Arterial Blood Gas (ABG) Interpretation: Practice Problems, Answers, & Cheatsheet

by Cathy Parkes July 17, 2020 Updated: July 29, 2021 2 min read 5 Comments

Review ABG Interpretation with Cathy!

Value	Normal Range	Abnormal Values
pH	7.35-7.45	pH < 7.35 indicates ACIDOSIS (ACID) ph > 7.45 indicates ALKALOSIS (BASE)
PaCO2(Respiratory System)	35-45	PaCO2 < 35 indicates ALKALOSIS (BASE) PaCO2 > 45 indicates ACIDOSIS (ACID)
HCO3(Metabolic System)	22-26	HCO3 < 22 indicates ACIDOSIS (ACID) HCO3 > 26 indicates ALKALOSIS (BASE)

With ABG interpretation problems, we are trying to figure out 3 things:

Is acidosis or alkalosis present (based on pH)?
If acidosis or alkalosis is present, which system is to blame: Respiratory system (PaCO2) or Metabolic system (HCO3)?
- Who is acting up?
Is compensation occurring? If so, is the acid/base imbalance partially or fully compensated?
- If the Respiratory system is acting up, is the Metabolic system trying to fix the situation?
- If the Metabolic system is acting up, is the Respiratory system trying to fix the situation?

Learn more in our article on respiratory acidosis.

pH	PaCO2	HCO3	Interpretation
Acid	Acid	Normal	Uncompensated respiratory acidosis.(Respiratory system is acting up, Metabolic system is NOT trying to fix the situation).
Acid	Acid	Base	Partially compensated respiratory acidosis.(Respiratory system is acting up, Metabolic system is TRYING to fix the situation).
Normal (but closer to acidic)	Acid	Base	Fully compensated respiratory acidosis.(Respiratory system is acting up, Metabolic system has FIXED the situation).

pH	PaCO2	HCO3	Interpretation
Base	Base	Normal	Uncompensated respiratory alkalosis.(Respiratory system is acting up, Metabolic system is NOT trying to fix the situation).
Base	Base	Acid	Partially compensated respiratory alkalosis.(Respiratory system is acting up, Metabolic system is TRYING to fix the situation).
Normal (but closer to basic)	Base	Acid	Fully compensated respiratory alkalosis.(Respiratory system is acting up, Metabolic system has FIXED the situation).

pH	PaCO2	HCO3	Interpretation
Acid	Normal	Acid	Uncompensated metabolic acidosis.(Metabolic system is acting up, Respiratory system is NOT trying to fix the situation).
Acid	Base	Acid	Partially compensated metabolic acidosis.(Metabolic system is acting up, Respiratory system is TRYING to fix the situation).
Normal (but closer to acidic)	Base	Acid	Fully compensated metabolic acidosis.(Metabolic system is acting up, Respiratory system has FIXED the situation).

pH	PaCO2	HCO3	Interpretation
Base	Normal	Base	Uncompensated metabolic alkalosis.(Metabolic system is acting up, Respiratory system is NOT trying to fix the situation).
Base	Acid	Base	Partially compensated metabolic alkalosis.(Metabolic system is acting up, Respiratory system is TRYING to fix the situation).
Normal (but closer to basic)	Acid	Base	Fully compensated metabolic alkalosis.(Metabolic system is acting up, Respiratory system has FIXED the situation).

Value	Normal Range	Abnormal Values
pH	7.35-7.45	pH < 7.35 indicates ACIDOSIS (ACID) ph > 7.45 indicates ALKALOSIS (BASE)
PaCO2(Respiratory System)	35-45	PaCO2 < 35 indicates ALKALOSIS (BASE) PaCO2 > 45 indicates ACIDOSIS (ACID)
HCO3(Metabolic System)	22-26	HCO3 < 22 indicates ACIDOSIS (ACID) HCO3 > 26 indicates ALKALOSIS (BASE)

With ABG interpretation problems, we are trying to figure out 3 things:

Is acidosis or alkalosis present (based on pH)?
If acidosis or alkalosis is present, which system is to blame: Respiratory system (PaCO2) or Metabolic system (HCO3)?
- Who is acting up?
Is compensation occurring? If so, is the acid/base imbalance partially or fully compensated?
- If the Respiratory system is acting up, is the Metabolic system trying to fix the situation?
- If the Metabolic system is acting up, is the Respiratory system trying to fix the situation?