Fluid And Electrolyte Homeostasis ✅ Flashcards

1
Q

How is fluidr distributed in the body?

A

Between intracellular fluid and extracellular fluid

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

How are the fluids in the intracellular and extracellular compartments different?

A

The volume composition differs

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

What maintains the solute composition of the intracellular and extracellular compartments?

A
  • Cell membrane pump activity

- Solute size and electrical charge

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

What effect will a 10% decrease in plasma water have on sodium?

A

Will lead to plasma sodium decrease from 140 to 154mmol/l

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

What effect will dilution of the plasma by 10% have on sodium?

A

Will decrease sodium to 126

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

What is the most important stimulus for the kidney?

A

Volume preservation (rather than serum sodium concentration )

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

How can the body detect serum sodium concentration?

A

There are no bodily receptors that can detect serum sodium levels directly, but changes in plasma tonicity can be detected by osmoreceptors in the brain

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

What do changes in plasma tonicity detected by osmoreceptorsin the brain affect?

A

Renal water handling

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

How do changes in plasma tonicity cause changes in renal water handling?

A

Via anti-diuretic hormone (vasopressin)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What happens when there is conflicting information regarding volume status and plasma tonicity?

A

The most important principle is preservation or restoration of a normal plasma volume, rather than sodium concentration

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

What is explained by the concept that plasma volume status is prioritised over plasma sodium concentration?

A
  • Even in the presence of hypernatraemic dehydration, urine sodium may be low
  • Urine sodium is usually elevated in SIADH or in acute water intoxication despite profound hyponatraemia
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What can biochemical parameters such as fractional excretion of sodium be useful for?

A

Assisting in determining plasma volume status

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

What is hyponatraemia defined as?

A

Plasma Na <135mmol/l

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

When does hyponatraemia occur?

A

When there is either water gain in excess of sodium gain, or sodium loss in excess of water loss

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

What can cause factitious hyponatraemia?

A

The presence of abnormal solutes in the ECF, eg: mannitol, sorbitol, or excessive glucose

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

How does the presence of abnormal solutes in the ECF lead to fictitious hyponatraamia?

A

The extra molecules result in a fluid shift which alters the sodium measurement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How can factitious hyponatraemia due to the presence of abnormal solutes in the ECF be detected?

A

High measured osmolality in contrast to calculated osmolality despite low serum Na

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How is calculated osmolality determined?

A

2 x (Na + K) + rea + glucose

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the principles for managing hyponatraemia?

A
  • Rapid correction only if symptomatic, and should stop once symptoms improve
  • Fluid restriction often helpful
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What symptoms indicate a need for rapid correction in hyponatraemia?

A
  • Coma

- Seizures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Who can initiate rapid correction of hyponatraemia?

A

Only specialists

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How can rapid correction of hyponatraemia be achieved?

A

2-3ml/kg of 3% NaCl

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the maximum rate of correction of hyponatraemia?

A

8-12mmol/24 hours

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Why is fluid restriction often helpful in the management of hyponatraemia?

A

Most cases are due to excess water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What might also be helpful in the management of hyponatraemia caused by excess water?

A

Furosemide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Why might furosemide be helpful in cases of hyponatraemia?

A

It increases free water clearance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

In what condition are fluid restriction and furosemide often used in?

A

SIADH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What drug is being explored for use in refractory hyponatraemia?

A

Tolvaptan

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is tolvaptan?

A

A vasopressin receptor 2 antagonist

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is required in the management of hyponatraemia where salt loss is in excess of water loss?

A

Replacement of volume deficit and ongoing losses with normal saline

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What is hypernatraemia defined as?

A

Plasma Na >145mmol/L

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What can cause hypernatraemia?

A
  • Sodium gain in excess of water gain

- Water loss in excess of sodium loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Why can the assessment of the degree of dehydration in hypernatraemic dehydration be difficult?

A

As sodium is the principle ECF osmole, the ECF volume is relatively well maintained and signs of dehydration/hypovolaemia are less apparent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What can severe hypernatraemia be associated with?

A

Brain damage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Why might severe hypernatraemia be associated with brain damage?

