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Year 5 Pathology - Week 1 > Sodium and fluid balance > Flashcards

Sodium and fluid balance Flashcards

1
Q

What controls sodium balance?

A

Water - controlled by ADH
Salt - Aldosterone

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2
Q

Where does ADH work?

A

V1 - vasoconstriction
V2 - aquaporin 2 inserted into collecting duct cells

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3
Q

What is the most common sodium abnormality?

A

Hyponatremia

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4
Q

Most common cause of hyponatremia

A

Fluid overload

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5
Q

If someone has hyponatremia, what do you have to assess?

A

Their fluid status - are they hypovolemic, euvolemic or hypervolemic

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6
Q

Clinical features of hypovolemia

A

Low BP
Tachycardia
Dry skin turgor
Low urine output
Low urine sodium <20

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7
Q

What is the best marker of HYPOVOLEMIA?

A

Low sodium in urine <20

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8
Q

Clinical features of hypervolemia

A

Oedema
Raised JVP
Bibasal crackles

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9
Q

Causes of hyponatremia in hypovolemia

A

If urine sodium less than 20:
Diarrhoea and vomiting
Excess sweating
Ascites/burns

If urine sodium more than 20: (kidney not retaining sodium)
Diuretics
Salt losing nephropathy
Addisons

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10
Q

Causes of hyponatremia in euvolemia

A

SIADH
Addisons/adrenal insufficiency
Hypothyroidism - low heart rate,

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11
Q

Causes of hyponatremia in hypervolemia

A

Urine sodium less than 20
Cardiac failure - low BP, increases ADH secretion
Cirrhosis - Nitric oxide release - vasodilation - low bp - ADH secretion

Urine sodium more than 20
Renal failure/nephrotic syndrome

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12
Q

Tests to identify hypovolemic hyponatremia

A

No tests as such, check if clinically hypovolemic

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13
Q

Tests to identify euvolemic hyponatremia cause - list three

A

TFTs

Short synACTHen test - to test for adrenal insufficiency (cortisol rise)

Plasma and urine osmolality for the SIADH (low plasma osmolality, high urine osmolality as osmolality is calculated from sodium)

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14
Q

Tests to identify hypervolemic hyponatremia

A

No tests as such, visually see if fluid overloaded

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15
Q

Causes of SIADH

A

CNS pathology
Lung pathology
Drugs - SSRIs, TCA, Opiates, PPis, carbamazepine
Tumours
Surgery

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16
Q

How would you diagnose SIADH?

A

Pt must not be:
hypovolemic
no hypothyroidism
no adrenal insufficiency

they do have:
reduced plasma osmolality
increased urine osmolality (over 100)

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17
Q

Management of someone with hypovolemic hyponatremia

A

Volume replacement with 0.9 percent saline - this reduces the stimulus for excess ADH

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18
Q

How would you manage hypervolemic hyponatremia?

A

Fluid restriction
Treat underlying cause

19
Q

How would you manage a euvolemic patient with hyponatremia?

A

Fluid restriction
Treat underlying cause e.g. thyroxine, gluocorticoids etc

20
Q

What clinical feature is a marker of severe hyponatremia?

A

If pt has reduced GCS
Seizures

21
Q

Management of SEVERE hyponatremia

A

CALL ON CALL CONSULTANT
Hypertonic 3 percent saline

22
Q

What is important to remember when correcting hyponatremia?

A

Serum sodium must not be corrected >8-10mmol / L in the first 24 hours as there is a risk of osmotic dehydration causing central pontine myelinolysis

23
Q

Symptoms of central pontine myelinolysis

A

Quadriplegia, dysarthria, dysphagia, seizures, coma, death

24
Q

Drugs used to treat SIADH

A

Demeclocycline

Tolvaptan

25
Q

Demeclocycline mechanism of action + what you must do if prescribing someone this drug

A

Reduces tubule cells’ response to ADH
but monitor U and E as risk of nephrotoxicity

26
Q

Tolvaptan mechanism of action

A

V2 receptor antagnoist

27
Q

Hyponatremia is mostly due to reduced body sodium or increased body water?

A

Increased extracellular body water

28
Q

What counts as hypernatremia?

A

Serum sodium over 145mmol/L

29
Q

Causes of hypernatremia

A

GI loss
Sweat loss
Renal loss
Osmotic diuresis
Reduced ADH release/action e.g. in diabetes insipidus

30
Q

Which type of patient often gest hypernatremia?

A

People who cannot control water intake e.g. children or elderly not drinking enough

31
Q

What investigations would you order in a patient with suspected diabetes inspidus? What tests are done to be excluded? What test is specifically done for diabetes inspidus diagnosis?

A

So they are peeing a lot because the ADH isn’t working, so:

Serum glucose to exclude DM
Serum potassium to exclude hypokalemia
Serum calcium to exclude hypercalcemia
Plasma and urine osmolality
Water deprivation test

32
Q

How do you treat hypernatremia?

A

Fluid replacement
Treat underlying cause

33
Q

70 yo man with 3 days of diarrhoea, altered mental status and dry mucous membranes. Serum sodium is 168 mmol/L. How do you manage?

A

Correct lack of water with 5 percent dextrose as this is causing the high sodium.

You also need to correct the extracellular fluid volume depletion - 0.9 percent saline

He also needs serial sodium measurements every 4-6 hours

34
Q

Do we use sodium chloride to correct hypernatremic lack of fluid?

A

NO you use 5 percent dextrose instead

35
Q

What are the effects of diabetes mellitus on serum sodium?

A

Variable:

Hyperglycemia can draw water out of the cells, causing hyponatremia (glucose can draw water into the vessels)
Osmotic diuresis (peeing it out) can cause loss of water and therefore hypernatremia

36
Q

How do hypercalcemia and hypokalemia cause you to pee out more?

A

Because it causes resistance to ADH, and therefore diabetes inspiidus

37
Q

Three problems causing you to pee loads

A

Hypercalcemia
Hypokalemia
Hyperglycemia

38
Q

How do you test whether it is a true hyponatremia?

A

Check serum osmolality - osmolarity

39
Q

If the osmolality is high, what does this mean?

A

There are other solutes in the blood, causing water to come in and dilute the sodium.

This is one type of pseudohyponatremia.

Causes: mannitol, glucose infusion

40
Q

In true hyponatremia, what should the osmolality be?

A

It should be low too

41
Q

If the osmolality is normal, what does this mean?

A

Lipids, paraproteins - these are detected by the lab as being water, so it comes back as normal

This is also pseudohyponatremia

Other causes:
Drip arm sample
False sample

42
Q

Name a procedure where you get hyponatremia

A

TURP - glycine 1.5 percent solution is absorbed from the irrigation, and dilutes the sodium

43
Q

How do you calculate osmolarity?

A

2 x (Na + K) + urea and + glucose

Year 5 Pathology - Week 1 (26 decks)

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