Arterial Blood Gases

What is an arterial blood gas?

An arterial blood gas (ABG) is a set of tests that measure the levels of oxygen and carbon dioxide in arterial blood, as well as the acidity (pH) and other related parameters.

They are usually carried out as 'point of care' tests, meaning the sample is run through an analyser that is present at the bedside (or more commonly close by) instead of being sent to a lab. This means the results are obtained quickly and can be acted upon without the delay usually associated with routine blood tests.

ABGs are commonly used to diagnose and monitor respiratory and/or metabolic disorders such as acute asthma, chronic obstructive pulmonary disease (COPD), pneumonia, sepsis, and renal dysfunction.

Arterial vs Venous

As the name implies, arterial blood gases are taken from an artery, usually in the wrist. This is a painful invasive procedure that should only be carried out when necessary.

Sampling blood from an artery means we get an accurate picture of the oxygen and carbon dioxide to assess respiratory function. If respiratory parameters are not required, consider sampling from a vein instead.

Learning outcomes

This resource has been designed to provide a level of understanding that will allow you to perform a basic assessment of ABG results.

This will include:

• The background physiology of acids, bases, and respiratory gases
• Bicarbonate and it's role in the blood plasma buffering system
• The structure of arterial blood gas results
• Indicators of respiratory failure
• Diagnosis of acidosis, and differentiation between respiratory and metabolic causes
• Diagnosis of alkalosis, and differentiation between respiratory and metabolic causes
• Other parameters on blood gases that can aid diagnosis