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Blood Gas Analysis Flashcards

1
Q

what does blood gas analysis measure?

A

partial pressure of gases in the blood

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2
Q

what other measurements are incorporated into blood gas analysis?

A

pH
electrolytes which affect pH

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3
Q

what is the relationship between acids and protons?

A

acids are proton donors

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4
Q

what is the relationship between bases and protons?

A

bases are proton acceptors

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5
Q

what ion is linked to pH?

A

Hydrogen

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6
Q

what is the relationship between hydrogen ions on pH?

A

pH is linked to H+ ion concentration. More H+ means lower pH

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7
Q

what is the normal blood pH?

A

7.4
(7.35-7.45)

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8
Q

what effect can small changes in pH have on H+?

A

can lead to big changes in H+ ion concentration

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9
Q

what happens to H+ concentration as pH falls?

A

H+ increases in larger and larger steps

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10
Q

why is it essential that pH is maintained in a narrow range?

A

enzymes are designed to work at a specific pH

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11
Q

what is the effect on enzymes of a change in pH?

A

rate of enzymatic reactions can be altered
enzymes can lose function and denature which has massive impact on physiology

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12
Q

what impact does disease have on pH?

A

pH often deranged in disease

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13
Q

other than disease how else may pH be altered?

A

iatrogenic (IVFT or drugs)

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14
Q

at what pH is death a risk?

A

less than 6.8
or above 7.6

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15
Q

what is a pH of above 7.45 known as?

A

alkalaemia

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16
Q

what is a pH of below 7.35 known as?

A

acidaemia

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17
Q

what must add up within the body to ensure it is electroneutral?

A

all negative and positive charges

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18
Q

what are common ions found within the body?

A

Na+
K+
Mg2+
Cl-
HCO3-
Ca2+

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19
Q

what other substances in the body aid determination of pH?

A

albumin
ketones

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20
Q

what is generated from water to balance charge differences?

A

H+

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21
Q

what range is normal pH?

A

7.35-7.45

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22
Q

does pH within the body vary between species?

A

yes between mammals

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23
Q

what does the suffix osis mean?

A

process of pH becoming more acidic or alkaline

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24
Q

what systems in the body are involved in maintenance of normal pH?

A

chemical buffers
respiratory system
renal system

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25
Q

what are the most important chemical systems involved in maintenance of normal pH?

A

phosphates
proteins
bicarbonate/carbonic acid system

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26
Q

what is described by the Henderson Hasselbalch equation?

A

relationship between pH, bicarb and CO2

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27
Q

describe the relationship between water, CO2, H+ and bicarb

A

excess CO2 is combined with water to give H+ ions and bicarb
excess H+ ions are combined with bicarb to form water and CO2

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28
Q

how is carbon dioxide excreted?

A

through the lungs

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29
Q

how are H+ ions excreted?

A

through the kidneys

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30
Q

what are buffers?

A

any particle capable of accepting or donating H+

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31
Q

what is the role of buffers?

A

act to soak up excess hydrogen and release it when necessary

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32
Q

how quickly do buffers work within the body?

A

fast - within seconds

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33
Q

what are the main buffers?

A

bicarbonate
heamoglobin
blood proteins (albumin)
phosphate
lactate

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34
Q

why is CO2 an acid?

A

within solution it is able to combine with water and form carbonic acid

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35
Q

what is the enzyme which forms carbonic acid from CO2 and water?

A

carbonic anhydrase

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36
Q

what are the main types of pH derangement?

A

respiratory acidosis
respiratory alkalosis
metabolic acidosis
metabolic alkalosis

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37
Q

what is respiratory acidosis and alkalosis caused by?

A

change in PaCO2 leading to a change in pH

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38
Q

what is metabolic acidosis and alkalosis caused by?

A

change in any other factor which may affect pH

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39
Q

what is the most common cause of metabolic acidosis and alkalosis?

A

change in HCO3- (bicarb)

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40
Q

what changes in bicarb can lead to metabolic acidosis and alkalosis?

A

loss or gain
to its role as a buffer to other acids

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41
Q

what does respiratory acidosis and alkalosis involve?

