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Kat's Pathology > Sodium and Fluid Balance > Flashcards

Sodium and Fluid Balance Flashcards

1
Q

What is the commonest electrolyte abnormality in hospitalised patients

A

Hyponatraemia

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2
Q

What is hyponatraemia

A

Serum sodium < 135mmol/L

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3
Q

What is the underlying pathogenesis of hyponatraemia

A

Increased extracellular water

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4
Q

What hormone controls water levels in the body

A

ADH (vasopressin)

Retains water through the action on water channels (aquaporin 2)

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5
Q

What is the MOA of ADH

A

Acts on V2 receptors in the collecting duct
Acts via inserting aquaporin 2 channels

Acts on V1 recptors on vascular smooth muscle as a vasoconstrictor at higher concentrations

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6
Q

Where are V1 receptors found

A

Vascular smooth muscle

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7
Q

What are the two main stimuli for ADH secretion

A

Serum osmolality (mediated by hypothalamic osmoreceptors)

Blood volume/pressure (mediated by baroreceptors in carotids, atria, aorta)

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8
Q

What is the effect of increased ADH secretion on serum sodium

A

Hyponataraemia

Increased water reabsorption leads to dilution of serum sodium

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9
Q

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

A

Clinical assessment of volume status

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10
Q

What are the three outcomes of a volume assessment

A

Hypovolaemic
Euvolaemic
Hypervolaemic

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11
Q

What are the clinical signs of hyponatraemic hypovolvaemia

A 
Tachycardia 
Postural hypotension 
Dry mucous membranes 
Reduced skin turgor 
Confusion/drowsiness 
Reduced urine output 
Low urine Na (<20)
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12
Q

What are the clinical signs of hyponatraemic hypervolaemia

A

Raised JVP
Bibasal crackles on chest auscultation
Peripheral oedema

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13
Q

Causes of hyponatraemic hypovolaemia

A

Extra-renal: Diarrhoea, Vomiting

Renal: Diuretics, Salt losing nephropathy

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14
Q

Causes of hyponatraemic euvolmaenia

A

Hypothyroidism
Adrenal insufficiency
SIADH

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15
Q

Causes of hyponatraemic hypervolaemia

A

Cardiac failure
Nephrotic syndrome, renal failure
Cirrhosis

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16
Q

What are the causes of SIADH

A 
CNS pathology 
Lung pathology 
Drugs (SSRI, TCA, opiates, PPIs, carbamazepine) 
Tumours 
Surgery
17
Q

Tests in a hyponatraemia hypovolaemic patient

A

Clinical assessment

18
Q

Tests in a hyponataemia euvolaemic patient

A

TFTs
Short synacthen test
Plasma and urine osmolality (low plasma and high urine osmolality)

19
Q

Tests in a hyponatraemic hypervolaemic patient

A

Fluid overload?

20
Q

Diagnosis of SIADH

A

No hypovolaemia
No hypothyroidism
No adrenal insufficiency
Reduced plasma osmolality AND increased urine osmolality (>100)

21
Q

Management of a hypovolaemic patient with hyponatraemia

A

Volume replacement with 0.9% saline

22
Q

Management of a hypervolaemic patient with hyponatraemia

A

Fluid restriction

Treat the underlying cause

23
Q

Management of a euvolaemic patient with hyponatraemia

A

Fluid restriction

Treat the underlying cause

24
Q

Signs of severe hyponatraemia

A

Reduced GCS
Seizures
Seek expert help! (treat with hypertonic 3% saline)

25
Q

What is the most important point to remember while correcting hyponatraemia

A

Serum sodium NOT be corrected >8-10mmol/L in the first 24 hours as there is risk of osmotic demyelination (central pontine myelinolysis)

26
Q

Signs of osmotic demyelination due to rapid correction of hyponatraemia

A 
QUadriplegia 
Dysarthria 
Dysphagia 
Seizures 
Coma 
Death
27
Q

Drugs used to treat SIADH

A

If water restriction is insufficient

Demeclocycline - reduces responsiveness of collecting tubule cells to ADH, monitor U&Es (risk of nephrotoxicity)
Tolvaptan - V2 receptor antagonist

28
Q

Hypernatraemia

A

Serum sodium >145mmol/L

29
Q

Main causes of hypernatraemia

A

Unreplaced water loss: GI losses, sweat losses, renal losses (osmotic diuresis, reduced ADH release/action (Diabetes insipidus)
Patient cannot control water intake (e.g. very young, very old)

30
Q

Investigations in a patient with suspected diabetes insipidus

A 
Serum glucose (exclude diabetes mellitus) 
Serum potassium (exclude hypokalaemia) 
Serum calcium (exclude hypercalcaemia) 
Plasma and urine osmolality 
Water deprivation test
31
Q

Treatment of hypernatraemia

A

Fluid replacement

Treat the underlying cause

32
Q

A 70 yr-old man
3-day history of diarrhoea
Altered mental status
Dry mucous membranes

Serum Na+ is 168 mmol/L

Management?

A

Correct water deficit - 5% dextrose

Correct extracellular fluid volume depletion - 0.9% saline

Serial sodium measurements - every 4-6 hours

33
Q

What are the effects of diabetes mellitus on serum sodium

A

Variable
Hyperglycaemia draws water out of the cells leading to hyponatraemia
Osmotic diuresis in uncontrolled diabetes leads to loss of water and hypernatraemia

Kat's Pathology (105 decks)

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