Case 1

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Assuming a normal barometric pressure, a normal respiratory quotient and pressure measured in kPa the alveolar gas equation simplifies to:

P_AO₂=FiO₂ x 94.5 - PaCO₂ x 1.25

In this case the exact FiO₂ is unknown but it is probably somewhere between 0.5 and 0.6. So the P_AO₂ lies between 42.875 and 52.325. Thus the A-a gradient is high indicating an oxygenation defect.

What is the acid-base abnormality?

To remind you the values are:

• pH 7.246
• PaCO₂ 3.5 kPa
• PaO₂ 27.13 kPa
• Actual bicarbonate 11.1
• Base excess -14.3

©Charles Gomersall, August, 2008 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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