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Residency Exam > Potassium Disorders (background lecture) > Flashcards

Potassium Disorders (background lecture) Flashcards

1
Q

What is the primary cation in the intracellular space?

A

Potassium

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2
Q

Describe the distribution of potassium in the plasma

A

Only a small fraction of total body potassium is found in the plasma

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3
Q

What are 3 important functions of potassium?

A
  1. Nerve transmission
  2. Cardiac contractility
  3. Muscle contractility
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4
Q

Describe the relationship between serum potassium levels and signs of toxicity

A

Signs of toxicity (especially cardiac arrhythmias) are directly related to plasma potassium

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5
Q

Describe the role of potassium in intracellular volume

A

It may play important roles in the control of intracellular volume, similar to the role of sodium in controlling extracellular volume

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6
Q

Describe the applicability of serum potassium to total body potassium

A

Serum concentration doesn’t reflect total body potassium very well, but it is still a relatively useful marker

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7
Q

What is a risk of giving high volumes of intravenous potassium?

A

This slows the heart

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8
Q

Where is potassium mainly found?

A

In muscle

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9
Q

What is the main mechanism of potassium clearance from the body?

A

It is 95% renally excreted

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10
Q

Why may a haemolysed sample lead to a false hyperkalaemia?

A

As there is potassium in red blood cells (erythrocytes)

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11
Q

What are 3 factors that increase the movement of potassium from the extracellular fluid to the intracellular fluid?

A

ß2-adrenergic stimulation
alkalosis
Insulin

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12
Q

What are 4 factors that increase the movement of potassium from the intracellular fluid to the extracellular fluid?

A
  1. Acidosis
  2. Plasma hyperosmolality
  3. ⍺-adrenergic stimulation
  4. Exercise
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13
Q

What are 5 factors which increase the urinary excretion of potassium?

A
  1. Plasma potassium levels
  2. Urine flow
  3. Kidney injury
  4. Aldosterone
  5. Sodium delivery
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14
Q

What are 5 factors which increase the urinary excretion of potassium?

A
  1. Plasma potassium levels
  2. Urine flow
  3. Kidney injury
  4. Aldosterone
  5. Sodium delivery
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15
Q

Describe the role of the kidneys in hyperkalaemia

A

It is very unlikely to have any degree of hyperkalaemia without at least some degree of renal impairment (even if mild)

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16
Q

Describe the relationship between serum potassium and body pH

A

Serum potassium will increase by 0.6 mmol/L for every 0.1 reduction in pH from 7.4, and decrease by 0.6 mmol/L for every 0.1 increase in pH from 7.4

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17
Q

Explain the activity of potassium in acidosis

A

Hydrogen is buffered intracellularly (pushed into cells) as a compensatory response, pushing potassium out of the cells, resulting in hyperkalaemia

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18
Q

Explain the activity of potassium in alkalosis

A

Hydrogen is buffered extracellularly (pushed out of cells) as a compensatory response, drawing potassium into the cells, resulting in hypokalaemia

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19
Q

Describe the activity of potassium in the kidneys

A

It is freely filtered in the glomerulus, but it is mostly reabsorbed prior to the distal tubule

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20
Q

Describe the activity of potassium in the kidneys

A

It is freely filtered in the glomerulus, but it is mostly reabsorbed prior to the distal tubule

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21
Q

How does hyperkalaemia affect aldosterone?

A

Hyperkalaemia causes and increase in aldosterone

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22
Q

Describe what determines the concentration of potassium in the urine

A

Immediate-relate is mostly a factor of potassium secretion in the distal tubule, rather than just glomerular filtration

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23
Q

What are the 2 aetiologies of hypokalaemia?

A
  1. Apparent deficit
  2. True deficit
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24
Q

What is an apparent potassium deficit?

A

Intracellular shifting of potassium

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25
Q

Decreased are 3 causes of a true potassium deficit?

A
  1. Decreased intake
  2. Increased output (extrarenal)
  3. Renal loss
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26
Q

What are 3 causes of intracellular shifting of potassium, leading to an apparent potassium deficit?

