Q

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

A

clinical assessment of water status

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8
Q

What are the clinical signs (7) of hypovolaemia?​ What is the MOST reliable?

A
  1. Tachycardia​
  2. Postural hypotension​
  3. Dry mucous membranes​
  4. Reduced skin turgor​
  5. Confusion/drowsiness​
  6. Reduced urine output
  7. Low urine Na+ (<20) ** MOST RELIABLE
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9
Q

After clinical assessment of hyponatraemic patient, what do you need to establish?

A

Whether patient is euvolaemic, hypovolaemic, or hypervolaemic.

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10
Q

Why is low urine Na+ indicative of hypovolaemic hyponatraemia?

A

B/c of low volume => kidneys hold onto salts to try to bring BP up (water follows salt) => low urine sodium!

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11
Q

What are the clinical signs (3) of hypervolaemia?​

A
  1. Raised JVP​
  2. Bibasal crackles (on chest examination)​
  3. Peripheral oedema
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12
Q

What is a contra-indications of interpreting urine sodium?

A

If patient is on diuretics, you cannot use urine sodium for interpretation

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13
Q

Causes of hypovolaemic hyponatraemia?

A
  • Diarrhoea
  • Vomiting
  • Diuretics
  • Salt-losing nephropathy (uncommon)
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14
Q

Causes of euvolaemic hyponatraemia?

A
  • Hypothyroidism
  • Adrenal insufficiency
  • SIADH
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15
Q

Causes of hypervolaemic hyponatraemia?

A
  • Cardiac failure
  • Cirrhosis
  • Nephrotic syndrome (from renal failure)
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16
Q

What are the causes of SIADH?​

A

CNS pathology
lung pathology
drugs (SSRI, TCA, opiates, PPI, carbamazepine)
=> brain, lungs, and drugs!
less common: tumours, surgery

17
Q

What investigations would you order in a patient with euvolaemic hyponatraemia?

A
  • hypothyroidism? => TFTs
  • adrenal insufficiency? => short synACTHen test
  • SIADH => only after above 2 are disproven & NO hypovolaemia => low plasma osmolality, high urine osmolality
18
Q

What are the right exclusions to make before diagnosing SIADH?

A

No Hypovolaemia​

No Hypothyroidism​

No Adrenal insufficiency​

*Reduced plasma osmolality AND​
Increased urine osmolality (>100)*

19
Q

How would you manage a hypovolaemic patient with hyponatraemia?

A

Volume replacement with 0.9% saline​

20
Q

How would you manage a hypervolaemic patient with hyponatraemia?

A
  • Fluid restriction (0.5-1L/day) ​
  • Treat the underlying cause such as HF
21
Q

How would you manage a euvolaemic patient with hyponatraemia?​

A
  • Fluid restriction (0.5-1L/day) ​
  • Treat the underlying cause
22
Q

What is severe hypontraemia? How would you treat it?

A
  1. Reduced GCS
  2. Seizures
    SEEK EXPERT HELP => treat with 3% hypertonic saline
23
Q

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

A

Serum Na must NOT be corrected > 8-10 mmol/L in the first 24 hours​ => risk of osmotic demyelination (central pontine myelionlysis)​

24
Q

What are the signs of central pontine myelinolysis? MOA?
How long after quick correction of hyponatraemia does it happen?
Can it be corrected?

A

quadriplegia, dysarthria, dysphgia, seizures, coma, death. MOA: a rapid shift of sodium leads to disruption of the BBB

a few days after quick sodium correction

Yes - explain to the patient and lower Na+ again!

25
Q

How would you manage a euvolaemic hyponatraemic patient with SIADH?

A

If fluid restriction is insufficient:

  1. Demeclocycline
    - Reduced responsiveness of collecting tubule to ADH
    - monitor U&Es (risk of nephrotoxicity)
  2. Tolvaptan
    - V2 receptor antagonist
26
Q

Hypernatramia serum Na+ range?

A

>145 mmol/L

27
Q

What are the main causes of hypernatraemia?​
​

A
  1. Unreplaced water loss​
  • Gastrointestinal losses, sweat losses​
  • Renal losses: osmotic diuresis, reduced ADH release/action (Diabetes insipidus)​

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

28
Q

What investigations would you order in a patient with suspected diabetes insipidus?​
​

A

water deprivation test? i think

29
Q

How to treat hypernatraemia?

A

Correct water deficit​ => 5% dextrose ​

Correct extracellular fluid volume depletion​ => 0.9% saline​

Serial Na+ measurements​ => every 4-6 hours

30
Q

A 70 yr-old man ​
3-day history of diarrhoea​
Altered mental status​
Dry mucous membranes​
​
Serum Na+ is 168 mmol/L

Diagnosis? Treatment?

A

Hypernatraemia

Needs correction of water deficit but you also need to give Na+ and Cl- since he has diarrhoea

5% dextrose + 0.9% saline with serial Na+ measurements

31
Q

What are the effects of diabetes mellitus on serum sodium?

A

Variable​

  1. Hyperglycaemia draws water out of the cells leading to hyponatraemia​
    VS
  2. Osmotic diuresis in uncontrolled diabetes leads to loss of water and hypernatraemia​

Pathology by week (70 decks)

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