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Gen Med (Renal) > Clinical Chemistry 1 - Sodium and Water > Flashcards

Clinical Chemistry 1 - Sodium and Water Flashcards

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1
Q

The renin-angiotensin-aldosterone system is responsible for the homeostasis of what?

A

Sodium, water and potassium

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2
Q

What is released from the juxtaglomerular apparatus of the kidney in response to low renal blood flow or raised sympathetic tone?

A

Renin

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3
Q

What is the role of renin?

A

Catalyses the conversion of angiotensin to angiotensin I

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4
Q

Angiotensin I is converted to angiotensin II via what?

A

Angiotensin converting enzyme (ACE)

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5
Q

What is the role of angiotensin II at the level of the glomerulus?

A

Vasoconstriction of the efferent arteriole

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6
Q

What effect does angiotensin II have on the peripheral circulation?

A

Vasoconstriction

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7
Q

Angiotensin II promotes the release of what hormone?

A

Aldosterone

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8
Q

Where does aldosterone act?

A

On the sodium/potassium pumps of the distal tubule of the nephron

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9
Q

What is the action of aldosterone?

A

Sodium and water reabsorption, potassium and hydrogen excretion

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10
Q

Sodium concentration in the body is mainly controlled via the action of what?

A

Aldosterone

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11
Q

Which group of hormones are responsible for reducing sodium reabsorption at the distal tubule and inhibiting the action of renin, in order to decrease sodium levels in the body?

A

Natriuretic hormones (ANP, BNP, CNP)

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12
Q

Raised plasma osmolarity causes thirst via the hypothalamic thirst centre and the release of what hormone?

A

ADH

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13
Q

Where does ADH exert its effect?

A

Collecting ducts of the nephrons

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14
Q

Low plasma osmolarity has what effect on ADH secretion?

A

Inhibition

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15
Q

Inappropriately high ADH levels cause excess water reabsorption by the kidney- this leads to what clinical condition?

A

SIADH

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16
Q

What are some examples of causes of SIADH?

A

Post-operative stress, small cell lung cancers

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17
Q

How can SIADH be treated non-pharmacologically?

A

Restriction of water intake

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18
Q

What drug class can be used to pharmacologically treat SIADH?

A

V2 vasopressin receptor antagonists (e.g. tolvaptan)

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19
Q

Inadequate vasopressin action leads to what clinical syndrome?

A

Diabetes insipidus

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20
Q

What are some causes of cranial (central) diabetes insipidus?

A

Brain tumours or head trauma

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21
Q

What is the pathology behind cranial (central) diabetes insipidus?

A

The pituitary gland does not release enough ADH

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22
Q

What is the pathology behind nephrogenic diabetes insipidus?

A

The kidney fails to respond to ADH

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23
Q

What are some electrolyte abnormalities which can lead to nephrogenic diabetes insipidus?

A

Hypokalaemia and hypercalcaemia

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24
Q

What are some drugs which can lead to nephrogenic diabetes insipidus?

