PetCO2 is influenced by which component of the alveolar gas?

PetCO2 is influenced by which component of the alveolar gas?

• A. Inhaled nitrogen concentration
• B. Pulmonary capillary blood flow
• C. Alveolar headspace CO2
• D. Ambient humidity

Answer: (C)

PetCO2 reflects the CO2 content of the gas inside the alveolar spaces—the CO2 that makes up the alveolar headspace and is expelled at the end of expiration. End-tidal CO2 is essentially an estimate of alveolar CO2 partial pressure, so the amount of CO2 present in the alveolar gas directly sets the PetCO2 value. Inhaled nitrogen doesn’t contribute CO2, and while blood flow to the lungs can influence how much CO2 is delivered to and exchanged in the alveoli, the measurement itself tracks the CO2 already in the alveolar gas. Ambient humidity has only a minor, indirect effect and does not determine PetCO2.

PetCO2 reflects the CO2 content of the gas inside the alveolar spaces—the CO2 that makes up the alveolar headspace and is expelled at the end of expiration. End-tidal CO2 is essentially an estimate of alveolar CO2 partial pressure, so the amount of CO2 present in the alveolar gas directly sets the PetCO2 value. Inhaled nitrogen doesn’t contribute CO2, and while blood flow to the lungs can influence how much CO2 is delivered to and exchanged in the alveoli, the measurement itself tracks the CO2 already in the alveolar gas. Ambient humidity has only a minor, indirect effect and does not determine PetCO2.