The respiratory specimens used in LOINC for each of the measurements include:
BLDMV – mixed venous
BLDC – capillary
BLDCoA – arterial cord
BLDCoV – venous cord
This would be a variety of LOINCs for each of the analytes, across Oxygen Saturation, Base Excess, pH, etc. In RELMA, see the Gas Panels for further information. In order to use them, your computer system would have been built with specimen distinct result codes for each analyte, e.g. Oxygen Sat arterial, Oxygen Sat venous.
If your system instead has a single field for each respiratory analyte, irregardless of arterial or venous, then there’s probably a specimen type field, to tell when the values are a venous set or arterial set. That Specimen source field would be mapped to 31208-2 Specimen source, and the individual analytes would best be mapped to BLD specimen.