(cardioresp) arterial blood gases & acid base regulation Flashcards
1
Q
which components are measured in an ABG?
A
pO2, pCO2, pH, HCO3, base excess (BE)
among others
2
Q
what is pO2 and what does it indicate?
A
partial pressure of oxygen
indicates the concentration of oxygen dissolved in arterial blood
3
Q
what does a low pO2 suggest?
A
suggests inadequate gas exchange in the lungs
4
Q
what is pCO2 and what does it indicate?
A
partial pressure of carbon dioxide
indicates the concentration of carbon dioxide dissolved in arterial blood
5
Q
what does a high pCO2 suggest?
A
suggest inadequate gas exchange in the lungs
maybe be hypercapnia due to hypoventilation
6
Q
what is pH and what does it indicate?
A
power of hydrogen (ions)
indicates the acidity, alkalinity, or neutrality of the blood
7
Q
why is it important that the pH is finely tuned?
A
as small deviations out of the reference range of pH 7.35-7.45 can significantly disrupt oxygen transport and delivery
8
Q
what is HCO3 and what does it indicate?
A
plasma bicarbonate
indicates the concentration of bicarbonate dissolved in arterial blood
9
Q
what does an abnormal HCO3 indicate?
A
if plasma bicarbonate is higher or lower than expected
= could be due to gas exchange imbalance
10
Q
what is BE and what does it indicate?
A
base excess
indicates the difference between the current concentration of bases (mainly bicarbonate) and the ‘expected concentration’
11
Q
what does a BE of 0 mean?
A
base excess in negligible
there is no difference between the current and expected base concentrations
12
Q
what does a BE of greater than 0 mean?
A
base excess is positive
the current base concentration is greater than the expected base concentration
13
Q
what does a BE of less than 0 mean?
A
base excess is negative = base deficit
the current base concentration is less than the expected base concentration
14
Q
what is a base deficit?
A
when the current base concentration is less than the expected base concentration
15
Q
which two circulations are present in the human body?
A
pulmonary circulation (loading oxygen, unloading carbon dioxide)
systemic circulation (unloading oxygen, loading carbon dioxide)
16
Q
what is a better term for deoxygenated blood?
A
mixed venous blood
17
Q
what is the pO2 of blood once it is pumped out of the aorta into the systemic circulation?
A
> 10kPa
18
Q
what is the sO2 (oxygen saturation) of blood once it is pumped out of the aorta into the systemic circulation?
A
> 95%
19
Q
what is the pCO2 of blood once it is pumped out of the aorta into the systemic circulation?
A
4.7-6.0 kPa
20
Q
what is the pO2 of blood once it is pumped back to the right atrium from the tissues?
A
4.0-5.3 kPa
21
Q
what is the sO2 (oxygen saturation) of blood once it is pumped back to the right atrium from the tissues?
A
approx 75%
22
Q
what is the pCO2 of blood once it is pumped back to the right atrium from the tissues?
A
5.3-6.7 kPa
23
Q
what is pulmonary transit time in alveolar capillaries?
A
approx 0.75 seconds
24
Q
define pulmonary transit time
A
the time during which the erythrocytes and the plasma (?) are in contact and able to participate in gas exchange
25
how long does it take to equilibrate the oxygen and carbon dioxide back to normal levels?
approx 0.25 seconds
| = known as the gas exchange time
26
how much of the pulmonary transit time is spent equilibrating the oxygen and CO2 levels to desired levels?
approx 1/3 of the 0.75 seconds of PTT
so 0.25 seconds
27
what is gas exchange time?
the amount of time it takes to equilibrate the oxygen and carbon dioxide to desired levels
28
what diffuses quicker across the alveolar-capillary membrane: CO2 or O2 - and why?
CO2 - as it has a higher solubility in plasma
29
how does exercise affect pulmonary transit time in the alveolar capillaries?
pulmonary transit time decreases BUT the blood is still fully oxygenated and removed of CO2 in healthy, exercising adults
30
how much time is required to fully oxygenate capillary blood (compared to PTT)?
(gas exchange time is) approx 0.25 seconds = 1/3 of the pulmonary transit time
31
how is pH calculated from [H+]?
pH = -log10[H+]
| find the inverse log10 of the H+ ion concentration
32
why is it important to measure the body temperature on an ABG?
changes to body temperature can affect enzyme function
e.g. temp increase can decrease the activity of or denature carbonic anhydrase = alters plasma H+ and HCO3- levels = alters pH
33
in which condition is the body temperature not at the desired 37 degrees and still acceptable?
during some surgical procedures = controlled hypothermic circulatory rest
wherein you induce hypothermia (lower temp than normal) in a patient to slow down cellular activity and metabolism
= so circulation can be stopped without any harm to the patient
= protects against cerebral and cardiac ischaemia
34
what is the haematocrit?
the percentage of whole blood that is composed of red blood cells
35
how does carbon monoxide affect oxygen saturation levels and why?
carbon monoxide (odourless, colourless, toxic gas) binds more willingly and forcefully to haemoglobin than oxygen, displacing it
= causing a conformational shape change
= becomes harder to bind oxygen
= oxygen saturation decreases
36
what is methaemoglobin?
another version of haemoglobin wherein the Fe2+ ion is replaced by an Fe3+ ion
= does not bind oxygen
= oxygen saturation decreases
37
how does methaemoglobin affect oxygen saturation levels?
decreases oxygen saturation levels
38
how is [H+] calculated using pH?
