Which is within the normal range for arterial carbon dioxide (PaCO2) in blood gas values?

Which is within the normal range for arterial carbon dioxide (PaCO2) in blood gas values?

• A. 25-35 mm Hg
• B. 35-45 mm Hg
• C. 40-60 mm Hg
• D. 45-60 mm Hg

Answer: (B)

PaCO2 shows how well the lungs are removing carbon dioxide, so its normal value reflects balanced ventilation and CO2 production. When ventilation is adequate, CO2 is cleared at a rate that keeps arterial CO2 in the middle of the observed ranges. If you breathe too rapidly or deeply, CO2 drops and you get hypocapnia; if you breathe too little, CO2 rises and you get hypercapnia. Among the options, the one that sits in this middle, normal window represents balanced ventilation and thus a normal PaCO2. The other ranges indicate too low or too high CO2, signaling hyperventilation or hypoventilation, respectively.

PaCO2 shows how well the lungs are removing carbon dioxide, so its normal value reflects balanced ventilation and CO2 production. When ventilation is adequate, CO2 is cleared at a rate that keeps arterial CO2 in the middle of the observed ranges. If you breathe too rapidly or deeply, CO2 drops and you get hypocapnia; if you breathe too little, CO2 rises and you get hypercapnia. Among the options, the one that sits in this middle, normal window represents balanced ventilation and thus a normal PaCO2. The other ranges indicate too low or too high CO2, signaling hyperventilation or hypoventilation, respectively.