Aerial blood gas of a 5-year-old child done at sees level gives the following results: pH 7.41, PaO2 100 mgHg, and PaCO2 40 mm Hg. The child is being ventilated with 80% oxygen. What is the (A-a) PO2?
570.4 mm Hg 520.4 mm Hg 470.4 mm Hg 420 mm Hg