A

Brain tissue shrinks as a result of intracellular dehydration and blood becomes hypercoaguable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What brain pathologies can result from hypernatraemia?

A
  • Encephalopathy
  • Cerebral haemorrhage
  • Thrombosis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What does the management of hypernatraemic dehydration include?

A
  • Avoidance of rapid correction

- Sodium chloride 0.45% or 0.9%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Why should rapid correction be avoided in hypernatraemia?

A

Can result in cerebral oedema

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Are boluses of normal saline given in hypernatraemic dehydration?

A

Only if there is shock

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

How quickly can acute hypernatraemia be corrected?

A

Over 24-48 hours

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

How does the speed of correction of chronic hypernatraemia compare to acute?

A

It should be slower in chronic

42
Q

How can cerebral oedema result from rapid correction of hypernatraemia?

A

Fluid can pass rapidly into cells

43
Q

At what rate can serum sodium be reduced in hypernatraemia?

A

No more than 0.5mmol/hour

44
Q

How quickly should normal hydration be achieved in hypernatraemia?

A

36-48 hours

45
Q

When might you want to delay normal hydration to over 72 hours in hypernatraemia?

A

If serum sodium >170

46
Q

What % of potassium is intracellular?

A

98%

47
Q

What is the result of potassium being primarily intracellular?

A

Plasma K is a poor representation of total body K

48
Q

Why are acute changes in potassium life threatening?

A

The ratio of intra- and extracellular K is a major determinant for the membrane potential of excitable cells, e.g. in the heart and nervous system

49
Q

What is the relationship between potassium and ECGs?

A

The pattern of the T wave on ECG reflects K concentration

50
Q

What is found on ECG in hypokalaemia?

A
  • ST depression
  • Flat T wave
  • Emergence of U wave
51
Q

What is found on ECG in hyperkalaemia?

A

Peaked T waves

52
Q

What effect does acidosis have on potassium?

A

It causes hyperkalaemia

53
Q

Why does acidosis cause hyperkalaemia?

A

As hydrogen ions displace potassium as the intracellular cation, and potassium shifts from the intracellular to extracellular compartment

54
Q

What controls the distribution of potassium between ICF and ECF?

A

Na/K-ATPase channels

55
Q

What is the result of the Na/K-ATPase channel controlling the distribution of potassium?

A

Compounds that enhance the activity of this pump can be used for the treatment of hyperkalaemia

56
Q

What drugs enhance the activity of the Na/K-ATPase channel?

A
  • Insulin

- Adrenergics (salbutamol)

57
Q

Where is most important K regulation done?

A

At the collecting duct

58
Q

What happens to K at the collecting duct?

A

It is exchanged for Na

59
Q

What controls the exchange of K for Na?

A

Aldosterone

60
Q

What will impair K excretion at the collecting duct?

A
  • Absence of aldosterone activity

- Insufficient sodium delivery

61
Q

What can be used to assess aldosterone activity?

A

The transtubular potassium gradient (TTKG)

62
Q

How is TTKG calculated?

A

(K in urine x serum osmolality) / (K in blood x urine osmolality)

63
Q

What will the TTKG be in the presence of normal aldosterone activity?

A

> 5

64
Q

What will the TTKG be in the absence of aldosterone?

A

<3

65
Q

What is required to be able to interpret TTKG?

A
  • Urinary Na is >20mmol/L

- Urine osmolality is equal to or greater than plasma

66
Q

Why do you need to ensure urinary Na is >20mmol/L when interpreting TTKG?

A

Confirms sodium delivery

67
Q

What is hyperkalaemia defined as?

A

K >5.5mmol/L

68
Q

What can cause artefactually high K?

A
  • Haemolysed blood sample
  • Improper collection
  • Delay in processing blood sample
  • Markedly raised platelets, leukocytes, or erythrocytes
69
Q

Give 2 ways in which improper collection can cause a falsely raised K?

A
  • EDTA contamination

- Squeezed sample

70
Q

Why is it essential that treatment for hyperkalaemia is started as soon as possible?

A

Severe hyperkalaemia can precipitate cardiac arrhythmias

71
Q

How is hyperkalaemia treated?

