Final answer:
The main determinant of PETCO2 during CPR is the level of carbon dioxide in the blood. This level increases when the heart stops beating and decreases as blood flow is restored through CPR. The respiratory activity of the brain during CPR is influenced by the systemic arterial concentrations of hydrogen ions.
Step-by-step explanation:
The main determinant of PETCO2 during CPR is the level of carbon dioxide in the blood.
During CPR, when the heart of a patient stops, the blood flow to the brain and other organs is compromised. This leads to an increase in carbon dioxide levels in the blood. One of the key goals of CPR is to restore blood flow and oxygenation to the organs, including the brain. As the blood flow is restored, the carbon dioxide levels decrease, leading to a decrease in the PETCO2 (partial pressure of end-tidal carbon dioxide).
The main factor influencing the respiratory activity of the brain during CPR is the systemic arterial concentrations of hydrogen ions.