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brs (phase 1b) > (cardioresp) arterial blood gases & acid base regulation > Flashcards

(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

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2
Q

what is pO2 and what does it indicate?

A

partial pressure of oxygen

indicates the concentration of oxygen dissolved in arterial blood

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3
Q

what does a low pO2 suggest?

A

suggests inadequate gas exchange in the lungs

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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

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5
Q

what does a high pCO2 suggest?

A

suggest inadequate gas exchange in the lungs

maybe be hypercapnia due to hypoventilation

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6
Q

what is pH and what does it indicate?

A

power of hydrogen (ions)

indicates the acidity, alkalinity, or neutrality of the blood

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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

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8
Q

what is HCO3 and what does it indicate?

A

plasma bicarbonate

indicates the concentration of bicarbonate dissolved in arterial blood

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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

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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’

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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

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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

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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

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14
Q

what is a base deficit?

A

when the current base concentration is less than the expected base concentration

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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)

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16
Q

what is a better term for deoxygenated blood?

A

mixed venous blood

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17
Q

what is the pO2 of blood once it is pumped out of the aorta into the systemic circulation?

A

> 10kPa

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18
Q

what is the sO2 (oxygen saturation) of blood once it is pumped out of the aorta into the systemic circulation?

A

> 95%

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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

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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

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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%

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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

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23
Q

what is pulmonary transit time in alveolar capillaries?

A

approx 0.75 seconds

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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

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25
Q

how long does it take to equilibrate the oxygen and carbon dioxide back to normal levels?

A

approx 0.25 seconds

= known as the gas exchange time

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26
Q

how much of the pulmonary transit time is spent equilibrating the oxygen and CO2 levels to desired levels?

A

approx 1/3 of the 0.75 seconds of PTT

so 0.25 seconds

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27
Q

what is gas exchange time?

A

the amount of time it takes to equilibrate the oxygen and carbon dioxide to desired levels

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28
Q

what diffuses quicker across the alveolar-capillary membrane: CO2 or O2 - and why?

A

CO2 - as it has a higher solubility in plasma

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29
Q

how does exercise affect pulmonary transit time in the alveolar capillaries?

A

pulmonary transit time decreases BUT the blood is still fully oxygenated and removed of CO2 in healthy, exercising adults

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30
Q

how much time is required to fully oxygenate capillary blood (compared to PTT)?

A

(gas exchange time is) approx 0.25 seconds = 1/3 of the pulmonary transit time

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31
Q

how is pH calculated from [H+]?

A

pH = -log10[H+]

find the inverse log10 of the H+ ion concentration

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32
Q

why is it important to measure the body temperature on an ABG?

A

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

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33
Q

in which condition is the body temperature not at the desired 37 degrees and still acceptable?

A

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

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34
Q

what is the haematocrit?

A

the percentage of whole blood that is composed of red blood cells

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35
Q

how does carbon monoxide affect oxygen saturation levels and why?

A

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

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36
Q

what is methaemoglobin?

A

another version of haemoglobin wherein the Fe2+ ion is replaced by an Fe3+ ion

= does not bind oxygen
= oxygen saturation decreases

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37
Q

how does methaemoglobin affect oxygen saturation levels?

A

decreases oxygen saturation levels

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38
Q

how is [H+] calculated using pH?

A

[H+] = 10^(-pH)

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39
Q

what is an acid?

A

any molecule that has a loosely bound H+ ion that it can donate

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40
Q

what is an H+ ion also known as?

A

proton

41
Q

what does a high pH mean in terms of H+ ion concentration?

A

low H+ ion concentration

42
Q

what does a low pH mean in terms of H+ ion concentration?

A

high H+ ion concentration

43
Q

what kind of molecule is a base and why is this important?

A

anionic molecule (negatively charged molecule)

= means it binds to free H+ ions to reduce the [H+] so the solution is less acidic

44
Q

what are the two categories of acid produced by the body?

A

respiratory acid

metabolic acids

45
Q

what is the only respiratory acid?

A

carbonic acid (from the dissolving of CO2 into the blood)

46
Q

what are the metabolic acids?

A

lactic acid, ketoacids, hydrochloric acid

47
Q

how does metabolic acid production compare to respiratory acid production and why?

A

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
Q

how does blood respond to the carbon dioxide produced by cells?

A

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
Q

explain the buffering capacity of the blood when the blood becomes acidaemic

A

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
Q

what are the two corrective compensatory mechanisms that correct acid-base imbalances in the human body?

A

rapid compensatory response by the lungs

slow compensatory response by the kidneys

51
Q

explain the rapid compensatory response by the lungs

A

= changes in ventilation rates (hyperventilation/hypoventilation)

= changes CO2 elimination rates

= increases or decreases carbonic acid concentration, altering blood pH

52
Q

why is the lung response a rapid corrective mechanism?

A

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
Q

explain the slow compensatory response by the kidneys

A

changes in HCO3- and H+ retention and secretion in the kidneys

= to increase/decrease pH

54
Q

what is acidosis?

A

increased acidity of the blood

i.e. too much acid present in the blood

55
Q

what is alkalosis?

A

increased alkalinity of the blood

i.e. too much base present in the blood

56
Q

how is acidosis corrected?

A

by an alkalosis

e.g. using an IV administration of sodium bicarbonate

57
Q

how is alkalosis corrected?

A

by an acidosis

e.g. administering drugs like ammonium chloride

58
Q

why is the kidney response a slow corrective mechanism?

