A B G Versus V B G

Overview

Arterial blood gas (ABG) sampling is painful and not without complications. Could venous blood gas (VBG) analysis be an acceptable alternative in some settings?

ABG versus VBG

Arterial blood gas (ABG) analysis is the gold standard to a patient’s acid-base balance and PaCO₂, but is not without risks such as bleeding, haematoma, thrombosis and nerve damage. It is also a painful procedure that can turn a patient’s stomach and can be difficult to perform when the pulse is feeble. There has been some interest over the years in using venous blood gas (VBG) analysis in some settings, since venous sampling is far simpler and gentler, especially if repeated sampling is likely to be required.

At present, most studies have found some correspondence between VBG and ABG gas and pH values, although the degree of agreement can be unacceptably wide. A recent meta-analysis (not open access) of studies performed in emergency departments concluded that:

• Venous and arterial pH and HCO₃^- agree quite well, but differ the most when values are abnormal.
• Normal PvCO₂ is a good predictor for normal PaCO₂. This can be used to exclude hypercapnia.
• Normal venous lactate predicts normal arterial lactate.

Further studies are required in more specific groups, but it is unlikely that ABG will ever lose its place on the podium.