Arterial Blood Gas (ABG)
Interpretation
Michaela Hill, MSN-Ed, RN
University of North Georgia
Learning Outcomes
1
Analyze the
components of ABGs
with a focus on normal
values and acid-base
status.
2
Interpret ABG results
with and without
compensation
occurring.
3
Determine ABG results
through utilizing the
Tic-Tac-Toe method.
ABGs
Arterial blood test
Evaluates oxygenation & acid-base status
Provides values for:
•
•
•
•
Potential of Hydrogen (pH)
Partial Pressure of Arterial Carbon Dioxide (PaCO2 )
Bicarbonate (HCO3-)
Partial Pressure of Arterial Oxygen (PaO2)
(Potter et al., 2016)
Components & Normal Values
Acid/Acidosis
pH
PaCO2
•
•
Respiratory component
Carbon Dioxide is an aCid
HCO3-
• Metabolic Component
• Bicarb is a Base
PaO2
•
Base/Alkalosis
7.35 45
-
(too many acids)
22
35 mmHg
(too few acids)
-
(too few bases)
7.45
26 mEq/L
(too many bases)
80-100 mmHg
Not always necessary for interpretation
(Cleveland Clinic, 2022)
Basic ABG Interpretation
(1st word: Metabolicor Respiratory)
Evaluate
HCO3- & PaCO2
(2nd word: Acidosisor Alkalosis)
Evaluate
pH
• If HCO3- is abnormal in the same
way as pH (both
acidotic/alkalotic)= Metabolic
• <7.35 = Acidosis
• If PaCO2 is abnormal with pH=
Respiratory
• >7.45 = Alkalosis
Acid
Normal
Base
Tic-Tac-Toe
Method
(Cresse, 2016).
Example:
Acid
Normal
Base
pH= 7.31
PaCO2= 57
HCO3-= 25
pH
HCO3-
PaCO2
Answer:
Respiratory Acidosis
Example:
pH= 7.25
PaCO2= 37
HCO3-= 20
Acid
pH
Normal Base
PaCO2
HCO3Answer:
Metabolic Acidosis
Compensation
Occurs when PaCO2 & HCO3- are inversely abnormal
If pH abnormality is due to a respiratory problem, the
metabolic system (kidneys) compensate
If pH abnormality is due to a metabolic problem, the
respiratory system (lungs) compensate
(Potter et al., 2016)
Image from: (Anderson, 1990)
Example with Partial
Compensation:
Acid
PaCO2
Normal Base
pH
pH= 7.51
PaCO2= 54
HCO3-= 31
HCO3Answer:
Metabolic Alkalosis with Partial Compensation
Example with Full
Compensation:
Acid
pH ➡️ PaCO2
pH= 7.44
PaCO2= 20
Normal Base
HCO3-
HCO3-= 20
• pH is normal- Look to
see if value is closer
to acid or base side.
• Here, the pH is closest
to the alkolotic side.
• pH must be normal to
be fully compensated!
Answer:
Respiratory Alkalosis with Full Compensation
References
Anderson, S. (1990). ABGs: Six easy steps to interpreting blood gases. The American Journal of
Nursing, 90(8), 42–45. https://doi.org/10.2307/3463952
Cleveland Clinic. (2022, February 18). Arterial blood gas (ABG).
https://my.clevelandclinic.org/health/diagnostics/22409-arterial-blood-gas-abg
Cresse, N.J. (2016, November 28). Tic tac toe ABGs: Interpretation and patient safety. Quality and
safety education for nurses (QSEN). https://qsen.org/tic-tac-toe-abgs-interpretation-and-patientsafety/
Potter, P., Perry, A., Hall, A., & Stockert, P. (2016). Fundamentals of nursing (9th ed.). Elsevier.