Get an ABG. Then use the A-a gradient equation: PAO2 - PaO2 = ([Patm - PH2O] x FiO2 - [PaCO2/Q]) - PaO2 = ([Patm - 47] x FiO2 - [PaCO2/0.8]) - PaO2 = (150 - [PaCO2/0.8]) - PaO2, when at sea level with a patient breathing room air.
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Get an ABG. Then use the A-a gradient equation:
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A-a gradient increases with age, use equation: (Age+10)/4.
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*PAO2 - PaO2
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*PAO2 = ([Patm - PH2O] x FiO2 - [PaCO2/Q])
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*PAO2 = ([Patm - 47] x FiO2 - [PaCO2/0.8])
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*PAO2 = (150 - [PaCO2/0.8]) (when at sea level with a patient breathing room air)
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Normal A-a gradient increases with age, use the equation: (Age+10)/4.