Which parameter is included on the calculation sheet as a gas exchange variable?

Which parameter is included on the calculation sheet as a gas exchange variable?

• A. Arterial-arterial gradient
• B. Pulse oximetry reading
• C. PAO2
• D. Arterial to venous oxygen difference

Answer: (C)

Gas exchange calculations hinge on the alveolar oxygen tension, PAO2, because it represents the oxygen available in the alveoli to diffuse into the blood and serves as the reference point for assessing how well oxygen transfer is working. PAO2 is estimated with the alveolar gas equation, which ties together FiO2, barometric pressure (adjusted for water vapor), and PaCO2 (divided by the respiratory quotient). This value is essential for computing the A-a gradient (PAO2 minus PaO2) and for judging whether the arterial oxygen level matches what’s expected given the ventilated oxygen fraction. Because of this role, PAO2 is included as a gas exchange variable on the calculation sheet. Pulse oximetry is useful clinically but provides a noninvasive saturation reading, not a calculated gas-exchange parameter. The arterial-arterial gradient isn’t a standard term in this context (the familiar measure is the A-a gradient between alveolar and arterial oxygen). The arterial to venous oxygen difference is another meaningful measure but is not the gas exchange variable typically singled out on the calculation sheet for assessing alveolar–arterial transfer.

Gas exchange calculations hinge on the alveolar oxygen tension, PAO2, because it represents the oxygen available in the alveoli to diffuse into the blood and serves as the reference point for assessing how well oxygen transfer is working.

PAO2 is estimated with the alveolar gas equation, which ties together FiO2, barometric pressure (adjusted for water vapor), and PaCO2 (divided by the respiratory quotient). This value is essential for computing the A-a gradient (PAO2 minus PaO2) and for judging whether the arterial oxygen level matches what’s expected given the ventilated oxygen fraction. Because of this role, PAO2 is included as a gas exchange variable on the calculation sheet.

Pulse oximetry is useful clinically but provides a noninvasive saturation reading, not a calculated gas-exchange parameter. The arterial-arterial gradient isn’t a standard term in this context (the familiar measure is the A-a gradient between alveolar and arterial oxygen). The arterial to venous oxygen difference is another meaningful measure but is not the gas exchange variable typically singled out on the calculation sheet for assessing alveolar–arterial transfer.