<prompt> Aerial blood gas of a 5 year old child done at sea level gives the following results: pH 7.41, PaO2, 100 mmHg, and PaCO2, 40 mmHg. The child is being ventilated with 80 oxygen. What is the A-a DO2.-570.4 mm Hg520.4 mm Hg470.4 mm Hg420.4 mm Hg  <response>: Alveolar air equation: Using the alveolar air equation - PAO2 - Data: Fraction of O2 in the inspired air 80 Barometric pressure 760 mm Hg sea level Water vapor pressure 47 mm Hg Respiratory quotient 0.8 Hence, Alveolar PO2 - 570.4 - 50 520.4 mm Hg Aerial PO2 is given 100 mm Hg Hence, A - a DO2 520.4 - 100 420.4 mm Hg 