A
  1. Alkalosis
  2. ß-2 adrenergic stimulation
  3. Insulin (more common with intravenous boluses or infusions)
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27
Q

What are 5 causes of decreased intake of potassium?

A
  1. Alcoholism
  2. Potassium-free diets
  3. Intravenous fluids
  4. Anorexia nervosa
  5. Bulimia
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28
Q

What are 4 causes of increased extrarenal output of potassium?

A
  1. Vomiting
  2. Diabetes
  3. Laxative abuse
  4. Intestinal fistulas
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29
Q

What are 6 causes of increased renal potassium loss?

A
  1. Corticosteroids (especially fludrocortisone and hydrocortisone)
  2. Amphotericin B
  3. Diuretics (loop and thiazide)
  4. Hyperaldosteronism
  5. Cushing’s syndrome
  6. Liquorice ingestion
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30
Q

If a patient with hypokalaemia has hypertension, what may this indicate?

A

This could be due to a mineralocorticoid excess

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31
Q

How can you check for mineralocorticoid excess?

A

Check the plasma aldosterone:renin

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32
Q

What are 3 causes of transient hypokalaemia?

A
  1. Adrenergic hypokalaemia (stress)
  2. Post-carbohydrate meals
  3. Post exercise
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33
Q

If a patient with hypokalaemia has normal/increased plasma bicarbonate, and their urine potassium is <20 mmol/L, what does this suggest?

A

Either inadequate intake or extrarenal loss

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34
Q

If a patient with hypokalaemia has normal/increased plasma bicarbonate, and their urine potassium is >20 mmol/L, what does this suggest?

A

Renal loss

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35
Q

If a patient with hypokalaemia has decreased plasma bicarbonate, and their urine potassium is <20 mmol/L, what does this suggest?

A

Acute diarrhoea

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36
Q

If a patient with hypokalaemia has decreased plasma bicarbonate, and their urine potassium is >20 mmol/L, what does this suggest?

A

Renal loss

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37
Q

What is the main indicator of renal loss of potassium?

A

Urinary potassium > 20 mmol/L

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38
Q

What is the main cause of urinary loss of potassium?

A

Renal impairment/poisoning

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39
Q

What effect does hypokalaemia have on the T-wave?

A

Decreased T-wave amplitude

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40
Q

What effect does hypokalaemia have on the T-wave?

A

Decreased T-wave amplitude

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41
Q

How does hypokalaemia affect blood pressure?

A

It causes hypotension

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42
Q

How does hypokalaemia affect digoxin?

A

Hypokalaemia increases the risk of digoxin toxicity

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43
Q

How does hypokalaemia affect the PR interval?

A

Severe hypokalaemia causes PR prolongation

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44
Q

How does hypokalaemia affect heart rhythm?

A

Hypokalaemia causes rhythm disturbances

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45
Q

How does hypokalaemia affect the ST segment?

A

Hypokalaemia causes ST segment depression

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46
Q

How does hypokalaemia affect the QRS complex?

A

Hypokalaemia causes QRS widening

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47
Q

How does hypokalaemia affect the QRS complex?

A

Hypokalaemia causes QRS widening

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48
Q

Describe the metabolic and endocrine effects of hypokalaemia

A

Most serve as compensatory mechanisms

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49
Q

How does hypokalaemia affect aldosterone release?

A

Hypokalaemia causes decreased aldosterone release

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50
Q

How does hypokalaemia affect insulin release?

A

Hypokalaemia causes decreased insulin release

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51
Q

How does hypokalaemia affect renal responsiveness to antidiuretic hormone?

A

Hypokalaemia reduces renal responsiveness to antidiuretic hormone

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52
Q

How does hypokalaemia affect reflexes?

A

Severe hypokalaemia causes areflexia

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53
Q

What are two common muscular symptoms of hypokalaemia?

A

Cramps and weakness

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54
Q

How does hypokalaemia affect smooth muscle?

A

Hypokalaemia causes loss of smooth muscle function (ileus and urinary retention with severe hypokalaemia)

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55
Q

How does hypokalaemia affect urine concentration?

A

Hypokalaemia results in inability to concentrate urine

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56
Q

How does hypokalaemia affect the kidneys?

