Alveolar Oxygen (A)
Alveolar Oxygen refers to the partial pressure of oxygen in
alveolar gas. It is calculated as follows:
%FIO
2
A = ––––– (B.P. - 0.045T2 + 0.84T - 16.5) -
100
%FIO
2
1-(%FIO2/100)
**PCO2 –––––– + –––––––––
100 0.8
Equation 26
where T = patient temperature
B.P. = barometric pressure
%FIO
2
= fraction inspired oxygen, as a percent
** Temperature corrected gas value
Arterial Alveolar Oxygen Tension Gradient (AaDO
2
)
The arterial alveolar oxygen tension gradient is a useful
index of gas exchange within the lungs and is dened as:
Aa DO
2
= A-
**
PO
2
Equation 27
** Temperature corrected gas value
NOTE: For capillary samples, AaDO2 results have an
asterisk (*). AaDO2 results are dependent on how
the samples are drawn and handled, thus care
must be taken when interpreting these calculated
results.
)
[
(
]
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