Final answer:
An effective CPR is indicated by a PETCO₂ reading of 35 mmHg, as this shows that chest compressions are adequately circulating blood and exchanging gases. The PETCO₂ levels mirror the normal range of 35-40 mmHg seen in healthy individuals. The diffusion gradient and solubility of carbon dioxide allow it to move from the blood, where its partial pressure is higher, into the alveoli during respiration.
Step-by-step explanation:
A sign of effective CPR includes a PETCO₂ reading of 35 mmHg. PETCO₂ stands for Partial End-Tidal Carbon Dioxide, which is the measurement of carbon dioxide pressure at the end of an exhaled breath. It reflects the effectiveness of chest compressions and the return of spontaneous circulation. A normal PETCO₂ level is generally between 35-40 mmHg in healthy individuals. A reading around this range during CPR suggests that the chest compressions are effectively circulating blood and thus oxygen and carbon dioxide.
In the scenario described, the partial pressure of carbon dioxide is 45 mm Hg in the blood and 40 mm Hg in the alveoli. Due to the partial pressure gradients and the high solubility of carbon dioxide as compared to oxygen, carbon dioxide diffuses from the blood into the alveoli despite the small partial pressure difference.