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Data Element (edit)
Field Name: AaDO2
CCMDB Label: <not in CCMDB>
CCMDB tab: Apache
Table: N/A
Data type: number
Length: N/A
Program: CC
Created/Raw: Created
Start Date: 1988-07-11
End Date: 2300-01-01
Sort Index: 34

The patient's Alveolar-arterial oxygen tension difference level in .

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Legacy implementation right in the table

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AaDO2 - Alveolar-arterial oxygen tension difference

Measures the difference in the partial pressure of oxygen between the alveoli and the arteries. This measures the efficiency of the oxygen exchange between the lung alveoli and the pulmonary capillaries.

  • A calculated component of APACHE II score when FIO2 being administered to a patient is >=50%.
  • To calculate the AaDO2:
    • AaDO2 =(( FIO2 X 713) - PaO2) - PaCO2
    • Example with FIO2 50%, PO2 85 and CO2 40:
    • ((0.5 X 713)- 85) - 40)) = 231.5

Apache Physiological Variable
variable name Alveolar-arterial oxygen tension difference
absolute max allowed
warning max
high score 4 >500
high score 3 >=350 and <500
high score 2 >=200 and <350
high score 1
score 0 <200
low score 1
low score 2
low score 3
low score 4
AP phys warnMin
AP phys absMin


This value is used to generate the APACHE Score.

Collecting Apache physiological variables

There are some specific rules to follow in choosing which one of several lab results to collect.

See APACHE physiological variable collection for details.

Cross Chcks

Rules described in APACHE_physiological_variable_collection#Exceptionally_high_or_low_values are implemented by Check APACHE physiological variable high low.


Why the constant 713?

The value 713 mmHg is the barometric pressure (Pb) used in the AaDO2 formula.

Normal Sea level Pb is 760 mmHg. (Winnipeg is close to sea level. We don't adjust for different elevations around the city nor do we adjust this value for the constant changes in Pb).

The barometric pressure is corrected for water vapor pressure (Pbc).

  • (vapor pressure is 47 mmHg @ a temperature of 37C).
  • (760-47)= Pbc of 713 mmHg.

can be less than 0

*4 AaDO2 can be 0 or negative

Unlike other physiological variables AaDO2 can be 0 or negative, so unlike the others the score for a 0 AaDO2 is 0 if AaDO2 < 200, which includes AaDO2<=0.

Note for programming only: The score is still null if the AaDO2 is null.

Data Integrity Checks

Data Integrity Checks (automatic list)

Check APACHE physiological variable high lowCCMDB.accdbimplemented