Second year medical student asking:
A 40 year old woman is admitted to the ICU with acute respiratory distress syndrome due to a life threatening case of pneumonia.
Her respiratory values are as follow BEFORE treatment:
pH = 7,36
PCO2 = 48 mmHg
PO2 = 70 mmHg
She is treated with 100% oxygen and the values after treatment are:
pH = 7,35
PCO2 = 52 mmHg
PO2 = 145 mmHg
I am now asked to calculate her alveolar-arterial gradient and thereafter explain whether this number is indicative of a Va/Q mismatch.
I calculate her A-a gradient to be 21 mmHg. An expected A-a gradient would be roughly 20 mmHg for her age.
This seems normal? I tried with an external calculator as well and the values are normal too?
Why is she admitted to the ICU if her A-a gradient is completely normal and then treated so that her A-a gradient goes severely down?
I think I'm misunderstanding the point of it all?