[H+] = 10^(-pH)
39
what is an acid?
any molecule that has a loosely bound H+ ion that it can donate
40
what is an H+ ion also known as?
proton
41
what does a high pH mean in terms of H+ ion concentration?
low H+ ion concentration
42
what does a low pH mean in terms of H+ ion concentration?
high H+ ion concentration
43
what kind of molecule is a base and why is this important?
anionic molecule (negatively charged molecule)
= means it binds to free H+ ions to reduce the [H+] so the solution is less acidic
44
what are the two categories of acid produced by the body?
respiratory acid
metabolic acids
45
what is the only respiratory acid?
carbonic acid (from the dissolving of CO2 into the blood)
46
what are the metabolic acids?
lactic acid, ketoacids, hydrochloric acid
47
how does metabolic acid production compare to respiratory acid production and why?
respiratory acid production is significantly greater than metabolic acid production
- lactic acid (main metabolic acid) production is RARE = by-product of energy release in muscles when there is not enough oxygen (does not happen often)
- carbonic acid production is much greater as CO2 is constantly produced by living cells SO carbonic acid is also constantly produced
48
how does blood respond to the carbon dioxide produced by cells?
1) non-enzymatic formation of carbonic acid
carbon dioxide dissolves in the plasma to form carbonic acid
2) enzymatic formation of carbonic acid
carbon dioxide diffuses into erythrocytes and carbonic anhydrase catalyses its conversion into carbonic acid which dissociates to form H+ and HCO3- ions (w bicarbonate ions transported out of the cells)
49
explain the buffering capacity of the blood when the blood becomes acidaemic
the blood has an enormous buffering capacity enabling it to react immediately to imbalances
= due to the presence of plasma proteins and anionic bicarbonates that will buffer an increase in [H+]
50
what are the two corrective compensatory mechanisms that correct acid-base imbalances in the human body?
rapid compensatory response by the lungs
slow compensatory response by the kidneys
51
explain the rapid compensatory response by the lungs
= changes in ventilation rates (hyperventilation/hypoventilation)
= changes CO2 elimination rates
= increases or decreases carbonic acid concentration, altering blood pH
52
why is the lung response a rapid corrective mechanism?
the rapid response relies on ventilation of the lungs and we can control breathing rate
= so elimination rate of CO2 and therefore pH changes can be brought about more quickly
(e.g. slowing down breathing in a panic attack w hyperventilation)
53
explain the slow compensatory response by the kidneys
changes in HCO3- and H+ retention and secretion in the kidneys
= to increase/decrease pH
54
what is acidosis?
increased acidity of the blood
| i.e. too much acid present in the blood
55
what is alkalosis?
increased alkalinity of the blood
| i.e. too much base present in the blood
56
how is acidosis corrected?
by an alkalosis
| e.g. using an IV administration of sodium bicarbonate
57
how is alkalosis corrected?
by an acidosis
| e.g. administering drugs like ammonium chloride
58
why is the kidney response a slow corrective mechanism?
kidney response that happens through altering the retention and secretion of H+ and HCO3- relies on ultrafiltration which is SLOW
59
what is the ABG interpretation procedure?
type of imbalance?
- acidosis
- alkalosis
- normal
aetiology of imbalance?
- respiratory/metabolic acidosis
- respiratory/metabolic alkalosis
- mixed
- normal
any homeostatic compensation?
- uncompensated
- partially compensated
- fully compensated
oxygenation?
- hypoxaemia
- normoxaemia
- hyperoxaemia
60
what are they types of ABG imbalances?
- acidosis
- alkalosis
- normal
61
what are the possible causes of ABG imbalances?
- respiratory/metabolic acidosis
- respiratory/metabolic alkalosis
- mixed
- normal
62
what are the classes of homeostatic compensation in ABG imbalances?
- uncompensated
- partially compensated
- fully compensated
63
what are the classes of oxygenation in ABG imbalances?