A

Hypokalaemia can cause nephropathy

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57
Q

What does the P wave represent?

A

Atrial contraction

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58
Q

What does the QRS complex represent?

A

Ventricular contraction

59
Q

What does the T wave represent?

A

Repolarisation

60
Q

How does hypokalaemia affect the P wave?

A

Hypokalaemia causes a slightly peaked P wave

61
Q

How does hypokalaemia affect the PR interval?

A

Hypokalaemia causes a slightly prolonged PR interval

62
Q

How does hypokalaemia affect the ST segment?

A

Hypokalaemia causes ST depression

63
Q

How does hypokalaemia affect the T-wave?

A

Hypokalaemia causes a shallow T-wave

64
Q

How does hypokalaemia affect the U-wave?

A

Hypokalaemia causes a prominent U-wave

65
Q

Describe the usual presence of a U-wave

A

U waves are usually not present

66
Q

When are U waves most commonly found?

A

In bradycardia and/or severe hypokalaemia

67
Q

What are 4 common drug causes of hypokalaemia?

A
  1. Diuretics (loop and thiazide)
  2. Aminoglycosides
  3. Salbutamol (and other ß agonists)
  4. Corticosteroids
68
Q

What is the potassium content of potassium chloride oral mixture?

A

1.33 mmol/L

69
Q

What is the potassium content of Chlorvescent?

A

14 mmol per tablet

70
Q

What is the potassium content of Slow K?

A

8 mmol per tablet

71
Q

Describe the speed of absorption of potassium chloride oral mixture

A

Absorption is rapid

72
Q

Describe the speed of absorption of potassium chloride oral mixture

A

Absorption is rapid

73
Q

Describe the speed of absorption of Chlorvescent

A

Absorption is rapid (increase in plasma concentration in 2 hours)

74
Q

What is the bicarbonate content of Chlorvescent?

A

6 mmol bicarbonate per tablet

75
Q

What is a practice point with Chlorvescent?

A

Tablets must be completely dissolved before administration

76
Q

Describe the speed of absorption of Slow K?

A

Slow release and delayed absorption

77
Q

What is the role of Slow K in practice?

A

It is used for mild or chronic hypokalaemia

78
Q

What is a practice point with Slow K?

A

Tablets must be swallowed whole

79
Q

What is mild hypokalaemia defined as?

A

Potassium 3.0-3.4 mEq/L

80
Q

What is moderate hypokalaemia defined as?

A

Potassium 2.5-2.9 mEq/L

81
Q

What is severe hypokalaemia defined as?

A

Potassium <2.5 mEq/L or symptomatic

82
Q

What is the first-line treatment option for mild hypokalaemia (3.0-3.4 mEq/L)?

A

Potassium tablets (72 mmol/day) or intravenous potassium infusion (75 mmol/day)

83
Q

What is the first-line treatment option for moderate hypokalaemia (2.5-2.9 mEq/L)?

A

Potassium tablets (96 mmol/day) or intravenous potassium infusion (100 mmol/day)

84
Q

What is the first-line treatment option for severe hypokalaemia (<2.5 or symptomatic)?

A

Intravenous replacement 40 mmol KCl in 1 L 0.9% sodium chloride (glucose 5% may be used)

85
Q

Describe the symptoms of mild hypokalaemia (3.0-3.4 mEq/L)

A

Mild hypokalaemia (3.0-3.4 mEq/L) is usually asymptomatic

86
Q

Describe the monitoring requirements in mild hypokalaemia (3.0-3.4 mEq/L)

A

Monitor potassium levels daily and adjust treatment accordingly

87
Q

When may intravenous potassium be considered for mild hypokalaemia (3.0-3.4 mEq/L)?

A

If the patient cannot tolerate oral potassium

88
Q

Describe the symptoms of moderate hypokalaemia (2.5 to 2.9 mEq/L)

A

Moderate hypokalaemia (2.5 to 2.9 mEq/L) usually has no or minor symptoms

89
Q

How often must potassium levels be monitored for moderate hypokalaemia (2.5 to 2.9 mEq/L)?

