How to Interpret an ABG Part 1
- RT Jaime
- Jun 4, 2021
- 3 min read
How to Interpret an ABG Part 1
Alright, so to keep things simple, we will start with how PaCO2 and HCO3- impact pH. There are other things that can impact pH, however, we will be discussing the foundation of interpreting ABG’s using only PaCO2 and HCO3- for now.
Normal Values
pH 7.35 - 7.45
PaCO2 35 - 45 mmHg
PaO2 80 -100 mmHg
HCO3- 22-26
Step 1
Determine if the pH is normal, acidic or basic.
Normal pH value: 7.35-7.45
Any pH below 7.35 will be deemed ACIDIC
Any pH above 7.45 will be deemed BASIC.
Step 2
Determine which of the two, the PaCO2 or HCO3- is the PRIMARY cause of the deviation in pH.
In order to do this you have to remember the relationships of both of these ions and their impact on pH.
pH and PaCO2
pH and PaCO2 are indirectly proportional which means if PaCO2 goes up, the pH will go down (ACIDIC) and vice versa.
pH and HCO3-
pH and HCO3- have a directly proportional relationship which means that if bicarbonate goes up the pH ALSO goes up and vice versa.
About PaCO2
PaCO2 is given the name respiratory since it’s balance comes from the lungs.
How fast or slow a patient breathes will impact the level of PaCO2 in their blood immediately. That is why people who are hyperventilating breathe into a brown bag so they don’t breath all their PaCO2 off and pass out. By using the bag, they REBREATHE their PaCO2 and prevent themselves from passing out due to hyperventilation. PaCO2 can be changed very quickly in the body just by breathing slowly or quickly within seconds to minutes.
Ready to practice ABG Interpretation with FLASHCARDS?
CLICK HERE to put your knowledge to the test with the RTRC
ABG Interpretation Flashcards!
About HCO3-
HCO3- is given the name metabolic since it’s balance comes from the kidneys. The kidneys are responsible for keeping the fluid balance in the body and meeting the metabolic demands of the patient. Whether a patient is fluid positive or negative can impact their bicarbonate levels as well. Bicarb takes longer to change in the body than PaCO2. Bicarb levels change naturally within 48 to 72 hours if needed for compensation in the body.
Step 3
Determining if the ABG is partially compensated or fully compensated.
What does “Compensated” mean?
To put it simply, there are two questions being asked when it comes to compensation
Did the body TRY OR ATTEMPT to correct the pH, but was unsuccessful?
Was the body SUCCESSFUL in its attempt to correct the pH?
Partially Compensated
This refers back to question 1.
Did the body TRY or ATTEMPT to correct the pH but was unsuccessful?
For example this means that if your PaCO2 is the cause of the pH imbalance, then did the bicarb change in order to correct and rebalance the pH, but fell short of achieving a normal pH?
Fully Compensated
This refers back to question 2.
Was the body SUCCESSFUL in its attempt to correct the pH?
For example this means that if your PaCO2 is the cause of the pH imbalance, then was the bicarb change ENOUGH TO SUCCESSFULLY BRING THE pH back into a NORMAL RANGE? If the Bicarb was successful in bringing the pH back into a normal range then it is a fully compensated gas.
Alright, I think that covers plenty for this blog post! Before I keep writing and writing and writing, let’s take a break and don’t forget to stay tuned for the NEXT BLOG post which will continue with ABG Interpretation!
.png)
Comments