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What is an Arterial Blood Gas?

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Arterial gasometry is a blood test that is usually performed on the wrist’s radial artery. It accurately measures levels of oxygen and carbon dioxide and the pH of the blood, and helps to assess how the lungs are working during gas exchange. It is a fundamental test to diagnose and monitor the evolution of respiratory failure.

Unlike a venous blood gas test, this technique provides an accurate measurement of how oxygenated the blood is and how respiratory gases are eliminated.

What is this test for?

Arterial gasometry measures three essential parameters:

The amount of oxygen (O₂) in arterial blood.

Carbon dioxide (CO₂) levels.

The pH, which reflects the body's acid-base balance.

These values are fundamental for:

Evaluating the severity of respiratory failure, both in chronic and acute cases.

Determining the need to initiate chronic home oxygen therapy.

Monitoring patients with chronic respiratory diseases, such as COPD and pulmonary fibrosis.

Assessing risk before thoracic or abdominal surgery in people with a history of respiratory problems.

How is gasometry performed?

The test is carried out on an outpatient basis, similar to a blood test. The professional applies local anaesthesia to the wrist area to minimise any discomfort. Then a small amount of blood is extracted from an artery, normally the radial artery. The procedure lasts only a few minutes.

How should I prepare myself?

No special preparation is needed. Fasting or stopping usual medications is not necessary, unless medically indicated.

For patients on home oxygen, if the doctor wishes to know the baseline values without the effect of additional oxygen, a request to remove it will be made 20 minutes before the test. Such patients will always be informed personally beforehand.

Who performs the test?

The extraction is carried out by nursing staff with specific experience in arterial techniques.

Who interprets the results?

The results are interpreted by a pneumologist, who interprets them within the context of the patient’s overall condition to guide diagnosis, adjust treatment or decide on oxygen therapy.

What sensations will I have during the test?

A brief stinging sensation may be felt when local anaesthesia is applied, although this is usually well tolerated. Removing the sample may leave a small mark, similar to that of a normal blood sample, although slight pressure may be felt in some cases.

Health personnel are present at all times to explain every step of the procedure and ensure patient comfort and safety.