- hypoxaemia
- normoxaemia
- hyperoxaemia
64
what is a mixed imbalance?
respiratory and metabolic BOTH
65
what is partial compensation?
if the pH is less deranged but not completely normal = imbalance is partially compensated for
= as either the respiratory or metabolic component is working to repair the initial disturbance
66
what are the references ranges for oxygenation?
above 10kPa is normal
8-10 = mild hypoxaemia
6-8 = moderate hypoxaemia
less than 6 = severe hypoxaemia
67
how do we report an arterial blood gas measurement?
assess the pH
assess the PaCO2
assess the BE
assess the PaO2
evaluate the acid-base status using pH, PaCO2 and BE
evaluate oxygenation
68
what are the references ranges for pH?
> 7.45 = high
7.35 - 7.45 = normal
< 7.35 = low
69
what are the references ranges for PaCO2?
< 4.7 kPa = low
4.7 - 6.4 kPa = normal
> 6.4 kPa = high
70
what are the references ranges for BE?
< -2 = low
-2 to 2 = normal
> 2 = high
71
what are the references ranges for PaO2?
< 10 kPa = low
10-13.5 kPa = normal
> 13.5 kPa = high (rarely a problem)
72
what are the references ranges for oxygenation?
increased = hyperoxaemia
normal = normoxaemia
decreased = hypoxaemia
73
what do the following readings collectively suggest?
low pH, high PaCO2, normal BE
uncompensated respiratory acidosis
74
what do the following readings collectively suggest?
high pH, low PaCO2, normal BE
uncompensated respiratory alkalosis
75
what do the following readings collectively suggest?
low pH, normal PaCO2, low BE
uncompensated metabolic acidosis
76
what do the following readings collectively suggest?
high pH, normal PaCO2, high BE
uncompensated metabolic alkalosis
77
what do the following readings collectively suggest?
low pH, high PaCO2, low BE
uncompensated mixed acidosis
78
what do the following readings collectively suggest?
high pH, low PaCO2, high BE
uncompensated mixed alkalosis
79
what do the following readings collectively suggest?
low pH, high PaCO2, high BE
partially compensated respiratory acidosis
80
what do the following readings collectively suggest?
high pH, high PaCO2, high BE
partially compensated metabolic alkalosis
81
what do the following readings collectively suggest?
low pH, low PaCO2, low BE
partially compensated metabolic acidosis
82
what do the following readings collectively suggest?
high pH, low PaCO2, low BE
partially compensated respiratory alkalosis
83
what do the following readings collectively suggest?
normal pH, low PaCO2, low BE
fully compensated respiratory alkalosis
OR
fully compensated metabolic acidosis
84
what do the following readings collectively suggest?
normal pH, high PaCO2, high BE
fully compensated metabolic alkalosis
OR
fully compensated respiratory acidosis
85
what do the following readings collectively suggest?
normal pH, normal PaCO2, normal BE
normal ABG
86
what is the characteristic feature of basic uncompensated disorders?
pH changes but only one of either BE or PaCO2 changes, while the other stays normal
87
what parameters change in a basic uncompensated disorder and how?
pH increases or decreases
either BE or PaCO2 increases or decreases while the other stays normal
88
what is the characteristic feature of mixed uncompensated disorders?
pH changes but the BE and PaCO2 change in OPPOSITE DIRECTIONS (i.e. one increases while the other decreases)
89
how do the parameters change in a mixed uncompensated disorder?
pH increases or decreases
BE and PaCO2 change in opposite directions: one increases, the other decreases
90
what is the characteristic feature of partially compensated disorders?
pH changes but the BE and PaCO2 change in the same direction (i.e. both increase OR both decrease)
91
how do the parameters change in a partially compensated disorder?
pH increases or decreases
BE and PaCO2 change in the SAME direction: both increase, or both decrease
92
what is the characteristic feature of fully compensated disorders?
pH is NORMAL but the BE and PaCO2 change in the same direction (i.e. both increase OR both decrease)
93
how do the parameters change in a fully compensated disorder?
pH normal
BE and PaCO2 change in the SAME direction: both increase, or both decrease
94
when does a partially compensated disorder go to becoming a fully compensated disorder?
partially compensated = pH not normal but BE has increased/decreased in accordance
fully compensated = pH now normal but BE is still increased/decreased according to the change that was required
95
how can you differentiate between a fully compensated respiratory alkalosis and a fully compensated metabolic acidosis?
cannot differentiate - cannot tell with a singular measurement which parameter (BE or PaCO2) changed first
if BE first = then metabolic
if PaCO2 first = then respiratory
96
what is the relationship between pH and proton concentration?
pH is inversely proportional to proton concentration
97
how does base excess respond to a low pH?
will increase so there are more bases to react with the protons
= so fewer protons are free in the blood
= increasing blood pH
98
what can be concluded if both BE and PaCO2 promote an alkalosis?
mixed disorder
