46 當一位30歲男性呼吸一般室內空氣時，其動脈血液氣體分析是PaO2 60 mmHg，PaCO2 48 mmHg，則其AaDO2（肺泡動脈血液氧氣分壓差）是多少？

0 mmHg 10 mmHg 20 mmHg 30 mmHg

AaDO2（肺泡動脈血液氧氣分壓差）= alveolar O2 - arterial O2

arterial O2 given: 60

compute for alveolar O2

which is = (FiO2 x713) - (PaCO2 x1.2)

= 0.21 x 713 - 48 x 1.2

= 92.13

92.13 - 60 = 30!

answer is D

normal AaDO2（肺泡動脈血液氧氣分壓差 is around 5-25 mmHg

if lower than this value: 1. due to respiratory depression. 2. in high altitude

if higher than this value: 1/ giving 100 % FiO2, 2. barrier problem: good oxygen supply but cannot get across the barrer: due to dead space or shunt

dead space: COPD asthma

shunt: pneumonia, pul edema