How is pO2 measured?

To measure pO2, blood is usually taken from an artery, most often at the wrist. This is called an arterial blood gas analysis and it gives accurate information about the current oxygen level. Venous blood is sometimes used instead, but the arterial value is more informative when it comes to assessing oxygen supply.

The measurement is usually carried out in specialist laboratories or directly at the patient's bedside using an analyser. Alongside pO2, other values such as the carbon dioxide partial pressure (pCO2) or the pH value are often measured at the same time.

What do pO2 values tell us?

The normal pO2 value in arterial blood in adults is typically between 75 and 100 mmHg. If the value is at the lower end or below this range, it suggests that oxygen uptake is reduced. This can have various causes, such as lung conditions, reduced breathing, or staying at high altitude where there is less oxygen in the air.

If pO2 is too low, it can lead to symptoms such as shortness of breath, tiredness, or difficulty concentrating. In serious cases, organs may not receive enough oxygen. A value that is too high is rare and usually only occurs when oxygen is being given artificially.

When is a measurement useful?

Measuring pO2 is especially important when there is a concern about a problem with oxygen supply. This is the case, for example, with acute breathlessness, chronic lung conditions such as COPD or asthma, severe lung infections, or during and after surgery. pO2 is also checked regularly in certain heart conditions or as part of intensive care monitoring.

This allows doctors to recognise early on whether additional oxygen is needed or whether other steps must be taken.

What affects pO2?

pO2 depends on several factors. The lungs play the most important role, as they are responsible for getting oxygen from the air we breathe into the blood. If the lungs are affected by inflammation, fluid build-up, or a chronic condition, pO2 can fall. Problems with circulation or breathing itself also have an effect.

External factors such as altitude above sea level and age also influence the value. Older people often have slightly lower pO2 values than younger people.

pO2 in medical reports and letters

If you come across the term pO2 in a medical letter or laboratory report, you will usually find a figure in mmHg or kPa along with a reference range. If your value is within the normal range, this suggests that oxygen supply is adequate. If the value is unusual, the treating doctor will always assess the result in the context of further tests and your symptoms.

pO2 is therefore an important value, but not the only deciding factor. A complete picture of the body's oxygen supply only emerges when it is considered alongside other blood gas values.

What does an abnormal pO2 value mean?

A pO2 that is too low can indicate a serious problem with breathing or gas exchange in the lungs. This can be the case, for example, with pneumonia, an asthma attack, or a chronic lung condition. Heart problems that affect blood flow through the lungs can also influence the value.

A value that is too high is usually harmless, as it is generally caused by deliberate oxygen administration, for example during treatment in hospital. Here, pO2 is intentionally raised to improve oxygen supply.

Whether an abnormal value needs treatment and how urgently depends on the symptoms, the cause, and the person's overall condition. If you are unsure or have noticeable symptoms, you should always speak with a doctor.

pO2 – a meaningful value, but always seen in context

pO2 is a key laboratory value when it comes to assessing the body's oxygen supply. It helps to identify problems early and to start the right treatment. However, its exact significance only becomes clear when it is considered alongside other findings and the individual situation. A single value on its own does not tell the whole story – the overall picture is always what matters most.