Chempath 12: Sodium And Fluid Balance Flashcards

1
Q

What is the most common pathogenesis of hyponatraemia ?

A

Increased extracellular water

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2
Q

How does ADH increase water reabsorption ?

A

ADH binds to V2 receptors and causes increased Aquaporin 2 insertion into the collecting duct

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3
Q

Which receptors are found in smooth muscle and cause vasoconstriction ?

A) V1 receptors
B) V2 receptors

A

A) V1 receptors

They bind Vasopressin and cause vasoconstriction

V2 are found in collecting ducts and respond to ADH

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4
Q

What are the 2 main stimuli for ADH secretion ?

A

Osmoreceptors- detects high osmolality

Baroreceptors- detect low blood volume/pressure

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5
Q

Where are Osmoreceptors found in the body ?

A

Hypothalamus

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6
Q

List 3 locations where Baroreceptors are found in the body ?

A

Carotid
Aorta
atria

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7
Q

What is the most reliable clinical sign of hypovolaemia ?

A

Low urine Na+

Doesn’t work if on diuretics

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8
Q

List 4 clinical signs of hypovolaemia?

A
Tachycardia
Postural hypotension
Reduced skin turgor
Dry mucous membranes 
Sunken eyes
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9
Q

List 4 causes of Hypovolaemic hyponatraemia ?

A

Diarrhoea
Vomiting
Diuretics
Salt losing nephropathy

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10
Q

List 3 causes of euvolaemic hyponatraemia ?

A

Hypothyroidism
Adrenal insufficiency
SIADH

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11
Q

List 3 causes of hypervolaemic Hyponatraemia ?

A

Cardiac failure
Nephrotic syndrome
Cirrhosis

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12
Q

How does liver cirrhosis cause hypervolaemic hyponatraemia ?

A

Cirrhosis causes release of Nitric oxide which causes vasodilation
This causes reduced blood pressure > sensed by baroreceptors
ADH release is increased.
More water is reabsorbed

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13
Q

How does hypothyroidism cause a Euvolaemic hyponatraemia ?

A

Hypothyroidism causes reduced cardiac contractility
This causes reduced blood pressure
This causes increased ADH release
More water is reabsorbed than Na+

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14
Q

List 3 causes of SIADH ?

A

CNS tumour
Small cell lung cancer
Meningitis/ subarachnoid haemorrhage
Drugs (psych drugs: SSRIs, Carbamazapine, Amitryptiline)

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15
Q

How do you treat hypovolaemic hyponatraemia ?

A

Volume replacement with 0.9% saline

If volume is returned to normal, the stimulus for ADH release is stopped so allows recovery.

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16
Q

How do you treat hypervolaemic and euvolaemic hyponatraemia ?

A

Fluid restriction

Treat underlying cause

17
Q

Name the complication that can occur as a result of increasing serum sodium faster than 8-10 mol/L in the first 24 hours ?

A

Central pontine myelinolysis

18
Q

Name 2 drugs used to treat SIADH ?

A

Tolvaptan - ADH receptor antagonist

Demeclocycline - reduces responsiveness of collecting duct cells to ADH

19
Q

What level of serum sodium defines hypernatraemia ?

A

> 145 mmol/L

20
Q

What level of serum sodium defines hyponatraemia ?

A

<135 mmol/L

21
Q

Give 3 causes of Hypernatraemia ?

A

Diarrhoea and vomiting
Diabetes mellitus
Diabetes insipidus

3Ds of hypernatraemia

22
Q

Name 2 tests used to diagnose diabetes insipidus ?

A

Serum and urine osmolality

Water deprivation test

23
Q

Describe the possible outcomes of the water deprivation test ?

A

Normal: urine becomes very concentrated (sodium >800)
Cranial Diabetes insipidus: unable to concentrate urine (sodium <300)
Nephrogenic Diabetes insipidus : unable to concentrate urine (sodium <300)
Polydipsia: slightly able to concentrate urine, but physiological function has been damaged overtime (sodium <500)

24
Q

What is the main treatment for hypernatraemia ?

A

5% Dextrose

25
How do you treat Hypovolaemic hypernatraemia ?
First correct the extravascular fluid volume with 0.9% saline Then give 5% dextrose
26
Explain the 2 methods by which diabetes mellitus affects Sodium ?
1- Hyperglycaemia causes water to leave cells and enter the extravascular compartment causing dilution of sodium (hyponatraemia) (check this one) 2- In diabetes you get an osmotic diuresis which causes increased water loss
27
List 2 causes of pseudo hyponatraemia ?
Hyperlipidaemia Hyperproteinaemia Dilution by excess molecules of lipid or protein in the circulation. Sodium conc. is normal
28
What is meant by true hyponatraemia ?
When the Na+ conc. is low + Serum osmolality is low
29
Sodium low Urine Osmolality > 20mmol/L Urea elevated Creatinine elevated Most likely diagnosis ? volume Type of hyponatraemia ?
CKD Hypervolaemic hyponatraemia CKD causes increased urine protein loss -> Oedema -> low circulating volume -> RAS activated -> Increased ADH release -> Increased water reabsorption
30
A tanned looking lady Na+ low K+ high BM (glucose) low Most likely diagnosis ?
Addisons Lack of Aldosterone -> Increased Na+ reabsorption + Reduced K+ Exretion High ACTH -> hyperpigmentation low cortisol -> less gluconeogenesis -> Hypoglycaemia
31
Hyponatraemia with a higher urine osmolality compared to Serum osmolality ? Most likely diagnosis?
SIADH
32
How do you calculate Osmolarity ?
2(Na + K) + Urea + Glucose
33
How do you calculate Anion gap ?
Na + K - CL - HCO3
34
How is osmolality determined ?
Measured using an osmometer
35
What is the normal range for Sodium ?
135-145mM/l
36
Which atypical pneumonia can cause hyponatraemia ?
Legionella Pneumophilia | hotel air conditioners