A

Daily (and adjust treatment accordingly)

90
Q

when may intravenous potassium be considered for moderate hypokalaemia (2.5 to 2.9 mEq/L)?

A

consider intravenous potassium if the patient cannot tolerate oral potassium

91
Q

What is the standard infusion rate of potassium chloride in severe hypokalaemia (<2.5 mEq/L)?

A

10 mmol/hour

92
Q

What is the maximum infusion rate of potassium chloride in severe hypokalaemia (<2.5 mEq/L)?

A

20 mmol/hour

93
Q

Describe the monitoring requirements for severe hypokalaemia (<2.5 mEq/L)

A

Check magnesium levels

94
Q

If a patient with severe hypokalaemia (<2.5 mEq/L) is hypomagnesaemic, what should be done?

A

Initially IV magnesium replacement, then start the first potassium chloride infusion, followed by further magnesium replacement

95
Q

If a patient with severe hypokalaemia (<2.5 mEq/L) is hypomagnesaemic, what should be done?

A

Initially IV magnesium replacement, then start the first potassium chloride infusion, followed by further magnesium replacement

96
Q

What are two groups of patients who may have a more pronounced response to potassium replacement?

A
  1. Patients with renal impairment
  2. Patients taking an ACE inhibitor or angiotensin receptor blocker
97
Q

Is there any way to accurately determine total body potassium?

A

No

98
Q

Describe the potassium content of a banana

A

There is 1 mmol per inch of banana

99
Q

What are the effects of Gitelman’s syndrome similar to?

A

Thiazide diuretics

100
Q

What are the effects of Bartter syndrome similar to?

A

Loop diuretics

101
Q

What are the effects of Gitelman’s syndrome similar to?

A

Thiazide diuretics

102
Q

What are the effects of Bartter syndrome similar to?

A

Loop diuretics

103
Q

Describe a biochemical difference observed between Gitelman’s syndrome and Bartter syndrome

A

Gitelman’s syndrome is associated with hypomagnesaemia

104
Q

Describe a biochemical difference observed between Gitelman’s syndrome and Bartter syndrome

A

Gitelman’s syndrome is associated with hypomagnesaemia

105
Q

Describe the acid-base disorder commonly seen in Gitelman’s syndrome

A

Hypochloraemic, hypokalaemic alkalosis

106
Q

Describe the acid-base disorder commonly seen in Gitelman’s syndrome

A

Hypochloraemic, hypokalaemic alkalosis

107
Q

Describe the acid-base disorder commonly seen in Bartter syndrome

A

Hypochloraemic, hypokalaemic alkalosis

108
Q

Describe a biochemical difference observed between Gitelman’s syndrome and Bartter syndrome

A

Gitelman’s syndrome is associated with hypomagnesaemia

109
Q

What is the treatment for Liddle’s syndrome?

A

Amiloride

110
Q

Describe the acid-base disorder commonly seen in Liddle’s syndrome

A

Hypernatraemia, hypokalaemic alkalosis

111
Q

What is the treatment for Gitelman’s syndrome?

A

Potassium-sparing diuretics

112
Q

What is the treatment for Bartter syndrome?

A

PG synthetase inhibitor

113
Q

What is the treatment for Liddle’s syndrome?

A

Amiloride

114
Q

Describe the plasma potassium ion concentration typically seen in proximal renal tubular acidosis

A

Plasma potassium is mildly decreased

115
Q

What are 5 common causes of hyperkalaemia?

A
  1. Decreased renal function
  2. Extracellular shifts of potassium
  3. Hypoaldosteronism
  4. Crush-injuries leading to intracellular release of potassium
  5. Haemolysis
116
Q

What are 5 common causes of hyperkalaemia?

A
  1. Decreased renal function
  2. Extracellular shifts of potassium
  3. Hypoaldosteronism
  4. Crush-injuries leading to intracellular release of potassium
  5. Haemolysis
117
Q

What are 5 common causes of hyperkalaemia?

A
  1. Decreased renal function
  2. Extracellular shifts of potassium
  3. Hypoaldosteronism
  4. Crush-injuries leading to intracellular release of potassium
  5. Haemolysis
118
Q

What are 5 common causes of hyperkalaemia?

