<prompt> Aerial blood gas of a 5 year old child done at sea level gives the following results: pH 7.41, Pa02100 mmHg, and PaCO2 40 mm Hg. The child is being ventilated with 80 oxygen. What is the A-a P02570.4 mm Hg520.4 mm Hg470.4 mm Hg420.4 mm Hg  <response>: D i.e. 420. 4 mm Hg PAO2 can be calculated by alveolar gas equation PAO2 FIO2 x Po - PH2O - PaCO2 R Where: PA02 1,102 PB PH2O PaCO2 R P02 of the alveolar air Fraction of 02 in the air Barometric pressure N-760 mm Hg Water vapour pressure N- 47 mm H20 Paial pressure of CO2 N - 40 mm Hg Respiratory quotient CO2output 200 ml 0 8 02 uptake 250 ml The data provided in the question is: Pa02 100 mm Hg PaCO2 40 mm Hg Fi02 8 mm Hg Fi02 - Fraction of inspired Oxygen At sea level 760 mm Hg pressure, the composition of air - 02 20; N2 80 20 So Fi02 is - 0.2 100 In this question, the child is being ventilated with 80 02 80 So Fi02 is ___ 0.8 100 Substituting these values PAO2 0.8 x 760-47 - 400.8 520.4 mm Hg Therefore PAO2 - Pa02 520.4 mm Hg - 100 mm Hg 420.4 mm Hg. 