A

abnormalities in the concentration (partial pressure) of CO2

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42
Q

what is the arterial concentration of CO2 inversely proportional to?

A

ventilation

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43
Q

what effect does hyperventilation have on PaCO2?

A

level falls

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44
Q

what effect does hypoventilation have on PaCO2?

A

level increases

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45
Q

what effect does falling PaCO2 have on pH?

A

rises pH

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46
Q

what effect does rising PaCO2 have on pH?

A

lowers pH

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47
Q

how rapidly can the respiratory system respond to changes in pH?

A

very quickly
acts in response to pH changes brought on by exercise

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48
Q

what systems in the body measure pH changes?

A

medulla
carotid body

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49
Q

what is one of the major routes of excretion of acid from the body?

50
Q

what substance amount is regulated by the kidney?

A

HCO3- (and other ions)

51
Q

what organ regulates the amount of bicarbonate in the body?

52
Q

how rapidly does the renal system work to clear excess acid?

A

slowly - hours to days

53
Q

what causes respiratory acidosis?

A

increased PaCO2

54
Q

what is the compensatory response to increased PaCO2?

A

increase HCO3-

55
Q

when may acute respiratory acidosis occur?

A

anaesthesia
respiratory obstruction

56
Q

what is the difference in response between acute and chronic respiratory acidosis?

A

acute sees a smaller increase in HCO3-, chronic has more support from the kidneys so more acid is excreted and more HCO3- retained

57
Q

why is there increased levels of HCO3- in chronic respiratory acidosis?

A

kidneys have longer to react

58
Q

what is respiratory alkalosis caused by?

A

fall in PaCO2

59
Q

what is a fall in PaCO2 caused by?

A

increased ventilation (pain, stress, hypoxaemia)

60
Q

what is the difference in response between acute and chronic respiratory alkalosis?

A

acute shows a small decrease in HCO3-
chronic shows a much larger decrease as the kidneys have longer to excrete HCO3-

61
Q

why are there decreased levels of HCO3- in chronic respiratory alkalosis?

A

the kidneys have longer to excrete HCO3-

62
Q

what signifies metabolic acidosis?

A

decreased HCO3-

63
Q

what is decreased HCO3- due to?

A

direct loss of bicarbonate
consumption of bicarbonate due to excessive levels of acids

64
Q

what is suggested by decreased HCO3-?

A

metabolic acidosis

65
Q

what is the respiratory compensation for metabolic acidosis?

A

fall in PaCO2 (hyperventilation)

66
Q

what signifies metabolic alkalosis?

A

increased HCO3-

67
Q

what is indicated by raised HCO3-?

A

metabolic alkalosis

68
Q

what causes increased HCO3-?

A

compensatory increase usually due to loss of chloride ions or albumin

69
Q

what is the respiratory compensation for metabolic alkalosis?

A

increase in PaCO2 caused by decreased ventilation

70
Q

is it possible to have acidosis and alkalosis at the same time?

A

yes - mixed disorder

71
Q

describe an example of mixed respiratory and metabolic derangements

A

colicing horse -
respiratory acidosis due to distention of the abdomen preventing effective respiration
metabolic acidosis due to GI obstruction leading to build up of lactic acid

72
Q

what does base excess describe?

A

amount of acid required to titrate 1L of blood to a pH of 7.4 at 37 degrees and PaCO2 of 40mmHg

73
Q

what is the purpose of using base excess calculations?

A

removes respiratory component so metabolic can be assessed

74
Q

how does bases excess make interpretation of blood gas easier?

A

fixes PaCO2 at 40mmHg so that any remaining pH change is due to metabolic process

75
Q

what is PaCO2 fixed at during base excess analysis?

76
Q

what is indicated by a positive base excess?

A

metabolic alkalosis

77
Q

what is indicated by negative base excess?

A

metabolic acidosis

78
Q

what is the normal pH range for arterial blood?

A

7.34-7.48 (7.4)

79
Q

what is the normal pH range for venous blood?

A

7.36-7.43 (7.4)

80
Q

what is the normal PaCO2 range for arterial blood?

