When arterial blood from a normal patient is exposed to room air, which of the following occurs?

When arterial blood from a normal patient is exposed to room air, which of the following occurs?

• A. pco2 increases; po2 decreases
• B. pco2 decreases; po2 increases
• C. pco2 decreases; po2 decreases
• D. pco2 increases; po2 increases

Answer: (B)

Gas diffusion driven by partial pressure gradients: room air has very little CO2 and a high O2 partial pressure compared with blood. When arterial blood is exposed to room air, CO2 leaves the blood and enters the air, so PCO2 falls. At the same time, O2 from the air diffuses into the blood, raising PO2 toward the ambient level. So the arterial CO2 decreases while the arterial O2 increases. This matches the option describing decreased PCO2 and increased PO2.

Gas diffusion driven by partial pressure gradients: room air has very little CO2 and a high O2 partial pressure compared with blood. When arterial blood is exposed to room air, CO2 leaves the blood and enters the air, so PCO2 falls. At the same time, O2 from the air diffuses into the blood, raising PO2 toward the ambient level. So the arterial CO2 decreases while the arterial O2 increases. This matches the option describing decreased PCO2 and increased PO2.