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The Respiratory System > Aterial Blood Gas Measurement > Flashcards

Aterial Blood Gas Measurement Flashcards

1
Q

How is haemoglobin saturation measured

A

Using absorption spectroscopy - saturated haemoglobin is red while unsaturated haemoglobin is blue so these absorb at different wavelengths and this allows deduction of the saturation of haemoglobin.

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2
Q

What is measured in blood gas analysis

A

Hydrogen ion concentration, oxygen and CO2 content.

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3
Q

What cannot be directly measured but has to be calculated from arterial blood gas measurement

A

Bicarbonate.

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4
Q

What is bound to carboxyhaemoglobin

A

Carbon monoxide

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5
Q

What is bound to carbaminohaemoglobin

A

Carbon dioxide

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6
Q

Why can’t oxygen bind to mathaemoglobin

A

Because the Fe2+ ion is replaced by an Fe3+ ion and oxygen cannot bind to Fe3+.

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7
Q

How does carbon monoxide poising come about and how is it treated

A

Because carbon monoxide has a higher affinity for haemoglobin compared to oxygen so displaces oxygen and causes hypoxia. It can be treated using high concentration oxygen.

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8
Q

What is the partial pressure of oxygen in the air

A

21kPa

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9
Q

What is the total pressure in the atmosphere

A

100kPa

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10
Q

What is a normal PaO2

A

Between 13 and 14 kPa.

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11
Q

What happens to the PaO2 if atmospheric pressure is reduced

A

The PaO2 also reduces

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12
Q

What facts do you need to know to figure out if someones oxygenation is effective and working properly

A

Their inspired oxygen (e.g. air, 60% oxygen etc) and there PaO2.

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13
Q

What may be the issue if someone has low PaO2 for their inspired oxygen concentration

A

V/Q mismatching. This may be caused by an area of consolidation such as in pneumonia. Exchange is impaired in pneumonia due to the filling of alveolar spaces so no matter how much you increase the inspired concentration of oxygen, perfusion of the blood is not going to increase.

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14
Q

Which type of receptors detect high carbon dioxide in the blood and stimulate hyperventilation

A

Chemoreceptors.

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15
Q

In what situation in V/Q mismatching may CO2 be high as well as oxygen low

A

This happens when the normal part of the lung cannot compensate for the high CO2 by hyperventilation. This happens when there is widespread V/Q mismatch.

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16
Q

What is type 1 respiratory failure

A

When there is low oxygen and normal carbon dioxide.

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17
Q

What may cause type 1 respiratory failure

A

Lobar pneumonia

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18
Q

What is type 2 respiratory failure

A

When there is both low oxygen and high carbon dioxide.

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19
Q

What may cause type 2 respiratory failure

A

A drug overdose.

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20
Q

What is acidaemia

A

When there is a high concentration of H+ ions in the blood.

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21
Q

What are the two types of acidaemia

A

Respiratory acidaemia and metabolic acidaemia

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22
Q

What happens in respiratory acidaemia

A

There is a respiratory failure so less carbon dioxide is being exhaled and therefore there is more carbon dioxide in the blood.

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23
Q

What happens in metabolic acidaemia

A

There is an increase in the production of acid or a decrease in the excretion of acid.

24
Q

What happens to bicarbonate in respiratory acidaemia

A

There is increased bicarbonate as there is increased carbon dioxide in the blood.

25
Q

What happens to bicarbonate in metabolic acidaemia

A

There is decreased bicarbonate as there is increased production of acid or reduced excretion of acid.

26
Q

What is the formula linking carbon dioxide, bicarbonate and acid

A

CO2 + H20 –> H2CO3

H2CO3 –> H+ + HCO3-

27
Q

Why is standard bicarbonate used

A

This is used as it is influenced only by metabolic effects so can help to determine if there is a metabolic component

28
Q

How is standard bicarbonate calculated

A

Using the actual H+ value and a PCO2 of 5.3kPa (Normal PCO2)

29
Q

How is actual bicarbonate calculated

A

Using actual H+ and PCO2 values.

30
Q

What does it mean if the standard bicarbonate is normal

A

Any acidaemia is solely respiratory

31
Q

Which component - respiratory or metabolic - does base excess give information regarding

A

The metabolic component.

32
Q

What is base excess

A

Base excess is the amount of base needed to be removed from a litre of blood at a normal PCO2 to bring the H+ back to normal.

33
Q

What is the normal value of base excess

A

0 (-2 to 2 is the normal range)

34
Q

What does it mean if the base excess value is positive

A

Metabolic alkalosis

35
Q

What does it mean if the base excess value is negative

A

Metabolic acidosis.

36
Q

what does it mean if the base excess and standard bicarbonate is normal but there is a high concentration of H+ ions.

A

Acidaemia is purely respiratory

37
Q

What is the metabolic compensation for respiratory acidaemia

A

The kidney retains HCO3 as metabolic compensation so the H+ returns towards a normal level.

38
Q

How can you tell from arterial blood gas measurement that there is respiratory failure

A

If the PO2 is low given the inspired oxygen.

39
Q

Other than drug overdose, what else can type 2 respiratory failure be a result of

A

A chest wall abnormality, scoliosis, asthma, muscular dystrophy

40
Q

How do you know an acidaemia is at least partly respiratory

A

If pCO2 is high

41
Q

How do you know if an acidaemia is at least partly metabolic

A

If the standard bicarbonate is low or the base excess is more negative than -2moll-1.

42
Q

What is the pKa

A

The half titration point of any buffer

43
Q

What does a high pKa mean

A

There is a strong base in the buffer

44
Q

What does a low pKa mean

A

There is a strong acid in the buffer

45
Q

When you are titrating an amino acid which group will have a low pKa

A

The COOH group will have a low pKa as it is more acidic.

46
Q

When you are titrating an amino acid which group will have a high pKa

A

The NH2 group will have a high pKa as it is more basic.

47
Q

What happens to an amino acid as the pH increases

A

More H+ ions are pulled off the structure and the molecule becomes more negative.

48
Q

When do buffers work best

A

When the acid is half ionised. This is when it is at its pKa value.

49
Q

What is the isoelectric point of a protein

A

The pH value at which the net charge of the protein is 0.

50
Q

Why is the bicarbonate buffer system of the body important

A

Because there is lots of bicarbonate in the plasma and this is under dynamic management by the body through the lungs and the kidney.

51
Q

Why is CO3^2- negligible

A

Because there is no significant concentration of this in the body.

52
Q

What is the Bohr effect

A

Oxyhaemoglobin is a stronger acid than deoxyhaemoglobin.

53
Q

What is the metabolic compensatory response to respiratory acidaemia

A

In respiratory acidaemia there is high CO2. This is compensated by an increase in bicarbonate by the metabolic system.

54
Q

What is the metabolic response to respiratory alkalaemia

A

In respiratory alkalaemia there is low CO2. This is compensated by a decrease in bicarbonate by the metabolic system.

55
Q

What does if mean if the parameters (carbon dioxide and bicarbonate) change in the same direction (both increase or both decrease)

A

There is a compensatory response to either a respiratory or metabolic problem. One parameter has changed in response to the other.

56
Q

What does it mean if only one parameter (CO2 or bicarbonate) has changed

A

There is no compensation.

57
Q

What does it mean if the parameters (CO2 and bicarbonate) change in different directions (one increases while the other decreases)

A

If both parameters have changed in opposite directions this means there are abnormalities both in the respiratory and metabolic systems - one is not compensating for the other.

The Respiratory System (20 decks)

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