EXAM AND ANSWERS FOR ABG INTERPRETATION 2025
Hypoxia = SpO2 <94%, shock, re-
duced consciousness, respiratory dis-
tress, smoke inhalation, chronic respira-
List the indications for an ABG.
tory disease, acutely unwell patient and
assessment for long term oxygen thera-
py.
1) check patient details
2) check PaO2 - are they hypoxic? Type 1
or 2 RF?
3) check pH - acidotic (pH<7.35/H+>45)
or alkalotic (pH>7.35/H+<45).
4) check CO2 - raised if acidotic and
decreased if alkalotic.
5) check HCO3 - raised if alkalotic and
decreased if acidotic.
Describe the methodology for looking at
to determine the primary disturbance
ABGs
look at each separately to see if they
match up to the pH = if they are deranged
this is the compensation. Partial compen-
sation = compensation is occurring but it
has not normalised the pH yet. Complete
compensation = compensation method
has worked and pH is normalised.
6) base excess, anion gap (metabolic
acidosis), lactate and electrolytes.
Hypoxia (reduced PaO2) with reduced or
normal PaCO2. It is the failure to oxy-
genate blood often due to VQ mismatch.
Either 1)reduced ventilation with normal
What is type 1 respiratory failure? perfusion = mucus plug in asthma/copd
or airway collapse in emphysema/pul-
monary oedema. Or 2) reduced perfu-
sion with normal ventilation = pulmonary
embolism.
hypoxia and hypercapnia (raised
PaCO2). It is due to a failure to oxygenate
What is type 2 respiratory failure? blood and a failure to remove CO2. Often
due to alveolar hypoventilation in severe
1/3
Hypoxia = SpO2 <94%, shock, re-
duced consciousness, respiratory dis-
tress, smoke inhalation, chronic respira-
List the indications for an ABG.
tory disease, acutely unwell patient and
assessment for long term oxygen thera-
py.
1) check patient details
2) check PaO2 - are they hypoxic? Type 1
or 2 RF?
3) check pH - acidotic (pH<7.35/H+>45)
or alkalotic (pH>7.35/H+<45).
4) check CO2 - raised if acidotic and
decreased if alkalotic.
5) check HCO3 - raised if alkalotic and
decreased if acidotic.
Describe the methodology for looking at
to determine the primary disturbance
ABGs
look at each separately to see if they
match up to the pH = if they are deranged
this is the compensation. Partial compen-
sation = compensation is occurring but it
has not normalised the pH yet. Complete
compensation = compensation method
has worked and pH is normalised.
6) base excess, anion gap (metabolic
acidosis), lactate and electrolytes.
Hypoxia (reduced PaO2) with reduced or
normal PaCO2. It is the failure to oxy-
genate blood often due to VQ mismatch.
Either 1)reduced ventilation with normal
What is type 1 respiratory failure? perfusion = mucus plug in asthma/copd
or airway collapse in emphysema/pul-
monary oedema. Or 2) reduced perfu-
sion with normal ventilation = pulmonary
embolism.
hypoxia and hypercapnia (raised
PaCO2). It is due to a failure to oxygenate
What is type 2 respiratory failure? blood and a failure to remove CO2. Often
due to alveolar hypoventilation in severe
1/3