A

kidney response that happens through altering the retention and secretion of H+ and HCO3- relies on ultrafiltration which is SLOW

59
Q

what is the ABG interpretation procedure?

A

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
Q

what are they types of ABG imbalances?

A
  • acidosis
  • alkalosis
  • normal
61
Q

what are the possible causes of ABG imbalances?

A
  • respiratory/metabolic acidosis
  • respiratory/metabolic alkalosis
  • mixed
  • normal
62
Q

what are the classes of homeostatic compensation in ABG imbalances?

A
  • uncompensated
  • partially compensated
  • fully compensated
63
Q

what are the classes of oxygenation in ABG imbalances?

A
  • hypoxaemia
  • normoxaemia
  • hyperoxaemia
64
Q

what is a mixed imbalance?

A

respiratory and metabolic BOTH

65
Q

what is partial compensation?

A

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
Q

what are the references ranges for oxygenation?

A

above 10kPa is normal

8-10 = mild hypoxaemia
6-8 = moderate hypoxaemia
less than 6 = severe hypoxaemia

67
Q

how do we report an arterial blood gas measurement?

A

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
Q

what are the references ranges for pH?

A

> 7.45 = high

7.35 - 7.45 = normal

< 7.35 = low

69
Q

what are the references ranges for PaCO2?

A

< 4.7 kPa = low

4.7 - 6.4 kPa = normal

> 6.4 kPa = high

70
Q

what are the references ranges for BE?

A

< -2 = low

-2 to 2 = normal

> 2 = high

71
Q

what are the references ranges for PaO2?

A

< 10 kPa = low

10-13.5 kPa = normal

> 13.5 kPa = high (rarely a problem)

72
Q

what are the references ranges for oxygenation?

A

increased = hyperoxaemia

normal = normoxaemia

decreased = hypoxaemia

73
Q

what do the following readings collectively suggest?

low pH, high PaCO2, normal BE

A

uncompensated respiratory acidosis

74
Q

what do the following readings collectively suggest?

high pH, low PaCO2, normal BE

A

uncompensated respiratory alkalosis

75
Q

what do the following readings collectively suggest?

low pH, normal PaCO2, low BE

A

uncompensated metabolic acidosis

76
Q

what do the following readings collectively suggest?

high pH, normal PaCO2, high BE

A

uncompensated metabolic alkalosis

77
Q

what do the following readings collectively suggest?

low pH, high PaCO2, low BE

A

uncompensated mixed acidosis

78
Q

what do the following readings collectively suggest?

high pH, low PaCO2, high BE

A

uncompensated mixed alkalosis

79
Q

what do the following readings collectively suggest?

low pH, high PaCO2, high BE

A

partially compensated respiratory acidosis

80
Q

what do the following readings collectively suggest?

high pH, high PaCO2, high BE

A

partially compensated metabolic alkalosis

81
Q

what do the following readings collectively suggest?

low pH, low PaCO2, low BE

A

partially compensated metabolic acidosis

82
Q

what do the following readings collectively suggest?

high pH, low PaCO2, low BE

A

partially compensated respiratory alkalosis

83
Q

what do the following readings collectively suggest?

normal pH, low PaCO2, low BE

A

fully compensated respiratory alkalosis

OR

fully compensated metabolic acidosis

84
Q

what do the following readings collectively suggest?

normal pH, high PaCO2, high BE

A

fully compensated metabolic alkalosis

OR

fully compensated respiratory acidosis

85
Q

what do the following readings collectively suggest?

normal pH, normal PaCO2, normal BE

A

normal ABG

86
Q

what is the characteristic feature of basic uncompensated disorders?

A

pH changes but only one of either BE or PaCO2 changes, while the other stays normal

87
Q

what parameters change in a basic uncompensated disorder and how?

A

pH increases or decreases

either BE or PaCO2 increases or decreases while the other stays normal

88
Q

what is the characteristic feature of mixed uncompensated disorders?

A

pH changes but the BE and PaCO2 change in OPPOSITE DIRECTIONS (i.e. one increases while the other decreases)

89
Q

how do the parameters change in a mixed uncompensated disorder?

A

pH increases or decreases

BE and PaCO2 change in opposite directions: one increases, the other decreases

90
Q

what is the characteristic feature of partially compensated disorders?

A

pH changes but the BE and PaCO2 change in the same direction (i.e. both increase OR both decrease)

91
Q

how do the parameters change in a partially compensated disorder?

A

pH increases or decreases

BE and PaCO2 change in the SAME direction: both increase, or both decrease

92
Q

what is the characteristic feature of fully compensated disorders?

A

pH is NORMAL but the BE and PaCO2 change in the same direction (i.e. both increase OR both decrease)

93
Q

how do the parameters change in a fully compensated disorder?

A

pH normal

BE and PaCO2 change in the SAME direction: both increase, or both decrease

94
Q

when does a partially compensated disorder go to becoming a fully compensated disorder?

A

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
Q

how can you differentiate between a fully compensated respiratory alkalosis and a fully compensated metabolic acidosis?

A

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
Q

what is the relationship between pH and proton concentration?

A

pH is inversely proportional to proton concentration

97
Q

how does base excess respond to a low pH?

A

will increase so there are more bases to react with the protons

= so fewer protons are free in the blood
= increasing blood pH

98
Q

what can be concluded if both BE and PaCO2 promote an alkalosis?

A

mixed disorder

brs (phase 1b) (71 decks)

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