What is the Difference Between Arterial and Venous Blood Gas?

Arterial blood gas (ABG) and venous blood gas (VBG) are tests used to assess a patient's oxygenation, ventilation, and acid-base status. The main difference between the two is how the blood samples are collected, with ABG being drawn from an artery, such as the radial artery, and VBG being collected from existing venous access, such as a central venous catheter.

Arterial blood gas is considered the gold standard for assessing oxygenation, ventilation, and acid-base status, but it is painful to obtain and can be contraindicated in some situations. Venous blood gas is less painful and easier to collect, making it a valuable alternative. However, there are some differences in the values obtained from ABG and VBG:

Peripheral venous blood gas (PVBG) has considerably less O2, more CO2, and a lower pH than arterial blood due to the high O2 utilization by organs.
The pH between a VBG and ABG correlates closely, but the average VBG pH is 0.03-0.04 less than ABG.

In some cases, central venous blood gas (CVBG) may not correlate with venous oxygen saturation (SvO2) during shock or in unstable patients, and arterial confirmation with ABG is recommended. Additionally, factors affecting blood circulation, such as sampling site, puncture site temperature, and blood flow rate, should be considered when choosing a venous sample over an arterial one.

In summary, while ABG is the gold standard for assessing oxygenation, ventilation, and acid-base status, VBG can be a useful alternative in certain situations, providing similar information with less discomfort and risk for the patient. However, it is essential to consider factors affecting blood circulation and the patient's clinical status when choosing between ABG and VBG.