A

Lithium and gentamicin

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25
How do patients with diabetes insipidus present clinically?
Polyuria and polydipsia
26
What happens to plasma osmolarity and plasma sodium levels in diabetes insipidus?
High
27
What happens to urine osmolarity and urine sodium levels in diabetes insipidus?
Low
28
What is the clinical test to diagnose diabetes insipidus?
Water deprivation test
29
In which type of diabetes insipidus will synthetic vasopressin cause a rise in urine osmolarity?
Cranial (central)
30
ADH levels are high in which type of diabetes insipidus?
Nephrogenic
31
ADH levels are low in which type of diabetes insipidus?
Cranial (central)
32
How is cranial (central) diabetes insipidus treated?
Intranasal desmopressin
33
What effect does Addison's disease have on sodium, water and potassium levels?
Hyponatraemia, hypovolaemia, hyperkalaemia
34
What effect do diuretics have on sodium levels?
Hyponatraemia
35
What effect does excess aldosterone levels (for whatever reason) have on sodium, water and potassium levels?
Hypernatraemia, hypervolaemia, hypokalaemia
36
What effect does renal failure have on sodium levels?
Hypernatraemia
37
Which electrolyte abnormality always causes hyperosmolarity?
Hypernatraemia
38
Most hypernatraemia arises from what?
Unreplaced water loss
39
The body volume in hypernatraemia is usually what?
Low
40
What is the body's main defence against hypernatraemia?
Thirst
41
What are some potential causes of hypernatraemia?
Fluid losses (D&V, burns), diabetes insipidus, primary hyperaldosteronism
42
What is a potential iatrogenic cause of hypernatraemia?
Excessive saline as IV fluid replacement
43
The early clinical features of hypernatraemia are caused by what?
Increased excitability of neurons
44
What are some examples of early neurological features of hypernatraemia?
Irritability, muscle twitches, brisk reflexes, spasticity
45
What are some examples of non-neurological features that may be experienced by someone with hypernatraemia?
Thirst, lethargy and weakness
46
What can hypernatraemia lead to if left untreated?
Seizures and coma
47
How is hypernatraemia treated if the patient is clinically well?
Oral water replacement
48
Generally, how is hypernatraemia managed?
Water replacement and treatment of the underlying cause
49
How is hypernatraemia treated if the patient is clinically unwell?
IV 5% dextrose solution (1 litre every 6 hours)
50
If a patient with hypernatraemia is hypovolaemic, what should be used for fluid replacement?
IV 0.9% saline
51
Which type of fluids should always be avoided in patients with hypernatraemia?
Hypertonic solutions
52
It is important not to correct sodium levels too quickly. You should aim for a change of no more than how many mmol/hour?
0.5mmol/hour
53
It is important not to correct sodium levels too quickly. You should aim for a change of no more than how many mmol/day?
12mmol/day
54
If a patient with hyponatraemia is dehydrated, is the cause too little sodium or too much water?
Too little sodium
55
If a patient with hyponatraemia is not dehydrated, is the cause too little sodium or too much water?
Too much water
56
If you have established that a person is hyponatraemic due to too little sodium, what is the next most important test to check to establish the diagnosis?
Urinary sodium levels
57
If a patient is hyponatraemic, dehydrated and has a urinary sodium level of > 20mmol/l, this suggests sodium is being lost from the kidneys. What are some potential causes of this?
Addison's disease, CKD, diuretic overuse
58
If a patient is hyponatraemic, dehydrated and has a urinary sodium level of < 20mmol/l, this suggests sodium is being lost from somewhere other than the kidneys. What are some potential causes of this?
D&V, burns, small bowel obstruction, fistulae
59
When a patient is hyponatraemic, what is the first thing that you want to establish?
Are they dehydrated or not
60
When a patient is hyponatraemic and not dehydrated, you know that the cause is too much water. In these cases, what is the first question you should ask yourself?
Is the patient oedematous
61
If a patient is hyponatraemic, not dehydrated and is oedematous, what is the likely underlying cause?
An oedema syndrome (e.g. cardiac, renal or hepatic failure)
62
If a patient is hyponatraemic, not dehydrated and not oedematous- what is the next test that you should look at to establish the diagnosis?
Urine osmolality
63
If a patient is hyponatraemic, not dehydrated or oedematous and has a urine osmolality of > 100mg/kg, what is the likely underlying cause?
SIADH
64
If a patient is hyponatraemic, not dehydrated or oedematous and has a urine osmolality < 100mg/kg, what is the likely underlying cause?
Fluid overload
65
Which patients are most vulnerable to the neurological effects of hyponatraemia?
Extremes of age, menstruating women and those with underling neurological or metabolic disorders
66
What effect does hyponatraemia have on the nervous system?
Depressed function
67
What are some neurological symptoms of hyponatraemia?
Confusion, muscle cramps, reduced reflexes
68
What are some non-neurological symptoms of hyponatraemia?
Lethargy, nausea
69
There is a risk of seizures and coma with hyponatraemia, particularly when sodium levels fall below what?
120mmol/l
70
What is the risk of treating hyponatraemia too quickly?
Central pontine myelinosis
71
How is asymptomatic, chronic hyponatraemia treated?
Fluid restriction and treatment of the underlying cause
72
How is acute or symptomatic hyponatraemia treated?
Cautious rehydration with 0.9% saline
73
If a patient with hyponatraemia is having a seizure or is in a coma- urgent help is needed. What can be considered as treatment?
Hypertonic saline +/- furosemide
74
What drug can be useful in the treatment of hypervolaemic or euvolaemic hyponatraemia?
Tolvaptan

Gen Med (Renal) (18 decks)

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