Question: why do vbg instead of abg?
Answer: Summary. In conclusion, the VBG is a useful, less painful, and more easily gathered test than ABG to asses for acidosis and hypercarbia. Multiple studies have shown that pH correlates well between VBG and ABG. As for PvCO2, using a cutoff of 45mmHg is very sensitive in determining whether there is arterial hypercarbia.