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EMS > Lecture 29 - Potassium and Hydrogen Homeostasis > Flashcards

Lecture 29 - Potassium and Hydrogen Homeostasis Flashcards

1
Q

What is homeostasis?

A

Homeostasis is defined as maintenance of the internal environment in a constant state despite external changes.

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2
Q

Give 5 examples of homeostasis?

A

Water Balance
Blood Pressure
Blood pH
Body Temperature
Blood glucose

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3
Q

Which ion is the major intracellular ion?

A

Potassium (K+)

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4
Q

What is the average intracellular concentration of potassium?

A

160 mmol/L

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5
Q

What is the normal plasma concentration range of potassium?

A

3.5-5.2 mmol/L

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6
Q

Why does serum have 0.4mmol/L more K+ than plasma?

A

serum is left to clot, to remove clotting factors, increasing K+

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7
Q

How does acidosis affect the movement of K+?

A

K+ leaches out into extracellular fluid causing hyperkalaemia metabolic acidosis

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8
Q

How does alkalosis affect the movement of K+?

A

K+ is pumped into cells cause hypokalaemia metabolic alkalosis

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9
Q

What are the 2 major areas for K+ control?

A
  1. The total body K+
  2. The distribution between intracellular and extracellular spaces
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10
Q

What 3 factors influence the balance between the passive loss out of cells and the active Na, K-ATPase pumping K+ in against the concentration gradient?

A
  1. Acid-base status
  2. Hormones- Insulin,Catecholamines
  3. ECF Osmolality
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11
Q

How does insulin affect the movement of K+?

A

insulin drives K+ into cells by stimulating the Na+/K+ ATPase pump

This is exploited in the treatment of hyperkalaemia

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12
Q

Give three examples of catecholamines that affect the movement of K+:

A

1) adrenaline

2) noradrenaline

3) dopamine

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13
Q

How do catecholamines affect the movement of K+? (3)

A

1) they trigger beta adrenergic receptors which promote cellular K+ uptake

2) they trigger alpha adrenergic receptors which promote cellular K+ loss

3) this leads to an overall net uptake

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14
Q

Describe how increase tonicity affects the movement of K+:

A

K+ passively leaches out of cells causing hyperkalaemia

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15
Q

Give 3 examples of when extracellular fluid osmolality would be increased:

A

1) infusion of hypertonic saline

2) hyperglycaemia in hyperosmolar hyperglycaemic state

3) mannitol

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16
Q

How does hyperkalaemia affect membrane potential?

A

hyperkalaemia raises the resting potential towards the threshold, making is easier for cells to fire

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17
Q

How does hypokalaemia affect membrane potential?

A

hypokalaemia lowers the resting potential making it harder for cells to fire

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18
Q

What % of K+ is reabsorbed before the filtrate enters the distal convoluted tubule?

A

95%

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19
Q

What is a major determinant of the resting cell- membrane potential?

A

Ratio of intracellular to extracellular K+

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20
Q

What 3 things does the resting potential play a vital role in?

A
  1. Function of skeletal muscle
  2. Function of cardiac muscle
  3. Function of nerve
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21
Q

What does decreased K+ mean for resting potential?

A

increased resting potential
decreased excitability

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22
Q

What does increased K+ mean for resting potential?

A

decreased resting potential
increased excitability

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23
Q

Aside from membrane potential, what 3 other major things does K+ play a role in?

A
  1. Protein Synthesis
  2. Acid- base balance
  3. Maintenance of intracellular osmolarity
24
Q

What is the effect of systemic acidosis on kidney K+ secretion?

A

reduced K+ secretion

25
Q

What is the effect of hyperkalaemia on aldosterone release?

A

hyperkalaemia triggers aldosterone release

26
Q

What is the effect of aldosterone on K+ levels?

A

aldosterone causes Na+ retention for K+ excretion as well as H+ secretion from cells in the collecting duct and distal convoluted tubule so that H+ can be excreted with K+ in exchange for Na+

27
Q

Give three key outputs of K+:

A

1) urinary output

2) faecal excretion

3) skin loss

28
Q

What does urine potassium concentration vary between?

