ABSTRACT
Several regression equations are available but none has an upper limit of over 75 years. Consequently, PaO2 values for ages above this are all reached by unreliable extrapolation.
PaO2 of over 1 kPa (7.5 mmHg) from the sitting to the supine position. Hence, the position of the patient should always be recorded with the results. A useful regression equation predicting the PaO2 between the ages of 15 and 75 years for a patient sitting propped to 70° with the legs horizontal is that of Mellemgaard:
• The marked effect that venous admixture has on the PaO2 occurs because of the non-linearity of the oxygen dissociation curve. It causes little change in the PaCO2, which remains constant throughout life.
