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)


If pH, PaCO2 and HCO3 are all in NORMAL range, we have HOMEOSTASIS!


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

    1. Is acidosis or alkalosis present (based on pH)?
    2. If acidosis or alkalosis is present, which system is to blame: Respiratory system (PaCO2) or Metabolic system (HCO3)?
      • Who is acting up?
    3. 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?

Acid/Base Imbalance

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).


Respiratory Alkalosis

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).


Metabolic Acidosis

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).


Metabolic Alkalosis

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).