A

5- 150 mmol/L

29
Q

How are clinical disorders of potassium classified?

A

based on the serum potassium

30
Q

What are the main causes of clinically significant changes of K+?

A

Transcellular shifts rather than total body K loss

31
Q

How much potassium is excreted through faeces per day?

A

5-10 mmol/day

32
Q

How much potassium is excreted through skin loss per day?

A

5-10 mmol/day

33
Q

What is the threshold for hyperkalaemia?

A

above 5.5 mmol/L

34
Q

What are the stages of hyperkalaemia?

A

Mild (serum potassium 5.5 - 6.0 mmol/L)
Moderate (6.1 - 6.9 mmol/L)
Severe (≥7.0 mmol/L)

35
Q

Give two common causes of fictitious hyperkalaemia:

A

1) leaving a blood sample out at room temperature allowing clotting to occur, increasing K+

2) using an EDTA blood sample bottle which already has K+ in it

36
Q

Give 8 clinical signs of hyperkalaemia:

A

1) cardiac arrhythmia

2) fatigue

3) vomiting

4) weakness

5) sudden death

6) paraesthesia

7) ECG changes

8) palpitations

37
Q

Give 4 ECG changes seen in hyperkalaemia:

A

1) tall T waves

2) prolonged PR intervals

3) widened QRS intervals

4) flattened P waves

38
Q

Give 8 causes of hyperkalaemia:

A

1) hypoaldosteronism

2) tissue damage

3) fictitious

4) renal failure

5) K+ sparing diuretics

6) hyperinsulinism

7) acidosis

8) drugs

39
Q

Give an example of a condition that causes hypoaldosteronism:

A

Addison’s disease

40
Q

Give an example of a K+ sparing diuretic:

A

Spironolactone

41
Q

Name 3 features of Hyperkalaemia in the neuromuscular system?

A

Weakness
Paraesthesia
Paralysis

42
Q

Name 3 features of Hyperkalaemia in the Cardiovascular system?

A

Conduction defects
Arrhythmias
Cardiac arrest

43
Q

Name 3 features of hyperkalaemia in the GI tract?

A

Nausea
Vomiting
Pain
Ileus

44
Q

Give the three steps used in hyperkalaemia treatment:

A

1) give 10ml of calcium gluconate

2) give insulin or salbutamol to shift K+ into cells

3) stop potassium intake (halting K+ rich drugs and food)

45
Q

Why is calcium gluconate given to treat hyperkalaemia?

A

to protect the cardiac membrane

46
Q

What is hypokalaemia?

A

Potassium level of <3.5mmol/L

47
Q

Give 8 clinical signs of hypokalaemia:

A

1) lethargy

2) respiratory failure

3) ventricular arrythmias

4) decreased tendon reflexes

5) cardiac arrest

6) tubular resistance to ADH

7) weakness and paralysis

8) ECG changes

48
Q

Give 4 ECG changes seen in hypokalaemia:

A

1) flattened T waves

2) ST segment depression

3) prolonged QT interval

4) tall U wave

49
Q

What is does U wave represent on an ECG?

A

repolarization of the purkinje fibres

50
Q

Give 4 causes of hypokalaemia:

A

1) insulin therapy

2) alkalosis

3) diuretic therapy

4) vomiting and diarrhoea

51
Q

When replenishing low K+, what other mineral is important to consider?

A

magnesium

52
Q

Give the two steps used to treat hypokalaemia?

A

1) place patient with suspected hypokalaemia on a heart monitor

2) direct K+ replacement therapy (oral or IV if severe)

53
Q

Name 2 features of Hypokalaemia in the neuromuscular system?

A

Weakness
Paralysis

54
Q

Name 3 features of Hypokalaemia in the Cardiac system?

A

Conduction defects
Arrhythmias
Digoxin toxicity

55
Q

Name 3 features of Hypokalaemia in the renal system?

A

Impaired concentrating ability
Tubular defects (resistance to ADH)
Metabolic alkalosis

56
Q

If the potassium level is less than 2.5 mmol/L, what should be given?

A

intravenous potassium

57
Q

What is difficult to replenish if serum magnesium levels are low?

A

Serum Potassium

EMS (54 decks)

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