PetCO2 is NOT determined by which of the following?

PetCO2 is NOT determined by which of the following?

• A. Metabolic rate
• B. Ventilation rate
• C. Alveolar headspace CO2
• D. Physiologic shunt

Answer: (D)

PetCO2 reflects the CO2 content in the alveolar gas at the end of expiration, determined by the balance between CO2 production (metabolic rate) and alveolar ventilation (how effectively CO2 is blown off). If metabolism increases, more CO2 is produced and PetCO2 goes up unless ventilation increases to remove it. If ventilation increases, CO2 is expelled more quickly and PetCO2 falls. The gas in the alveolar space (alveolar headspace CO2) sets this end-tidal value as long as ventilation is adequate. A physiologic shunt, which causes blood to bypass some gas-exchange units, mainly alters arterial CO2 and overall gas exchange rather than setting the end-tidal CO2. It can create a bigger gap between PaCO2 and PetCO2, but PetCO2 itself is still governed by production and ventilation and the CO2 content of the alveolar gas in ventilated regions.

PetCO2 reflects the CO2 content in the alveolar gas at the end of expiration, determined by the balance between CO2 production (metabolic rate) and alveolar ventilation (how effectively CO2 is blown off). If metabolism increases, more CO2 is produced and PetCO2 goes up unless ventilation increases to remove it. If ventilation increases, CO2 is expelled more quickly and PetCO2 falls. The gas in the alveolar space (alveolar headspace CO2) sets this end-tidal value as long as ventilation is adequate.

A physiologic shunt, which causes blood to bypass some gas-exchange units, mainly alters arterial CO2 and overall gas exchange rather than setting the end-tidal CO2. It can create a bigger gap between PaCO2 and PetCO2, but PetCO2 itself is still governed by production and ventilation and the CO2 content of the alveolar gas in ventilated regions.