A
  1. Decreased renal function
  2. Extracellular shifts of potassium
  3. Hypoaldosteronism
  4. Crush-injuries leading to intracellular release of potassium
  5. Haemolysis
119
Q

Describe the plasma potassium ion concentration typically seen in classic distal tubular acidosis

A

Plasma potassium is mildly to severely decreased

120
Q

What are 5 common causes of hyperkalaemia?

A
  1. Decreased renal function
  2. Extracellular shifts of potassium
  3. Hypoaldosteronism
  4. Crush-injuries leading to intracellular release of potassium
  5. Haemolysis
121
Q

What is hyperkalaemia defined as?

A

Potassium > 5.5 mmol/L

122
Q

What are 5 common causes of hyperkalaemia?

A
  1. Decreased renal function
  2. Extracellular shifts of potassium
  3. Hypoaldosteronism
  4. Crush-injuries leading to intracellular release of potassium
  5. Haemolysis
123
Q

What are 5 common causes of hyperkalaemia?

A
  1. Decreased renal function
  2. Extracellular shifts of potassium
  3. Hypoaldosteronism
  4. Crush-injuries leading to intracellular release of potassium
  5. Haemolysis
124
Q

What is a common cause of extracellular shifting of potassium?

A

Severe acidosis

125
Q

What are 8 drugs associated with hyperkalaemia?

A
  1. Potassium-sparing diuretics
  2. ACE inhibitors
  3. NSAIDs
  4. Angiotensin receptor blockers
  5. Unfractionated heparin
  6. trimETHOPRIM
  7. CYCLOPHOSPHamide
  8. Potassium supplements
126
Q

How does Addison disease affect potassium?

A

Addison’s disease can lead to hyperkalaemia

127
Q

What are the neuromuscular symptoms of hyperkalaemia?

A

Lower extremity weakness and paraesthesias

128
Q

What ECG changes are seen in hyperkalaemia > 6 mmol/L?

A

Peaked T waves

129
Q

What ECG changes are seen in hyperkalaemia > 7 mmol/L?

A

Widening of the QRS complex

130
Q

What ECG changes are seen in hyperkalaemia > 8 mmol/L?

A

Cardiac arrhythmias and death

131
Q

What do we do to stop the heart intraoperatively?

A

Give a bolus of potassium

132
Q

How does hyperkalaemia affect the P wave?

A

Hyperkalaemia causes a wide, flat P wave

133
Q

How does hyperkalaemia affect the R wave?

A

Hyperkalaemia causes reduced R wave amplitude

134
Q

How does hyperkalaemia affect the PR interval?

A

Hyperkalaemia causes a prolonged PR interval

135
Q

How does hyperkalaemia affect the QRS complex?

A

Hyperkalaemia causes a widened QRS complex

136
Q

How does hyperkalaemia affect the T wave?

A

Hyperkalaemia causes a tall, peaked T wave

137
Q

How does hyperkalaemia affect the ST segment?

A

Hyperkalaemia causes a depressed ST segment

138
Q

What are 3 medical conditions which increase the risk of hyperkalaemia?

A
  1. Diabetes mellitus
  2. Congestive heart failure
  3. Chronic kidney disease
139
Q

What are the 3 pillars of treatment for hyperkalaemia?

A
  1. Stabilise cell membranes with a calcium injection
  2. Move potassium intracellularly with sodium bicarbonate and/or insulin (with glucose)
  3. Remove potassium from the body using ion exchange resins or dialysis
140
Q

What are 3 examples of potassium sparing diuretics?

A
  1. Amiloride
  2. Spironolactone
  3. Triamterene
141
Q

What are 3 medical conditions which increase the risk of hyperkalaemia?

A
  1. Diabetes mellitus
  2. Congestive heart failure
  3. Chronic kidney disease
142
Q

What is patiromer?

A

A cation exchange polymer that increases potassium excretion via the gastrointestinal tract

143
Q

What are 3 medical conditions which increase the risk of hyperkalaemia?

A
  1. Diabetes mellitus
  2. Congestive heart failure
  3. Chronic kidney disease

Residency Exam (22 decks)

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