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acute care and rehabilitation > ABG analysis > Flashcards

ABG analysis Flashcards

1
Q

what does ABG stand for?

A
  • arterial blood gases
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2
Q

how do you get ABG? what does it assess?

A
  • blood test from an artery (not a vein)
  • rapid assessment of patient physiology
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3
Q

what are the 3 main factors that ABG assesses?

A
  • oxygen concentration (02 delivery)
  • carbon dioxide concentration (C02 elimination)
  • pH (acid-base balance)
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4
Q

what should you assess ABG in?- give an example

A
  • assess in the context
    e.g., if the patient is on oxygen or ventilated
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5
Q

what happens if pH becomes deranged?

A
  • normal cell metabolism is affected
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6
Q

what is the normal pH value?

A

7.35- 7.45

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7
Q

what is the normal Pa02 value?

A

9.3 - 13.3 kPa
(80-100mmHg)

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8
Q

what is the normal PaC02 value?

A

4.7- 6.0 kPa
(35-35mmHg)

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9
Q

what is the normal HC03 value?

A

22 - 26 mmol/ L

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10
Q

what is the normal BE value?

A

-2 to + 2 mmol/ L

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11
Q

what is pH? what is it a balance of?

A
  • measure of hydrogen ions (H+) in the blood
  • balance of acids and bases in the blood
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12
Q

what is pH influenced by?

A
  • metabolic (HC03)
  • respiratory (C02)
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13
Q

what is low pH? what is it called?

A

< 7.35
- acidosis

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14
Q

what is high pH? what is it called?

A

> 7.45
- alkalosis

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15
Q

what is Pa02?

A
  • partial pressure of oxygen dissolved in the arterial blood
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16
Q

what does Pa02 determine?

A
  • determines oxygen binding to Hb (Sa02)
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17
Q

what doesn’t Pa02 determine?

A
  • doesn’t determine the acid- base status or influence pH, but it is vitally important
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18
Q

what is too low of oxygen called? what can it be?

A
  • hypoxia is serious
  • can be an early warning sign for acute illness or cardiac arrest
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19
Q

what is the value for someone with hypoxia or severe hypoxia?

A

< 9.3kPa on room air= hypoxia
< 8.0kPa on room air= severe hypoxia

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20
Q

what are the three clinical features of hypoxia?

A
  • cyanosis
  • confusion
  • delirium
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21
Q

what is PaC02?

A
  • partial pressure of carbon dioxide dissolved in the arterial blood
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22
Q

what does PaC02 assess?

A
  • assesses the effectiveness of ventilation
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23
Q

what is high Pac02 value? what is it called?

A

> 6.0 kPa
- called hypercarbia or hypercapnia

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24
Q

what are the 4 clinical features of hypercapnia?

A
  • headaches
  • confusion
  • drowsiness
  • fatigue
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25
Q

what is high PaC02 associated with?

A
  • chronic lung disease
  • acute illness
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26
Q

what does high PaC02 indicate?

A
  • respiratory acidosis
  • under- ventilation
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27
Q

what is low PaC02 value? what is it called?

A

< 4.7
- hypocarbia or hypocapnia

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28
Q

what are the four clinical features of hypercapnia?

A
  • headache
  • nausea
  • vomiting
  • fatigue
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29
Q

what is low PaC02 caused by?

A
  • hyperventilation (rapid breathing rate)
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30
Q

what does low PaC02 indicate?

A
  • respiratory alkalosis and over- ventilation
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31
Q

what does bicarbonate do?

A
  • acts as chemical buffer of pH balance
  • helps to mop up hydrogen ions
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32
Q

what compensates to maintain balance of pH?

A
  • kidneys compensate
33
Q

what does bicarbonate indicate?

A
  • whether there is a metabolic component
34
Q

what is a low HC03? what is it called and why?

A

<22
- metabolic acidosis (more free hydrogen ions)

35
Q

what is a high HC03 value? what is it called and why?

A

> 26
- metabolic alkalosis
- as the hydrogen ions are mopped up

36
Q

when can HC03- becomes abnormal?

A
  • when the kidneys are working to compensate for a respiratory problem and to help normalise pH
37
Q

what does base excess assess?

A
  • metabolic component of acid- base disorder
38
Q

when is base excess negative? what is its name?

A

< -2
- metabolic acidosis

39
Q

when is base excess positive? what is its name?

A

>

  • 2
  • metabolic alkalosis
40
Q

what does metabolic acidosis consist of?

