ABG

Question 1

What does ABG stand for?

Answer 1

Arterial Blood Gas

Question 2

What does arterial blood gas (ABG) measure?

Answer 2

• pH
• PaO₂ (partial pressure of oxygen in the arterial blood)
• PaCO₂ (partial pressure of carbon dioxide in the arterial blood)
• HCO₃- (bicarbonate – a base/alkali)
• Base excess (measurement of bases/alkali)

Question 3

Why would ABGs be done on a patient?

Answer 3

to check the function of the patient’s lungs & how well they are able to move oxygen and remove carbon dioxide

Question 4

What is the partial pressure of oxygen (PaO2) in the atmosphere?

Answer 4

21.1kPa (159mmHg)

Question 5

What is the partial pressure of carbon dioxide (PaCO2) in the atmosphere?

Answer 5

0.04kPa (0.3mmHg)

Question 6

What is the partial pressure of carbon dioxide (PaCO2) in alveolar air?

Answer 6

5.3kPa (40mmHg)

Question 7

What is the partial pressure of oxygen (PaO2) in alveolar air?

Answer 7

13.8kPa (104mmHg)

Question 8

How does increased CO2 affect the blood?

Answer 8

= increased H+ = decreased pH = acidic blood

Question 9

How does decreased CO2 affect the blood?

Answer 9

= decreased H+ = increased pH = alkalitic blood

Question 10

What is the normal pH of arterial blood?

Answer 10

pH 7.35-7.45

Question 11

What is the normal pH of venous blood?

Answer 11

pH 7.31-7.41

Question 12

What are the normal values for PaO2 in an ABG?

Answer 12

10.7-13.3 kPa

Question 13

What are the normal values for PaCO2 in an ABG?

Answer 13

4.7-6.0 kPa

Question 14

What are the normal values for HCO3- in an ABG?

Answer 14

22-26 mmol/l

Question 15

What are the normal values for Base Excess (BE) in an ABG?

Answer 15

-2 to +2

Question 16

Who needs an ABG?

Answer 16

• All critically ill patients
• Stable patient who suddenly drops their oxygen saturations
• Stable patient who requires an increase on FiO2 to maintain oxygenation and keep within their target range

Question 17

What is hypoxia?

Answer 17

Occurs when oxygen is insufficient at the tissue level to maintain adequate homeostasis

Question 18

What is hypoxaemia?

Answer 18

Low oxygen in arterial blood/abnormally low concentration of O2 in the blood where PaO2 is less than 80mm Hg or 10.6 kPa

Question 19

What is hypercapnia?

Answer 19

Condition characterised by increased CO2 concentration in the blood/increase in partial pressure of carbon dioxide (PaCO2) above 45 mm Hg or 6.0

Question 20

What is cyanosis?

Answer 20

Abnormal blue (blue-ish-purple) discolouration of the skin, nail beds and mucous membranes caused by a shortage of oxygenation of the blood

Question 21

What are the respiratory mechanisms of H+ removal from the body?

Answer 21

Increased CO₂ = increased H⁺ = decreased pH = increased depth and rate of breathing to blow off more CO₂

Question 22

What are the metabolic mechanisms of H+ removal from the body?

Answer 22

• Kidneys are responsible for excreting metabolic acids
• They secrete H⁺ ions into the urine and reabsorb HCO₃- (a base) from the urine = reduce H⁺ ions in the blood
• Kidneys can adjust H⁺ and HCO₃- excretion in response to changes in metabolic acid production

Question 23

What is compensation when maintaining acid-base balance?

Answer 23

• The metabolic (renal) and respiratory systems work jointly to maintain blood pH (within 7.35-7.45)
• If one system is overwhelmed, causing a change in pH, the other system usually adjusts automatically

Question 24

What is acidosis related to?

Answer 24

Decreased pH

Question 25

What is alkalosis related to?

Answer 25

Increased pH

Question 26

What causes Respiratory Acidosis?

Answer 26

• Decreased pH
• Increased PaCO2

Question 27

What causes Metabolic Acidosis?

Answer 27

• Decreased pH
• Decreased HCO3- or BE

Question 28

What causes Respiratory Alkalosis?

Answer 28

• Increased pH
• Decreased PaCO2

Question 29

What causes Metabolic Alkalosis?

Answer 29

• Increased pH
• Increased HCO3- or BE