Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MedEd + PathSoc + Laz's Qs + Romesh Path > ChemPath 12: Sodium and Fluid Balance > Flashcards

ChemPath 12: Sodium and Fluid Balance Flashcards

1
Q

What is the definition of hyponatraemia?

A

Sodium concentration < 135 mmol/L

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the underlying pathogenesis of hyponatraemia?

A

Increased extracellular water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the two main stimuli for ADH release?

A

Increased serum osmolality (via hypothalamic osmoreceptors)

Blood volume/pressure (via baroreceptors)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the first step in the management of hyponatraemia?

A

Assess their volume status

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

List some clinical features of hypovolaemia.

A

Tachycardia
Postural hypotension

Dry mucous membranes
Reduced skin turgor

Confusion
Reduced urine output

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the most reliable clinical test of hypovolaemia? what is this like in hypervolaemia?

A

Low urine sodium (suggests that you are trying to retain fluid)

<20 - hypovolaemia
>20 - hypervolaemia

NOTE: this may be high in patients on diuretics

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

List some clinical features of hypervolaemia

A

Raised JVP

Bibasal crackles

Peripheral oedema

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

List some causes of hyponatraemia - Hypovolaemic?

A

Extra-renal:
- Diarrhoea + Vomiting

Renal:

  • Diuretics
  • Salt-losing nephropathy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

List some causes of hyponatraemia - Euvolaemic?

A

Adrenal insufficiency (addisons)

Hypothyroidism

SIADH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

List some causes of hyponatraemia - Hypervolaemic?

A

Cirrhosis

Cardiac failure

Renal failure
Nephrotic syndrome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How does cirrhosis lead to hyponatraemia?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

List some causes of SIADH.

A

CNS pathology
Lung pathology
Tumours

Drugs (SSRIs, TCAs, opiates, PPIs, carbamazepine)
Surgery

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

List the main investigative feature of SIADH

A

Low plasma osmolality

High urine osmolality

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Which tests would you do for euvolaemic hyponatraemia to diagnose as SIADH

A

TFTs

Short synacthen test

Plasma and urine osmolality

17
Q

Outline the treatment of:

  • Hypovolaemic hyponatraemia
  • Euvolaemic hyponatraemia
  • Hypervolaemic hyponatraemia
A

Hypovolaemic hyponatraemia:

  • Volume replacement with 0.9% saline
  • This replenishes the circulating fluid volume and switches off the stimulus for ADH release

Euvolaemic hyponatraemia:

  • Fluid restriction
  • Treat underlying cause

Hypervolaemic hyponatraemia:

  • Fluid restriction
  • Treat underlying cause
18
Q

What are some clinical features of severe hyponatraemia?

A

Reduced GCS

Seizures

19
Q

What is the maximum rate of correction of hyponatraemia?

A

8-10 mmol/L per 24 hours

20
Q

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

21
Q

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

22
Q

Define hypernatraemia

A

Serum sodium > 145 mmol/L - decreased extracellular water

23
Q

List some causes of hypernatraemia

A

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

Normaly can just drink enough water to replace - hence hypernatraemia only really affects really young / old people

24
Q

List some investigations that are used in suspected diabetes insipidus

A

Rule out causes of osmotic diuresis:
Plasma glucose (rule out DM)
Plasma K+ (rule out hypokalaemia)
Plasma Ca2+ (rule out hypercalcaemia)

Plasma and urine osmolality
Water deprivation test

25
Q

How is hypernatraemia treated + special case? what happens if too quickly replaced

A

Fluid replacement – use 5% dextrose because this will replace the fluid without adding to the salt + serial Na measurements

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

Rapid correction can lead to cerebral oedema!

26
Q

How often should serial Na+ measurements be taken in someone being treated for hypernatraemia?

A

4-6 hours

27
Q

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

28
Q

You are bleeped to review John Doe. A 68-year-old gentlemen on the cardiology ward admitted with Heart Failure. John had contracted Norovirus whilst on the ward is suffering from severe D&V.

On examination, he has dry mucous membranes and reduced skin turgor

Which of the following is the most accurate descriptor of John’s current condition?

  • Hypovolaemia Hyponatraemia
  • Hypochloraemic Hypokalaemic Metabolic Alkalosis
  • Euvolaemic Hyponatraemia
    Hypernatraemia
  • Hypervolaemic Hyponatraemia
A

Hypovolaemia Hyponatraemia

29
Q

Why do you end up with Excess Water in hypovolaemic hyponatraemia?

A

Low Blood Volume -> Baroreceptors -> ADH Release

30
Q

Why do you end up with excess water in the different causes of hypervolaemic hyponatraemia?

A

Cardiac Failure – Low BP -> Baroreceptors -> ADH Release

Liver Cirrhosis – Releases vasodilators -> Low BP -> Baroreceptors -> ADH Release

Renal Failure – Reduced Water Excretion

31
Q

How do you get excess water w/ euvolaemic hyponatraemia?

A

All of the above (somehow?) cause a spur of ADH to be released

The reabsorption of water increases the circulating volume and therefore increases BP.

The increase in BP is detected in the Atria which release ANP release – Natriuresis.

32
Q

What can cause SIADH?

A
  • > CNS Pathology
  • > Lung Pathology
  • > Drugs (SSRI, TCA, Opiates, PPI, Carbamazepine)
  • > Tumours
  • > Surgery
33
Q

How to treat euvolaemic hyponatraemia?

A
  • > If fluid restriction isn’t enough
  • > Demeclocycline (Reduce cell responsiveness to ADH)
  • > Tolvaptan (Antagonist to V2 receptor)
34
Q

You are bleeped to review John Doe. A 46-year-old gentlemen on the respiratory ward with a diagnosis of Lung Cancer,
On Examination, He appears cachectic ‘but of normal fluid status’,

Low Na+, everything else normal

What is the most appropriate management plan?

A

Fluid restrict + treat underlying cause - Euvolaemic hyponatraemia

35
Q

You are bleeped to review Jane Doe. A 46-year-old lady in A&E with a significant background of alcohol abuse who has presented feeling ‘confused’.

On Examination, she has a raised JVP, splenomegaly and shifting dullness.

Low Na+, everything else normal

Which of the following is the most likely cause of her ‘Hypervolaemic Hyponatraemia’?

Renal Failure
Diuretic Use
Hypothyroidism
Liver Cirrhosis
Heart Failure
A

Liver Cirrhosis – Releases vasodilators -> Low BP -> Baroreceptors -> ADH Release

36
Q

You are bleeped to review Jane Doe. A 98-year-old lady in A&E with poorly controlled Diabetes Mellitus – ‘who lives alone and her water jug is typically too far for her to reach’.

On examination, she has dry mucous membranes and reduced skin turgor.

Raised Na+, everything else normal

What is the most appropriate management plan? what else is needed along side this?

IV 0.9% Saline 
IV 0.9% Saline + 5% Dextrose 
5% Dextrose
Fluid Restrict 
No Management Required
A

IV 0.9% Saline + 5% Dextrose + Serial Na+ Measurements (4-6h)

MedEd + PathSoc + Laz's Qs + Romesh Path (99 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions