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Hypo- and hypernatraemia Flashcards

1
Q

What is hyponatraemia?

A

A low serum sodium level, defined as serum sodium < 135mmol/l

Normal serum sodium levels range from 135-145mmol/l.

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2
Q

Why is hyponatraemia important?

A

It is the commonest electrolyte abnormality seen in hospital admissions and can be life-threatening.

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3
Q

What are the common causes of hyponatraemia?

A

Sodium loss and water gain.

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4
Q

What is the normal range for serum sodium?

A

135-145mmol/l.

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5
Q

What percentage of total body water do men and women have?

A

Men: 60% (42 litres), Women: 55% (38 litres).

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6
Q

What are the main compartments of total body water?

A
  • Intracellular: ~30 litres
  • Interstitial: ~9 litres
  • Vascular: 3 litres
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7
Q

What is the significance of sodium in the body?

A

Sodium is the primary extracellular cation and osmole, critical for water balance.

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8
Q

What happens if we lose salt?

A

We will lose water, leading to hypovolaemia.

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9
Q

What happens if we gain water?

A

We will dilute our sodium, potentially leading to hyponatraemia.

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10
Q

What are the volume states associated with hyponatraemia?

A
  • Normovolaemic hyponatraemia
  • Hypovolaemic hyponatraemia
  • Hypervolaemic hyponatraemia
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11
Q

What is pure water gain associated with in terms of volume status?

A

Normovolaemic or mild hypervolaemia.

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12
Q

What clinical scenario can lead to normovolaemic hyponatraemia?

A

SIADH, hypothyroidism, or iatrogenic causes.

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13
Q

What is hypovolaemic hyponatraemia?

A

Occurs when both salt and water loss happen, but water loss is insufficient to concentrate sodium.

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14
Q

What is hypervolaemic hyponatraemia?

A

Occurs when water gains exceed sodium gains.

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15
Q

What physiological responses occur in cardiac failure?

A
  • Reduced cardiac output
  • Reduced effective circulating volume
  • Stimulation of renin/angiotensin/aldosterone and ADH
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16
Q

What can cause confusion in patients with hyponatraemia?

A

Hypotonic fluids diluting the extracellular space and causing cerebral oedema.

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17
Q

What are common clinical scenarios for fluid loss?

A
  • Haemorrhage
  • Vomiting
  • Diarrhoea
  • Burns
  • Diuretic states
  • Sequestration
  • Iatrogenic causes (e.g., diuretics, stomas)
18
Q

What are common clinical scenarios for fluid gain?

A
  • Heart failure
  • Liver failure
  • Renal failure
  • Hypothyroidism
  • Psychogenic causes
  • ADH excess
19
Q

What is the vicious cycle in cardiac failure related to hyponatraemia?

A

Fluid overload worsens left ventricular function, leading to worsening hyponatraemia.

20
Q

What is the key takeaway regarding salt and water balance?

A

Hyponatraemia is common and usually reflects water movement rather than sodium movement.

21
Q

Fill in the blank: Sodium is the primary _______ cation.

A

extracellular

22
Q

True or False: Water movement is passive, while sodium movement requires energy.

23
Q

What is hypernatraemia?

A

A condition characterized by elevated sodium levels in the blood

Major cause is concentration by water loss.

24
Q

What is the major cause of hyponatraemia?

A

Dilution by water gain

This occurs when water intake exceeds sodium intake.

25
What are the important terms related to sodium and water homeostasis?
* Hyponatraemia * Hypernatraemia * Normo (or eu-) volaemia * Hypovolaemia * Hypervolaemia ## Footnote These terms describe various states of sodium and fluid balance in the body.
26
What are the common clinical signs of hypernatraemia?
Signs include confusion, weakness, and thirst ## Footnote Symptoms may vary based on severity and rapidity of onset.
27
Fill in the blank: The major cause of hypernatraemia is _______.
concentration by water loss.
28
What are the common clinical scenarios leading to water loss?
* Haemorrhage * Vomiting * Diarrhoea * Burns * Diuretic states * Sequestration * Miscellaneous renal diseases ## Footnote These conditions can cause significant fluid loss leading to hypernatraemia.
29
True or False: Hypervolaemia is commonly associated with hypernatraemia.
False ## Footnote Hypernatraemia is almost always associated with hypovolaemia.
30
What specific causes can lead to hypernatraemia?
* Pure water loss * Reduced water intake * High sodium intake ## Footnote This includes conditions like diabetes insipidus and excessive sweating.
31
What is the role of ADH in water homeostasis?
ADH regulates water reabsorption in the kidneys ## Footnote Abnormalities in ADH secretion can lead to disorders like SIADH and diabetes insipidus.
32
What does SIADH stand for?
Syndrome of Inappropriate Antidiuretic Hormone secretion ## Footnote It leads to excessive water reabsorption and dilutional hyponatraemia.
33
What are the specific tests for investigating altered sodium and water homeostasis?
* Plasma osmolality * Urine osmolality * Urine sodium concentration ## Footnote These tests help differentiate between causes of sodium imbalance.
34
What is the recommended rate of correction for asymptomatic hyponatraemia?
4-10 mmol/l/day ## Footnote Rapid correction can lead to complications like central pontine myelinolysis.
35
What are the clinical features of volume depletion?
* Postural hypotension * Tachycardia * Absence of JVP * Reduced skin turgor ## Footnote Symptoms include thirst, dizziness, weakness, and confusion.
36
What are the clinical features of volume excess?
* Hypertension * Tachycardia * Raised JVP * Oedema ## Footnote Symptoms may include nausea, dyspnoea, and confusion.
37
How is hyponatraemia managed?
Restrict water intake ## Footnote Treatment focuses on correcting the underlying water imbalance.
38
How is hypernatraemia managed?
Administer water ## Footnote Oral intake is preferred, but IV fluids like 5% dextrose can be used.
39
What is the significance of urine osmolality in diagnosing diabetes insipidus?
Urine osmolality is usually low in diabetes insipidus ## Footnote This reflects the kidneys' inability to concentrate urine due to insufficient ADH.
40
What are the causes of cranial diabetes insipidus?
* Pituitary tumor * Head injury * Meningitis * Genetic factors ## Footnote These conditions can affect ADH production.
41
What is nephrogenic diabetes insipidus?
A condition where there is reduced tubular response to ADH ## Footnote Causes include genetic factors and certain medications like lithium.

Renal and urology (12 decks)

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