Alveolar Gas Equation Study Guide is a series of multiple choice question designed to solve for every possible variable in the calculation.

  • PAO2: Alveolar partial pressure of oxygen in mmHg
  • FiO2: Inspired oxygen (expressed as a decimal)
  • Patm: Atmospheric pressure in mmHg
  • pH2O: Water vapour pressure, 47 mmHg saturated at 37°C
  • PaCO2: Arterial partial pressure of carbon dioxide in mmHg
  • RQ: Respiratory exchange ratio

1.  Given the following: FiO2 = 0.21, Patm = 760 mmHg, pH2O = 47 mmHg, RQ = 0.8, and PaCO2 = 40 mmHg. What is the patient’s Alveolar Partial Pressure of Oxygen?

A. 103.95 mmHg
B. 99.73 mmHg 
C. 80.0 mmHg 
D. 112.35 mmHg

Answer: B.


2. Given the following FiO2 = 0.40, Patm = 760 mmHg, pH2O = 47 mmHg, RQ = 0.8, and PaCO2 = 60 mmHg. Calculate the Alveolar Gas Tension?

A. 310.2 mmHg
B. 99.73 mmHg
C. 40.2 mmHg
D. 210.2 mmHg

Answer: D.


3. What does the Alveolar Gas Equation mean?

A. The Alveolar Gas Equation relates to the alveolar concentration of oxygen, equivalently the partial pressure of oxygen in the alveoli.
B. The Alveolar Gas Equation relates to the alveolar concentration of oxygen, equivalently the partial pressure of oxygen in the artery.
C. The Alveolar Gas Equation relates to the arterial concentration of oxygen, equivalently the partial pressure of oxygen in the alveoli.
D. The Alveolar Gas Equation relates to the arterial concentration of oxygen, equivalently the partial pressure of oxygen in the artery.

Answer: A.


4. Given the following FiO2 = 0.21, Patm = 760 mmHg, pH2O = 47 mmHg, PQ = 0.8, and PAO2= 120 mmHg. Calculate the partial pressure of Carbon Dioxide ( PaCO2).

A. 23.78 mmHg
B. 29.13 mmHg
C. 65.22 mmHg
D. 14.23 mmHg

Answer: A.


5. Calculate the FiO2 given the following: PaCO2 = 50 mmHg, Patm = 760 mmHg, pH2O = 47 mmHg, RQ = 0.8, and PAO2 = 100 mmHg.

A. 0.23
B. 0.25
C. 0.27
D. 0.20

Answer: A.

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6. During rounds the Doctor asks you to calculate the patient’s Alveolar Partial Pressure of Oxygen? The Doctor gives you the following information: FiO2 = 0.50, Patm = 760 mmHg, pH2O = 47 mmHg, RQ = 0.8, and PaCO2 = 70 mmHg. 

A. 221.28 mmHg
B. 269.00 mmHg 
C. 80.0 mmHg 
D. 112.35 mmHg

Answer: B.


7. A fellow Respiratory Therapy Student wants to know what the PaCO2 is given the following: FiO2 = 0.50, Patm = 760 mmHg, pH2O = 47 mmHg, RQ = 0.8, and the Alveolar Gas Tension is 244.00 mmHg?

A. 90 mmHg
B. 76 mmHg
C. 34 mmHg
D. 102 mmHg

Answer: A.


8. Given the following: FiO2 = 0.35, Patm = 760 mmHg, pH2O = 47 mmHg, RQ = 0.8, and PAO2 = 168.30 mmHg. Calculate the partial pressure of Carbon Dioxide.

A. 90 mmHg
B. 76 mmHg
C. 34 mmHg
D. 65 mmHg

Answer: D.


9. Given the following: FiO2 = 0.21, Patm = 760 mmHg, pH2O = 47 mmHg, PQ = 0.8, and PAO2= 109.73 mmHg, and  PaCO2 = 40.  Calculate the Respiratory quotient (RQ).

A. 0.8
B. 0.9
C. 1.0
D. 1.1

Answer: C.


10. Calculate the Patm given the following: PaCO2 = 40 mmHg, pH2O = 47 mmHg,FiO2 = 0.21, RQ = 0.8, and PAO2 = 100.78 mmHg.

A. 765 mmHg
B. 755 mmHg
C. 745 mmHg
D. 735 mmHg

Answer: A.


11. Calculate the Vapor pressure given the following: PaCO2 = 40 mmHg, Patm = 760 mmHg,FiO2 = 0.21, RQ = 0.8, and PAO2 = 100.78 mmHg.

A. 765 mmHg
B. 755 mmHg
C. 745 mmHg
D. 735 mmHg

Answer: A.

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