A
  • low pH
  • decreased bicarbonate
41
Q

what is blood acidity (metabolic) due to?

A
  • metabolic/ kidney derangement
42
Q

what does metabolic acidosis include?

A
  • diabetes
  • shock
  • renal failure
43
Q

what does metabolic alkalosis consist of?

A
  • high pH
  • increased bicarbonate
44
Q

what is metabolic alkalosis due to?

A
  • metabolic/ kidney derangement
45
Q

what does metabolic alkalosis include?

A
  • chronic vomiting
  • hypokalaemia
  • sodium bicarbonate overdose
46
Q

what is the carbonic acid- bicarbonate system?

A
  • chemical buffer
47
Q

what does the body have the ability to do regarding pH?

A
  • ability to eliminate chemicals from either end of the chemical reaction to maintain pH
48
Q

what is the worded equation of the carbonic acid - bicarbonate system?

A

carbon dioxide + water = carbonic acid= hydrogen ion + bicarbonate ion

49
Q

what is the symbol equation of the carbonic acid- bicarbonate system?

A

C02 + H20 - H2C03 - H+ + HC03

50
Q

what happens to H+ in acidosis?

A
  • H+ concentration up
51
Q

what happens to H+ in alkalosis?

A
  • H+ concentration down
52
Q

why is the carbonic acid- bicarbonate buffering system effective?

A
  • ability to convert carbonic acid to carbon dioxide through the enzyme carbonic anhydrase
  • removes C02 from the body through respiration
53
Q

what happens on the other side of the carbonic- bicarbonate equation that makes the buffering system effective?

A
  • excess acid or excess alkali can be removed through the kidney
54
Q

what is respiratory acidosis?

A
  • increased PC02
55
Q

what is respiratory alkalosis?

A
  • decreased PC02
56
Q

what is metabolic acidosis?

A
  • decreased bicarbonate
57
Q

what is metabolic alkalosis?

A
  • increased HC03+ (bicarbonate)
58
Q

what is the first step in analysing ABG?

A
  • look at the P02
59
Q

what is type 1 respiratory failure?

A
  • when the body is hypoxia/ there is not enough oxygen
  • pH and PC02 are within normal range
60
Q

what is the management of someone with type 1 respiratory failure?

A
  • oxygen therapy
61
Q

what is the second step of analysing the ABG?

A
  • look at pH
62
Q

what can you determine in step 2 of analysis ABG?

A
  • determine if this is driven by respiratory or metabolic disturbances
63
Q

what is step 3 when analysing ABG? what does a high/ low value represent

A
  • look at the PC02
    high PC02= acidosis
    low PC02= alkalosis
64
Q

what question can be answered in step 3 of analysing ABG?

A
  • is the change in pH due to respiratory component, driven by PC02?
65
Q

what is type 2 respiratory failure?

A
  • when the body has low oxygen
  • and too much carbon dioxide (hypercapnia)
66
Q

what is the management of someone with type 2 respiratory failure?

A
  • invasive or non- invasive ventilation
67
Q

what is the 4th step when analysing ABG? what does a low/ high value show?

A
  • look at the HC03
    low HC03= metabolic acidosis present
    high C03= metabolic alkalosis present
68
Q

what question can be answered in stage 3 when analysing ABG?

A
  • is the change in pH due to a metabolic component, driven by HC03?
69
Q

what is the final step of ABG analysis?

A
  • is there compensation for the pH disturbance?
70
Q

what compensate for each other to return the pH to normal?

A
  • pulmonary and renal systems compensate for each other
71
Q

what do the lungs compensate for? what do they change?

A
  • compensate for metabolic inspiratory
  • change C02 excretion
72
Q

how long does lung compensation take?

A
  • occurs rapidly
73
Q

what do the kidneys compensate for? what do they alter?

A
  • compensate for respiratory instability
  • alter bicarbonate retention and H+ secretion
74
Q

how long does kidney compensation roughly take?

75
Q

how do you compensate in respiratory acidosis?

A
  • low pH, high C02
  • increase in HC03
76
Q

why do you increase bicarbonate when in respiratory acidosis?

A
  • excess hydrogen is excreted in the urine in exchange for bicarbonate ions, therefore making the blood more alkaline
77
Q

how do you compensate in respiratory alkalosis?

A
  • high pH, low C02
  • decrease bicarbonate
78
Q

why do you decrease bicarbonate for respiratory alkalosis?

A
  • renal excretion of bicarbonate increases to retain the hydrogen ions, therefore making the blood more acidic

acute care and rehabilitation (10 decks)

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