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'''AaDO2 - Alveolar-arterial oxygen tension difference ''' *See [[APACHE Scoring table]] *See [[FiO2 |APACHE FIO2 Table]] 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 | FIO2]] being administered to a patient is >=50%. *To calculate the AaDO2: **'''AaDO2 =(([[FiO2 | 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 |AP phys name= Alveolar-arterial oxygen tension difference |AP phys unit= |AP H4= >500 |AP H3= >=350 and <500 |AP H2= >=200 and <350 |AP 0= <200 }} ==Background == === 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. <!-- Julie and Tina discussed 2021-09-29 - there really should never be a null because [[cross check]]s would catch this, but if there every is, this is as good as any solution. --> == Data Integrity Checks == {{Data Integrity Check List}} [[Category:ABG]] [[Category:APACHE II]]
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