ATS Pulmonary Function Laboratory Manual

ATS Pulmonary Function Laboratory Management & Procedure Manual | 3rd Edition

Table 21.6

Alveolar Air Equation

( PB − 47 ) −

[

F O 2 + ( 1 + /R )],

F O 2

P O 2

= F O 2

Pa CO 2

where:

Pa O 2 Fi O 2 = partial pressure of oxygen (O 2 = fractional concentration of inspired O 2 PB = barometric pressure (mm Hg) Pa CO 2 = arterial carbon dioxide tension R = respiratory exchange ratio (respiratory quotient) ) in the alveoli

Notes: 1. If the Fi O 2

is 1.00, the entire term in the right-hand parentheses becomes 1 and can be ignored.

2. R varies between 0.6 and 1.2. If not measured, it is usually assumed to be 0.8. 3. A simplified version of the alveolar air equation often used clinically is: P O 2 = F O 2 ( PB − 47 ) − ( Pa CO 2 /0 . 8 )

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