A
  • Measures to internalise potassium from extracellular to intracellular
  • Potassium binders
  • Stabilise myocardium
72
Q

What measures can internalise potassium from extracellular to intracellular?

A
  • Correction of acidosis
  • Insulin glucose infusion
  • Beta 2 agonist e.g. salbutamol
73
Q

How is acidosis corrected in the treatment of hyperkalaemia?

A

Bicarbonate

74
Q

Give an example of a potassium binder?

A

Calcium resonium resin

75
Q

How do potassium binders work in hyperkalaemia?

A

They decrease the body potassium store

76
Q

How is the myocardium stabilised in hyperkalaemia?

A

IV calcium gluconate

77
Q

What is the first step in identifying the underlying aetiology of hyperkalaemia?

A

Assessment of renal function

78
Q

Why is assessment of renal function the first step in the identified of the cause of hyperkalaemia?

A

Renal failure from any cause will lead to hyperkalaemia

79
Q

What can aggravate hyperkalaemia caused by renal failure?

A

Other coincidental factors, e.g.;

  • Use of drugs
  • Increased K load
80
Q

What drugs can contribute to hyperkalaemia?

A
  • ACEi
  • ARBs
  • Beta blockers
  • Trimethoprim
81
Q

What can cause an increased K load?

A
  • Tumour lysis syndrome
  • Intravascular haemolysis
  • Rhabdomyolysis
82
Q

What are the causes of hyperaemia?

A
  • Renal failure
  • Acidosis
  • Adrenal insufficiency
  • Cell lysis
  • Excessive potassium intake
83
Q

What needs to be excluded as a cause of hyperkalaemia in the critically ill neonate?

A

Inadequate cardiac output

84
Q

What is hyperkalaemia in the presence of normal GFR usually due to?

A
  • Failure of delivery of sodium to distal tubules

- Aldosterone deficiency/resistance

85
Q

What can cause failure of delivery of sodium to the distal tubules?

A

Hypovolaemia

86
Q

Give 2 causes of aldosterone deficiency/resistance?

A
  • Congenital adrenal hyperplasia

- Primary hypoaldosteronism

87
Q

What is hypokalaemia defined as?

A

K <3.5mmol/L

88
Q

How can hypokalaemia present?

A
  • Lethargy
  • Confusion
  • Muscle weakness
  • Intestinal ileus
89
Q

How can muscle weakness caused by hypokalaemia progress in severe cases?

A

To paralysis

90
Q

What are the potential pathological processes causing hypokalaemia?

A
  • Decrease in total body potassium

- Shift of potassium to the intracellular space

91
Q

What are the causes of hypokalaemia?

A
  • Diarrhoea
  • Alkalosis
  • Volume depletion
  • Primary hyperaldosteronism
  • Diuretic abuse
92
Q

What suggests renal loss in hypokalaemia?

A

A fractional excretion of >10%

93
Q

What can cause hypokalaemia with volume excess?

A
  • Aldosterone excess

- Renal artery stenosis

94
Q

What is hypokalaemia and volume excess due to hyperaldosteronism known as?

A

Conn’s syndrome

95
Q

What causes hypokalaemia with acidosis?

A

Renal tubular acidosis

96
Q

What causes hypokalaemia with low urinary potassium?

A

Extrarenal loss of potassium, e.g. diarrhoea

97
Q

When is IV potassium treatment required in hypokalaemia?

A

If cardiac arrhythmias or respiratory insufficiency secondary to paralysis

98
Q

Why should very rapid infusion of potassium be avoided in hypokalaemia?

A
  • Potential to cause major adverse effects

- Very concentrated potassium solutions damaging to peripheral veins

99
Q

What is considered to be a ‘very concentrated’ potassium solution?

A

> 40mmol/L

100
Q

What safety measures should be taken when emergency IV potassium replacement is required?

A
  • Under ECG monitoring

- In PICU

101
Q

What other electrolyte should be checked in hypokalaemia?

A

Magnesium

102
Q

Why is it important to treat low serum magnesium in hypokalaemia?

A

It can increase the risk of cardiac arrhythmias