Arterial Blood Gases (ABG's)
What is an ABG? Answer- a measurement of the partial pressure of O2, CO2, pH, and
HCO3 in arterial blood
Who normally draws this bloodwork? Where is it drawn from? Answer- Respiratory
therapists draw for this profile most commonly from the radial, brachial, and femoral
arteries.
What is acidosis? Answer- It is characterized by an abundance of H+ ions in the arterial
blood, with a pH of less than 7.35.
What are the acids? Answer- H+, CO2, and H2CO3 (carbonic acid)
How are acids produced? Answer- They are produced during metabolic processes.
How are acids excreted from the body? Answer- Some exit via the lungs; others are
buffered and excreted via kidneys.
What is alkalosis? Answer- It is characterized by a decrease of H+ ions in the arterial
blood, with a pH of more than 7.45.
What are the bases? Answer- HCO3 (bicarbonate)
What is a buffer? Answer- A chemical substance that reduces changes in systemic pH
by either releasing or binding H+ ions. It is considered to be a moment by moment
regulation.
Why is CO2 considered a "potential acid"? Answer- Because it forms carbonic acid
when combined with H2O.
What are compensatory mechanisms? Answer- Mechanisms that try to prevent large
changes in pH and/or attempt to correct alterations in acid-base balance; compensatory
mechanisms ALWAYS alter the pH towards a normal level.
Give 2 examples of compensatory mechanisms. Answer- Lungs and Kidneys
What is partial pressure? Answer- Pressure exerted by a single gas.
What is the goal in the regulation of pH? Answer- To maintain or restore body pH to a
normal level - either through buffers or compensatory mechanisms.
, What are some examples of buffers? Answer- proteins, carbonic acid - bicarbonate,
phosphate
How do the lungs function as a compensatory mechanism? Answer- By expiration, in
which CO2 is eliminated from the body, thereby reducing the amount of acids. (note that
the lungs cannot eliminate H+ ions)
How is additional expiration from the lungs initiated? What is the timeframe involved?
Answer- Through chemoreceptors in the brain. It occurs within 1-3 minutes of detected
imbalance, and lasts 12-24 hours.
How do the kidneys function as a compensatory mechanism? Answer- In alkalosis :
they excrete HCO3
In acidosis : they excrete H+ in addition to increasing production and retention of HCO3
What is the timeframe involved in kidney compensation? Answer- It begins to work
within approximately 24 hours and continues until pH is WNL
What is the normal range for pH? Answer- 7.35 - 7.45
What are the normal limits for PCO2? Answer- 35 - 45 mmHg
What are the normal limits for HCO3? Answer- 22 - 26 mEq/L
What is the normal range for PO2? Answer- 80-100 mmHg
What does a low PO2 indicate and what is the potential (respiratory) result? Answer- A
low PO2 indicated hypoxia and can result in hyperventilation.
ABG Interpretation : What does the relationship between pH and PCO2 indicate?
Answer- A respiratory problem
ABG Interpretation : What does the relationship between pH and PHCO3 indicate?
Answer- A metabolic problem
If pH and PCO2 are going in opposite directions, what does this indicate? Answer- A
respiratory problem
If pH and PHCO3 are going in the same direction, what does this indicate? Answer- A
metabolic problem
What type of compensation is indicated if either pH and PCO2 or pH and PHCO3 are
out of range (i.e. only 2 components)? Answer- Uncompensated compensation
What type of compensation is idicated if pH, PCO2, and PHCO3 are all out of range?
Answer- Partially compensated compensation
What is an ABG? Answer- a measurement of the partial pressure of O2, CO2, pH, and
HCO3 in arterial blood
Who normally draws this bloodwork? Where is it drawn from? Answer- Respiratory
therapists draw for this profile most commonly from the radial, brachial, and femoral
arteries.
What is acidosis? Answer- It is characterized by an abundance of H+ ions in the arterial
blood, with a pH of less than 7.35.
What are the acids? Answer- H+, CO2, and H2CO3 (carbonic acid)
How are acids produced? Answer- They are produced during metabolic processes.
How are acids excreted from the body? Answer- Some exit via the lungs; others are
buffered and excreted via kidneys.
What is alkalosis? Answer- It is characterized by a decrease of H+ ions in the arterial
blood, with a pH of more than 7.45.
What are the bases? Answer- HCO3 (bicarbonate)
What is a buffer? Answer- A chemical substance that reduces changes in systemic pH
by either releasing or binding H+ ions. It is considered to be a moment by moment
regulation.
Why is CO2 considered a "potential acid"? Answer- Because it forms carbonic acid
when combined with H2O.
What are compensatory mechanisms? Answer- Mechanisms that try to prevent large
changes in pH and/or attempt to correct alterations in acid-base balance; compensatory
mechanisms ALWAYS alter the pH towards a normal level.
Give 2 examples of compensatory mechanisms. Answer- Lungs and Kidneys
What is partial pressure? Answer- Pressure exerted by a single gas.
What is the goal in the regulation of pH? Answer- To maintain or restore body pH to a
normal level - either through buffers or compensatory mechanisms.
, What are some examples of buffers? Answer- proteins, carbonic acid - bicarbonate,
phosphate
How do the lungs function as a compensatory mechanism? Answer- By expiration, in
which CO2 is eliminated from the body, thereby reducing the amount of acids. (note that
the lungs cannot eliminate H+ ions)
How is additional expiration from the lungs initiated? What is the timeframe involved?
Answer- Through chemoreceptors in the brain. It occurs within 1-3 minutes of detected
imbalance, and lasts 12-24 hours.
How do the kidneys function as a compensatory mechanism? Answer- In alkalosis :
they excrete HCO3
In acidosis : they excrete H+ in addition to increasing production and retention of HCO3
What is the timeframe involved in kidney compensation? Answer- It begins to work
within approximately 24 hours and continues until pH is WNL
What is the normal range for pH? Answer- 7.35 - 7.45
What are the normal limits for PCO2? Answer- 35 - 45 mmHg
What are the normal limits for HCO3? Answer- 22 - 26 mEq/L
What is the normal range for PO2? Answer- 80-100 mmHg
What does a low PO2 indicate and what is the potential (respiratory) result? Answer- A
low PO2 indicated hypoxia and can result in hyperventilation.
ABG Interpretation : What does the relationship between pH and PCO2 indicate?
Answer- A respiratory problem
ABG Interpretation : What does the relationship between pH and PHCO3 indicate?
Answer- A metabolic problem
If pH and PCO2 are going in opposite directions, what does this indicate? Answer- A
respiratory problem
If pH and PHCO3 are going in the same direction, what does this indicate? Answer- A
metabolic problem
What type of compensation is indicated if either pH and PCO2 or pH and PHCO3 are
out of range (i.e. only 2 components)? Answer- Uncompensated compensation
What type of compensation is idicated if pH, PCO2, and PHCO3 are all out of range?
Answer- Partially compensated compensation
