A 36-year-old woman is found comatose at her home and is life-flighted to the nearest regional medical center. Blood gases reveal a normal PaO₂ but a lower-than- normal arterial O₂ saturation. Which of the following conditions is most consistent with the findings?
a. Anemia
b. Carbon monoxide poisoning
c. Hypoventilation
d. Low ratio
e. Right-to-left shunt