A

35-45 mmHg (40)

81
Q

what is the normal PaCO2 range for venous blood?

A

38-48mmHg (40)

82
Q

what is the normal HCO3 range for arterial blood?

A

22-29 mmol/l (24)

83
Q

what is the normal HCO3 range for venous blood?

A

22-29 mmol/l (24)

84
Q

what is the normal base excess range for arterial blood?

A

2-5 mmol/L (4)

85
Q

what is the normal base excess range for venous blood?

A

2-5 mmol/L (4)

86
Q

what is the other gas measured alongside CO2 during blood gas analysis?

87
Q

what is the normal arterial pressure of oxygen on room air?

A

90-100 mmHg

88
Q

what is the normal venous value of oxygen at room air?

A

40-50 mmHg

89
Q

how does arterial partial pressure usually compare to fresh inspired?

A

arterial partial pressure ~5x FiO2

90
Q

why is venous oxygen partial pressure lower then arterial?

A

due to oxygen extraction for metabolism

91
Q

what is hypoxaemia defined as?

A

less than 80mmHg PaO2

92
Q

what PaO2 is expected under anaesthesia when the patient is maintained on 100% O2?

A

400-500mmHg

93
Q

at 95% oxygen saturation what is the PaO2 of oxygen?

94
Q

what other blood gas values are measured by blood gas machines?

A

electrolytes
lactate
haematocrit
glucose
some will also provide calculated values (e.g. base excess)

95
Q

what is used to provide the sample for blood gas analysis?

A

venous or arterial blood sample

96
Q

what is the best sample for learning about gas exchange within the body?

97
Q

when should an arterial blood gas sample be taken?

A

ideally over a few breaths

98
Q

under what conditions should a blood gas sample be taken?

A

anaerobically

99
Q

why do blood gas samples need to be taken anaerobically?

A

to prevent air from altering the reading

100
Q

what syringe is best used for blood gas if sample analysis is going to be delayed?

101
Q

where should samples be kept if blood gas analysis is to be delayed?

A

on ice in a glass syringe

102
Q

why should blood gas samples be kept on ice if analysis is delayed?

A

to prevent blood metabolism from altering the sample

103
Q

what can plastic blood gas sampling syringes be used for?

A

short term (5-10 min) storage at room temperature

104
Q

what is usually found within blood gas syringes?

A

anticoagulant such as heparin

105
Q

what is the role of heparin in blood sampling?

A

prevention of clot formation

106
Q

how should blood be handled before blood gas analysis is run?

A

roll syringe of blood in hand to mix anticoagulant
discard the first drop of blood

107
Q

why does the first drop of a blood gas sample need to be disguarded?

A

often clotted

108
Q

what are the common artifacts found in blood gas analysis?

A

air contamination
saline
clotting

109
Q

how is air contamination of a blood gas sample shown?

A

CO2 unexpectedly low
O2 closer to 150mmHg

110
Q

how is saline contamination of a blood gas sample shown?

A

high chloride

111
Q

how is saline contamination of a blood gas sample caused?

A

when sampling from catheters

112
Q

how is clotting of a blood gas sample shown?

A

low PVC / HCT

113
Q

what is the anion gap?

A

difference between cations and anions

114
Q

what is the anion gap value usually?

115
Q

what is demonstrated by an increased anion gap?

A

lactic acidosis
ketoacidosis

116
Q

what is indicated by a normal anion gap?

A

GI bicarbonate loss

117
Q

what is indicated by a decreased anion gap?

A

hypoproteinaemia

118
Q

what is measured by the anion gap?

A

the difference between the negatively charged and positively charged electrolytes in blood

119
Q

what does an increased anion gap suggest about blood acidity?

A

blood is more acidic (acidaemia) (more + ions)

120
Q

what does a decreased anion gap suggest about blood acidity?

A

blood is more alkaline (alkalaemia) (more - ions)

121
Q

what acid base derangement is the anion gap used to measure?

A

metabolic acidosis or alkalosis

Advanced Clinical Nursing Theory (36 decks)

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