Siemens RAPIDLAB 248 Operator's Manual page 134

Page G-10
Gas Exchange Indices
Gas exchange indices are a quick way to estimate the relationship
between pulmonary dysfunction and hypoxia, and to quantitatively
determine the degree of pulmonary shunting. However, they do not
have a high level of correlation with the actual measurement of arterial
and mixed venous blood and should be used with discretion. The gas
exchange indices are provided for convenience. Final judgment of their
use is in the hands of the physician. The gas exchange indices require
an arterial sample and use measured values at patient temperature.
Alveolar O
Alveolar O
oxygen in alveolar gas. It is a primary component in the detection of gas
exchange indices. The following equation
alveolar O
where
Arterial-Alveolar Oxygen Tension Difference
The arterial-alveolar oxygen tension difference (pO
is useful as an index of gas exchange within the lungs if ctO
measurements are not available. The following equation
where pO
gas, and pO
arterial blood.
Arterial-Alveolar Oxygen Tension Ratio
The arterial-alveolar oxygen tension ratio (pO
provides an index of oxygenation that remains relatively stable when
F
The following equation
where pO
gas, and pO
arterial blood.
NOTE:
calculated.
2
, referred to as pO
2
:
2
pO (A)(T) = F O /100 x (pAtm – pH
2 I 2
T = patient temperature (°C)
pH O = 10 (0.0244 x T + 0.7655)
2
pO (A–a)(T) = pO (A)(T) – pO
2 2
(A)(T) is the temperature corrected oxygen tension of alveolar
2
(a)(T) is the temperature corrected oxygen tension of
2
O changes. It is useful in predicting oxygen tension in alveolar gas.
I 2
pO (a)(T)
2
pO (a/A)(T) =
2
pO (A)(T)
2
(A)(T) is the temperature corrected oxygen tension of alveolar
2
(a)(T) is the temperature corrected oxygen tension of
2
If F O value is not entered, the gas exchange indices will not be
I 2
(A) or p O , is the partial pressure of
2 A 2
14,19
O) – pCO
2
+ 0.4
(a)(T)
2
20 is used:
248 Operator's Manual
is used to estimate the
(T) x (1.25 – 0.25 x F
2 I
(A–a)), (or A–aDO
2
2
14,19
is used:
(a/A)), (or a/A ratio)
2
O /100)
2
)
2