Does the Vena Cava carry oxygen?
the vena cava carries erythrocytes / hemoglobin that have oxygen
attached. However, the de-oxygenation "blood" volume is not
completely bereft of O2. See SvO2, CaO2 & CvO2 -- typical
consumption is 25% of the oxygen carried arterially. Ex (Lungs):
20.1% ml/dl arterial vs. 15.5% ml/dl venous (Edwards
LifeScience)