What happens to PtcO2 readings when perfusion is poor?

What happens to PtcO2 readings when perfusion is poor?

• A. They underestimate PaO2
• B. They overestimate PaO2
• C. They match PaO2
• D. They reflect PaCO2 instead

Answer: (A)

When tissue perfusion is poor, oxygen delivery to the tissue drops, so the oxygen tension inside the tissue (PtcO2) falls below what the arterial blood carries (PaO2). PtcO2 reflects the local tissue oxygen level, which is highly dependent on perfusion; if delivery is limited, the tissue becomes relatively hypoxic even if PaO2 is adequate. That means PtcO2 readings under these conditions underestimate PaO2. PtcO2 does not overestimate PaO2 or stay in line with it when perfusion is compromised, and it does not directly reflect PaCO2.

When tissue perfusion is poor, oxygen delivery to the tissue drops, so the oxygen tension inside the tissue (PtcO2) falls below what the arterial blood carries (PaO2). PtcO2 reflects the local tissue oxygen level, which is highly dependent on perfusion; if delivery is limited, the tissue becomes relatively hypoxic even if PaO2 is adequate. That means PtcO2 readings under these conditions underestimate PaO2.

PtcO2 does not overestimate PaO2 or stay in line with it when perfusion is compromised, and it does not directly reflect PaCO2.