A patient is breathing air at sea level and has a respiratory exchange ratio of 1.0. The aerial blood values are: PO2 90 mm Hg ;PCO2 20 mm Hg and pH 7.30. These indicate that the:
The alveolar PO2 is found from the alveolar gas equation: PAO2 = PIO2 - PACO2/R We can assume that the inspired PO2 is the sea level normal value of 149 mm Hg. Therefore, neglecting the small correction factor, the alveolar PO2 is 149 - 20/1 or 129 mm Hg. Thus the alveolar-aerial PO2 diffusion is 129 - 90 = 39 mm Hg. The PCO2 of 20 mm Hg means that the patient is hyperventilating. The combination of the low PCO2 and low pH means that plasma bicarbonate concentration is reduced. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 35. Gas Transpo & pH. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds),Ganong's Review of Medical Physiology, 24e.
Alveolar-aerial PO2 difference exceeds 20 mm Hg.
Plasma bicarbonate concentration is low
Patient is hyperventilating
All of the above