Arterial Blood Gas Measurement

Question 1

What does ABG measure? (5)

Answer 1

Partial pressure of oxygen

Partial pressure of carbon dioxide

pH

Plasma bicarbonate

Base excess

Question 2

What does PO2 measure?

Answer 2

The partial pressure of oxygen: This variable indicates how much oxygen is dissolved in the arterial blood, and if it is particular low it can suggest inadequate gas exchange in the lungs.

Question 3

What does PCO2 measure?

Answer 3

The partial pressure of carbon dioxide: This variable indicates how much carbon dioxide is dissolved in arterial blood, and if it is particularly high it can suggest inadequate gas exchange in the lungs.

Question 4

What does pH measure?

Answer 4

The ‘power of hydrogen’: This variable describes the acidity, neutrality or alkalinity of the blood. The pH of arterial blood is finely tuned, and small deviations can affect oxygen transport and delivery.

Question 5

What does plasma bicarbonate measure?

Answer 5

This variable describes the concentration of bicarbonate dissolved in arterial blood. If plasma bicarbonate is higher or lower than normal, this could be evidence of gas exchange imbalance.

Question 6

What does base excess measure?

Answer 6

This variable describes the concentration of bases (predominantly bicarbonate) compared with the ‘expected concentration’. An exact match is 0, an excess of base is positive, and a base deficit is negative.

Question 7

What is the oxygen saturation of mixed venous blood?

Answer 7

75%

Question 8

How does oxygen bind to haem groups within erythrocytes?

Answer 8

Through cooperative binding

Question 9

What is oxygen flux?

Answer 9

The amount of oxygen delivered to peripheral tissue per minute

Question 10

What is pulmonary transit time?

Answer 10

The amount of time it takes for a molecule to cross the gaseous exchange surface 0.75s, oxygen can equilibrate within this length of time

Question 11

What decreases pulmonary transit time?

Answer 11

• Carbon dioxide is soluble within plasma, therefore enabling ability to dissolve quickly into the alveoli. Cardiac output increases during exercise -Decreases pulmonary transit time (Improves ability to increase oxygen saturation of haemoglobin, oxygen loading is faster).

Question 12

What is an acid?

Answer 12

Acids have the ability to donate hydrogen ions (Weak association). H+ (protons  Valency of +1 has no electrons or neutrons). A greater concentration of H+ ions - Lower pH.

Question 13

What is a base?

Answer 13

Base: Anionic (negative charged ions) molecule capable of reversibly binding protons, reducing the available dissociated H+ ions within the plasma.
H+A-⇌H++ A-

Question 14

Which enzyme catalyses the formation of carbonic acid within RBCs?

Answer 14

Carbonic anhydrase

Question 15

What is the fate of carbonic acid within RBCs?

Answer 15

Dissociates into respective hydrogen and bicarbonate ions

Question 16

Which transporter regulates bicarbonate-chloride exchange?

Answer 16

AE1 transporter

Question 17

How is carbon dioxide primarily transported through circulation?

Answer 17

As bicarbonate

As carbaminohaemoglobin

Dissolved in plasma

Question 18

What is alkalaemia?

Answer 18

Refers to elevated blood pH in respect to standard

Question 19

What is acidaemia?

Answer 19

Refers to lower than standard blood pH

Question 20

What is alkalosis?

Answer 20

Describes circumstances that will decrease [H+] & increase pH.

Question 21

What is acidosis?

Answer 21

Describes circumstances that will increase [H+] and decrease pH.

Question 22

What is respiratory compensation?

Answer 22

Changes in ventilation can stimulate a rapid compensatory response to alter carbon dioxide elimination, therefore altering the pH.

Question 23

What is metabolic compensation?

Answer 23

Changes in HCO3- & H+ retention/secretion in the kidneys can stimulate a slow compensatory response to pH change  Metabolic compensation

• An acidosis will need an alkalosis to correct
• An alkalosis will need an acidosis to correct

Question 24

What is the following diagnosis for:

Low pH
High Carbon dioxide
Normal Base excess

Answer 24

Uncompensated respiratory acidosis

Question 25

What is the following diagnosis for:

High pH
Low Carbon dioxide
Normal Base excess

Answer 25

Uncompensated respiratory alkalosis

Question 26

What is the following diagnosis for:

Low pH
Normal Carbon dioxide
Low BE

Answer 26

Uncompensated metabolic acidosis

Question 27

What is the following diagnosis for:

High pH
Normal Carbon dioxide
High Base excess

Answer 27

Uncompensated metabolic alkalosis

Question 28

What is the following diagnosis for:

Low pH
High Carbon dioxide
Low Base excess

Answer 28

Uncompensated mixed acidosis

Question 29

What is the following diagnosis for:

High pH
Low Carbon dioxide
High Base excess

Answer 29

Uncompensated mixed alkalosis

Question 30

What is the following diagnosis for:

Low pH
High Carbon dioxide
High Base excess

Answer 30

Partially compensated respiratory acidosis

Question 31

What is the following diagnosis for:

High pH
High Carbon dioxide
High Base excess

Answer 31

Partially compensated metabolic alkalosis

Question 32

What is the following diagnosis for:

Low pH
Low Carbon dioxide
Low Base excess

Answer 32

Partially compensated metabolic acidosis

Question 33

What is the following diagnosis for:

High pH
Low Carbon dioxide
Low Base excess

Answer 33

Partially uncompensated respiratory alkalosis

Question 34

What is the following diagnosis for:

Normal pH
Low Carbon dioxide
Low Base excess

Answer 34

Fully compensated respiratory alkalosis/ metabolic acidosis

Question 35

What is the following diagnosis for:

Normal pH
High Carbon dioxide
High Base excess

Answer 35

Fully compensated respiratory acidosis/metabolic alkalosis