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ChemPath > Sodium > Flashcards

Sodium Flashcards

1
Q
  1. What is the definition of hyponatraemia?
A

Sodium concentration < 135 mmol/L

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2
Q
  1. What is the underlying pathogenesis of hyponatraemia?
A

Increased extracellular water

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3
Q
  1. Describe the action of ADH.
A

Acts on V2 receptors in the collecting duct
Leads to insertion of AQP2 molecules and an increase in the reabsorption of water
Acts on V1 receptors on vascular smooth muscle leading to vasoconstriction

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4
Q
  1. What are the two main stimuli for ADH release?
A

Increased serum osmolality (via hypothalamic osmoreceptors)

Blood volume/pressure (via baroreceptors)

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5
Q
  1. What is the first step in the management of hyponatraemia?
A

Assess their volume status

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6
Q
  1. List some clinical features of hypovolaemia.
A 
Tachycardia 
Postural hypotension 
Dry mucous membranes
Reduced skin turgor 
Confusion
Reduced urine output
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7
Q
  1. What is the most reliable clinical sign of hypovolaemia?
A

Low urine sodium (suggests that you are trying to retain fluid)
NOTE: this may be high in patients on diuretics

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8
Q
  1. List some clinical features of hypervolaemia.
A

Raised JVP
Bibasal crackles
Peripheral oedema

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9
Q
  1. List some causes of hyponatraemia:

a. hypovolaemic
b. euvolaemic
c. hypervolaemic

A 
a.	Hypovolaemic
Diarrhoea
Vomiting 
Diuretics 
Salt-losing nephropathy 
b.	Euvolaemic
Adrenal insufficiency 
Hypothyroidism
SIADH
c.	Hypervolaemic
Cirrhosis 
Cardiac failure 
Nephrotic syndrome
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10
Q
  1. Explain how patients with hypovolaemic hyponatraemia have too much water.
A

Diarrhoea and vomiting leads to loss of water and salt

This leads to increased ADH release which causes reabsorption of more water than salt leading to hyponatraemia

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11
Q
  1. How does cirrhosis lead to hyponatraemia?
A

Causes the release of various mediators that cause a drop in perfusion pressure

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12
Q
  1. List some causes of SIADH.
A 
CNS pathology
Lung pathology 
Drugs (SSRIs, TCAs, opiates, PPIs, carbamazepine)
Tumours 
Surgery
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13
Q
  1. List the main investigative feature of SIADH.
A

Low plasma osmolality

High urine osmolality

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14
Q
  1. Which tests would you do for euvolaemic hyponatraemia?
A

TFTs
Short synacthen test
Plasma and urine osmolality

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15
Q
  1. Outline the treatment of:
    a. hypovolaemic
    b. euvolaemic
    c. hypervolaemic
A 
a.	Hypovolaemic hyponatraemia 
Volume replacement with 0.9% saline 
This replenishes the circulating fluid volume and switches off the stimulus for ADH release 
b.	Euvolaemic hyponatraemia
Fluid restriction 
Treat underlying cause 
c.	Hypervolaemic hyponatraemia
Fluid restriction 
Treat underlying cause
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16
Q
  1. What are some clinical features of severe hyponatraemia?
A

Reduced GCS

Seizures

17
Q
  1. What is the maximum rate of correction of hyponatraemia?
A

8-10 mmol/L per 24 hours

18
Q
  1. What is the main danger of rapidly correcting hyponatraemia?
A

Can cause central pontine myelinolysis (osmotic demyelination)
This can lead to quadriplegia, dysarthria, dysphagia, seizures, coma and death

19
Q
  1. Name and describe the mechanism of action of two drugs used to treat SIADH if fluid restriction is insufficient.
A

Demeclocycline – reduces the responsiveness of collecting duct cells to ADH
• NOTE: monitor U&E because it can be nephrotoxic
Tolvaptan – V2 receptor antagonist
Alternative: fluid restriction + salt tablets + diuretics

20
Q
  1. Define hypernatraemia.
A

Serum sodium > 145 mmol/L

21
Q
  1. List some causes of hypernatraemia.
A

GI losses
Sweat losses
Renal losses (e.g. osmotic diuresis, DI)

22
Q
  1. List some investigations that are used in suspected diabetes insipidus.
A 
Plasma glucose (rule out DM)
Plasma K+ (rule out hypokalaemia)
Plasma Ca2+ (rule out hypercalcaemia)
Plasma and urine osmolality 
Water deprivation test
23
Q
  1. How is hypernatraemia treated?
A

Fluid replacement – use dextrose because this will replace the fluid without adding to the salt
NOTE: if someone is hypovolaemic with hypernatraemia, they may initially be given 0.9% saline to treat the hypovolaemia before switching to dextrose to treat the hypernatraemia

24
Q
  1. How often should serial Na+ measurements be taken in someone being treated for hypernatraemia?
A

4-6 hours

25
Q
  1. How can diabetes mellitus affect serum sodium?
A

Hyperglycaemia will draw water out of cells (i.e. into the ECF) thereby leading to hyponatraemia
However, high plasma glucose can also lead to an osmotic diuresis (renal losses) which can lead to hypernatraemia

ChemPath (11 decks)

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