ABG analysis Flashcards
1
Q
what does ABG stand for?
A
- arterial blood gases
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
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)
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
5
Q
what happens if pH becomes deranged?
A
- normal cell metabolism is affected
6
Q
what is the normal pH value?
A
7.35- 7.45
7
Q
what is the normal Pa02 value?
A
9.3 - 13.3 kPa
(80-100mmHg)
8
Q
what is the normal PaC02 value?
A
4.7- 6.0 kPa
(35-35mmHg)
9
Q
what is the normal HC03 value?
A
22 - 26 mmol/ L
10
Q
what is the normal BE value?
A
-2 to + 2 mmol/ L
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
12
Q
what is pH influenced by?
A
- metabolic (HC03)
- respiratory (C02)
13
Q
what is low pH? what is it called?
A
< 7.35
- acidosis
14
Q
what is high pH? what is it called?
A
> 7.45
- alkalosis
15
Q
what is Pa02?
A
- partial pressure of oxygen dissolved in the arterial blood
16
Q
what does Pa02 determine?
A
- determines oxygen binding to Hb (Sa02)
17
Q
what doesn’t Pa02 determine?
A
- doesn’t determine the acid- base status or influence pH, but it is vitally important
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
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
20
Q
what are the three clinical features of hypoxia?
A
- cyanosis
- confusion
- delirium
21
Q
what is PaC02?
A
- partial pressure of carbon dioxide dissolved in the arterial blood
22
Q
what does PaC02 assess?
A
- assesses the effectiveness of ventilation
23
Q
what is high Pac02 value? what is it called?
A
> 6.0 kPa
- called hypercarbia or hypercapnia
24
Q
what are the 4 clinical features of hypercapnia?
A
- headaches
- confusion
- drowsiness
- fatigue
25
what is high PaC02 associated with?
- chronic lung disease
- acute illness
26
what does high PaC02 indicate?
- respiratory acidosis
- under- ventilation
27
what is low PaC02 value? what is it called?
< 4.7
- hypocarbia or hypocapnia
28
what are the four clinical features of hypocapnia?
- headache
- nausea
- vomiting
- fatigue
29
what is low PaC02 caused by?
- hyperventilation (rapid breathing rate)
30
what does low PaC02 indicate?
- respiratory alkalosis and over- ventilation
31
what does bicarbonate do?
- acts as chemical buffer of pH balance
- helps to mop up hydrogen ions
32
what compensates to maintain balance of pH?
- kidneys compensate
33
what does bicarbonate indicate?
- whether there is a metabolic component
34
what is a low HC03? what is it called and why?
<22
- metabolic acidosis (more free hydrogen ions)
35
what is a high HC03 value? what is it called and why?
> 26
- metabolic alkalosis
- as the hydrogen ions are mopped up
36
when can HC03- becomes abnormal?
- when the kidneys are working to compensate for a respiratory problem and to help normalise pH
37
what does base excess assess?
- metabolic component of acid- base disorder
38
when is base excess negative? what is its name?
< -2
- metabolic acidosis
39
when is base excess positive? what is its name?
> + 2
- metabolic alkalosis
40
what does metabolic acidosis consist of?
- low pH
- decreased bicarbonate
41
what is blood acidity (metabolic) due to?
- metabolic/ kidney derangement
42
what does metabolic acidosis include?
- diabetes
- shock
- renal failure
43
what does metabolic alkalosis consist of?
- high pH
- increased bicarbonate
44
what is metabolic alkalosis due to?
- metabolic/ kidney derangement
45
what does metabolic alkalosis include?
- chronic vomiting
- hypokalaemia
- sodium bicarbonate overdose
46
what is the carbonic acid- bicarbonate system?
- chemical buffer
47
what does the body have the ability to do regarding pH?
- ability to eliminate chemicals from either end of the chemical reaction to maintain pH
48
what is the worded equation of the carbonic acid - bicarbonate system?
carbon dioxide + water = carbonic acid= hydrogen ion + bicarbonate ion
49
what is the symbol equation of the carbonic acid- bicarbonate system?
C02 + H20 - H2C03 - H+ + HC03
50
what happens to H+ in acidosis?
- H+ concentration up
51
what happens to H+ in alkalosis?
- H+ concentration down
52
why is the carbonic acid- bicarbonate buffering system effective?
- ability to convert carbonic acid to carbon dioxide through the enzyme carbonic anhydrase
- removes C02 from the body through respiration
53
what happens on the other side of the carbonic- bicarbonate equation that makes the buffering system effective?
- excess acid or excess alkali can be removed through the kidney
54
what is respiratory acidosis?
- increased PC02
55
what is respiratory alkalosis?
- decreased PC02
56
what is metabolic acidosis?
- decreased bicarbonate
57
what is metabolic alkalosis?
- increased HC03+ (bicarbonate)
58
what is the first step in analysing ABG?
- look at the P02
59
what is type 1 respiratory failure?
- when the body is hypoxia/ there is not enough oxygen
- pH and PC02 are within normal range
60
what is the management of someone with type 1 respiratory failure?
- oxygen therapy
61
what is the second step of analysing the ABG?
- look at pH
62
what can you determine in step 2 of analysis ABG?
- determine if this is driven by respiratory or metabolic disturbances
63
what is step 3 when analysing ABG? what does a high/ low value represent
- look at the PC02
high PC02= acidosis
low PC02= alkalosis
64
what question can be answered in step 3 of analysing ABG?
- is the change in pH due to respiratory component, driven by PC02?
65
what is type 2 respiratory failure?
- when the body has low oxygen
- and too much carbon dioxide (hypercapnia)
66
what is the management of someone with type 2 respiratory failure?
- invasive or non- invasive ventilation
67
what is the 4th step when analysing ABG? what does a low/ high value show?
- look at the HC03
low HC03= metabolic acidosis present
high C03= metabolic alkalosis present
68
what question can be answered in stage 3 when analysing ABG?
- is the change in pH due to a metabolic component, driven by HC03?
69
what is the final step of ABG analysis?
- is there compensation for the pH disturbance?
70
what compensate for each other to return the pH to normal?
- pulmonary and renal systems compensate for each other
71
what do the lungs compensate for? what do they change?
- compensate for metabolic inspiratory
- change C02 excretion
72
how long does lung compensation take?
- occurs rapidly
73
what do the kidneys compensate for? what do they alter?
- compensate for respiratory instability
- alter bicarbonate retention and H+ secretion
74
how long does kidney compensation roughly take?
- few days
75
how do you compensate in respiratory acidosis?
- low pH, high C02
- increase in HC03
76
why do you increase bicarbonate when in respiratory acidosis?
- excess hydrogen is excreted in the urine in exchange for bicarbonate ions, therefore making the blood more alkaline
77
how do you compensate in respiratory alkalosis?
- high pH, low C02
- decrease bicarbonate
78
why do you decrease bicarbonate for respiratory alkalosis?
- renal excretion of bicarbonate increases to retain the hydrogen ions, therefore making the blood more acidic
