ABG interpretation

Question 1

What is the reference range for the PaCO2?

Answer 1

4.7-6.0

Question 2

What is the reference range for the PaO2?

Answer 2

11-13 kPa

Question 3

What is the reference range for the HCO3-?

Answer 3

22-26 mEq/L

Question 4

If a patient is receiving O2 therapy, what should their PaO2 be?

Answer 4

PaO2should be approximately10kPa less thanthe% inspired concentration FiO2

Question 5

When, according to an ABG, is a patient hypoxaemic?

Answer 5

PaO2is <10 kPa on air

Question 6

When, according to an ABG, is a patient severely hypoxaemic?

Answer 6

PaO2is <8 kPa on air

Question 7

What is type 1 respiratory failure?

Answer 7

hypoxaemia(PaO2<8 kPa) withnormocapnia(PaCO2<6.0 kPa)

Question 8

What is type 2 respiratory failure?

Answer 8

hypoxaemia(PaO2<8 kPa) withhypercapnia(PaCO2>6.0 kPa)

Question 9

What causes type 1 respiratory failure?

Answer 9

1. Reduced ventilation and normal perfusion (pulm oedema, bronchoconstriction)
2. Reduced perfusion with normal ventilation (PE)

Question 10

What causes type 2 respiratory failure?

Answer 10

• Increased resistance as a result of airway obstruction (COPD).
• Reduced compliance of the lung tissue/chest wall (pneumonia, rib fractures, obesity).
• Reduced strength of the respiratory muscles (Guillain-Barré, motor neurone disease).
• Drugs acting on the respiratory centre reducing overall ventilation (opiates).

Question 11

What are the ABG values of someone in respiratory acidosis?

Answer 11

pH low
CO2 high
HCO3 normal

Question 12

What are the ABG values of someone in respiratory alkalosis?

Answer 12

pH high
CO2 low
HCO3 normal

Question 13

What are the ABG values of someone in respiratory acidosis with partial compensation?

Answer 13

pH low
CO2 high
HCO3 high

Question 14

What are the ABG values of someone in respiratory alkalosis with partial compensation?

Answer 14

pH high
CO2 low
HCO3 low

Question 15

What are the ABG values of someone in metabolic acidosis?

Answer 15

pH low
HCO3 low
CO2 normal

Question 16

What are the ABG values of someone in metabolic alkalosis?

Answer 16

pH high
HCO3 high
CO2 normal

Question 17

What are the ABG values of someone in metabolic alkalosis with partial compensation?

Answer 17

pH high
HCO3 high
CO2 high

Question 18

What are the ABG values of someone in metabolic acidosis with partial compensation?

Answer 18

pH low
HCO3 low
CO2 low

Question 19

What are the causes of respiratory acidosis?

Answer 19

• Respiratory depression (e.g. opiates)
• Guillain-Barre: paralysis leads to an inability to adequately ventilate
• Asthma
• Chronic obstructive pulmonary disease (COPD)
• Iatrogenic (incorrect mechanical ventilation settings)

Question 20

What are the causes of respiratory alkalosis?

Answer 20

• Anxiety (i.e. panic attack)
• Pain: causing an increased respiratory rate.
• Hypoxia: resulting in increased alveolar ventilation in an attempt to compensate.
• Pulmonary embolism
• Pneumothorax
• Iatrogenic (e.g. excessive mechanical ventilation)

Question 21

What are the causes of metabolic acidosis?

Answer 21

• Diabetic ketoacidosis (↑ production)
• Lactic acidosis (↑ production)
• Aspirin overdose (ingestion of acid)
• Gastrointestinal loss of HCO– (e.g. diarrhoea, ileostomy, proximal colostomy)
• Renal tubular acidosis (retaining H)
• Addison’s disease(retaining H)

Question 22

What are the causes of metabolic alkalosis?

Answer 22

• Gastrointestinal loss of Hions (e.g. vomiting, diarrhoea)
• Renal loss of Hions (e.g. loop and thiazide diuretics, heart failure, nephrotic syndrome, cirrhosis, Conn’s syndrome)
• Iatrogenic (e.g. addition of excess alkali such as milk-alkali syndrome)

Question 23

What can cause a mixed respiratory and metabolic acidosis

Answer 23

Cardiac arrest

Multi-organ failure

Question 24

How does a mixed respiratory and metabolic acidosis present on an ABG?

Answer 24

pH low
CO2 high
HCO3- low